16:30 - 18:00
Parallel sessions 3
16:30 - 18:00
Room: HSZ - N5
Chair/s:
Elisabeth Hein
In order to perceive and meaningfully interact with the world around us, our sensory systems need to interpret the incoming information. This interpretation process is well illustrated in the case of illusions. With some illusions we perceive very different things in one and same input, as for example in the famous Necker cube or “The dress”, which can be seen blue and black or white and golden. Other illusions make us perceive colors where there are none, as in the watercolor illusion, or cause-and-effect relationships and animacy with simple dots. Therefore, illusions are a wonderful tool to understand more about how perception works. In the symposium, we will look at this question using a variety of different experimental methods and very different illusions in order to learn more about different aspects of perception ranging from auditory motion perception to robotic vision. In particular, in the first talk Meike Kriegeskorte and colleagues will use auditory apparent motion to investigate which factors influence how object correspondence is established, i.e. object identity is perceived despite changes in location across time. In the second talk Shalila Freitag and colleagues will talk about EEG correlates of perceptual (un-)certainty and the role of stimulus predictability when participants observe stimuli with varying degree of ambiguity/visibility (Necker lattices and smiley faces). In the third talk Ben Sommer and colleagues will investigate perceived causality in a paradigm in which a disc can either be perceived as launching another disc or as passing across the other disc. In particular, they use visual adaptation to look at the influence of a launch or pass context on an ambiguous display. In the fourth talk Vebjørn Ekroll will use examples of magic tricks around the illusion of absence that work better than one would expect based on the method of the trick and how perception works. In the last talk Aravind Rao Battaje and colleagues will present work on whether robotic perceptual models could predict population-level and individual human responses to visual illusions, using the example of the fill-in color aftereffect and Silencing by motion.
Submission 437
Perceptual (Un)Certainty Needs to Be Predictable to Be Measured in the EEG
SymposiumTalk-02
Presented by: Shalila Freitag
Shalila Freitag 1, 2, 3, 4, Ellen Joos 2, 3, 4, Mareike Wilson 1, 2, 3, 4, Ludger Tebartz van Elst 3, 4, Jürgen Kornmeier 1, 2, 3, 4
1 Faculty of Biology, University of Freiburg, Germany
2 Perception and Cognition Lab, Institute for Frontier Areas of Psychology and Mental Health, Freiburg, Germany
3 Department of Psychiatry and Psychotherapy, Medical Center, University of Freiburg, Germany
4 Faculty of Medicine, University of Freiburg, Germany
Visual stimuli without one clear interpretation of highest likelihood (e.g., certain illusions) induce perceptual uncertainty. In a series of studies, we found EEG correlates of this perceptual uncertainty with smaller ERP (Event Related Potential) amplitudes with ambiguous/low-visibility stimuli (perceptual uncertainty) compared to disambiguated/high-visibility stimulus variants (perceptual certainty) (Cohen’s d = 0.6-1.2). The underlying experimental paradigm showed only one stimulus variant (e.g., disambiguated or ambiguous) per condition creating high predictability of successive stimuli. Preliminary results from a pilot study with random presentation of both ambiguous and disambiguated stimulus variants indicated absence of this ERP Uncertainty Effect. The aim of the present study was to confirm this finding and to find the necessary number of repetitions to maximize the ERP Uncertainty Effect.

In an EEG study, we presented Necker lattices (ambiguous/disambiguated) or smiley faces (low/high visibility of emotional expression) in predictably ordered blocks of 12, 48 (Necker and smileys) and 120 (Necker) repetitions. We also showed ambiguous and disambiguated variants of the Necker lattice in random order for 120 stimulus repetitions. The ERP Uncertainty Effect was absent when stimuli were presented randomly. When the order was predictable, the ERP Uncertainty Effect was present for all block lengths tested in both Necker and smiley conditions. Further analysis revealed the effect to reach its maximum after 6 to 10 stimulus repetitions (8.4 to 14 seconds). Our results confirm the importance of predictability to measure perceptual certainty via EEG and give further insights into the timescale of the underlying processes.