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A Psychophysical Measurement and Analysis of Motion Perception in Normal and Binocularly Deprived Monkeys

¹ From the Department of Psychology, ² Division of Visual Science, Yerkes Regional Primate Research Center, and the ³ Department of Ophthalmology, Emory University, Atlanta, Georgia.

PURPOSE. To measure psychophysically the thresholds for motion detection in the nasal and temporal directions under monocular viewing conditions in monkeys reared under conditions of daily alternating monocular occlusion (AMO). The hypothesis was that motion perception would be asymmetric with more sensitivity for motion in the nasal direction.

METHODS. Three monkeys subjected to AMO (AMO monkeys) and three normal monkeys were studied. All were trained with operant conditioning techniques to discriminate coherent from random motion in a random dot display. The percentage of dots in the display that moved either left or right was varied. Thresholds for motion detection of nasally directed and temporally directed stimuli were measured to determine whether the motion perception of AMO monkeys was asymmetric, as predicted.

RESULTS. A two-factor analysis of variance revealed a statistically significant difference between treatment groups (normal versus AMO) and directions (nasal versus temporal) and a significant interaction. The interaction was due to a significant difference between nasal and temporal directions for the AMO group, but no significant difference for the normal group. Planned comparisons were performed based on each animal’s best eye (eye most sensitive to nasal motion) and worst eye (eye least sensitive to temporal motion). No significant differences were found between the two groups in the best eyes’ responses to the nasal direction, but the worst eyes’ responses in the temporal direction were significantly poorer in the AMO group. A neural model that can account for these findings is based on a Hebbian teacher located in the nucleus of the optic tract that strengthens connections of a subpopulation of directionally selective cortical neurons.

CONCLUSIONS. AMO rearing results in asymmetric motion perception. Thresholds for detecting nasally directed motion are normal, whereas thresholds for detecting temporally directed motion are deficient. These results demonstrate that motion-processing mechanisms in primates exhibit experience-dependent developmental neural plasticity. The locus of the neural plasticity could be a subpopulation of directionally selective neurons in the striate cortex (V1).

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