Wa Wijnand IJsselsteijn

A survey of perceptual evaluations and requirements of three-dimensional TV

A high-quality three-dimensional (3-D) broadcast service (3-D TV) is becoming increasingly feasible based on various recent technological developments combined with an enhanced understanding of 3-D perception and human factors issues surrounding 3-D TV. In this paper, 3-D technology and perceptually relevant issues, in particular 3-D image quality and visual comfort, in relation to 3-D TV systems are reviewed. The focus is on near-term displays for broadcast-style single- and multiple-viewer systems. We discuss how an image quality model for conventional two-dimensional images needs to be modified to be suitable for image quality research for 3-D TV. In this respect, studies are reviewed that have focused on the relationship between subjective attributes of 3-D image quality and physical system parameters that induce them (e.g., parameter choices in image acquisition, compression, and display). In particular, artifacts that may arise in 3-D TV systems are addressed, such as keystone distortion, depth-plane curvature, puppet theater effect, cross talk, cardboard effect, shear distortion, picket-fence effect, and image flipping. In conclusion, we summarize the perceptual requirements for 3-D TV that can be extracted from the literature and address issues that require further investigation in order for 3-D TV to be a success.

Using Behavioral Realism to Estimate Presence: A Study of the Utility of Postural Responses to Motion Stimuli

We recently reported that direct subjective ratings of the sense of presence are potentially unstable and can be biased by previous judgments of the same stimuli (Freeman et al., 1999). Objective measures of the behavioral realism elicited by a display offer an alternative to subjective ratings. Behavioral measures and presence are linked by the premise that, when observers experience a mediated environment (VE or broadcast) that makes them feel present, they will respond to stimuli within the environment as they would to stimuli in the real world. The experiment presented here measured postural responses to a video sequence filmed from the hood of a car traversing a rally track, using stereoscopic and monoscopic presentation. Results demonstrated a positive effect of stereoscopic presentation on the magnitude of postural responses elicited. Posttest subjective ratings of presence, vection, and involvement were also higher for stereoscopically presented stimuli. The postural and subjective measures were not significantly correlated, indicating that nonproprioceptive postural responses are unlikely to provide accurate estimates of presence. Such postural responses may prove useful for the evaluation of displays for specific applications and in the corroboration of group subjective ratings of presence, but cannot be taken in place of subjective ratings.

Perceived depth and the feeling of presence in 3DTV

The present study investigates the subjective feeling of presence elicited by 3DTV and its relationship to perceived depth and image content. Subjective methods of assessing presence that have been used or proposed to date do not provide a measure of temporal variation. To overcome this limitation, we have applied the continuous assessment methodology (ITU-R, BT 500-7) to the assessment of presence, perceived depth and naturalness of depth. Twelve observers continuously rated their instantaneous perception of presence, depth and naturalness of depth when viewing stereoscopic footage. The results indicate that subjective presence ratings are subject to considerable temporal variation depending on the image content and camera techniques used. The correlations between the different attributes suggest that an increase in depth may lead to an enhanced sense of presence, provided depth is perceived as natural. A qualitative analysis of the data in relation to the image content provides evidence for the hypothesis that the extent of sensory information available to an observer is a determinant of presence, as proposed by T.B. Sheridan, Musings on telepresence and virtual presence, Presence: Teleoperators and Virtual Environments 1 (1992) 120‐125. q 1998 Elsevier Science B.V.

Mediated social touch: a review of current research and future directions

In this paper, we review research and applications in the area of mediated or remote social touch. Whereas current communication media rely predominately on vision and hearing, mediated social touch allows people to touch each other over a distance by means of haptic feedback technology. Overall, the reviewed applications have interesting potential, such as the communication of simple ideas (e.g., through Hapticons), establishing a feeling of connectedness between distant lovers, or the recovery from stress. However, the beneficial effects of mediated social touch are usually only assumed and have not yet been submitted to empirical scrutiny. Based on social psychological literature on touch, communication, and the effects of media, we assess the current research and design efforts and propose future directions for the field of mediated social touch.

It is always a lot of fun!: exploring dimensions of digital game experience using focus group methodology

This paper focuses on digital game experience: the feelings and experiences people have when they play digital games. Digital game experience is not a one-dimensional concept. Great variety exists in game genres and game players, and game experiences will differ accordingly. To date, game experience is studied in a rather fragmented way. As such, the field still lacks a common vocabulary and a shared taxonomy of the different dimensions of game experience. In this paper we describe a focus group study and present a tentative, but comprehensive categorisation of game experience. Focus groups with various types of gamers were organised to capture a full first-hand account of game experiences and second, findings were discussed in an expert meeting in which empirical findings were consolidated with existing theoretical findings. The categorisation bears relevance for both game theorists and game developers wanting to get to the heart of digital game experience.

