Evidence for a Latent Bottleneck After Extensive Dual-Task Practice of a Visual-Manual and an Auditory-Verbal Task

Practicing two simultaneous tasks in an extensive manner reduces the performance impairments (i.e., dual-task costs) that occur in dual-task situations compared to single-task situations. The present study provides empirical tests of the latent bottleneck model to explain this reduction and thus the practice-related improvement in dual-task performance. To do so, in three experiments, participants practiced a visual-manual and an auditory-verbal task in single-task and dual-task trials for several sessions. In these experiments, we changed the duration of the response selection stages of the two tasks after practice and analyzed the resulting effects on the reaction times (RTs) during subsequent transfer. The results showed a pattern of selective prolongations of the RTs in the two tasks, which depends on the location of the manipulated process relative to a presumed latent processing bottleneck. The manipulation of the time at bottleneck stages in the longer (auditory-verbal) task did not propagate into the RTs of the shorter task, while prolongations of bottleneck stages of a shorter (visual-manual) task propagated into longer task RTs after practice. These results are consistent with a latent bottleneck model of dual-task practice.