[P300 as a reflection of a mental set--P300 in the paradigm of Wisconsin Card Sorting Test].

We studied P300 at Pz in Wisconsin card sorting test (WCST) paradigm in 16 young normals. As it is well known that both the amplitude and the latency of P300 are affected by stimulus probability, we recorded P300 in the two different experimental conditions; in one condition we changed sorting category implicitly after every two successive correct responses of the subject (WCST2 condition), in the other condition we changed it tacitly after every five successive responses (WCST5 condition). In both conditions P300s were recorded following two types of feedback signals respectively; feedback signal of correct response (FC), and feedback signal of error response (FE). These experimental conditions were controlled by microcomputer. During the experiment the number of FCs and FEs were recorded, and frequencies of the feedback signals were calculated respectively. Analysis of variance revealed that P300s were more prolonged and more enlarged in FE than in FC significantly, and there is no difference between the two experimental conditions. The correlations between both the latency and the amplitude of P300s and frequency of feedback signals were low and not significant except between P300 amplitude and frequency of FE under WCST5 condition. This result shows that in WCST paradigm the main factor which affects the latency and amplitude of P300 is the meaning of the stimulus. Although WCST has been considered to be a test of concept formation, the subject must change or maintain his/her sorting category properly following the examiner's feedback declaration. From this point of view, WCST can be considered as a test of a mental set, in which FC demands maintaining a mental set and FE demands its change.(ABSTRACT TRUNCATED AT 250 WORDS)