Abstract
Using functional magnetic resonance imaging (fMRI), we measured brain activity of human participants while they performed a sentence congruence judgment task in either the visual or auditory modality separately, or in both modalities simultaneously. Significant performance decrements were observed when attention was divided between the two modalities compared with when one modality was selectively attended. Compared with selective attention (i.e., single tasking), divided attention (i.e., dual-tasking) did not recruit additional cortical regions, but resulted in increased activity in medial and lateral frontal regions which were also activated by the component tasks when performed separately. Areas involved in semantic language processing were revealed predominantly in the left lateral prefrontal cortex by contrasting incongruent with congruent sentences. These areas also showed significant activity increases during divided attention in relation to selective attention. In the sensory cortices, no crossmodal inhibition was observed during divided attention when compared with selective attention to one modality. Our results suggest that the observed performance decrements during dual-tasking are due to interference of the two tasks because they utilize the same part of the cortex. Moreover, semantic dual-tasking did not appear to recruit additional brain areas in comparison with single tasking, and no crossmodal inhibition was observed during intermodal divided attention.
Highlights
Performing several tasks is demanding and often leads to decrements in performance speed and accuracy (Pashler, 1994)
The ANOVA with three Task levels showed a main effect of Task type (F(2,32) = 23.69, p < 0.001) and subsequent post hoc tests revealed that the percentage of correct responses was significantly lower during divided attention than during attention in the unimodal condition (p < 0.001) or intermodal selective attention (p < 0.005) conditions, and significantly lower during selective attention than during attention in the unimodal condition (p < 0.05)
An ANOVA was conducted on the three selective attention to text conditions in order to determine the effect of Auditory distractor type, and a similar ANOVA was conducted for the three selective attention to speech conditions to study the effects of Visual distractor type
Summary
Performing several tasks is demanding and often leads to decrements in performance speed and accuracy (Pashler, 1994). These decrements may be due to a bottleneck in executive task-coordination systems recruited by multitasking (D’Esposito et al, 1995; Collette et al, 2005). Competition may occur beyond the sensory cortices in brain areas related to carrying out the component tasks in case these component tasks require similar (e.g., phonological or spatial) processing (Baddeley and Hitch, 1974). We asked (i) whether dividing attention recruits specialized executive task-coordinating systems; (ii) how attention modulates activity in the sensory cortices during bimodal linguistic stimulation; and (iii) how brain areas showing attention-related and task-specific activations react when two simultaneous tasks requiring similar processing are performed
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