Functional magnetic resonance imaging and evoked potential correlates of conscious and unconscious vision in parietal extinction patients

We describe recent functional magnetic resonance imaging (fMRI) and event-r elated potential (ERP) studies of visual extinction in patients with right parietal damage who can detect isolated visual stimuli on either side, yet often miss contralesional (left) stimuli during bilateral stimulation. We c onsider the neural fate of such extinguished visual stimuli and how neural responses differ for consciously detected versus extinguished stimuli. fMRI findings indicate that extinguished stimuli evoke activity in striate and ventral extrastriate visual cortex, despite escaping awareness, Activations for extinguished stimuli can be found even in category-specific (face-resp onsive) areas of the fusiform gyrus, On the other hand, activations in visu al cortex are stronger for consciously detected versus extinguished stimuli , with parietal and frontal areas of the intact left hemisphere also implic ated in this comparison. Recent ERP data likewise suggest differential neur al responses for consciously detected versus extinguished stimuli. We discu ss these findings in relation to current speculations about the neural basi s of conscious and unconscious perception. (C) 2001 Academic Press.