Karl K. Kopiske

The functional subdivision of the visual brain: Is there a real illusion effect on action? A multi-lab replication study

It has often been suggested that visual illusions affect perception but not actions such as grasping, as predicted by the two-visual-systems hypothesis of Milner and Goodale (1995, The Visual Brain in Action, Oxford University press). However, at least for the Ebbinghaus illusion, relevant studies seem to reveal a consistent illusion effect on grasping (Franz & Gegenfurtner, 2008. Grasping visual illusions: consistent data and no dissociation. Cognitive Neuropsychology). Two interpretations are possible: either grasping is not immune to illusions (arguing against dissociable processing mechanisms for vision-for-perception and vision-for-action), or some other factors modulate grasping in ways that mimic a vision-for perception effect in actions. It has been suggested that one such factor may be obstacle avoidance (Haffenden Schiff & Goodale, 2001. The dissociation between perception and action in the Ebbinghaus illusion: nonillusory effects of pictorial cues on grasp. Current Biology, 11, 177-181). In four different labs (total Nxa0=xa0144), we conducted an exact replication of previous studies suggesting obstacle avoidance mechanisms, implementing conditions that tested grasping as well as multiple perceptual tasks. This replication was supplemented by additional conditions to obtain more conclusive results. Our results confirm that grasping is affected by the Ebbinghaus illusion and demonstrate that this effect cannot be explained by obstacle avoidance.

Adaptation effects in grasping the Müller-Lyer illusion

&NA; Recent results have shown that effects of pictorial illusions in grasping may decrease over the course of an experiment. This can be explained as an effect of sensorimotor learning if we consider a pictorial size illusion as simply a perturbation of visually perceived size. However, some studies have reported very constant illusion effects over trials. In the present paper, we apply an error‐correction model of adaptation to experimental data of N = 40 participants grasping the Müller‐Lyer illusion. Specifically, participants grasped targets embedded in incremental and decremental Müller‐Lyer illusion displays in (1) the same block in pseudo‐randomised order, and (2) separate blocks of only one type of illusion each. Consistent with predictions of our model, we found an effect of interference between the two types when they were presented intermixed, explaining why adaptation rates may vary depending on the experimental design. We also systematically varied the number of object sizes per block, which turned out to have no effect on the rate of adaptation. This was also in accordance with our model. We discuss implications for the illusion literature, and lay out how error‐correction models can explain perception‐action dissociations in some, but not all grasping‐of‐illusion paradigms in a parsimonious and plausible way, without assuming different illusion effects.

Do visual illusions affect grasping? Considerable progress in a scientific debate. A reply to Whitwell & Goodale, 2016

Karl K. Kopiske , Nicola Bruno , Constanze Hesse , Thomas Schenk d and Volker H. Franz e a Center for Neuroscience and Cognitive Systems@UniTn, Istituto Italiano di Tecnologia (IIT), Rovereto, TN, Italy b Dipartimento di Neuroscienze, Universit a di Parma, Unit a di Psicologia, Parma, Italy c University of Aberdeen, School of Psychology, William Guild Building, Kings College, Aberdeen, United Kingdom d Ludwig-Maximilians Universit€ at München, Department of Psychology, Munich, Germany e University of Tübingen, Institute of Computer Sciences, Department of Experimental Cognitive Sciences, Tübingen, Germany

On the response function and range dependence of manual estimation

Manual estimates without vision of the hand are thought to constitute a form of cross-modal matching between stimulus size and finger opening. However, few investigations have systematically looked at how manual estimates relate a perceived size to the response across different ranges of stimuli. In two experiments (Nu2009=u200918 and Nu2009=u200914), we sought to map out the response properties for (1) manual estimates of visually presented stimuli as well as (2) visual estimates of proprioceptive stimuli, and to test whether these properties depend on the range of stimuli. We also looked at whether scalar variability is present in manual estimates, as predicted by Weber’s Law for perceptual tasks. We found that manual estimates scale linearly and with a slope of close to 1 with object sizes up to 90xa0mm, before participants’ hand size limited their responses. In contrast, we found a shallower response slope of about 0.7 when participants performed the inverse task, adjusting the size of a visual object to match a not actively chosen, induced finger opening. Our results were mixed with regards to scalar variability in large objects. We saw some indication of a plateau, but no evidence for an effect of mechanical constraints in the range studied (up to 90xa0mm). Participants also showed a clear tendency to overestimate small differences when a set of objects differed little in size, but not when stimulus differences were more pronounced.

