This dissertation extends previous work by examining the temporal relationships of N200, P300 and reaction time (RT) following both speed and accuracy instructions during several levels of a short-term memory scanning task. Twenty male students were presented a set of 1, 2, 3, 4, 5, 6, or 7 letters to memorize. Following memorization, subjects were presented with 50 probe letters and instructed to indicate whether or not the probe was a member of the memory set. Twenty-five of the probe letters belonged to the memory set (YES response) and 25 did not (NO response). Following training, two experimental rounds, consisting of all 7 memory set sizes, were presented. For one round subjects were instructed to respond maximizing speed while maximizing accuracy for the other.

RT increased as a function of memory set size and was shorter for the YES response set. This observation was evident following both accuracy and speed instructions. However, following accuracy instructions, RT was consistently longer relative to speed instructions for both YES and NO responses.

N200 average amplitude and peak amplitude increased as memory set size increased and was larger following the NO responses. When comparing speed with accuracy instructions, N200 amplitude was larger following accuracy instructions, but no differences were observed for N200 peak latency.

P300 average amplitude and peak amplitude decreased as a function of memory set size and were largest following the YES responses. P300 peak latency increased as a function of increasing memory set size. However, when comparing speed with accuracy instructions, no differences in P300 average amplitude, peak amplitude or peak latency were observed. These data are consistent with previous hypotheses relating N200 to processes involved in stimulus classification/response selection and P300 to ancillary processes such as stimulus evaluation.