Figure 1.

A showcase trial sequence on the computerized WCST [12,13,14] which was used in this study [15]. On Trial t, the stimulus card depicts one green cross. It could be sorted by the color category (inner left key card, response 2), the number category (far left key card, response 1), or the shape category (inner right key card, response 3). The observation of response 3 indicates that the shape category was applied. A subsequent positive feedback (i.e., “REPEAT”) indicated that this response was correct and that the shape category should be repeated on the upcoming trials. However, on Trial t + 1, response 3 was pressed, indicating that the number category was applied. Erroneous switches of the applied category following positive feedback are called set-loss errors. Next, a negative feedback (i.e., “SWITCH”) indicates that this response was incorrect, implying that a category switch is required. On Trial t + 2, the number category was erroneously repeated as response 2 was pressed. Erroneous repetitions of categories after negative feedback are called perseveration errors.