The Plausibility Paradox for Resized Users in Virtual Environments
Matti Pouke, Katherine J. Mimnaugh, Alexis Chambers, Timo Ojala, Steven M. LaValle
TThe Plausibility Paradox For Resized Users inVirtual Environments
Matti Pouke , ∗ , Katherine J. Mimnaugh , Alexis Chambers , Timo Ojala andSteven M. LaValle Center for Ubiquitous Computing, Faculty of Information Technology and ElectricalEngineering, University of Oulu, Oulu, Finland
Correspondence*:Matti Poukematti.pouke@oulu.fi
ABSTRACT
This paper identifies and confirms a perceptual phenomenon: when users interact with simulatedobjects in a virtual environment where the users’ scale deviates greatly from normal, there is amismatch between the object physics they consider realistic and the object physics that wouldbe correct at that scale. We report the findings of two studies investigating the relationshipbetween perceived realism and a physically accurate approximation of reality in a virtual realityexperience in which the user has been scaled by a factor of ten. Study 1 investigated perceptionof physics when scaled-down by a factor of ten, whereas Study 2 focused on enlargement by asimilar amount. Studies were carried out as within-subjects experiments in which a total of 84subjects performed simple interaction tasks with objects under two different physics simulationconditions. In the true physics condition, the objects, when dropped and thrown, behavedaccurately according to the physics that would be correct at that either reduced or enlarged scalein the real world. In the movie physics condition, the objects behaved in a similar manner as theywould if no scaling of the user had occurred. We found that a significant majority of the usersconsidered the movie physics condition to be the more realistic one. However, at enlarged scale,many users considered true physics to match their expectations even if they ultimately believed movie physics to be the realistic condition. We argue that our findings have implications for manyvirtual reality and telepresence applications involving operation with simulated or physical objectsin abnormal and especially small scales.
Keywords: Virtual Reality, Perception, Scaling, Plausibility, Human Factors
Many studies have confirmed the so-called ”body-scaling effect”: if presented with mismatching size cues,humans tend to use their visible body as the dominant cue when perceiving sizes and distances (Banakouet al. 2013; Langbehn et al. 2016a; Linkenauger et al. 2013; van der Hoort et al. 2011; Ogawa et al. 2017).For example, if a person was somehow shrunk to the size of a doll, the person would be inclined to regardthe world as scaled-up and him/herself as normal-sized (van der Hoort et al. 2011). In this paper, weinvestigate the human perception of physics, specifically when subjects have been either scaled down orup by a significant amount. We believe this relatively underrepresented topic has implications to variousvirtual reality (VR) and telepresence applications. More specifically, we focus on the subjective credibilityof rigid body dynamics when subjects are presented with realistic and unrealistic approximations of objectmotions when either scaled down or scaled up by a factor of ten. Previously, we investigated the perceptionof physics in VR when subjects were scaled down by a factor of ten (Pouke et al. 2020). We found out a r X i v : . [ c s . H C ] F e b ouke et al. Plausibility Paradox for Resized Users
Figure 1.
First person perspective from the subject’s point of view in the VE at the start of the experimentin Study 1.that subjects considered a physics model of regular human scale to be more realistic than an accurateapproximation of physics in the scaled down environment. This offered additional proof of humans beingoriented to Newtonian physics taking place at human scale, and anything deviating much from that scaleappears unnatural. In this paper we extend our prior work by considering scaled-up subjects allowing us tocompare the perception of physics in VR both in small and large scales.Currently, not much is known about how scaling a person would affect their perception of physicalphenomena, such as accelerations. Interestingly, if we consider the interaction of scaled-down characterswith their surroundings in many works of fiction, the tendency to represent the world as scaled up incomparison to normal-sized protagonists can be observed. Early examples can be seen in the classicfilm
The Incredible Shrinking Man . When the main character throws grains of sand off the table whileinsect-sized, the grains accelerate and fall as if they were boulders - when they should be falling downinstantly. Similarly, when the character is awash with rainwater holding onto a pencil, the water and thepencil act more akin to a river and a log when the pencil should be bobbing with few waves and no visiblewhitewater should be apparent. Although the deficiencies in the realism of the
Incredible Shrinking Man can be attributed to 1950s technologies, similar inaccuracies still remain in modern movies from
Honey IShrunk the Kids to Downsizing . These inaccuracies are not necessarily resulting from directors’ lack ofunderstanding of physics, but might be conscious choices to represent what the viewers would expect.VR and telepresence applications allow humans to live through experiences such as the
IncredibleShrinking Man through the eyes of a scaled-down entity. A specific category of virtual environments(VEs) providing such experiences are multiscale collaborative virtual environments (mCVEs), in whichmultiple users can collaborate in, for example, architectural or medical visualizations across multiple,nested levels of scale (e.g., Kopper et al. (2006); Zhang and Furnas (2005)). In addition, the scaling ofusers has been utilized in several collaborative mixed reality (MR) systems (e.g., Billinghurst et al. (2001);Piumsomboon et al. (2018b,a)). Teleoperation of robots can allow humans to interact with the physicalworld at micro- and nanoscale. Similar to mCVEs, robotic teleoperation systems using multiple scales arebeginning to emerge (Izumihara et al. 2019). Although teleoperation in the physical world can leveragestereoscopic camera systems resembling immersive VR applications (Hatamura and Morishita 1990),purely virtual representations leveraging computer graphics can be used in, for example, educational andtraining systems for micro- and nanoscale tasks (Bolopion and R´egnier 2013; Millet et al. 2008). Roboticsurgery systems can perform operations at a microscopic level (Hongo et al. 2002) whereas stereoscopicVR can be utilized in telesurgery (Shenai et al. 2014). The benefits of VEs have been identified in various
Preprint ouke et al. Plausibility Paradox for Resized Users design and prototyping processes (Mujber et al. 2004) that can be extended into small-scale VEs, aswell. Already two decades ago, both the design (Li and Sitte 2001) and assembly (Alex et al. 1998) ofmicroelectromechanical systems (MEMS) were prototyped through desktop VEs. Recent studies have alsoinvestigated self-scaling as a method to help with aspects related to architectural and interior design (Zhanget al. 2020a,b).Understanding human perception of scale-varying phenomena will be useful for the future design ofapplications such as those listed above. Although existing research has addressed many perceptual questions,such as the perception of distance and dimensions after altering one’s virtual size (e.g., van der Hoortet al. (2011); Banakou et al. (2013); Kim and Interrante (2017)), the perception of the behavior of physicalobjects has received relatively little attention. There are many potential future use cases for user scalingthat might require interaction with physical or physically simulated objects. We argue that it is not intuitivefor humans to correctly perceive physical phenomena, such as rigid body dynamics, in scales that differgreatly from a normal human scale. An object dropped from 20 cm takes significantly less time to fallthan an object dropped from 2 m, and their perceived accelerations are different. Additional physicalphenomena, such as fluid dynamics, frictions, and static electricity might affect interactions even furtheras the scale of the operations becomes smaller. For this reason, additional consideration is required whendesigning systems in which real or virtual interactions take place on atypical scales, and thus it is importantto understand human perception of physical phenomena on those atypical scales.In this paper, we present our results on human perception of physics at abnormal scales. First, we focuson the mismatch between perceived realism and a physically accurate approximation of reality wheninteracting in a VE while scaled down by a factor of ten. Then, we present the results of a similar studywhere subjects were scaled up by a factor of ten and compare the results between the two studies. Basedon previous research, we believe that humans generally perceive themselves at the correct scale whenpresented with mismatching size cues, as long as visual body cues are present (Langbehn et al. (2016b)).We also believe humans are generally accustomed to rigid body dynamics taking place at a human scaleand under normal gravity conditions (McIntyre et al. (2001)). Therefore, we hypothesize that subjectsneither accept the realistic approximation of physics at an abnormal scale, nor are they blind to changesin scale. Instead, when presented with two different scale-dependent rigid body dynamics, they are morelikely to consider the physically inaccurate one to be the more perceptually realistic one.This paper is structured as follows. Section 2 reviews previous research related to this work. Section 3presents the research method, experimental setup and the results of Study 1. Section 4 similarly reportsStudy 2 and also compares the results of both studies. Section 5 discusses our findings and Section 6concludes the paper.
The manipulation of a user’s scale can be accomplished by changing various properties of the virtualcharacter the user is controlling in the VE. Changing these properties has various subjective effects. Whenscaling a user’s virtual size, one of the most obvious properties to change is the viewpoint height, as itdefines the virtual camera origin in relation to the VE, simulating a change in physical size. Viewpointheight affects egocentric distance perception (Leyrer et al. 2011; Zhang and Furnas 2005). Interestingly,minor changes in viewpoint height might go unnoticed by users (Leyrer et al. 2011; Deng and Interrante2019). Users’ interaction capabilities such as locomotion speed and interaction distance can be changedaccording to scale, depending on the purpose of the application (Zhang and Furnas 2005). When using
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Figure 2.
A screenshot of the VE from the subject’s perspective when looking forward and upward withbook and tabs below the line of sight (A) and when looking left (B) .a head mounted display (HMD), the scaling of the user can also affect the virtual interpupillary distance(IPD), which is the distance between the two virtual cameras that are used to render the environment for theuser. Changing this distance can affect the user’s sense of their own size relative to the VE (Piumsomboonet al. (2018a); Kim and Interrante (2017)).
As already mentioned, body scaling refers to humans utilizing their own body as a primary scale cue,hence the virtual representation of the user’s body greatly affects their perception of sizes and distancesin a VE (Ogawa et al. 2019; Ogawa et al. 2017). Linkenauger et al. (2013) studied the role of one’s handas a metric for size perception; they conducted an experiment where they scaled the users’ virtual handand found out that it had a strong correlation with perceived object size. Ogawa et al. (2019) studiedthe effect of hand visual fidelity on object size perception and found that the visual realism of the handaffects the extent of the body scaling effect. van der Hoort et al. (2011) embodied the entire user in a doll’sbody as well as in a giant’s body using a stereoscopic video camera system and an HMD. They foundthat the embodiment significantly affected the users’ distance and size perceptions, especially if the userexperienced a strong body ownership illusion (Slater et al. 2009) with the virtual body. Banakou et al.(2013) compared the effects of embodying the user as a child versus as a scaled-down adult. They foundthat the effect of altered size and distance perceptions was even larger when embodied as a child, and italso made the users associate themselves with childlike personality traits.
