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TWK: 7th Tübingen Perception Conference
30th Jan - 1st Feb 2004
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Introduction
Dirk Kerzel (Justus-Liebig-Universität Gießen)
A key visual function for animals and humans is spatial localization. We need to know where an object is before we can grasp it, hit it with a tennis bat, or catch it. However, there are significant information processing delays within the nervous system. For instance, it takes about 30-100 ms between the stimulation of the photoreceptors and a neural response in primary visual cortex. While this delay may not be a problem for actions toward static objects, it poses a major problem when dealing with moving objects: Moving objects change their position while information is being relayed. If visual processing delays were not taken into account, our actions would therefore lag behind the real-world positions of moving objects. However, successful performance in high-speed ball games such as tennis or baseball, as well as experimental investigations, show that motor responses to moving objects are highly accurate. One of the themes in this symposium will be how and where neuronal delays are compensated for, and what mechanisms have evolved to deal with moving objects.
A related problem is that moving objects are often hidden from view. They may go out of sight, or may be covered by other objects. Human actions therefore often rely on mental representations of object position and motion. For successful performance, it would be advantageous if object motion was extrapolated in visual-short term memory such that the represented target position would closely follow the true target position. As a consequence, position information may be distorted in visual-short term memory.
Finally, the visual system has to consider that retinal motion may not only be produced by object motion, but also by eye or body movements. To distinguish between these two possibilities, extraretinal information about eye movements and motion signals from the retina have to be combined. The question is whether and how the visual system achieves accurate synchronization of incoming extraretinal and retinal information. Current evidence indicates that temporal mismatches on the order of 100 ms go uncorrected such that spatial errors result. |
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