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Temporal resolution of ensemble visual motion signals in primate retina
E.J. Chichilnisky
Salk Institute
Recent studies have examined the temporal precision of spiking in
visual system neurons, but less is known about the time scale that is
relevant for behaviorally important visual computations. We examined
how spatio-temporal patterns of activity in ensembles of primate
retinal ganglion cells convey visual motion information to the brain.
The direction of motion of a bar was estimated by comparing the
timing of responses in ensembles of parasol
(magnocellular-projecting) retinal ganglion cells simultaneously
recorded, using a cross-correlation approach similar to standard
models of motion sensing. To identify the temporal resolution of
motion signals, spike trains were low-pass filtered before estimating
the direction of motion. The filter time constant that resulted in
most accurate motion sensing was 10-50 ms for a range of stimulus
speeds and contrasts, and was on average comparable to the
inter-spike interval. Motion-sensitive neurons in the brain could
filter their inputs on this time scale, discarding the precise times
of indvidual spikes in afferent signals in order to sense motion most
reliably.