The environment, whether real or virtual, affects the perception of scale. There is evidence of humansgenerally underestimating egocentric distances in VEs, except when the VE is faithfully modeled torepresent a real environment (Renner et al. 2013). However, if a familiar room is scaled slightly up or down,underestimations are reintroduced (Interrante et al. 2008). Familiar size cues also affect the sensitivity toeye height manipulations (Deng and Interrante 2019). Langbehn et al. (2016a) studied the effect of bodyand environment representations as well as the scale of external avatars on users’ perception of dominantscale in mCVEs (the dominant referring to the “true” scale in an mCVE system where users can coexist inmultiple scales). They found that humans tended to use their body as the primary metric for judging theirown size and the environment if the representation of one’s own body was not available. In addition, anenvironment with familiar size cues helps in the determination of scale, whereas an abstract environmentdoes not. They also found that the majority of subjects tended to estimate external avatars to be at thedominant scale instead of themselves.
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Previous research suggests that humans have an internal physics model according to which they expectthe world to function. Studies in micro- and nanoscale teleoperation have revealed that, due to changes inphysics, interactions at these scales can become difficult for the human operator, but education inside virtualreality environments has been found to alleviate this drawback (Millet et al. 2008; Sitti 2007). McIntyreet al. (2001) reported a study in which astronauts’ movements to catch a vertically moving ball weremore inaccurate in zero gravity (0g) in comparison to earth gravity (1g); this was interpreted as evidencethat the central nervous system utilizes an internal model of gravity in addition to visual judgement ofacceleration to synchronize movements. Senot et al. (2005) used VR to study human estimation capabilitiesto intercept moving balls and found further evidence on subjects being more capable of intercepting objectsaccelerating according to normal gravity. Yao and Hayward (2006) created a haptic illusion of an objectrolling or sliding inside a cavity and studied the subjects’ capability of estimating the lengths of virtualtubes. According to their results, the subjects performed better than chance in estimating the tube lengthseven using reduced sensory cues, indicating a capability to estimate object movements under the influenceof gravity.Ullman et al. (2017) compared humans’ internal physics model to a contemporary game engine. Theirfindings suggest that although humans are not entirely capable of accurately predicting object motions,they are capable of making noisy, ”good enough” approximations of Newtonian physics which can becompared to the physics simulations generated by physics engines that are integrated in contemporarygame engines. McCoy and Ullman (2019) asked more than a thousand subjects to rate the ’effort’ requiredby various imaginary magical spells violating physics and found the subjects’ responses as strikinglyconsistent. Despite describing completely imaginary phenomena, the subjects were very consistent indefining relative efforts that seemed to depend not only the type of the spell (such as levitate or conjure)but the size of the target as well. Although this finding is not directly related to the perception of physicalphenomena, it again speaks for internal intuitive physics model that is consistent across humans.
The concepts of immersion (Slater and Wilbur 1997), presence and plausibility (Slater 2009) are relevantfor this study. In Slater’s classical definition, the level of immersion refers to the level of technical fidelityof the VR system (i.e., resolution, field of view, vividness of graphics; Slater and Wilbur 1997). In addition,the realism of the user’s response to the VR system depends on two orthogonal components, presence orplace illusion (PI) and the plausibility illusion (PSI; Slater 2009). PI refers to the sensation of being inanother place, whereas PSI refers to the perceived credibility of the virtual scenario or experience (theillusion of being there versus the realness of what is happening; Rovira et al. 2009). PSI depends on theextent to which the VE can produce authentic responses for user actions. Rovira et al. (2009) argued thatfor PSI to occur, participants must perceive themselves as beings that exist in the VE; user actions mustelicit actions in the VE and the VE must acknowledge the user (for example, virtual characters react to theuser). In addition, the VE should match the users’ prior knowledge and expectations. Skarbez et al. (2017b)used the term coherence to refer to the aspects of a VE that contribute to PSI, such as virtual humans andthe behavior of virtual objects. They argued that although immersion is a technical attribute that affects PI,coherence is a similar technical attribute affecting PSI.In Study 1, we used the concept of PSI to study human perception of the behavior of physical objectswhile the subject was scaled down and interacting in a normal-sized environment. In Study 2, we repeatedthe same procedure for scaled-up subjects. However, we delimited virtual characters out from the scopeof in both studies. Instead, we were interested in how subjects would perceive the coherence in terms
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Plausibility Paradox for Resized Users of behavior of virtual objects, when it would be reasonable to expect a mismatch between expectationsand correctly simulated reality. In addition, we investigated whether the extent of PI affected PSI in thisparticular context.Building on the terminology discussed by Skarbez et al. (2017a, 2020), the phenomenon studied inthis paper could also be referred to as coherence - fidelity mismatch; the logic expected by the usersmismatches with more faithful representation of reality. It is expected that coherence differs from realityin, for example, fantasy games or other entertainment applications where PSI is maintained even whenunearthly phenomena are taking place. However, we consider the mismatch studied here to be specificallyinteresting due to its implications for VR and telepresence applications taking place at abnormal scales. The specific objective of Study 1 was to investigate the PSI of subjects in two different physicsconditions. The purpose of both conditions was to visually represent a scaled-down subject in a normal-sized environment, and the physics simulations differed between the conditions as follows. In the truephysics condition, the rigid body dynamics affect virtual objects in an approximately similar way to whatwould be accurate at that scale. In the movie physics condition (named after physical behavior as typicallyseen in Hollywood movies in scenes depicting scaled-down characters), rigid body dynamics behave inwhat would be the approximation of a normal human scale.Our assumption was that the users would be able to distinguish the difference between true physics and movie physics , and we predicted that subjects would be more likely to expect and feel the movie physics condition to be the more perceptually realistic representation. This would suggest a Plausibility Paradox, amismatch between perceived realism and the correct approximation of realism.
We hypothesized that in the true physics conditions, the behavior of physical objects would feel incorrectfor subjects despite their knowledge of being virtually shrunk down. More specifically, our hypotheseswere as follows:H1: For a scaled-down user, movie physics is more likely to feel realistic than true physics .H2: For a scaled-down user, movie physics is more likely to match the user’s expectations than true physics . We designed a VE for the two physics conditions described above using Unreal Engine 4.22 (UE). Inboth conditions, the scaling operations took place in one order of magnitude, giving the impression of adoll-sized perspective. We did not use full body tracking or attempt to induce a strong body ownershipillusion (Slater et al. 2009), so there was no visualization of any body parts in the VE other than the subject’shands. We used the default UE VR hand visualization for interaction and to present a medium-fidelity bodysize cue (Ogawa et al. 2019). There was no difference between the conditions regarding how the handsfunctioned or how the user was able to move.To help in providing accurate size cues, we modeled the VE to resemble a location in the main corridorof the campus in which the study took place. The dimensions and materials of the VE were modeled afterthe real environment. In addition, we took measurements of various real-world objects, such as chairs,tables, and leaflets, which we modeled and scaled accordingly and placed in the VE as static objects.
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The scaling of the user in the true physics condition was achieved by shrinking the user with the UE’sbuilt-in
World to Meters parameter, which automatically scales the player character’s height, virtual IPDand interaction distance. The skeletal meshes representing the player character’s virtual hands were scaleddown manually. In the movie physics condition, the player character properties were kept as default and theVE was scaled up instead. The purpose for this approach was to give the visual illusion of a scaled-downuser, while retaining physics conditions that correspond to the normal human scale. The sizes and relativedistances of scene objects were increased by a factor of ten. In addition, the properties of lights andreflection capture objects were adjusted so that the overall visual appearance of both conditions were keptas similar as possible.
The interaction task consisted of the manipulation of virtual soda can pull tabs approximately 3 cm inlength and 1.9 cm in width (as presented in Fig. 1). The tabs were chosen for the experiment both for theirsmall, consistent mass as well as for being a reasonably authentic object that could be seen in the simulatedVE. We considered a lightweight object to be most practical for simulating throwing in VR so that wewould not have to simulate the decrease in hand acceleration due to increased inertia at the end of the armor limitations due to arm strength (Cross 2004). In both conditions, the subjects would try dropping andthrowing five tabs. Picking up and throwing the tabs took place utilizing the default mechanism in UE,similar to contemporary VR applications in general. The subjects simulated grabbing objects by squeezingthe trigger of the motion controller and dropping them by releasing the trigger. Virtual throwing took placeby swinging the motion controller and then releasing the trigger, and the object thrown retained its velocityat the moment of release, simulating throwing.In the true physics condition, the tabs would drop down fast, similarly as to if they were dropped fromthe height of 15-20 cm (simulated falling speed approximately 0.175 s at 20 cm in UE). In addition,the throwing distances would appear short because of the limited velocity that can be actuated due toreal hand movements scaled down by an order of magnitude. The movie physics condition, on the otherhand, simulated the tabs as falling down more slowly, similarly to an object dropped from human height(simulated falling speed approximately 0.6375 s at 2 m in UE). In addition, the throwing distances weremuch larger in the movie physics condition due to the larger velocity that the subjects were able to actuateon the tabs by virtual throwing.Due to the simulated size, the tabs were also different between conditions in terms of their bounciness(there were no changes in physics simulation properties, such as restitution). In the movie physics condition,the tabs bounced visibly off surfaces, or jittered slightly after being dropped. However, in the true physics condition, there was little to no visible bounciness.The tabs were placed on top of a large book so that the subjects would not have to pick them up fromthe floor. The book also provided an additional size cue. We gave the book a neutral, non-distractingappearance and a general title so that it was recognizable as a book, but would not otherwise draw toomuch attention. A Coca-Cola can was placed as a familiar sized cue on the left side of the book. Fig. 1shows the book and the tabs as seen in the beginning of the simulation. Fig. 2 A and B show the scene asseen at the beginning of the simulation when looking forward (A) and left (B).The virtual mass of the tabs was set at 1g in both conditions. Default physics settings in UE were utilized,with the exception of turning on the physics sub-stepping for additional physics accuracy by enablingphysics engine updates between frames. Drag by air resistance was set to zero in both conditions. Thesimulation itself ran at stable 80 FPS which is the maximum frame rate of Oculus Rift S.
