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R. J. Dolomount, S. Shankar, C. G. Ellard; Estimating time-to-collision: Further investigations of an animal model.. Journal of Vision 2001;1(3):190. doi: https://doi.org/10.1167/1.3.190.
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When Mongolian gerbils are trained to run down a dark corridor to a visual target, kinematic analyses show that their velocity profiles are influenced by the dynamic properties of the target. Increasing or decreasing target size in synchrony with the animals' movements lead to early or late braking, respectively  Experiments in our laboratory  have shown that visual modulation of braking is dependent on a small region of visual cortex lateral to VI. The present experiments are aimed at refining our understanding of the manner in which vision modulates braking, in order to better understand the role of this region of visual cortex in motion processing. We report several new findings: 1. There is a strong negative correlation between peak running velocity and time of braking. Such a correlation is normally taken as evidence for the use of tau — a perceptual invariant that can be used to predict time-to-collision. 2. There is a linear relationship between the rate at which the target expands or contracts and the magnitude of retarded or accelerated braking, respectively, but the size of this effect is always considerably smaller than that predicted by the hypothesis that the gerbils are using tau alone. Collectively, these results provide some evidence that gerbils are using tau to estimate time-to-collision, but they also suggest that gerbils are combining these estimates with other information to compute a stable, long-term estimate of target location.
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