Speed encoding in correlation motion detectors as a consequence of spatial structure |
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Authors: | Andrew Isaac Meso Johannes M Zanker |
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Institution: | (1) Computational Vision Lab, Department of Psychology, Royal Holloway University of London, Egham, TW20 0EX, UK;(2) McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue West Rm. H4-14, Montreal, QC, H3A1A1, Canada |
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Abstract: | For animals to carry out a wide range of detection, recognition and navigation tasks, visual motion signals are crucial. The
encoding of motion information has therefore, attracted much attention in the experimental and computational study of brain
function. Two main alternative mechanisms have been proposed on the basis of behavioural and physiological experiments. On
one hand, correlation-type and motion energy detectors are simple and efficient in the design of their basic mechanism but
are tuned to temporal frequency rather than to speed. On other hand, gradient-type motion detectors directly represent an
estimate of speed, but may require more demanding processing mechanisms. We demonstrate here how the temporal frequency dependence
observed for sine-wave gratings can disappear for less constrained stimuli, to be replaced by responses reflecting speed for
stimuli like square waves when a phase-sensitive detection mechanism is employed. We conclude from these observations that
temporal frequency tuning is not necessarily a limitation for motion vision based on correlation detectors, and more generally
demonstrate in view of the typical Fourier composition of natural scenes, that correlation detectors operating in such environments
can encode image speed. In the context of our results, we discuss the implications of the loss of phase sensitivity inherent
in using a linear system approach to describe neural processing. |
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Keywords: | Motion vision Reichardt detector Pattern dependence Speed tuning |
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