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16:30 - 18:00
Parallel sessions 3
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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 551
Causal Illusions: Visual Adaptation of Causality Via Perceptual Grouping
SymposiumTalk-03
Presented by: Ben Sommer
Ben Sommer, Martin Rolfs, Sven Ohl
Humboldt-University, Berlin, Germany
The perception of causality turns mere visual sequences into meaningful cause-and-effect relations. When a moving disc stops right next to a second disc that then begins moving in the same direction, we typically perceive that the first disc launched the movement of the second disc. Conversely, increasing the overlap between the discs, leads observers to report that one disc is passing over the other. Context events, such as concurrent launching events or concurrent motion onsets, result in a causal illusion that increases the perceived causality. In contrast, visual adaptation to launches (i.e., the repeated presentation of launches) subsequently reduces the proportion of reported launches in subsequent test events.

Here, we asked whether illusory launches may drive visual adaptation of causal perception similarly to a physical launch. Both before and after presenting a visual adaptor, we quantified the perception of causality by parametrically varying the disc overlap in the test events and fitting psychometric functions to the proportion of reported launches as a function of disc overlap. The adaptor was either a classical launch, an illusory launch (a concurrent motion onset grouped with the test event), or a control condition featuring a context event not grouped with the test event.

Importantly, only the classical launch adaptor reduced the proportion of causal reports. Illusory launches did not result in such negative aftereffects. Thus, although context-driven causal illusions induce impressions of causality, visual adaption of causal perception operates exclusively based on the spatiotemporal (as opposed to the perceived illusory) characteristics of launching events.