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The experiment was carried out as a within-subjects experiment, in which 44 subjects (23 females and21 males) performed both conditions during one session. Two participants were excluded due to issueswith the functionality of the VR equipment or due to vision impairments. The order of the conditions wascounterbalanced so that there was an equal number of male and female participants starting with eachcondition. The subjects’ ages ranged from 19 to 66, mean and median ages being 30 and 26, respectively.The standard deviation for the ages was 10.4. The study was conducted either in English (12 femalesand 7 males) or in Finnish (11 females and 14 males), depending on the preference of the subject. Eachparticipant was rewarded with a gift voucher of two euros.
The experiment was set in a laboratory in which the subjects used the Oculus Rift S system with providedOculus Touch controllers for the experiment. The Rift S has a variable IPD software setting, so theIPD was set to 62.5 for females and 64.5 for males, the closest approximation available based on theaverages reported for adults by Dodgson (2004). In the beginning of a session, the subject read through awritten
Information for Subjects document and signed an informed consent sheet. The subject was theninstructed on using the VR hardware, specifically how to use the Rift S Touch motion controllers forpicking up and throwing objects. Next, the subject was instructed to stand on a particular starting spotin the laboratory marked with a masking tape. When the subject was wearing the HMD and the motioncontrollers comfortably, an instruction script was read in English or Finnish. The script stated that thesubjects were at the university central hallway, shrunk down 10-fold to a size of a doll, and were to dropand throw the tabs placed on top of a book in front of them.Active noise-cancelling headphones were placed on the subject to block out any potential external noisefrom other rooms in the building, and then the experiment began. After performing both conditions, theheadphones and the VR hardware were removed and the subject was asked to respond to a post-experimentquestionnaire as well as a background questionnaire on a different laptop. The subject was asked for anyadditional comments or questions, and if he/she could be contacted for future studies, and then givenher/his gift voucher. The average duration of the session was 20 minutes per subject.
We collected plausibility related data using two forced choice questions (main questions 1 and 2),two open-ended questions (O1 and O2) and a 7-point Likert scale questionnaire regarding the behaviorof the tabs (L1-L5). In addition, the subjects filled out the extended version of the Slater-Usoh-Steed(SUS) Presence questionnaire (Slater et al. 1994; Usoh et al. 2000), as well as a background informationquestionnaire. The main questions 1 and 2 were as follows:1.
Thinking back how the pull tabs were behaving in the experiment, which felt more realistic (like whatwould happen in the real world if you had been shrunk down), the first or the second time? Thinking back how the pull tabs were behaving in the experiment, which matched your expectations(similar to what would happen in the real world if you had been shrunk down), the first or the secondtime?
The main questions were coupled with open-ended questions (O1 and O2), that were simply stated as ”Why?” . The purpose of the open-ended questions was to evaluate to what extent the subjects’ responseswere related to the physics or other reasons.The forced-choice and open-ended questions were followed by a 7-point Likert scale questionnaire askingsubjects to judge how they perceived various aspects related to the behavior of the tabs. Each question was
Preprint ouke et al. Plausibility Paradox for Resized Users stated twice in the questionnaire, referring to the first time and the second time subject interacted withthe tabs (either using the true physics and then the movie physics or vice versa). The first three questions(L1-L3) were bipolar, whereas the last two (L4, L5) were unipolar. The Likert questions L1-L5 and theirassociated scales were as follows:L1
The falling speed of pull tabs (too slow, too fast) L2 The speed of pull tabs when thrown (too slow, too fast) L3 The distance of pull tabs when thrown (too close, too far) L4 The way the pull tabs were bouncing when thrown (incorrect, correct) L5 The impact of gravity on the pull tabs (incorrect, correct)
Similarly to Study 1, we gathered qualitative data, subject background data as well as questionnaire datato better understand the responses given by the subjects.All questions were presented in either English or Finnish, depending on which was chosen as the preferredlanguage by the subject when signing up for the experiment.
According to the responses to the main questions, the majority of the subjects considered the moviephysics condition as the more realistic one. Out of 44 subjects, 32 participants (73%) responded to thefirst question that they considered the movie physics condition more realistic, which confirms H1. For thesecond question, 40 out of 44 (91%) subjects responded that the movie physics matched their expectationsbetter, which confirms H2. Furthermore, we analyzed the frequencies of responses to questions 1 and 2with a binomial test and found their corresponding two-tailed p values as p = 0 . and p = 1 . − ,respectively. From this we can conclude that it is unlikely that the responses to questions 1 and 2 weredue to chance. In addition, this indicates that subjects were able to distinguish between the two physicsconditions and more consistently selected the movie physics condition, which was the inaccurate physicscondition.Out of twelve respondents who considered true physics more realistic, nine responded that the moviephysics matched their expectations more. Only one subject considered the movie physics more realisticwhile simultaneously stating that the true physics better matched her/his expectations. We gathered supplementary data to further understand the results. These data include responses to open-ended questions O1 and O2, Likert-scale questions L1-L5, as well as subject background and self-reportedlevel of presence.The purpose of the open-ended questions was to evaluate to what extent the subjects’ responses to themain questions 1 and 2 were related to the perceived realism of the physics. The responses consisted ofone-sentence statements typed by the subjects. Thematic analysis with an inductive approach (e.g., Patton(2005)) was carried out independently by two researchers and used to identify codes in the response data.A summary of the codes can be viewed in Fig. 3 A and B). Examples of responses in O1 can be seen inTable 1, whereas examples of responses in O2 can be seen in Table 2.In short, the responses to questions O1 and O2 indicate that majority of users (38 out of 44) made theirchoices primarily according to reasons related to the behavior of the physically simulated tabs. Other
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Figure 3.
Qualitative codes for responses O1 ( A ) and O2 ( B ) according to perceived realism in Study 1. Table 1.
Examples of O1 responses (justification to main question 1) in Study 1.
Codes Preference Response
Gravity, natural Movie physics ”Gravity felt more natural”Gravity, natural Movie physics ”At the second time, the objects fell to the ground faster, which feltunreal”Gravity True physics ”I think when the height of the object is not that high, it should reachthe ground faster.”Physics, visual Movie physics ”movement in space felt more realistic, but the objects lacked 3D, ringpulls are not paper thin”Ability, distancetraveled, physics Movie physics ”because I was more comfortable with the controllers after using themfor some time, and i knew i could do more things now like throwing morefar away after some time, and also they were moving more smoothly”Bounciness,throwing, distancetraveled, ability Movie physics ”I am not sure but I think the second time they still moved a bit afterI dropped them to the floor, before being completely still. I think I alsomanaged to throw one of the pull tabs the second time, which felt morerealistic than them dropping very quickly just right in front of me afterI tried to throw them (but this could also just have been my inability tothrow the first time).”Weight Movie physics ”Second time they felt too heavy”.Weight, strength, size True physics ”Pull tabs are not heavy and when I’m small, I probably would not havethe strength to throw them afar”.Ability Movie physics ”I was able to act more normal in the second round. I had worked outthe mechanics of the VR better and spent less time attempting to makethe task work”. primary reasons were related to general interaction and becoming accustomed to controllers. Few referenceswere made to visual details (appearance of tabs and colors) as secondary reasons or general remarks.
Inspecting the Likert responses for questions L1-L5, we found that the movie physics condition was closerto perceived realism (median responses closer to 4 in questions 1 and 3 and closer to 7 in questions 4 and5) in all questions except L2, in which the median response was the same for both conditions. We analyzedthe responses to questions L1-L5 with the Wilcoxon Signed Rank test and found that the responses weresignificantly different (p < movie physics condition more realistic due to differences in the behavior ofthe physically simulated tabs. A summary of responses including, median, mode and standard deviation forquestions L1-L5 can be seen in Table 6. In addition, box plots visualizing the medians, interquartile rangesas well as minimum and maximum responses can be seen in Fig. 4 A and B. Preprint ouke et al. Plausibility Paradox for Resized Users
Table 2.
Examples of O2 responses (justification to main question 2) in Study 1.
Codes Preference Response
Distance traveled Movie physics ”As I was taking a swing with my arms I was expecting them to land faraway from me which they did only during the first time.”Speed of motion Movie physics ”In the second time the tabs were falling down surprisingly fast”Size, weight Movie physics(different from O1) ”I was not thinking I was shrunk. So it felt estrange to have such heavypull tabs”Physics, size Movie physics(different from O1) ”I didn’t think at first (until I saw the previous question) shrinking downwould also affect the time it takes for the objects to reach the ground.The physics first time behaved just like in normal life.”Size Movie physics(different from O1) ”Even though I knew I was shrunk down, I still could not think that waywhen doing the experiment”Natural, physics Movie physics ”The behavior seemed more natural, although probably the laws of thephysics tell otherwise”Ability, throwing Movie physics(different from O1) ”I thought throwing the pull tabs would be relatively easy, like in thesecond time”.Weight Movie physics ”Intuitively I figured things would be light”.Size, novelty True physics ”I felt that I was really small in that world for the first time.”.Natural Movie physics ”First time. Felt somehow more natural. They didn’t have muchdifference, though”.
Table 3.
Summary of Likert data in Study 1. Responses perceived closer to realism are emphasized inbold.
