Journal of Neuroscience, Vol 10, 3079-3086, Copyright © 1990 by Society for Neuroscience
The role of directionally selective neurons in the perception of global motion
T Pasternak, JE Albano and DM Harvitt
Department of Neurobiology and Anatomy, University of Rochester, New York 14627.
Dynamic random dot targets consisting of many localized motion vectors have
been used to study the pooling of local motion signals into a global motion
percept (Williams and Sekuler, 1984). In such displays, the dots are
displaced with a constant step size and the direction of motion for each
dot is chosen at random from a specified distribution. When the
distribution extends over 360 deg, the display consists only of local
random motion of individual dots and no coherent motion is reported.
However, when the distribution is less than 360 deg (biased), the stimulus
appears to flow in a single direction. We examined the effects of reducing
the number of directionally selective (DS) cortical neurons on this
integration process. Normal cats and cats with severely reduced proportions
of DS neurons were trained on 2 direction discrimination tasks. The
discrimination of opposite directions was examined while varying either the
range of directions of local motion, or the proportion of dots moving with
biased distribution. When all dots in the display were directionally
biased, cats with reduced numbers of DS neurons performed the task as well
as normal cats and humans (threshold range: 280-320 deg). However, when the
proportion of biased dots decreased, these animals had severe deficits.
Thus, in the absence of noise, even a very small number of DS neurons can
perform spatial pooling of local directional signals, and support normal
discrimination of opposite directions. However, a full complement of
directional detectors appears necessary when the motion signal is masked by
noise. The discrimination of small differences in direction revealed far
more severe deficits, even when all the dots in the display were
directionally biased (no noise).(ABSTRACT TRUNCATED AT 250 WORDS)
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