N250 latency and decision time

Abstract

Eight subjects counted the rarer of two clicks under two levels of difficulty of discrimination. Event-related potentials showed a significant lengthening of N250 and P300 latency when the discrimination was more difficult. These findings confirm those of Ritter et al. (1979) despite the following procedural differences: (1) Stimuli differed in intensity rather than pitch, (2) the task involved silent counting rather than reaction time, and (3) statistical analyses were computed across subjects rather than within subjects. We conclude that the N250 latency shift reflects an increase in decision time as a consequence of greater difficulty. The current findings also support the Ritter et al. (1979) conclusion that the P300 latency increase is secondary to the N250 increase. Although P300 amplitude decreased with increased task difficulty, as predicted by the equivocation formulation of Ruchkin and Sutton (1979), this trend failed to reach the required .01 level of statistical significance. © 1980, The psychonomic soceity, inc. All rights reserved.