Question Condition Median Mode STDL1: true physics movie physics
L2: true physics movie physics L3: true physics movie physics
L4: true physics movie physics
L5: true physics movie physics
Furthermore, we used a binary logistic regression to analyze the effects of subject background andpresence on their responses to main question 1. We used educational background, gender, age, vr experience,gaming experience, SUS average and SUS score as independent variables and the response to main question1 as the dependent variable.For analysis purposes, we transformed the Background Questionnaire responses to educationalbackground into a binary variable consisting of roughly equal sized groups of natural sciences andengineering (25 subjects) and social sciences (19 subjects). In addition, the open responses to
VR experience and gaming experience was transformed into respective ordinal variables ranging from 0 (no experience) to4 (plenty of experience). When interpreting the gaming experience responses, additional emphasis wasgiven to recent experience as well as experience regarding PC and console based 3D gaming (such as firstperson shooters and simulators) due to the tendency of such games to contain game physics simulationssimilar to those used in this experiment. The responses to SUS scores were transformed into two ordinalvariables consisting of the average of responses as well as the computed SUS score.
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Figure 4.
Study 1 Likert responses L1-L3 ( A ) and L4-L5 ( B ) visualized as box plots, interquartile rangesand minimum and maximum responses. In ( A ), responses closer to 4 are perceived as closer to realism,whereas in ( B ) responses closer to 7 are perceived as closer to realism.The logistic regression model was unable to predict the response using the independent variables. Themodel explained 17% of the variance (Nagelkerke’s R ) in perceived realism. Although the overallclassification rate was 72.7%, only 16.7% (two responses) of the true physics responses were correctlyclassified. None of the independent variables had a significant effect on the prediction of the response(p = 0.184 - 0.858). According to this analysis, the perception of realism was not significantly affectedby the background, education or gaming experience of our subjects. The level of presence according toself-reported SUS score did not have any effect either. Although we never queried subjects directly regarding the physical properties of the tabs themselves,several subjects commented on the weight of the tabs or their own strength when interacting with the tabs.Five of the subjects who responded in English commented on the feeling of the perceived heaviness ofthe tabs (see Table. 1). It is interesting to consider these spontaneous responses regarding differences inthe weight of the tabs given than there was no change in the controllers that the subjects used for eachcondition. This could be an indication of a pseudohaptic effect (L´ecuyer 2009) (for example, manipulatingthe control-to-display ratio of the visual feedback when lifting an object can give the user an illusion ofincreased weight (Samad et al. 2019)). However, it is possible that the subjects were simply referring to thevisible trajectories and falling speed of objects (as in the tabs seemed heavier instead of the tabs feelingheavier ). Several of the responses in Finnish specifically contemplated the assumed weight of the tabs inregards to how more much power they would have needed to use to throw the tabs given their reduction insize. To investigate these findings further, we added additional pseudohaptic related questions in Study 2.
In Study 2, we wanted to investigate the perception of rigid body dynamics while the user was enlargedby a factor of ten. We followed a methodology similar to Study 1 so that we could easily compare subjects’perceptions in small and large scales. We introduced minor methodological changes described below.
Our hypotheses for Study 2 were similar to those of Study 1.H3: For a scaled-up user, movie physics is more likely to feel realistic than true physics . Preprint ouke et al. Plausibility Paradox for Resized Users
H4: For a scaled-up user, movie physics is more likely to match a user’s expectations than true physics . Study 2 portrayed the subject as a giant, 10 times larger than a regular human. Similarly to Study 1, theVE was also based on a real-world environment we expected to be familiar for most of our subjects. Morespecifically, the VE depicted a marketplace and its surroundings located in the center of the City of Oulu,Finland. The environment used 3D assets from the ”Virtual Oulu” model described in Alatalo et al. (2016).The assets were imported into a UE 4.24 scene. Some of the original materials were remade to follow acontemporary physically-based rendering (PBR) workflow for improved aesthetics. To enrich the modelwith additional size cues, the marketplace area of the model was augmented with additional detail such asstreet furniture, trees and foliage that were placed using Google Maps photographs and satellite photos asreference. GIS data from the City of Oulu were used to generate non-textured faraway buildings seen inthe background of the scene. Also, generic textured building blocks were used in some areas to generatebuildings not present in the original Virtual Oulu model but close enough to the viewer so that untexturedmodels were not feasible. Although our aim was to make the scene appear realistic for the subjects, wetook minor liberties in the placement of certain scene objects to make the scene more appropriate for theexperiment. Namely, the immediate marketplace surroundings were left relatively empty to prevent thesubjects from hitting random objects and making unwanted plausibility noise. In addition, the position oftrees next to the shoreline were adjusted so that the logs have a free passage to water (see Fig. 5 A).In addition to Virtual Oulu assets, GIS data and self-modeled assets, several commercial packages fromthe Unreal Marketplace were used in the VE. Animated seagulls and pigeons from the
Birds packagewere scaled to correct size (approximated wingspans 70 cm and 140 cm, respectively) and deployed inthe scene to provide animated size cues. The commercial packages ”Nordic Harbour”, ”Country Side”,”Vehicle Variety Pack”, ”Modern City Downtown”, ”Sky Pack” as well as ”Trucks and Trailers” were alsoutilized for foliage, vehicles, street furniture and other minor details, such as traffic signs. Water shader andbuoyancy for logs was generated using the
Waterline Pro package. Screenshots of the scene can be seen inFig. 5 A and B.Similarly to Study 1, the scale-changing effect was achieved by scaling the world-to-meters parameter ofUE and player character properties, this time making the user to appear 10 times larger instead of smaller.Similarly to Study 1, we defined the rigid body dynamics as simulated by the game engine to act as the truephysics condition. For the movie physics condition, we upscaled the default gravity Z and bounce threshold (as instructed by UE when scaling gravity) properties by 10 to generate conditions similar to human scale.This approach was taken to avoid generating two different-sized versions of the level so that we couldeliminate visual difference. These approaches resulted in object free fall times of 1.97 seconds and 0.68seconds, when object is dropped from the height of 18m in true physics and movie physics respectively.
The interaction task in Study 2 resembled the task in Study 1, consisting of dropping and throwingobjects. Since the subject was a giant instead of doll-sized, the objects used in the interaction task werelarger as well. Considering a handful of alternatives, we determined wooden logs as suitable objects forinteraction, since they are somewhat familiar sized objects for most locals and frequently seen around townafter being culled from local forests. The logs were approximately 2.9 m in length and 26.7 cm in diameter,matching the dimensions and mass of commercial pine logs. We placed the logs on top of a container, sothat the subjects would not need to reach all the way down to the ground to grab the logs. The containerwith the logs can be seen in Fig. 6 A.
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Figure 5.
The VE used in Study 2 as seen by subjects in the beginning of the experiment when lookingforward (A) and right (B)
In Study 1, the subjects were allowed to drop and throw the pull tabs in any way they wished. However,in Study 2 we instructed the subjects to drop exactly three logs to their right and throw two logs into the seavisible in front of the subjects (see Fig. 5 A). We also placed a ”Drop Here” text on the ground to depictwhere exactly the logs should be dropped (see Fig. 6 B). There was a particle splashing effect when thelogs hit the water surface as well a buoyancy effect. However, these effects were very subtle due to thedistance to the water surface.The specific instructions for interaction were included because in Study 1 we received feedback indicatingthat more specific instructions would have helped in observing the motions of the pull tabs. In addition,since the subjects were interacting in a large-scale urban environment, there were countless opportunitiesfor ”plausibility noise” which we wanted to avoid (such as subjects expecting logs to realistically breakwindows, dent cars, knock over tables, and so on). By giving specific instructions, we aimed to ensure thatthe subjects’ responses were based on the motions of the logs only.
Figure 6.
The container with the logs as seen in the beginning of the experiment (A) and the area in whichthe first three logs were to be dropped (B)
Similarly to Study 1, the experiment was carried out as a gender-counterbalanced within-subjectexperiment, this time with 40 participants (20 males and 20 females). Three participants were excluded dueto failure to follow instructions or not giving their consent for data use. We did not allow people who hadalready participated in Study 1 to participate again to keep subjects naive for the purpose of the experiment.
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Figure 7.
A photo of the research space during Study 2 taken behind a see-through barrier. The sameresearch space was used in both studies.The subjects’ ages ranged from 20 to 57, with mean and median ages being 26 and 25, respectively. Thestandard deviation of the ages was 6.0. Each participant was remunerated with a movie ticket worth 10euros.
Apart from COVID-19 related safety guidelines discussed below, the procedure was largely similar toStudy 1. In Study 2, however, the subjects did not wear noise-cancelling headphones as there was no soundin the VE or from students in the laboratory hallways, and thus they were unnecessary.In Study 1, a researcher checked the HMD before each participant to ensure that the Oculus main menuor other anomalies were not present when starting the experimental apparatus. In Study 2, however, weasked the subject to report what he/she saw in the beginning of the experiment since we could not be inclose proximity to the subjects to check ourselves. In addition to checking anomalies, this also allowed usto check whether the subject recognized the VE as the Oulu marketplace. After this, an instructions scriptwas read for the subject. The script confirmed that the subjects were at Oulu marketplace, enlarged 10-foldto a size of a giant, and they were to throw and drop the logs placed on a container in front of them. At theend of the experiment, the subject was given her/his movie ticket.The experiment in Study 2 was conducted during the COVID-19 pandemic, hence additional safetyprecautions were taken. At the time of the experiment, the regional state of the epidemic was at so-called”baseline level” . Due to the relatively calm local state of the epidemic, it was possible to conduct temporaryon-campus work as long as university safety guidelines were followed.The research space allowed for a maximum of two researchers who kept within safety distance to theparticipant. The researchers were also separated from the subject with a see-through barrier. The researcherswore safety masks, which were also offered for subjects. The participants were instructed to operate the Defined by Finnish Institute of Healthcare as follows: ”The baseline corresponds to the situation in Finland in the middle of the summer, 2020. The incidenceof infections is low, and the proportion of endemic infections is small.”
