Responses of primate visual cortical neurons to stimuli presented by flash, saccade, blink, and external darkening.

Our visual experience constitutes an unending chain of transient events, including those caused by saccadic eye movements, by blinks, and by localized or global changes in the external world. The categorical perception of objects is maintained across different classes of transient events, suggesting that the neural circuitry underlying visual perception responds to different transient events in a similar manner. However, different sorts of transients do have different perceptual impacts: for example, the sudden changes in a scene due to a saccade or a blink do not disturb our perceptual continuity of a visual scene as much as an external change does. We recorded the responses of 103 single visual cortical neurons in two rhesus monkeys (V1: n = 38, V2: n = 19, V3V/VP: n = 30, V4V: n = 16) to the onset and offset of a visual stimulus that was elicited by four different conditions: 1) stimulus flashed on and off while the eyes remain fixed; 2) stimulus turned on and off along with the entire scene (external darkening); 3) stimulus constant, onset and offset induced by rapid saccadic eye movements; and 4) offset induced by an eyeblink. For most neurons the onset and offset of a visual stimulus elicited qualitatively similar responses regardless of condition. We found no systematic effect of different conditions across the neuronal population. Previously we have shown that when the visual scene is occluded by a blink V1 neuronal firing declines in a similar manner as when the external scene is darkened and the eyes left open. Here we show that this is also the case in V2, V3V/VP, and V4V. However, for a substantial minority of neurons, the response varied strongly as a function of the transient event. This overall pattern was the same in all four cortical areas studied here. We hypothesize that most neurons in visual cortex constitute a passive "filter bank", analyzing the scene for specific details regardless of condition. However, there are neurons that respond in a qualitatively different manner depending on how a stimulus is presented, and we hypothesize that these signals may be important for determining the perceptual salience of a visual event.