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Gi Yeul Bae, Jonathan Flombaum; Invisible causal capture in the tunnel effect. Journal of Vision 2010;10(7):127. doi: 10.1167/10.7.127.
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© ARVO (1962-2015); The Authors (2016-present)
Beyond identifying individual objects in the world, the visual system must also characterize the relationships between objects, for instance when objects occlude one another, or when they cause one another to move. Here we explored the relationship between perceived causality and occlusion. Can causality be perceived behind an occluder? Participants watched a series of events and simply had to judge whether a centrally presented event involved a single object passing behind an occluder, or one object causally launching another. With no additional context, the centrally presented event was always judged as a pass, even when the occluded and disoccluding objects were different colors —an illusion known as the ‘tunnel effect’ that results from spatiotemporal continuity. However, when a nearby context event involved an unambiguous causal launch synchronized with the occlusion event, participants perceived a causal launch behind the occluder. In other words, participants experienced invisible causal capture, perceiving a casual relationship in an occluded location. Crucially, when the context event involved two distinct objects, but no causal relationship between them, no casual launch was perceived behind the occluder. Thus invisible causal capture did not depend merely on the suggestion that two objects might exist behind the occluder, but instead on the causal nature of the context. Perhaps most surprisingly, invisible causal capture was perceived even when the two disks in the central occlusion event shared the same color. Thus spatiotemporal synchrony trumped featural similarity in the interpretation of the hidden event. Related context events illustrate that invisible causal capture depends upon grouping by common motion. Taken together, these results emphasize the inherent ambiguity that the visual system faces while inferring the relationships between objects.
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