2.6.3. Wisconsin Card Sorting Test (WCST)
Cognitive flexibility was assessed using a computerized version of WCST-64 (Kongs et al., 1993). Each trial required participants to sort test cards according to one of three possible categories: number (1-4), shape (triangle, circle, cross, star), or color (red, blue, yellow, green). Every time participants made a choice, feedback was displayed on the screen in the form of ”correct” or ”wrong”. Since the sorting rules were not be instructed, participants needed to discover the rules themselves through the feedback provided. Whenever participants correctly sorted a series of ten cards, the rule changed. Each participant completed 64 trials and finished 1 to 6 sorting sequences depending on their performance. Although the WCST-64 provides several measures as indicators of cognitive flexibility, the primary outcome of interest within the present study was perseverative errors, which indicate a continued application of a card sorting rule that is no longer appropriate instead of shifting to the use of a new rule (Miyake et al., 2000). Prior studies have noted that perseverative errors on the WCST are the outcome most affected by acute stress, consistent with earlier studies showing that perseverative errors point to a lack of cognitive flexibility (Kalia et al., 2018; Nyhus & Barceló, 2009).