Effects of Sensory Information and Prior Experience on Direct Subjective Ratings of Presence

We report three experiments using a new form of direct subjective presence evaluation that was developed from the method of continuous assessment used to assess television picture quality. Observers were required to provide a continuous rating of their sense of presence using a handheld slider. The first experiment investigated the effects of manipulating stereoscopic and motion parallax cues within video sequences presented on a 20 in. stereoscopic CRT display. The results showed that the presentation of both stereoscopic and motion parallax cues was associated with higher presence ratings. One possible interpretation of Experiment 1 is that CRT displays that contain the spatial cues of stereoscopic disparity and motion parallax are more interesting or engaging. To test this, observers in Experiment 2 rated the same stimuli first for interest and then for presence. The results showed that variations in interest did not predict the presence ratings obtained in Experiment 1. However, the subsequent ratings of presence differed significantly from those obtained in Experiment 1, suggesting that prior experience with interest ratings affected subsequent judgments of presence. To test this, Experiment 3 investigated the effects of prior experience on presence ratings. Three groups of observers rated a training sequence for interest, presence, and 3-Dness before rating the same stimuli as used for Experiments 1 and 2 for presence. The results demonstrated that prior ratings sensitize observers to different features of a display resulting in different presence ratings. The implications of these results for presence evaluation are discussed, and a combination of more-refined subjective measures and a battery of objective measures is recommended.

Perceived quality of compressed stereoscopic images: Effects of symmetric and asymmetric JPEG coding and camera separation

JPEG compression of the left and right components of a stereo image pair is a way to save valuable bandwidth when transmitting stereoscopic images. This paper presents results on the effects of camera-base distance (B) and JPEG coding on overall image quality, perceived depth, perceived sharpness, and perceived eye strain. In the experiment, two stereoscopic still scenes were used, varying in depth (three different camera-base distances: 0, 8, and 12 cm) and compression ratio (4 levels: original, 1:30, 1:40, and 1:60). All levels of compression were applied to both the left and right stereo image, resulting in a 4 × 4 matrix of all possible symmetric and asymmetric coding combinations. The observers were asked to assess image quality, sharpness, depth, and eye strain. Results showed that an increase in JPEG coding had a negative effect on image quality, sharpness, and eye strain, but had no effect on perceived depth. An increase in camera-base distance increased perceived depth and reported eye strain, but had no effect on perceived sharpness. Results on asymmetric and symmetric coding showed that the relationship between perceived image quality and average bit rate is not straightforward. In some cases, image quality ratings of a symmetric coded pair can be higher than for an asymmetric coded pair, even if the averaged bit rate for the symmetric pair is lower, than for the asymmetric pair. Furthermore, sharpness and eye strain correlated highly and medium, respectively, with perceived image quality.

Connecting the family with awareness systems

Awareness systems have attracted significant research interest for their potential to support interpersonal relationships. Investigations of awareness systems for the domestic environment have suggested that such systems can help individuals stay in touch with dear friends or family and provide affective benefits to their users. Our research provides empirical evidence to refine and substantiate such suggestions. We report our experience with designing and evaluating the ASTRA awareness system, for connecting households and mobile family members. We introduce the concept of connectedness and its measurement through the Affective Benefits and Costs of communication questionnaire (ABC-Q). We inform results that testify the benefits of sharing experiences at the moment they happen without interrupting potential receivers. Finally, we document the role that lightweight, picture-based communication can play in the range of communication media available.

Persuasive technology for human well-being: setting the scene

In this short paper we aim to give a brief introduction to persuasive technology, especially as it pertains to human well-being. We discuss a number of current research opportunities in areas of healthcare, environmental conservation, and education. We conclude by highlighting what we regard as the key research challenges that need to be addressed, focusing on context sensing and appropriate feedback, the need for longitudinal user studies, and ethical concerns.

Is This My Hand I See Before Me? The Rubber Hand Illusion in Reality, Virtual Reality, and Mixed Reality

This paper presents a first study in which a recently reported intermodal perceptual illusion known as the rubber hand illusion is experimentally investigated under mediated conditions. When ones own hand is placed out of view and a visible fake hand is repeatedly stroked and tapped in synchrony with the unseen hand, subjects report a strong sense in which the fake hand is experienced as part of their own body. In our experiment, we investigated this illusion under three conditions: (i) unmediated condition, replicating the original paradigm, (ii) virtual reality (VR) condition, where both the fake hand and its stimulation were projected on the table in front of the participant, and (iii) mixed reality (MR) condition, where the fake hand was projected, but its stimulation was unmediated. Dependent measures included self-report (open-ended and questionnaire-based) and drift, that is, the offset between the felt position of the hidden hand and its actual position. As expected, the unmediated condition produced the strongest illusion, as indicated both by self-report and drift towards the rubber hand. The VR condition produced a more convincing subjective illusion than the MR condition, although no difference in drift was found between the mediated conditions. Results are discussed in terms of perceptual mechanisms underlying the rubber hand illusion, and the illusions relevance to understanding telepresence.