Smaller backward crosstalk effects for free choice tasks are not the result of immediate conflict adaptation

In dual-task situations, mutual interference phenomena are often observed. One particularly interesting example of such phenomena is that even Task 1 performance is improved if Task 2 requires a compatible (e.g., both responses are given on the left side) instead of an incompatible response (e.g., one response is given on the right side, and the other on the left side). This is called the compatibility-based backward crosstalk effect (BCE). In a previous paper, we observed support for a critical role of stimulus–response (S–R) links in causing this effect: The BCE was smaller when one of the two tasks was a free choice task. However, an alternative explanation for this observation is that free choice tasks lead to immediate conflict adaptation, thereby reducing the interference from the other task. In the present two experiments, we tested this explanation by varying the amount of conflict assumed to be induced by a free choice task either sequentially (Exp. 1) or block-wise (Exp. 2). While we replicated a sequential modulation of the BCE with two forced choice tasks, we observed (1) no reduction of the BCE induced by (compatible) free choice trials nor (2) an effect of block-wise manipulations of the frequency of free choice trials on the size of the BCE. Thus, while the BCE is sensitive to sequential modulations induced by the (in)compatibility of two forced choice responses, which might point to conflict adaptation, the reduced BCE in dual-task situations involving a free choice task is likely due to its weaker S–R links.