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Abstract:
Power and phase locking characteristics of steady-state
visual evoked potentials (VEPs) were investigated at four
frequencies of stimulation (21, 28, 42 and 85 Hz) in 11 normal
controls and 5 schizophrenics. A high-contrast image, subtending
4.9 degrees of visual angle, was presented at each frequency on a
computer monitor. VEPs were collected with a 14 electrode montage
and processed offline. Power was determined with a Fourier analysis
and phase locking values were computed using Varela's method.
Average single trial power for normal individuals was maximal at 21
Hz and decreased as frequency increased. Power for schizophrenic
subjects remained low and constant across all frequencies. At 21
and 28 Hz, normal subjects showed significantly more phase locking
of the Oz electrode site to the stimulus, while schizophrenics
demonstrated significantly more phase locking of the Oz electrode
site to all other sites in the montage. These results support a
deficit in neural synchronization in schizophrenia which may be
associated with disturbances in perceptual binding.
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