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VR equipment by themselves during the experiment and a researcher intervened only if necessary (forexample, in cases of Oculus room setup resetting).Virtual reality equipment was sanitized between each participant using a ”Cleanbox” device. In addition,all equipment and surfaces were wiped with alcohol disinfectants. Researchers wore rubber gloves duringthe cleaning process and the experiments. The default face padding of Oculus Rift S was covered with asilicone hygiene cover for easier cleaning. In addition, the subjects were offered optional disposable paperface hygiene covers. The research space was air-conditioned and ventilated between subjects. Participantswere also asked to use hand disinfectant available in the research space. Participants were asked to join theexperiment only when feeling completely healthy. The research space can be seen in Fig. 7. The questionnaires in Study 2 were kept mostly similar to Study 1, consisting of two forced choicequestions (main questions 1 and 2), two open-ended questions (O1 and O2), a 7-point Likert questionnaireconcerning log physics (L1-L5), and the extended SUS questionnaire Slater et al. (1994); Usoh et al. (2000).In addition, we added extra 7-point Likert-scale questions L6-L8 concerning the experience of being largeand pseudohaptics.Main questions 1 and 2 were identical to Study 1, except replacing ”pull tabs” with ”logs”. Similar toStudy 1, both main questions were followed by open-ended questions O1 and O2 stating ”Why?” .Questions L1, L3, L4 and L5 were kept similar to Study 1 so that only ”pull tabs” were changed into”logs.” Since the wording of L2 in Study 1 was found to be problematic, we paraphrased it from ”the speedof pull tabs when thrown (slow - fast)” into ”time of flight (slow - fast)” .The new questions L6-L8 assessed the feeling of size and the sensation of weight of the logs in bothconditions. The questions were phrased as follows.L6
During the experiences, did you feel more like a giant in a normal-sized city, or more like a normal-sizedperson in a miniature city? (normal-sized person, giant) L7 When picking up or holding the logs, did you feel a sensation of actual weight? (not at all, very muchso) L8 The logs felt... (light, heavy)
Similarly to Study 1, all questions were presented either in English, or Finnish, depending on thepreference of the subject.
Again, majority of the subjects considered the movie physics condition as the realistic one, but theexpectations of the subjects were more mixed, however. For main question 1, 28 out of 40 (70%) subjectschose movie physics . As for response to the main question 2, 25 out of 40 subjects (63%) consideredthat movie physics matched their expectations better. Following the procedure in Study 1, we analyzedthe frequencies of responses with a binomial test, and found their corresponding two-tailed p-values as p = 0 . and p = 0 . . This indicates that the responses to main question 1 were significantly biasedtowards movie physics , whereas responses to main question 2 were closer to a random distribution. Theseresults confirm H1, but not H2. Most of the subjects clearly considered movie physics as the more realistic Preprint ouke et al. Plausibility Paradox for Resized Users condition, but their expectations were more evenly split between true physics and movie physics . Almostevery subject mentioned recognizing the scene as the Oulu downtown marketplace.
Thematic analysis using the inductive approach (Patton 2005) was used to analyze the open-endedquestions. The responses were first coded by two independent researchers, after which the final codes wereagreed upon. One subject did not respond to the open-ended questions. A summary of codes and theirfrequencies per each question can be seen in Fig. 8.The responses indicate that majority of the subjects considered the motions of the logs as their primaryreason of preference; the logs were either moving at a speed they did not feel was realistic, or were underthe effect of abnormal gravity. This is especially true for the subjects that perceived movie physics asmore realistic. For the subjects choosing true physics , the ability to throw logs especially far came uprelatively more often than for movie physics respondents. This could mean that these subjects considered agiant being capable of throwing the logs farther due to increased strength. However, similarly to Study1, we did not simulate muscle strength per se; the ability to throw the logs far was due to the increasedvelocity the subjects were able to impart due to being scaled 10-fold. There was only one response to O1, inwhich strength was specifically mentioned, whereas for O2, strength came up in four responses. Examplesof responses for O1 can be seen in Table 4. For O2, examples can be seen in Table 5. Distributions ofqualitative codes in Study 2 can be seen in Fig. 8.
Figure 8.
Qualitative codes for responses O1 ( A ) and O2 ( B ) according to pereived realism in Study 2 Similarly to Study 1, we analyzed questions L1-L5 ( falling speed, time of flight, distance when thrown,bounciness and gravity ) to get additional insight into the subjects’ perceptions of the motions of the logs.In all questions, the respondents favored movie physics , with the median and mode closer to 4 in L1-L3and closer to 7 in L4 and L5. A Wilcoxon Signed Rank test showed that the responses were significantlydifferent ( p < . between the conditions for all of the questions except L4 ( p = 0 . . A summary ofthe responses can be seen in Table 9. Box plots visualizing medians, interquartile ranges, as well as theminimum and maximum responses can be seen in Fig. 9. Similarly to Study 1, we acquired self-reported presence data according to the SUS questionnaire. Thirtyout of 40 subjects (75%) had an SUS score higher than 0, indicating at least some level of presence. The
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Table 4.
Examples of O1 responses (justification to main question 1) in Study 2
Codes Preference Response
Gravity Movie physics ”me being big should not affect the gravity of other objects”Speed of motion True physics ”Not really sure, but when I picture a giant it feels like that way. Likethings going on slow motion.”Speed of motion,gravity Movie physics ”It happened with normal speed/gravity”Physics, gravity Movie physics ”Acceleration felt somewhat realistic, the latter felt like surface of themoon”Throwing distance True physics ”when using a strong force, the logs was thrown far away, matching myexpectation”Throwing distance True physics ”If I were a giant, the logs would fly a little farther, which washighlighted in the second time”Novelty, physics,bounciness,interaction True physics ”Everything felt new, not only that you were in VR in the first place, butalso the point of view, which was of course higher than normal. It alsofelt like, in terms of physics, the logs were behaving more realisticallyin the first time, because I was handling them more carefully. Onthe second time I just dropped the logs from high up, and they werebouncing any which way”.Gravity, weight,naturalness Movie physics ”The gravity and motion of the logs felt more natural. In the other one,they were floating like feathers in space and were clearly lighter thanreal”.Gravity, speed ofmotion, strength Movie physics ”According to my own assumptions, objects would feel like they weremoving more slowly in relation to myself if I were a giant, but the firsttime felt more like I was underwater. In my opinion, the second time wasmore real, even if it was a little fast-ish. I did feel as if I was stronger inthe second time, though.”.
Table 5.
Examples of O2 responses (justification to main question 2) in Study 2
Codes Preference Response
Naturalness,speed of motion True physics(different fromO1) ”This bias might be partly because of movies, but also in many reallife videos, big objects fall ”more slowly” when seen from afar. Inthe first version the logs were much more slower, which matched myexpectations more.”Naturalness,speed of motion Movie physics(different fromO1) ”Somehow faster motions felt more natural”Naturalness Movie physics ”Logs felt more credible in the second experiment”Physics True physics ”The second time matched my expectations more since the motions ofthe logs were more realistic”Speed of motion Movie physics ”Because the logs acted as they should. A log in the real would not fallslowly.”Interaction,bounciness,throwing Movie physics ”I find it easy to grab and on throwing it was more realistic. When I dropthe log it bounced back as well, making it more realistic. In second, Iwas also able to see the log clearly when it was in air during the throw.”Speed of motion Movie physics ”Still the first one. I can not realistically think the world working inslow motion.”.Speed of motion True physics ”because of the speed when I drop the logs”.Strength,throwing distance True physics ”As a giant I would expect to be stronger, therefore being able to throwthe logs further. ”. median SUS score was 1. Again, we divided the subjects into groups of high presence (SUS score >
2) andlow presence (SUS score < true physics , whereas only five subjects out of 24 (21%) from low presence group didthe same. However, according to Fisher’s exact test, this difference was not significant ( p > . ), which Preprint ouke et al. Plausibility Paradox for Resized Users
Figure 9.
Study 2 Likert responses L1-L3 ( A ) and L4-L5 ( B ) visualized as box plots, interquartile rangesand minimum and maximum responses. In ( A ), responses closer to 4 are perceived as closer to realism,whereas in ( B ) responses closer to 7 are perceived as closer to realism. Table 6.
Summary of Likert data in Study 2. Responses perceived closer to realism are emphasized inbold.
Question Condition Median Mode STDL1: true physics movie physics
L2: true physics movie physics
L3: true physics movie physics
L4: true physics movie physics
L5: true physics movie physics means we can assume that belonging to either high or low presence group did not affect the response tomain question 1.
We added three new questions L6-L8 to investigate the subjects’ perception of his/her own size, as wellas pseudohaptic sensations. It appears that although the subjects generally considered movie physics asthe more realistic condition, true physics was able to more successfully convey the sensation of beinglarge. The median and mode responses to L6, feeling of own size , were 6 and 6, respectively, for the truephysics conditions. As for movie physics , these responses were 4 and 2, respectively. This is somewhatsupported by the responses to open-ended questions O1 and O2 (for example, subjects considering truephysics more natural, see Table 5). We found these differences to be statistically significant using theWilcoxon Signed-Rank test ( p = 0 . ).When inspecting the open-ended data from Study 1, we found a number of subjects mentioning the pulltabs feeling heavier in one condition or another. To investigate this further, we added new questions L7and L8 to inquire about pseudohaptic sensations. However, these sensations were reported as very low ingeneral. For L7, sense of actual weight , the median and mode responses were 1.5 and 1 for true physics and 2 and 1 for movie physics , respectively. As for L8, logs felt light/heavy , median and mode was 2 and 1for true physics and 3 and 1 for movie physics . Out of 40 subjects, 4 and 6 subjects reported pseudohapticsensations stronger than 4 out of 7 in the true physics and movie physics conditions, respectively. However, Preprint 19 ouke et al.
