Event-related potentials associated with detected targets in a vigilance task were analyzed in two ways: (i) by sorting the potentials in terms of sequential reaction time bins of 50 milliseconds and (ii) by examining the single trial waveforms. A negative component (N2) covaried in latency with reaction time. These results support the hypothesis that N2 reflects a decision process which controls behavioral responses in sensory discrimination tasks.

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Event‐related potentials were studied while subjects performed physical and semantic discrimination tasks. Two negative components, NA and N2, were observed in both kinds of discriminations. The earlier component, NA, had a constant onset latency, but its peak latency varied as a function of stimulus complexity. N2 latency varied in relation to changes in the peak of NA. RT and P3 followed N2 by similar amounts of time across tasks. The NA and N2 components were interpreted as reflecting partially overlapping sequential stages of processing associated with pattern recognition and stimulus classification, respectively.

The timing of two event-related potential components was differentially affected by two experimental variables. The earlier component (NA) was affected by degradation of the stimuli and the later component (N2) by the nature of a classification task. The results support the hypothesis that NA and N2 reflect sequential stages of information processing, namely, pattern recognition and stimulus classification.