Effects of sustained, voluntary attention on amplitude and latency of steady-state visual evoked potential: a costs and benefits analysis

Objective: Steady-state visual evoked potentials (VEPs) were recorded to study the mechanisms that underlie visual attention. Methods: VEPs were recorded from 1 cycle/degree sinusoidal grating contrast reversed at various temporal frequencies (6-10 Hz). This was displayed in one hemifield. A letter search display was flashed at a random rate in the other hemifield. The subject performed a demanding task on the recording stimulus (attended condition) or on the opposite side stimulus (unattended condition). Alternatively, he/she passively fixated on the fixation point (passive condition). Results: Relative to the passive condition, attended stimuli elicited enhanced-amplitude and shortened-latency VEP (benefits). Costs (i.e. responses to passive vs. unattended stimuli) were more marked for latency. Conclusions: VEP latency may be the key of a priority-based attention mechanism acting at an early level.