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Study 2 might have been less appropriate to study the sensations of weight reported by subjects in Study1, since in Study 2 the physics ranged from normal to perceptually slower, instead of vice versa. Again,using the Wilcoxon Signed-Rank test, we found statistical differences for L7 ( physical sensation of weight )to be insignificant ( p > . ). However, there was a statistically significant difference ( p = 0 . ) inresponses for L8 (the logs were light/heavy) . These results could be interpreted so that the subjectsgenerally considered the logs simulated heavier in the true physics condition, but failed to notice anydifferences regarding pseudohaptic sensations, however. Similarly to Study 1, we analyzed the effects of subject background and self-reported presence on theirpreference on physics. This time around, we also added responses to L6 as variables own size true and own size movie to estimate whether subjects’ perception of their own size (in essence, the extent of feelinglike a giant) affected responses. Using the same categories and the same coding mechanisms as in Study 1(this time with 22 subjects categorized having a background in
Natural Sciences and Engineering and 17subjects with a
Social Science background), we performed binary logistic regression analysis. The modelexplained 38% of the variance (Nagelkerke’s R ) with 79.5% overall accuracy. Although we found, similarto Study 1, that background, gaming or VR experience and self-reported presence did not affect responses,the variable own size movie had a significant effect ( p = 0 . ). This finding indicates that true physics respondents felt smaller specifically during the movie physics condition. However, since the distributions ofboth true physics and movie physics responses were quite large, but the number of true physics respondentswas rather small, we would hesitate to put too much confidence in this implication until further evidence isfound. The percentage of subjects that chose movie physics for main question 1 was 73% in Study 1 and 70%in Study 2. As for main question 2, these percentages were 91% for Study 1 and 63% for Study 2. Wecompared the results for main questions 1 and 2 from Studies 1 and 2 with Fisher’s exact test. We foundthat responses to main question 1 were statistically similar ( p > . ), whereas responses to main question2 were different ( p = 0 . ). This suggests that a majority of similar proportions considered movie physics more realistic in both studies. The proportions were largely different for main question 2. Although almostall subjects considered movie physics as better matching their expectations in Study 1, only a statisticallyinsignificant majority considered the same in Study 2.The results for Likert questions L1, L3, and L5 were very similar in Studies 1 and 2, consistently favoring movie physics . Responses to L2 were very mixed in Study 1, which we attribute to bad wording of thequestion. In Study 2, the responses were more consistent and clearly favored movie physics . In Study 2, theresponses for L4 were mixed while in Study 1 movie physics was preferred.In both studies, we examined the effect of various contributing factors in an effort to gather additionalinsights for interpreting the results. In Study 1, we used background data as well as self-reported presenceas predictors to main question 1. In Study 2, we also added two new variables own size true and own sizemovie . In Study 1, however, we did not find any significant predictors. In Study 2, a new variable, own sizemovie came out as significant.If we compare the presence scores to those of Study 1, we can see that subjects in Study 2 experiencedsomewhat less presence. In Study 1, some presence (SUS score >
0) was experienced by 82% of theparticipants with median SUS score being 3. In addition, the proportion of high and low presence groupswere almost equal in Study 1 (53% experiencing high sense of presence). In Study 2, 75% responded withSUS score > Preprint ouke et al. Plausibility Paradox for Resized Users
40% and 60% respectively. However, despite these differences, the SUS scores for Study 1 (44 subjects)and Study 2 (40 subjects) were not statistically different (Mann-Whitney U test p > . ). Also, presencedid not have a predictive capability on the preference of realism in either study. Our results demonstrate that we have identified a strong paradox concerning PSI in VEs in which the userhas been scaled either up or down. However, this fits the definition of PSI: the plausibility illusion is moredependent on the expectations of the subjects than objective reality (Slater et al. 1994; Skarbez et al. 2017a).We believe that this paradox has implications for VR and telepresence applications.The proportion of the subjects that chose movie physics in main question 1 was almost identical in Study1 and Study 2. Close to a 3/4ths majority (73% in Study 1 and 70% in Study 2) chose movie physics as therealistic representation. As for main question 2, the responses were quite different, however. In Study 1,91% of subjects considered movie physics as matching their expectations more, whereas in Study 2 only63% of the subjects considered the same. It appears that realistically approximated physical phenomenonat a small scale was surprising for almost all subjects. However, many subjects considered true physics tobetter match their expectations at a large scale, even if they actually regarded movie physics as the realisticone.The purpose of open-ended questions regarding the reason why subjects rated one of the physicsconditions being more realistic (O1) or matching their expectations better (O2), was first to confirm thatthe subjects gave their responses according to object motions and not other plausibility related factors, andsecond to give additional insights, for example regarding different responses to O1 and O2.In Study 1, according to O1 and O2, almost all of the subjects considered their perception of realismto be related to the physics behavior of the tabs. In addition, a small number of subjects gave responsesmotivated by general interaction, including learning how to use the controllers correctly. A few secondaryreasons or remarks were made referring to a scene object or other visual details. According to the responsesto O2, most of the subjects preferring true physics as the realistic one stated that during the experiment itwas difficult to understand why the physics functioned the way that it did - the behavior of the tabs wasstill surprising even if they considered it realistic.As for Study 2, the reasons given by the subjects were also most often related to the behavior of the logs.Some exceptions included interaction (learning to use controllers or other interaction related issues) andnovelty (for example, the experience being more overwhelming in the first part of the experiment). In Study2, no visual aspects came up in the open-ended responses.Whereas in Study 1, only one subject responded with movie physics in O1 and true physics in O2, thiswas the case for five subjects in Study 2. The most popular reason in these cases was the ability to throwthe logs farther (3 responses). The other reason was that the slower motions somehow seemed more natural,even if unrealistic, as a giant (2 responses). Another difference to Study 1 was that for Study 2, subjectschoosing true physics in O1 usually gave the same response also to O2; the behavior of the logs at largescale was not surprising to the same extent as the behavior of the tabs in small scale.We used Likert scale rating questionnaires to gather additional insight into our findings. The questionsfocused on various dynamic properties of the objects so that we could more specifically pinpoint theeffects of physics simulations on perceived realism. These responses indicated preferences towards moviephysics as well, with significant differences regarding the perceived realism of the object behavior (withthe exceptions of question L2, speed when thrown, in Study 1 and L4, bouncincess, in Study 2). The
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Likert data further confirms that physically accurate representations of physics in abnormal scales are notinherently intuitive for VR users.According to our results, accurate accelerations and falling speeds of objects were perceived as unrealistic.The distance that the subjects were able to throw the objects was seen mostly as too short in Study 1 andtoo long in Study 2. However, there were also responses in both studies that considered movie physics to betoo extreme.In Study 1, responses regarding the bounciness of the of the tabs indicated that subjects expected the tabsto behave as if they were enlarged 10-fold. In Study 2, however, the reactions to bounciness were muchmore mixed; even if median and mode responses preferred movie physics , the responses were too mixedto cross the threshold of significance at p = 0 . . We believe the main reason for the difference for theseresponses is the scale. In Study 1, the tabs were not practically bouncing at all in the true physics condition.In Study 2, however, the logs were bouncing in both conditions.In Study 2, we inquired about the extent to which the subjects felt like a giant in a normal-sized city insteadof a regular-sized person in a miniature city. We found a significant difference between the conditions,indicating the subjects in the true physics condition felt larger. This may mean that even if the subjects didnot generally believe the true physics condition to be realistic, it succeeded better in providing the illusionof being large.We inspected the effects of various aspects of the subjects’ background on their responses to O1. Itcould be that the subjects with knowledge of physics, for example, might prefer the true physics condition.However, we found no such effects in either of our subject groups. In addition, we did not find theself-reported level of presence (Slater et al. 1994), either as SUS scores or by dividing subjects into groupsof high and low presence, to affect the response to O1 in either study. In Study 2, we found a significanteffect for the variable L6 feeling of own size - movie physics . This suggests that the extent to which thesubjects experienced the illusion of being a giant in the movie physics condition had at least some effecton the subjects’ perception of physics. However, the overall performance of the classifier was not verygood, and the distributions of the subjects’ responses were very large. For this reason, we believe furtherinvestigation is necessary before we can claim whether or not the extent of the small-scale or large-scaleillusion affects the perception of physics.In Study 2, we also studied pseudohaptic sensations experienced by the subjects and found that the overallextent of the sensations was very low. A handful of subjects reported strong pseudohaptic sensations. Therewas, as expected, a perceived difference regarding the overall weight of the logs between conditions.We found that the level of presence experienced by subjects in Study 2 was somewhat lower. However, asof now, we do not have evidence to claim whether the illusions of being small or large affected self-reportedpresence or whether, for example, the properties of the VEs used in the studies would explain thesedifferences. Slater (2009) discussed the role of conformity to expectations, prior beliefs and knowledge for causingand maintaining PSI. Skarbez et al. (2020) conceptualized the former as coherence , the reasonable behaviorof the VE, which, according to Skarbez, is related to PSI similarly as immersion is related to PI.Looking at the results against this framework, we can see that in Study 1, movie physics was clearly thereasonable behavior for subjects. Even if 27% of subjects considered true physics as real, only a handful of
Preprint ouke et al. Plausibility Paradox for Resized Users subjects considered it matching their expectations. Therefore according to the results of Study 1, realisticobject behavior in small scale clearly violated coherence.According to the results of Study 2, it is somewhat unclear which behavior is the coherent one, even ifthe results are somewhat pointing towards movie physics . Although a significant majority did consider movie physics as the realistic behavior, the expectations of subjects were matched almost even. Becauseof this mixed response to expectations, it is not straightforward to say, which model would yield goodcoherence in VEs.If one was to design a multiscale VR application that would aim at maximizing coherence instead ofrealism, it would make sense simply to match the physics with the scale of the user, at least in small-scale applications. If the user is allowed to change scale, the physics behavior would follow similarly toHollywood movies such as
Honey I Shrunk the Kids where object motions constantly change in speed fromscene to scene according to perspective changes. In large scales, however, this type of behavior might leadto bad coherence. In addition, in mCVEs this approach would break since the physics model would not beable to feasibly accommodate all users’ perspectives simultaneously during multi-user interaction.If realistic physics are intended, then users’ expectations would have to be modified by some type oftraining so that realistic behavior does not come up as surprising. According to Skarbez et al. (2020) badcoherence in VEs, especially in relation to unexpectedly behaving environment, can lead to stress anddiscomfort. In addition, there might be cases where human interaction capabilities are reduced due tounexpected physics. Micro- and nano-evel robotics operations are an example of this Sitti (2007). For thisreason we consider interaction at abnormal scales and perceptual training as important future researchdirections; even if users would expect realistic physics, their performance might still be affected.Through recent advances in consumer VR hardware as well as sub-microscopic (Plisson and Zotkina2015) and even atomic (Zheng et al. 2017) level imaging techniques, it is possible that we will witnessan increasing exploitation of scaled-down VR applications in the future. They could potentially includecommercial systems such as teleoperated maintenance robots or commercial virtual design solutions at amicroscopic scale. However, at this stage, it is unclear whether it would be intuitive for humans to operateat small scales, especially if it involves operating in the real world or with realistically simulated physics.As can be seen from our results, the perception of physical phenomena as a scaled-down entity is likely tobe unintuitive for most. However, it was interesting to note that half of the subjects experienced a strongPI despite the apparent improbability of the experience of being doll-sized. As the scale of operationdecreases, perceived frictions and accelerations increase, which has already been found problematic forhumans in robotic micro- and nano-level operations (Sitti 2007). As the scale decreases further, theseperceived distortions amplify, and additional phenomena such as fluid dynamics and static electricity,come into play as well. Relative changes in the environment would also provide additional challenges inthe physical domain. For example, a floor that is experienced as smooth at a regular scale might becomebumpy and full of cracks. Grit and dirt might become actual obstacles for navigation. Vibrations frompassersby otherwise indistinguishable might feel like earthquakes. We also investigated the perception ofphysics at large scale. Study 2 enlarged the subjects 10-fold while giving them a similar interaction task.Although the users believed movie physics as realistic similarly to Study 1, the expectations of users wasmuch more mixed. We believe this finding might be useful for designing abnormal-scale VEs where PSI ismore important than realism such as games. Realistic physics in small-scale interactions greatly violatedthe expectations of users while in large-scale slow, realistic motions sometimes seemed natural, even ifultimately unrealistic.
