Auditory event-related potentials to deviant stimuli during drowsiness and stage 2 sleep.

Twelve subjects were tested using a 3-tone auditory oddball paradigm consisting of a standard 1000 Hz tone (P = 80%) and two deviants, namely, a 1200 Hz tone and a 2000 Hz tone (both P = 10%). Testing took place in 3 conditions: (1) attend, in which the subject had to count one of the deviant tones; (2) ignore, in which the subject read a book; and (3) sleep, in which the subject was encouraged to go to sleep during presentation of the tones. In the awake conditions stimulus deviance elicited mismatch negativity (MMN) and P3. During drowsiness, no separate mismatch negativity (MMN) could be detected, but the 2000 Hz tone evoked a broad fronto-central early negative deflection, suggesting an overlap of N1 and MMN. In the same condition, P210, N330 and P430 appeared, all being sensitive to magnitude of deviance. During stage 2, the P210, N330 and P430 amplitudes increased, most notably to the large deviant. These data indicate that differential processing of auditory inputs is maintained during drowsiness and stage 2 sleep, but do not support the notion that MMN or P3 activity comparable to the waking state occurs to oddball stimuli during this stage. It is hypothesised that during light sleep, scanning of the environment is performed by a different system than in the awake state and that during drowsiness a gradual switch between these two systems takes place.

P3b peak latency dependency on the point of information delivery within a stimulus.

An acoustic matching experiment was conducted consisting of three quasirandom conditions in which the sequence of tones comprising the second stimulus was changed at the beginning, at the end, or not at all. Latency of maximum positivity (P3b) was measured for each subject between Pz and the averaged mastoids. Evaluation of mismatch conditions demonstrated that peak latency depended on the point of information delivery within the stimulus. Further, peak latency within both mismatch conditions, when adjusted for the timing of tone sequence change, was approximately equally delayed in comparison to match. The implications of the results for information processing models of attention are discussed.

A longitudinal investigation of event-related potentials in depression.

A longitudinal investigation of the evoked potential to a warning stimulus, and of the CNV, was conducted with reactive depressives and controls under incentive and nonincentive conditions in a long interstimulus interval paradigm. A smaller group of endogenous depressives were recorded once. The application of multivariate analysis, which controlled for experimental and session effects, indicated that the CNV, as a multiple-component potential, is not capable of distinguishing reactive depressives from controls. Significant univariate interactions involving late CNV area and peak latency were obtained, possibly indexing psychomotor retardation. Analysis of the evoked potential did reveal significant group differences which were explained in terms of main and interaction effects in the P240 and interaction effects involving N120. The findings suggested that groups differed in their responsiveness to experimental demands, and modified their responses differently over time. Mann-Whitney U analysis of endogenous depressives produced no group differences in the CNV measures, but did for N120 amplitude.

A comparative investigation of ERP components and the SCR in a habituation and dishabituation paradigm.

The present experiment investigated the trial-by-trial habituation in the event-related potential (ERP) and the skin conductance response (SCR) to repeated stimuli and dishabituation to rare stimuli. In a balanced design, two groups of subjects passively observed either large black discs as repeated stimuli and small as rare, or vice versa. No consistent effects of stimulus size were obtained between the groups. Late positivity was composed of a double peak at Cz, containing contributions from P3a and P300; the latter only was observed at Pz. The SCR and P3a and P300 at Cz demonstrated habituation, but not the N100 or P200, nor the P300 at Pz. Rare stimuli elicited an enhancement, albeit nonsignificant, in SCR amplitude only. No dishabituation of any of the responses by these stimuli was observed. The SCR correlated significantly with late positivity at Cz and Pz. Discussion focuses on SCR and late positivity as OR components.