Jisien Yang
Yang’s iris illusion
Authors
Jisien Yang (University of Zurich )
Adrian Schwaninger (University of Zurich)
A new visual illusion in face perception is demonstrated. Faces were mirrored and combined so that the distance between the resulting four irises were equal. In Experiment 1, Caucasian and Asian face stimuli were used. Dot stimuli were created by deleting all face areas except the irises. The stimuli were presented either upright or inverted. Participants from two different ethnic groups (Swiss and Taiwanese) were asked to judge whether the distance between the middle two irises is larger, shorter or equal to the distance between the left two or right two irises. Participants perceived the distance between the middle two irises as shorter than the other distances regardless of orientation and participant race. The illusion was found in face stimuli but not in dot stimuli. Interestingly, the illusion magnitude was larger for Asian than Caucasian faces. In Experiment 2, the face stimuli were replaced by line drawings of the eyes and irises. The dot stimuli and the procedure were identical to Experiment 1. Similar results were obtained in Experiment 2 suggesting that the illusion is caused by the shape of the eyes only independent of facial context.
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Sylvain Delplanque
Temporal unfolding of novelty and pleasantness appraisals of odors.
Authors
Sylvain Delplanque (University of Geneva)
Christelle Chrea (University of Geneva)
Didier Grandjean (University of Geneva)
Laurence Aymard (FIRMENICH SA, Geneva)
David Sander (University of Geneva)
Klaus Scherer (University of Geneva)
The aim of this research consists in investigating the effects of odours on appraisal processes and consequent emotional responses. The temporal sequence of novelty detection and intrinsic pleasantness evaluations is the main interest of this experiment. The main hypothesis is that a stimulus is detected as perceptually novel before being evaluated as pleasant or unpleasant. In order to tackle this issue, we have adopted a multicomponential approach consisting in measuring motor (facial EMG) and physiological reactions (ECG, respiratory frequency and EDA) to odours. Participants were engaged in a delayed matching to sample recognition task in which several pairs of unpleasant or pleasant odours (composed by a sample and a target odours) were presented. Within a pair, the sample and the target could be either identical or different. The effect of novelty was tested by comparing identical and different target odours. The effect of pleasantness was examined through the comparison between unpleasant and pleasant sample odours. Results show earlier differentiations on facial muscles and heart rate variations in response to novelty detection as compared to pleasantness evaluation, suggesting the existence of a sequence of appraisal process in the emotional reaction.
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Marco Boi
Non-retinotopic feature attribution: everything moves, but not everything fuses
Authors
Marco Boi (Swiss Federal Institute of Technology Lausanne)
Thomas U. Otto (Swiss Federal Institute of Technology Lausanne;)
Haluk Ogmen (University of Houston (USA))
Michael Herzog (Swiss Federal Institute of Technology Lausanne)
We presented a set of three squares in a first frame followed, after an ISI of 100 ms, by the same set of squares shifted one position to the right (Ternus-Pikler display). The squares are perceived to move as a group rightwards. As with Verniers (Ogmen, H. et al., 2006, Vision Research, 46, 3234-3242), elements such as Gabors or faces, superimposed on the central square of the first frame are predominantly perceived at the central square of the second frame in accordance with group motion (non-retinotopic feature attribution). If a Gabor in anti-phase is presented at the central square of the second frame, the two Gabors are perceived superimposed in temporal alternation on this square. No fusion of the Gabors occurs. However, when Verniers instead of faces or Gabors are displayed, the Verniers fuse, that is, offsets are integrated without being perceived as alternating. Hence, element fusion is not an automatic outcome of feature attribution since its occurrence depends on stimulus parameters.
Acknowledgements: This research was supported by the Pro*Doc “Processes of Perception” of the SNF.
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Bilge Sayim
How grouping by color and contrast affects contextual modulation
Authors
Bilge Sayim (Swiss Federal Institute of Technology Lausanne)
Michael Herzog (Swiss Federal Institute of Technology Lausanne)
Gerald Westheimer (University of California, Berkeley (USA))
In contextual modulation, neighboring elements often impede performance on a target. For example, vernier offset discrimination deteriorates if lines flank the vernier. Explanations are usually based on local spatial interactions. However, we have recently shown that increasing the number of flanks can improve performance arguing against an explanation purely based on local interactions. We proposed that contextual interference diminishes when the flanks are grouped and the vernier stands out from the configuration. Here, we show analogous results for grouping based on color and contrast polarity. A red vernier flanked by arrays of 10 red lines yielded much higher vernier thresholds than when flanked by arrays of 10 isoluminant green lines. Similarly, a black vernier flanked by white lines yields higher performance then when flanked by black lines. We suggest that in configurations with different vernier and flank features the vernier stands out from the flanks. If there is no feature that establishes a grouping process, the vernier does not stand out and performance is low. Our results add further evidence that grouping plays an important role in the contextual modulation of low level vision tasks.
This research was supported by the Pro*Doc "Processes of Perception" of the SNF.
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Raoul Jenni
Biological Motion Perception: Discrimination between Self and Others
Authors
Raoul Jenni (University of Geneva)
Olivier Renaud (University of Geneva)
Claude-Alain Hauert (University of Geneva)
Humans are inevitably in relation with others and their environment. Thus, they possess an impressive visual sensitivity in perceiving and differentiating their actions from those of others. The present study, using point-light stimuli (Johansson, 1973), aims at better understanding this visual ability to recognize and distinguish between ones own and others movements.
This issue was considered in relation with the type of visual control involved in the production of movements: mainly foveal (manual grasping) or peripheral (walking). We expected a paradoxically better ability to recognize ones own movements (as explained by personal kinaesthetic memory automatically activated by the visual stimuli) than those produced by others (Beardsworth & Buckner, 1981; Loula et al., 2005). For the same reason, this advantage was expected more pronounced for walking movements (which involve a lower level of visual control when compared to manual grasping).
The main results showed (a) a large interindividual variability in responses, (b) an effect of the factor self/other manifesting by higher level of correct responses for actions produced by others, (c) an interaction between the two factors, limiting this effect to walking sequences, and (d) that the sensibility of participants to recognize their own movements is superior to chance level only for the grasping sequences. Such unexpected results lead to re-evaluate the hypothesis of a kinaesthetic processing of visual biological motion.
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