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Plausibility Paradox for Resized Users
We argue that our study opens up interesting avenues for future VR research. VR education has alreadybeen seen as a potential remedy for some issues of small-scale activities in the field of teleoperation(Millet et al. 2008). Further research on the effect of perception-related mismatches on interaction andperformance in various applications could yield interesting findings. Also, as of now, we do not knowwhether the body-scaling effect affects the perception of physics the same way it affects the perceptionof sizes and distances (eg. van der Hoort et al. (2011)). In both studies, we used virtual hands to providea body-based size cue, but we did not investigate the effect the absence of these cues would have had.Langbehn et al. (2016a) found that groups of human avatars can override the dominant scale otherwisedictated by body-based size cues. Theoretically, this could have implications for perception of physics, aswell.
Outliers in responses were L2 in Study 1 and L4 in Study 2. Inspecting the distribution of responses inquestion L2 in Study 1, we see that the true physics condition contains responses that are rather uniformlydistributed in comparison to the movie physics condition; the STD in the true physics condition is twiceas large as in the movie physics condition. Whereas in responses to L2 the movie physics conditionwas considered realistic (4, neither too fast nor two slow) by a vast majority, the real physics conditionreceived an almost equal number of responses between 2 (too slow) and 6 (too fast). We suspect that theuncharacteristic distribution of the responses might be due to a poor wording of L2 (
The speed of pulltabs when thrown ). Although we tried to ask how the subjects perceived the time of flight of the tabs, itcould be that subjects had other interpretations of the question resulting in inconsistent responses. Similarinconsistency was found in responses from both Finnish and English speaking subjects, so we do not thinkthe confusion could be attributed to the specific wordings in either language. Rather, we speculate thatsome subjects thought we meant the speed of the tab in leaving their hand (resulting in short flight distance)upon throwing, and others thought we meant the speed that the tab moved through the air. Alternateinterpretations could have resulted from misinterpreting the action of the tabs as having been caused bytheir own inability to throw the tabs correctly. We changed the wording of this question in Study 2 to ”Timeof Flight” .In Study 2, L4 (the bounciness of the logs) received mixed responses. Although mean and mode responsespreferred movie physics similarly to other questions, the responses were overall more mixed. We considerbounciness as the most unrealistic aspect of Study 2, since we did not simulate splintering, or otherwisebreaking the log due to impact. We considered these aspects as confounding variables in a study that mainlyfocused on the perception of rigid body dynamics.In Study 1, according to both verbal comments during the experiment as well as responses to questionsO1 and O2, some of the subjects starting with the true physics condition thought that the reason for theirdifficulty in throwing the tabs to a far distance was their own inability to use the controllers and not relatedto aspects of the VE. Although some subjects realized during the subsequent movie physics condition thatthe behavior of the tabs was an experimental manipulation and not due to their own failure, there were stillthree subjects that stated as their main reason for preferring the movie physics condition to be the fact thatthey had learned how to use the controllers. For subjects experiencing movie physics first, there did notseem to be any ambiguity that the difference in the behavior of the tabs was related to the VE. Althougha training session helping to learn the controllers might have been helpful, we believe that it could haveintroduced unwanted priming of the subjects regarding the expected behavior of physics. We received thesetypes of responses far less in Study 2, which might be due to opposite behavior of objects when throwing.
Preprint ouke et al. Plausibility Paradox for Resized Users
Another obvious limitation is the fact that it is currently difficult to realistically simulate object mass inVR since subjects can feel only the weight of the controllers. Although we chose the soda can pull tabsfor the task in Study 1 partly because of their light mass, there was some speculation among responses toO1-O2 on whether the weight of the object and/or simulated arm strength affected object manipulation.There were responses in Study 2 as well that considered throwing distance to be affected by the armstrength of the giant. However, simulating muscle strength in itself was not in the scope of either study.Human-scale arm motions were simply scaled either down or up by a factor of ten, which resulted in eithervery small or very large velocity imparted on the thrown object.During a few experimental sessions, there were occurrences which could have broken presence or causeddifferences in the experiences of the participants. Two subjects in Study 1 became very active in the VEand accidentally bumped into furniture in the research space. In Study 2, one subject accidentally steppedon the HMD cord during the session. In Study 1, a physics engine bug caused a single tab to land in anunrealistic orientation during the true physics condition for two subjects. For one subject trying to throwthe tab with two hands, a bug caused the tab to catapult unrealistically far. We are not sure to what extentthe subjects noticed these bugs or if it affected their responses. In Study 2, we did not observe physics bugsas obvious as those seen in Study 1. This might be partly due to the instructions for object manipulationbeing stricter and the scale of the objects being less prone for errors in the physics engine. Even still, wecannot guarantee that the bounciness of the logs was realistic at all times.Additionally, although we tried to keep the visual appearances of the two conditions as similar as possiblein Study 1, the differences in the VE scale in the UE to simulate the two types of physics led to verysubtle differences in their brightness. This deficiency was fixed in Study 2 by simulating human-scale andgiant-scale physics by manipulating gravity instead of scaling the scene objects.Finally, there were subjects who were not always paying close attention to the flying or fallingcharacteristics of the tabs, or did not wait until the instructions were read in their entirety. This limitationwas somewhat alleviated in Study 2 due to the stricter instructions given to the subjects.
In this paper, we studied a phenomenon regarding the plausibility of physical interactions for scaled-downand scaled-up users in normal-sized VEs; when users interact with physically simulated objects in a VEwhere the user is scaled 10-fold smaller or larger from a regular human scale, there is a mismatch betweenexpected physics and the accurate approximation of physics at that scale. A similarly sized and significantmajority of both scaled-down and scaled-up subjects judged rigid-body dynamics close to human-scalerealistic instead of what would be the correct approximation of realism at the resized scale the subjectswere on. Almost all subjects at a small-scale considered rigid-body dynamics at that scale to be surprising,while the expectations of large-scale subjects were more mixed. We argue that these findings open manyinteresting avenues for future research regarding mCVEs, scaled-down user VR applications in general, aswell as telepresence and teleoperation taking place at a modified scale. In addition, our findings can proveuseful to designers of VR applications utilizing abnormal scales, who wish to maintain PSI, or who areseeking to find a trade-off between PSI and realism.In the future, we intend to study the body scaling effect and its influence on interactions with physicallysimulated objects. In addition, we will investigate interaction, performance, and perceptual training atabnormal scales. We will consider scales smaller than 1 order of magnitude since we expect them to provideeven greater plausibility mismatches in physical interactions. We will also seek to confirm the existence ofour finding outside VR, for example using robotic teleoperation or telepresence at small scale. Moreover,
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Plausibility Paradox for Resized Users we will seek further evidence as to whether the extent of the illusion of being small or being large affectsthe perception of physics.
CONFLICT OF INTEREST STATEMENT
The authors declare that the research was conducted in the absence of any commercial or financialrelationships that could be construed as a potential conflict of interest.
FUNDING
This work was supported by the PIXIE project (331822) as well as the PERCEPT project (322637) fundedby the Academy of Finland. This work was also supported by the COMBAT project (293389) funded by theStrategic Research Council at the Academy of Finland as well as the HUMORcc project (6926/31/2018)funded by Business Finland.
ACKNOWLEDGMENTS
This paper extends the previous work by Pouke et al. (2020) titled ”The Plausibility Paradox For Scaled-Down Users in Virtual Environments” originally published in the IEEE Conference on Virtual Reality and3D User Interfaces (IEEE VR 2020). Parts of the original article are reused with permission. The authorsalso wish to thank all the subjects for their participation in this study.
