Information conveyed by onset transients in responses of striate cortical neurons

Normal eye movements ensure that the visual world is seen episodically, as a series of often stationary images. In this paper we characterize the resp onses of neurons in striate cortex to stationary grating patterns presented with abrupt onset. These responses are distinctive. In most neurons the on set of a grating gives rise to a transient discharge that decays with a tim e constant of 100 msec or less. The early stages of response have higher co ntrast gain and higher response gain than later stages. Moreover, the varia bility of discharge during the onset transient is disproportionately low. T hese factors together make the onset transient an information-rich componen t of response, such that the detectability and discriminability of stationa ry gratings grows rapidly to an early peak, within 150 msec of the onset of the response in most neurons. The orientation selectivity of neurons estim ated from the first 150 msec of discharge to a stationary grating is indist inguishable from the orientation selectivity estimated from longer segments of discharge to moving gratings. Moving gratings are ultimately more detec table than stationary ones, because responses to the former are continuousl y renewed. The principal characteristics of the response of a neuron to a s tationary grating-the initial high discharge rate, which decays rapidly, an d the change of contrast gain with time-are well captured by a model in whi ch each excitatory synaptic event leads to an immediate reduction in synapt ic gain, from which recovery is slow.