Figure 1.

Exemplary trial sequences on a computerized variant of the WCST (i.e., the cWCST) [25]. (A). The stimulus card on Trial t depicts one green cross. Applicable cognitive sets are the number category (far left key card, response 1), the color category (inner left key card, response 2), and the shape category (inner right key card, response 3). The execution of response 3 indicates the application of the shape category. A succeeding negative feedback cue (i.e., “SWITCH”) indicates that response 3 was incorrect and that the shape category should be switched on the upcoming trial. Trial t + 1 therefore constitutes a switch trial. Perseveration errors are erroneous repetitions of the applied cognitive set on switch trials (e.g., the shape category on trial t + 1). (B). Trial t depicts the same stimulus card and response as in A. However, the application of the shape category is now followed by a positive feedback cue (“REPEAT”), indicating that the execution of response 3 was correct and that the shape category should be repeated on the upcoming trial. Set-loss errors are erroneous switches of the applied cognitive set on repeat trials (e.g., the color or number category on Trial t + 1). (C). On Trial t, the execution of response 3 indicates the application of the shape category, which is followed by a negative feedback cue. The execution of response 3 on Trial t + 1 indicates a switch to the number category. A subsequently presented negative feedback cue indicates that response 3 was incorrect and that the number category should also be switched. On trial t + 2, the participant received all necessary information to infer the prevailing category (i.e., sorting by the shape and the number category were incorrect; thus, the application of the color category must be correct). Hence, trial t + 2 constitutes an inference trial [22,23,24]. Failures to infer the prevailing cognitive set (as indicated by the application of any other category than color on trial t + 2) are scored as inference errors.