EVIDENCE OF VISUAL PROCESSING NEGATIVITY WITH ATTENTION TO ORIENTATION AND COLOR IN CENTRAL SPACE

The aim of this study was to determine whether the visual frontal proc essing negativity reported in our earlier paper (Karayanidis, F. and M ichie, P.T. Electroenceph. clin. Neurophysiol., 1996, 99: 38-56) is re lated to selection of spatial location, or occurs regardless of the st imulus features used to define the target. Subjects were instructed to respond to infrequent target stimuli of a particular combination of o rientation, color and size. All stimuli were presented at central fixa tion. Posteriorly, orientation selection enhanced P125 amplitude over the right hemisphere but neither orientation nor color selection had a n effect on N190. Posterior selection negativities emerged for orienta tion, color and their conjunction. At anterior sites, widespread effec ts of orientation and color processing were evident. The effect of loc ation selection on the anterior N1 seen in our previous study was not evident with orientation selection. Instead, selection of orientation, color and their conjunction resulted in P145-250 frontally. Two later anterior negativities emerged. The early negativity (vPNe) was affect ed independently by orientation and color selection while the late neg ativity (vPNI) was affected only by selection of feature conjunction. Thus, the present results show that, like its auditory counterpart, th e visual processing negativity occurs with a variety of stimulus class ification features and is not exclusively related to spatial selection . (C) 1997 Elsevier Science Ireland Ltd.