Multiple distance cues do not prevent systematic biases in reach to grasp movements

The perceived distance of objects is biased depending on the distance from the observer at which objects are presented, such that the egocentric distance tends to be overestimated for closer objects, but underestimated for objects further away. This leads to the perceived depth of an object (i.e., the perceived distance from the front to the back of the object) also being biased, decreasing with object distance. Several studies have found the same pattern of biases in grasping tasks. However, in most of those studies, object distance and depth were solely specified by ocular vergence and binocular disparities. Here we asked whether grasping objects viewed from above would eliminate distance-dependent depth biases, since this vantage point introduces additional information about the object’s distance, given by the vertical gaze angle, and its depth, given by contour information. Participants grasped objects presented at different distances (1) at eye-height and (2) 130xa0mm below eye-height, along their depth axes. In both cases, grip aperture was systematically biased by the object distance along most of the trajectory. The same bias was found whether the objects were seen in isolation or above a ground plane to provide additional depth cues. In two additional experiments, we verified that a consistent bias occurs in a perceptual task. These findings suggest that grasping actions are not immune to biases typically found in perceptual tasks, even when additional cues are available. However, online visual control can counteract these biases when direct vision of both digits and final contact points is available.

Comparing Symbolic and Nonsymbolic Number Lines: Consistent Effects of Notation Across Output Measures

The mental number line (MNL) is a popular metaphor for magnitude representation in numerical cognition. Its shape has frequently been reported as being nonlinear, based on nonlinear response functions in magnitude estimation. We investigated whether this shape reflects a phenomenon of the mapping from stimulus to internal magnitude representation or of the mapping from internal representation to response. In five experiments, participants (total N = 66) viewed stimuli that represented numerical magnitude either in a symbolic notation (i.e., Arabic digits) or in a nonsymbolic notation (i.e., clouds of dots). Participants estimated these magnitudes by either adjusting the position of a mark on a ruler-like response bar (nonsymbolic response) or by typing the corresponding number on a keyboard (symbolic response). Responses to symbolic stimuli were markedly different from responses to nonsymbolic stimuli, in that they were mostly powershaped. We investigated whether the nonlinearity could be explained by effects of previous trials, but such effects were (a) not strong enough to explain the nonlinear responses and (b) existed only between trials of the same input notation, suggesting that the nonlinearity is due to input mappings. Introducing veridical feedback improved the accuracy of responses, thereby showing a calibration based on the feedback. However, this calibration persisted only temporarily, and responses to nonsymbolic stimuli remained nonlinear. Overall, we conclude that the nonlinearity is a phenomenon of the mapping from nonsymbolic input format to internal magnitude representation and that the phenomenon is surprisingly robust to calibration.

The SNARC Effect in Chinese Numerals: Do Visual Properties of Characters and Hand Signs Influence Number Processing?

The SNARC effect refers to an association of numbers and spatial properties of responses that is commonly thought to be amodal and independent of stimulus notation. We tested for a horizontal SNARC effect using Arabic digits, simple-form Chinese characters and Chinese hand signs in participants from Mainland China. We found a horizontal SNARC effect in all notations. This is the first time that a horizontal SNARC effect has been demonstrated in Chinese characters and Chinese hand signs. We tested for the SNARC effect in two experiments (parity judgement and magnitude judgement). The parity judgement task yielded clear, consistent SNARC effects in all notations, whereas results were more mixed in magnitude judgement. Both Chinese characters and Chinese hand signs are represented non-symbolically for low numbers and symbolically for higher numbers, allowing us to contrast within the same notation the effects of heavily learned non-symbolic vs. symbolic representation on the processing of numbers. In addition to finding a horizontal SNARC effect, we also found a robust numerical distance effect in all notations. This is particularly interesting as it persisted when participants reported using purely visual features to solve the task, thereby suggesting that numbers were processed semantically even when the task could be solved without the semantic information.

The SNARC effect and visual and semantic features of Chinese numerals

The SNARC (spatial numerical association of response codes) effect refers to an association between numbers and spatial properties of responses. The effect occurs in a multitude of stimulus notations, such that it is commonly thought to be amodal and notation-independent. In two experiments, we tested for a horizontal SNARC effect in participants from mainland China in Arabic digits, simple-form Chinese characters and Chinese hand signs to investigate whether the spatial mapping of numbers varied between notations with different visuospatial properties. We found a horizontal SNARC effect in all notations, the first time that a horizontal SNARC effect has been demonstrated in Chinese characters and Chinese hand signs. Chinese hand signs and Chinese characters were of particular interest to us, as these notations are represented non-symbolically through numerosity for low numbers (1…5 and 1…3, respectively) but symbolically for higher numbers, thus giving us a control condition within the same notation to investigate effects of numerosity on the processing of numbers. Our data indicate that numerosity is processed in parallel to number magnitude and substantially influenced the strength of the SNARC effect. We discuss both purely perceptual mechanisms for this influence, considering processing times and the different visual complexity of symbolically and non-symbolically represented numbers, and cognitive mechanisms taking into account previous studies on the role of reading and finger counting habit in numerical processing. Meeting abstract presented at VSS 2015.