The P300 component of the human average evoked potential has been associated with a host of stimulus and S variables, such as information delivery and stimulus salience. P300 is emitted by the brain in response to either attended events that are surprising or to unattended events that produce orienting. P300 does not appear to be a real-time index of signal (target) selection, since attended low-probability nonsignals also result in P300 and its latency is too long. P300 further appears to be independent of response selection; its latency therefore may or may not correlate with RT, depending on the experimental context. P300 latency does appear to index stimulus evaluation time in that it is not emitted until the stimulus has been cognitively evaluated. P300 amplitude appears sensitive to manipulations of perceptual limited capacity but not sensitive to manipulations of motor limited capacity. It has been proposed that P300's functional role in human information processing is the updating of neurocognitive models concerning future events, although other functions have also been proposed. (5 p ref)
"1/f-like" power spectrum scaling is a ubiquitous feature of complex systems. In such scaling, the power spectrum of a given time series is dominated by an inverse power law, resulting in an inverse linear relation between log power and log frequency. The 1/f-like power spectrum scaling properties of human, resting eyes-closed and eyes-open EEG were examined. For both eyes-closed and eyes-open EEG, log power had a significant inverse linear relation with log frequency. The slope of this relation was not correlated with previously-calculated Grassberger-Procaccia dimension estimates for the same data, indicating that the EEG is not a 1/f-like stochastic process. Further, the degree of deviation from perfect log power versus log frequency linearity was related to power in the 8-12 Hz alpha frequency band. It is speculated that this deviation may be related to the low dimension of a chaotic alpha rhythm relative to other EEG rhythms.
In this article I review findings relating schizophrenia to four of the leading event-related brain voltage potential (ERP) components of interest to cognitive psychophysiologists. Research indicates that schizophrenics manifest the following cognitive ERP abnormalities relative to control subjects: (a) a diminished contingent negative variation (CNV) in warned reaction time paradigms during the warning stimulus-imperative stimulus interval; this CNV continues beyond presentation of the imperative stimulus as the postimperative negative variation (PINV). Contingent negative variation attenuation may reflect a state marker of psychosis in acute schizophrenics, whereas serving as a trait marker regardless of current symptoms in more chronic patients. In contrast, the PINV may be more of a state marker for both acute and chronic patients. (b) A pattern of P100–N100 reducing in acute schizophrenics that is not seen in chronic and paranoid patients. (c) Evidence of an attenuated enhancement of N100 (actually superimposed Nd or processing negativity) to stimuli presented in an attended channel, especially at slower event rates. (d) A diminished late positive complex (LPC) apparently due more to a diminished P300 than a diminished slow wave. The LPC attenuation in schizophrenics may to a degree reflect a trait marker of high risk for schizophrenia as well as a residual deficit state that often remains following the remission of positive symptoms. (e) Finally, with the possible exception of the PINV elicited in standard CNV paradigms, these ERP abnormalities do not appear to be specific to schizophrenia, as they are found in association with a variety of other disorders as well. The implication of each of these abnormalities for the conceptualization of the schizophrenic disorder is discussed, as is the “impaired performance” problem associated with doing ERP research with clinical groups.
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