Backward crosstalk and the role of dimensional overlap within and between tasks.

In dual-task situations, which often involve some form of sequential task processing, features of Task 2 were shown to affect Task 1 performance, a phenomenon termed "backward crosstalk effect" (BCE). Most previous reports of BCEs are based on manipulations of code compatibility between tasks, while there is no clear picture whether and how mere Task 2 response selection difficulty (in the absence of cross-task dimensional code overlap, including effector system overlap) may also affect Task 1 performance. In the present study, we systematically manipulated response-response (R1-R2) relation (compatible, incompatible, arbitrary) and the stimulus-response (S-R) relation in Task 2 (S2-R2: compatible, incompatible, arbitrary; i.e., a classic manipulation of Task 2 response selection difficulty) to study the impact of dimensional overlap and compatibility within and across tasks using an integrated stimulus for both a vocal Task 1 and a manual Task 2. Results revealed a replication of a classic (spatial) R1-R2 compatibility BCE (based on code compatibility), demonstrating that our paradigm is principally suited to capture typical BCEs. Importantly, conditions involving a removal of dimensional code overlap between tasks still yielded an effect of mere Task 2 response selection difficulty on Task 1 performance. Both types of BCEs (i.e., BCEs based on code compatibility and BCEs based on Task 2 difficulty) could be assumed to be rooted in anticipation of response selection difficulty triggered by stimuli indicating either R1-R2 or S2-R2 incompatibility. The results are in line with recent theoretical claims that anticipations of response characteristics (or effects) play an important role for BCEs in particular and for conflict resolution in action control in general.