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Abstract:
Schizophrenia is associated with sensory as well as cognitive
processing deficits, including impaired recognition of fragmented
stimuli (Doniger et al., submitted). We investigated a simpler
process - recognition of illusory contours (IC). Previously, we
associated this process with early ERP modulation (~90ms) over
lateral occipital sites (Murray et al., Soc. Neurosci. Abstr.
2000). Here, we used high-density (64-channel) electrical mapping
to investigate IC processing in schizophrenia. Patients recognized
IC shapes as accurately as controls. As before, controls showed
larger responses to IC present vs. absent conditions at ~90ms.
Patients showed the same modulation. However, patient waveforms
differed in two ways from those of controls. First, patients showed
reduced visual P1 amplitude (50-90ms), although there was no
modulation based on IC in either group. Second, patients, but not
controls, showed an IC present vs. absent difference over frontal
sites. The diminished P1 response in schizophrenic patients may
reflect decreased dorsal visual stream activation by all stimuli.
Diminished P1 amplitude was not associated with reduced IC
responses over ventral stream areas from which IC processing is
thought to first occur. An IC effect over frontal areas only for
patients may indicate that patients recruit these additional areas
to compensate for diminished automatic processing.
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