EVENT-RELATED POTENTIALS DURING COVERT ORIENTATION OF VISUAL-ATTENTION - EFFECTS OF CUE VALIDITY AND DIRECTIONALITY

Covert orientation of attention was studied in 30 adults who fixated w arning cues and pressed a button at target onset, Directional cues (ar rows) indicated the most probable (p = 0.8) side of target occurence, Subjects responded fastest when validly cued, slowest to invalidly cue d targets, and at an intermediate rate when the cue (a cross) was not directional. Directional cues took longer to evaluate (increased N1 an d P2 latencies) and produced more focussed attention and greater respo nse preparation (enhanced CNV and P3 amplitude) than non-directional c ues, These findings indicate that the expectancy of a target can be ma nipulated by a spatial cue at three levels, sensory, attention, and re sponse preparation, and lead to changes in the sensory perceptual proc essing of the target. Validly cued targets produced an increase in P1 amplitude reflecting attention enhanced sensory processing whereas inv alidly cued targets increased N1 and P3 amplitudes reflecting the re-o rientation of attention, and further processing and updating of inform ation required of low probability stimuli respectively. P3 latency to invalidly cued targets was also delayed reflecting the additional proc esses required to shift attention to a new location. The P3 latency va lidity effect was smaller than that found for response time suggesting response execution may also be affected by spatial attention.