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The relationship between temporal integration and onset and offset latency for a velocity white-noise stimulus in direction selective neurons in V1 and MT/V5

Wyeth Bair and J. Anthony Movshon

NYU

Using extracellular, single-unit recording, we have studied the temporal dynamics of direction selective (DS) cells in primary visual cortex (V1) and in area MT/V5 in anesthetized macaque monkeys. Visual stimuli consisted of sinusoidal gratings that were optimized in size and orientation for each neuron and were moved randomly along the neuron's axis of preferred motion according to a white-noise velocity signal. We compared integration time, onset and offset latency, and response strength as a function of the variance of the velocity signal and the spatial frequency and contrast of the sinusoidal grating. Generally, integration time and response latency were longest in DS cells in both V1 and MT/V5 for slowly moving, high spatial frequency, and low contrast stimuli. We compared the neuronal responses to predictions from a motion energy model and to predictions from a phenomenological model built from adaptive linear filters and an integrate-and-fire compartment with excitatory and inhibitory conductances. The latter model accounts for many of the temporal response properties that we have observed.