Concurrent recording of steady-state and transient event-related potentials as indices of visual-spatial selective attention

Objectives: The present study investigated the effects of spatial attention on concurrently recorded visual event-related potentials (ERPs) and steady-state visual evoked potentials (SSVEPs) to isoluminant color changes embedded in rapidly flickering stimuli. Methods: EEG was recorded while subjects attended to flickering LEDs in either the right or left visual hemifield and responded by a button press to isoluminant color changes (targets). Results: Target isoluminant color changes elicited the typical ERP components P1, N1, N2 and P3, which were enhanced for attended targets compared to unattended targets. Consistent with previous findings, SSVEP amplitude was enlarged for attended flicker stimuli at posterior electrode sites contralateral to the attended visual hemifield. In addition, significant correlations were found between the N1, N2 and the SSVEP attention effects, whereas no such correlations were found between the P1, P3 and SSVEP attention effects. Conclusions: Results suggest that the SSVEP and ERP reflect partially overlapping attentional mechanisms that facilitate the discriminative processing of stimuli at attended locations.