Behavioral task
The dual task consisted of a visual discrimination task (Task 1) and an auditory discrimination task (Task 2), which were performed in close succession. In order to increase processing similarities between the two tasks as the basis for crosstalkStimuli were presented in Arial font (font size 30) and in white on a black background with a viewing distance of approximately 60 cm. S1 was responded to with the left middle and index finger pressing the 'a' and 's' keys, respectively. Task 2 consisted of easy to discriminate auditory stimuli (S2), i.e., a high or low tone of 900 and 300 Hz, presented via a loudspeaker. Responses to S2 were provided by pressing the 'k' and 'l' keys using the right index and middle finger, respectively. Half of the participants responded to H and high tones with both index fingers and T and low tones with both middle fingers. The other half of the participants received the reversed assignment. Stimulus presentation and data recording were realized on a Pentium I computer with a Windows 10 platform using E-prime software (Version 3)The participants were instructed to respond first as fast and accurately as possible to S1 and only subsequently as fast and accurately as possible to S2. Each trial began with an 800 ms fixation period, in which a plus sign was presented in the center of the screen, followed by the onset of the visual S1. After a variable stimulus onset asynchrony (SOA) of 40, 130, or 300 ms, the auditory S2 was presented for 150 ms. S1 remained on screen for a maximum of 2500 ms (plus SOA duration) or until responses to both tasks were given. In the case of erroneous responses or wrong order, error feedback ("Falsch" or "Falsche Reihenfolge," respectively) was presented for 500 ms. The next trial started after a blank screen was presented for a random inter-trial-interval (ITI) between 0 and 1000 ms. Figure Trial procedure of the study. After the fixation sign, the visual stimulus for Task 1 (H or T) was presented. The auditory stimulus for Task 2 (high or low tone, represented by the speaker symbol) was delivered after one of three stimulus onset asynchronies (SOA, 40, 130, 300 ms). In the case of an erroneous response, feedback (i.e., “Falsch,” German for wrong) was presented.In each session, the experiment started with 12 dual-task trials to instruct stimulus–response mappings, followed by one practice block and eight experimental blocks consisting of 72 trials each. The 72 trials consisted of 36 compatible and incompatible trials. Of the 36 trials, in each compatibility condition, the three SOAs were presented 12 times each. That is, each combination of 2(S1) × 2(S2) × 3(SOA) was presented six times per block. The practice block was excluded from the analysis. Thus, 576 trials per session were considered for analysis.