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Cognition in Motion: Do we Represent Change-Over-Time?


Thornton,  IM
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Thornton, I. (2005). Cognition in Motion: Do we Represent Change-Over-Time?. Poster presented at 8th Tübingen Perception Conference (TWK 2005), Tübingen, Germany.

In this talk I want to suggest that motion—or more generally change-over-time—are aspects of vision that have wide ranging implications for our understanding of brain function. An observer from another field of study might find such a claim surprising if they were to randomly sample a selection of recent vision research papers. While the perception of motion is a well established domain of research—as the existence of this symposium illustrates—it is nonetheless a specialist area, taught and studied in isolation from other topics in vision. While such specialisation occurs for many other topics as well, motion processing has another barrier to overcome. The problem is that vision science continues to be dominated by what I will call the “pictorial brain” assumption. Briefly stated this assumption is that visual processing begins at the level of some static retinal “image” and ends with representations that attempt to capture the static, spatial structure of the input. Central to this assumption is that processing operates on a series of “snapshots”. What is missing from such a view of visual processing is any consideration of time. I will argue that time is not a separable dimension of vision that can be added, post-hoc, to a collection of extracted features. Our concepts of visual features and in particular visual representations need to be modified to capture the temporal continuity that is so much a part of the physical environment in which we have evolved. Perhaps this caricature of “pictorial” processing described above is very far away from the way you think about vision. But it is worth reflecting for a moment on how you do think visual processing proceeds. What are the basic building blocks of vision? What is a feature? What is the nature of the input? Is it discrete or continuous? Does time, temporal continuity, change-over-time, play any role in your basic concepts? Part of the problem here is that pictorial metaphors are so embedded in the way we work, in the language we adopt and the tools we use that they are very rarely questioned. There can be no denying that the vast majority of experimental paradigms continue to present static stimuli, whether in the context of human, animal and machine observers. As the input is bound to partly determine the output, the use of such static stimuli can be seen as problematic. More dangerous, in my opinion, is the influence that such pictorial metaphors have on our hypotheses and models, how they constrain our thinking about vision and visual representations. The issues that I will raise in this talk are not new ones. Many of these concerns have been raised more than once during the relatively brief history of vision science. As yet, however, there has been no acceptable solution that has allowed time to be more generally integrated into our current models of visual processing. In this talk, I will also not be able to provide such a general solution. My goal here is rather to bring this issue back into the spotlight and to emphasise the importance of considering both space and time in vision. I will describe recent experiments from our group and others illustrating that the visual system often responds quite differently to dynamic rather than static input. In some domains at least, such differences often manifest themselves in terms of measurable performance advantages for dynamic stimuli.