Abstract
Single-cell recordings indicate that a visual stimulus elicits a wave of rapid neuronal activation that propagates so fast that it might be free of intracortical feedback. We traced the time-course of early feedforward activation by measuring pointing responses to color targets preceded by color stimuli priming either the same or opposite response as the targets. Effects of visual attention at the prime/target locations were studied by giving either an endogenous or an exogenous attentional cue, varying both the cue-prime and the prime-target SOA (stimulus onset asynchrony). Early pointing kinematics were time-locked to prime onset and independent of target onset, indicating that initial responses were controlled exclusively by the feedforward information elicited by the primes. However, early pointing dynamics were clearly modulated by attention at optimal cue-prime SOAs. Results indicate that visual attention modulates cortical feedforward dynamics in advance of critical stimuli.