Effects of Input Modality on Vocal Effector Prioritization in Manual-Vocal Dual Tasks

Doing two things at once (vs. one in isolation) usually yields performance costs. Such decrements are often distributed asymmetrically between the two actions involved, reflecting different processing priorities. A previous study (Huestegge & Koch, 2013) demonstrated that the particular effector systems associated with the two actions can determine the pattern of processing priorities: Vocal responses were prioritized over manual responses, as indicated by smaller performance costs (associated with dual-action demands) for the former. However, this previous study only involved auditory stimulation (for both actions). Given that previous research on input-output modality compatibility in dual tasks suggested that pairing auditory input with vocal output represents a particularly advantageous mapping, the question arises whether the observed vocal-over-manual prioritization was merely a consequence of auditory stimulation. To resolve this issue, we conducted a manual-vocal dual task study using either only auditory or only visual stimuli for both responses. We observed vocal-over-manual prioritization in both stimulus modality conditions. This suggests that input-output modality mappings can (to some extent) attenuate, but not abolish/reverse effector-based prioritization. Taken together, effector system pairings appear to have a more substantial impact on capacity allocation policies in dual-task control than input-output modality combinations.