Mental Setの反映としてのP300—Wisconsin Card Sorting TestによるP300の導出

P300 as a Reflection of a Mental Set : P300 in the Paradigm of Wisconsin Card Sorting Test

　正常若年者を対象に，Wiscosin card sorting test（WCST）遂行時に，検査者から示される正答宣言と誤答宣言に関連したP300を各々Pzで記録し，両者の差異を検討した。WCSTについては，その分類基準の変更が2回連続正答後に行われる場合と5回連続正答後に行われる場合の2つの条件を設定し，両条件の比較を通して刺激頻度がP300に及ぼす影響も併せて検討した。その結果P300振幅・潜時は刺激頻度に関係なく，誤答宣言を受けた時のほうが正答宣言を受けた時より，有意に大きく，延長していることが示された。この結果はWCSTにより導出されるP300においては，潜時・振幅の主要な決定因子が与えられる刺激の意味そのものであることを示している。このことはWCSTがP300の導出に有効なparadigmであることを示唆するとともに，WCSTの認知上の意味から，P 300はmental setの変化を反映している可能性を示すと考えられた。

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 cor-rect 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 condi-tions were controled by microcomputer. During the experiment the number of FCs and FEs were record-ed, 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 fre-quency 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 follow-ing the examininer'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. In this point of view, the results of our experiment show that the latency of P300 in WCST paradigm can be regarded to reflect a state of a mental set. Some authors consider that P300 is a manifestation of context updating in human information processings, which looks like change of a mental set. P300 may be a electrophysiological parameter of a mental, set, and WCST is a very useful paradigm to record P300.