The attentional effects of peripheral cueing as revealed by two event-related potential studies

Objective: The mechanism of visual spatial attention elicited by peripheral cueing was investigated in two studies. Method: Event-related potentials (ERPs) were recorded when the subjects wer e performing a spatial frequency discrimination task and a location discrim ination task. Stimuli were randomly hashed in the left or right visual fiel d. Prior to each stimulus a peripheral cue was presented with a validity of 75%. Results: The subjects responded faster to valid trials than to invalid tria ls. The earliest visual ERP component, C1, was not modulated by the cue val idity, suggesting that visual spatial attention elicited by peripheral cuei ng does not involve striate cortex. Valid trials elicited larger contralate ral P1 but a smaller contralateral N1 than invalid trials. The early onsets of these attentional effects show that spatial attention affects stimulus processing at early sensory/perceptual stages. The latencies of contralater al pi and contralateral N1 were shorter for invalid trials, however. The ip silateral N1 was enhanced by valid trials in the spatial frequency discrimi nation task but was not in the location discrimination task, whereas the co ntralateral N1 was larger for invalid trials than for valid trials in both tasks. Conclusion: The results indicate that involuntary allocation of attention i nvolves different mechanisms from voluntary allocation of attention. (C) 20 01 Elsevier Science Ireland Ltd. All rights reserved.