SUSTAINED VISUAL-SPATIAL ATTENTION PRODUCES COSTS AND BENEFITS IN RESPONSE-TIME AND EVOKED NEURAL ACTIVITY

This study investigated the simple reaction time (RT) and event-relate d potential (ERP) correlates of biasing attention towards a location i n the visual field. RTs and ERPs were recorded to stimuli flashed rand omly and with equal probability to the left and right visual hemifield s in the three blocked, covert attention conditions: (i) attention div ided equally to left and right hemifield locations; (ii) attention bia sed towards the left location; or (iii) attention biased towards the r ight location. Attention was biased towards left or right by instructi ons to the subjects, and responses were required to all stimuli. Relat ive to the divided attention condition, RTs were significantly faster for targets occurring where more attention was allocated (benefits), a nd slower to targets where less attention was allocated (costs). The e arly P1 (100-140 msec) component over the lateral occipital scalp regi ons showed attentional benefits. There were no amplitude modulations o f the occipital N1 (125-180 msec) component with attention. Between 20 0 and 500 msec latency, a late positive deflection (LPD) showed both a ttentional costs and benefits. The behavioral findings show that when suffciently induced to bias attention, human observers demonstrate RT benefits as well as costs. The corresponding P1 benefits suggest that the RT benefits of spatial attention may arise as the result of modula tions of visual information processing in the extrastriate visual cort ex. (C) 1998 Elsevier Science Ltd. All rights reserved.