The influence of fixational eye movements on grating-elicited responses of V1 neurons

In alert monkeys, as in humans, small eye movements- tremor, drift and small saccades- occur during fixation periods. These movements constantly shift retinal image, thusmodifying the stimulus-generated responses. We analyzed the effects of eye movementson responses of simple and duplex (“complex-like”) cells to drifting sinusoidal gratings.Eye positions were recorded from monkeys trained to perform a fixation task. Duringfixation extracellular responses of V1 neurons in parafoveal region and eye positionswere recorded. From the eye position records we identified epochs of fast movements,slow drifts and stable fixation and compared patterns of neuronal firing during thevarious eye movement phases. Neuronal responses were sensitive to both fast and sloweye movements that occurred during grating presentations. In the case when no periodsof eye movements were excluded from the records, averaging across many repetitionsof the grating temporal cycle resulted in smearing of the response time course, althougheach individual sweep produced a modulated response. Eye movements affect neuronalresponses in a way that depends on eye movement trajectory, stimulus parameters andreceptive field properties. In particular, eye movements caused shifts in response phaseand/or duration, produced spurious firing bursts or caused cells to miss a response. Ourresults suggest that fixational eye movements account for variations in neuronalresponses over successive grating presentations and that these movements should beconsidered in analysis of grating-evoked activity