REFERENCES
Alatalo, T., Koskela, T., Pouke, M., Alavesa, P., and Ojala, T. (2016). VirtualOulu: collaborative, immersiveand extensible 3d city model on the web. In
Proceedings of the 21st International Conference on Web3DTechnology (ACM), 95–103Alex, J., Vikramaditya, B., and Nelson, B. (1998). A virtual reality teleoperator interface for assembly ofhybrid MEMS prototypes. In
Proceedings of DETC . vol. 98, 13–16Banakou, D., Groten, R., and Slater, M. (2013). Illusory ownership of a virtual child body causesoverestimation of object sizes and implicit attitude changes.
Proceedings of the National Academy ofSciences
Computers & Graphics
25, 745–753Bolopion, A. and R´egnier, S. (2013). A review of haptic feedback teleoperation systems formicromanipulation and microassembly.
IEEE Transactions on automation science and engineering
American Journal of Physics
72, 305–312Deng, Z. and Interrante, V. (2019). Am I floating or not?: Sensitivity to eye height manipulations inHMD-based immersive virtual environments. In
ACM Symposium on Applied Perception . 1–6Dodgson, N. A. (2004). Variation and extrema of human interpupillary distance. In
Stereoscopic Displaysand Virtual Reality Systems XI (International Society for Optics and Photonics), vol. 5291, 36–46Hatamura, Y. and Morishita, H. (1990). Direct coupling system between nanometer world and humanworld. In
IEEE Proceedings on Micro Electro Mechanical Systems, An Investigation of Micro Structures,Sensors, Actuators, Machines and Robots.
Neurosurgery
51, 985–988; discussion 988
Preprint ouke et al. Plausibility Paradox for Resized Users
Interrante, V., Ries, B., Lindquist, J., Kaeding, M., and Anderson, L. (2008). Elucidating factors that canfacilitate veridical spatial perception in immersive virtual environments.
Presence: Teleoperators andVirtual Environments
17, 176–198Izumihara, A., Sasaki, T., Ogino, M., Takamura, R., and Inami, M. (2019). Transfantome: transformationinto bodies of various scale and structure in multiple spaces. In
ACM SIGGRAPH 2019 EmergingTechnologies . 1–2Kim, J. and Interrante, V. (2017). Dwarf or giant: The influence of interpupillary distance and eye height onsize perception in virtual environments. In
Proceedings of the 27th International Conference on ArtificialReality and Telexistence and 22nd Eurographics Symposium on Virtual Environments (EurographicsAssociation), 153–160Kopper, R., Tao Ni, Bowman, D. A., and Pinho, M. (2006). Design and Evaluation of NavigationTechniques for Multiscale Virtual Environments. In
IEEE Virtual Reality Conference (VR 2006) .175–182Langbehn, E., Bruder, G., and Steinicke, F. (2016a). Scale matters! Analysis of dominant scale estimationin the presence of conflicting cues in multi-scale collaborative virtual environments. In . 211–220Langbehn, E., Bruder, G., and Steinicke, F. (2016b). Scale matters! Analysis of dominant scale estimationin the presence of conflicting cues in multi-scale collaborative virtual environments. In . 211–220L´ecuyer, A. (2009). Simulating haptic feedback using vision: A survey of research and applications ofpseudo-haptic feedback.
Presence: Teleoperators and Virtual Environments
18, 39–53Leyrer, M., Linkenauger, S. A., B¨ulthoff, H. H., Kloos, U., and Mohler, B. (2011). The influence of eyeheight and avatars on egocentric distance estimates in immersive virtual environments. In
Proceedingsof the ACM SIGGRAPH Symposium on Applied Perception in Graphics and Visualization (New York,NY, USA: ACM), APGV ’11, 67–74. Event-place: Toulouse, FranceLi, Z. and Sitte, R. (2001). Virtual reality modeling aid in MEMS design. In
Electronics and Structures forMEMS II (International Society for Optics and Photonics), vol. 4591, 153–162Linkenauger, S. A., Leyrer, M., B¨ulthoff, H. H., and Mohler, B. J. (2013). Welcome to wonderland: Theinfluence of the size and shape of a virtual hand on the perceived size and shape of virtual objects.
PloSone
8, e68594McCoy, J. and Ullman, T. (2019). Judgments of effort for magical violations of intuitive physics.
PloS one
14, e0217513McIntyre, J., Zago, M., Berthoz, A., and Lacquaniti, F. (2001). Does the brain model newton’s laws?
Nature neuroscience
4, 693–694Millet, G., L´ecuyer, A., Burkhardt, J.-M., Haliyo, D. S., and R´egnier, S. (2008). Improving perception andunderstanding of nanoscale phenomena using haptics and visual analogy. In
International Conferenceon Human Haptic Sensing and Touch Enabled Computer Applications (Springer), 847–856Mujber, T. S., Szecsi, T., and Hashmi, M. S. J. (2004). Virtual reality applications in manufacturing processsimulation.
Journal of Materials Processing Technology
Proceedings of the 8th Augmented Human International Conference (ACM),35Ogawa, N., Narumi, T., and Hirose, M. (2019). Virtual hand realism affects object size perception inbody-based scaling. In . 519–528Patton, M. Q. (2005). Qualitative research.
Encyclopedia of statistics in behavioral science
Preprint 27 ouke et al.
Plausibility Paradox for Resized Users
Piumsomboon, T., Lee, G. A., Ens, B., Thomas, B. H., and Billinghurst, M. (2018a). Superman vsgiant: A study on spatial perception for a multi-scale mixed reality flying telepresence interface.
IEEETransactions on Visualization and Computer Graphics
24, 2974–2982Piumsomboon, T., Lee, G. A., Hart, J. D., Ens, B., Lindeman, R. W., Thomas, B. H., et al. (2018b).Mini-me: An adaptive avatar for mixed reality remote collaboration. In
Proceedings of the 2018 CHIconference on human factors in computing systems . 1–13Plisson, H. and Zotkina, L. V. (2015). From 2d to 3d at macro- and microscopic scale in rock art studies.
Digital Applications in Archaeology and Cultural Heritage
2, 102–119Pouke, M., Mimnaugh, K. J., Ojala, T., and LaValle, S. M. (2020). The plausibility paradox for scaled-downusers in virtual environments. In (IEEE), 913–921Renner, R. S., Velichkovsky, B. M., and Helmert, J. R. (2013). The Perception of Egocentric Distances inVirtual Environments - A Review.
ACM Comput. Surv.
46, 23:1–23:40Rovira, A., Swapp, D., Spanlang, B., and Slater, M. (2009). The use of virtual reality in the study ofpeople’s responses to violent incidents.
Frontiers in behavioral neuroscience
3, 59Samad, M., Gatti, E., Hermes, A., Benko, H., and Parise, C. (2019). Pseudo-haptic weight: Changing theperceived weight of virtual objects by manipulating control-display ratio. In
Proceedings of the 2019CHI Conference on Human Factors in Computing Systems . 1–13Senot, P., Zago, M., Lacquaniti, F., and McIntyre, J. (2005). Anticipating the effects of gravitywhen intercepting moving objects: differentiating up and down based on nonvisual cues.
Journalof Neurophysiology
94, 4471–4480Shenai, M. B., Tubbs, R. S., Guthrie, B. L., and Cohen-Gadol, A. A. (2014). Virtual interactive presencefor real-time, long-distance surgical collaboration during complex microsurgical procedures.
Journal ofNeurosurgery
IEEE Robotics& Automation Magazine
14, 53–60Skarbez, R., Brooks, F., and Whitton, M. (2020). Immersion and coherence: Research agenda and earlyresults.
IEEE Transactions on Visualization and Computer Graphics
Skarbez, R., Brooks, F. P., Jr, and Whitton, M. C. (2017a). A survey of presence and related concepts.
ACM Computing Surveys (CSUR)
50, 1–39Skarbez, R., Neyret, S., Brooks, F. P., Slater, M., and Whitton, M. C. (2017b). A PsychophysicalExperiment Regarding Components of the Plausibility Illusion.
IEEE Transactions on Visualization andComputer Graphics
23, 1369–1378Slater, M. (2009). Place illusion and plausibility can lead to realistic behaviour in immersive virtualenvironments.
Philosophical Transactions of the Royal Society B: Biological Sciences
Frontiers in neuroscience
3, 29Slater, M., Usoh, M., and Steed, A. (1994). Depth of presence in virtual environments.
Presence:Teleoperators & Virtual Environments
3, 130–144Slater, M. and Wilbur, S. (1997). A framework for immersive virtual environments (FIVE): Speculationson the role of presence in virtual environments.
Presence: Teleoperators & Virtual Environments
Trends in cognitive sciences
21, 649–665
Preprint ouke et al. Plausibility Paradox for Resized Users
Usoh, M., Catena, E., Arman, S., and Slater, M. (2000). Using presence questionnaires in reality.
Presence:Teleoperators & Virtual Environments
9, 497–503van der Hoort, B., Guterstam, A., and Ehrsson, H. H. (2011). Being Barbie: The size of one’s own bodydetermines the perceived size of the world.
PLoS One
6, e20195Yao, H.-y. and Hayward, V. (2006). An experiment on length perception with a virtual rolling stone. In
Proceedings of Eurohaptics . 325–330Zhang, J., Dong, Z., Lindeman, R., and Piumsomboon, T. (2020a). Spatial scale perception for designtasks in virtual reality. In
Symposium on Spatial User Interaction . 1–3Zhang, J., Piumsomboon, T., Dong, Z., Bai, X., Hoermann, S., and Lindeman, R. (2020b). Exploringspatial scale perception in immersive virtual reality for risk assessment in interior design. In
ExtendedAbstracts of the 2020 CHI Conference on Human Factors in Computing Systems . 1–8Zhang, X. and Furnas, G. W. (2005). mCVEs: Using cross-scale collaboration to support user interactionwith multiscale structures.
Presence: Teleoperators & Virtual Environments
14, 31–46Zheng, S. Q., Palovcak, E., Armache, J.-P., Verba, K. A., Cheng, Y., and Agard, D. A. (2017). MotionCor2:anisotropic correction of beam-induced motion for improved cryo-electron microscopy.
Nature methods
14, 33114, 331