Dual-task interference and the cerebral hemispheres.

Pashler, Harold; O’Brien, Shannon · 1993 · Journal of Experimental Psychology Human Perception & Performance

DOI: 10.1037/0096-1523.19.2.315

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Summary

This paper investigates the relationship between dual-task interference and cerebral hemisphere specialization, aiming to reconcile two conflicting theoretical traditions: the Psychological Refractory Period (PRP) approach and the cerebral hemispheres approach. The PRP approach posits a central bottleneck in response selection that prevents simultaneous processing of two tasks, regardless of the specific cognitive resources involved. Conversely, the hemispheres approach suggests that dual-task interference is reduced when tasks are processed by separate cerebral hemispheres, implying independent resource pools for each side. Previous studies supporting the hemispheric view often utilized tasks with minimal response uncertainty, which do not typically engage the central bottleneck. Pashler and O'Brien sought to determine whether hemispheric separation could alleviate the severe interference characteristic of the PRP effect when both tasks require independent response selection. To address this, the authors conducted five experiments using the PRP paradigm, where subjects performed two tasks in rapid succession. Crucially, unlike previous hemispheric studies, these tasks required independent choice responses for each stimulus, ensuring engagement of the response-selection bottleneck. The researchers manipulated task lateralization using standard techniques, such as presenting stimuli in specific visual fields (left or right) and requiring responses with corresponding hands or vocalizations, to encourage one hemisphere to handle one task and the other hemisphere to handle the second. For instance, in Experiment 1, subjects made vocal responses to auditory tones (presumed left-hemisphere dominant) and manual keypresses to visual disks presented in either the left or right visual field. The design allowed for comparisons between conditions where both tasks relied on the same hemisphere versus conditions where they relied on different hemispheres. The results across the experiments consistently showed that dual-task interference was not modulated by hemispheric manipulations. Significant PRP effects, characterized by substantial delays in the second response time at short stimulus onset asynchronies, were observed regardless of whether the tasks were assigned to the same or different hemispheres. Statistical analyses revealed no significant interaction between hemispheric assignment and the magnitude of interference. For example, in Experiment 1, the slowing of the second response due to the concurrent first task was comparable whether the visual stimulus appeared in the left or right visual field. These findings held true across various task combinations involving lateralized input, lateralized output, and processing codes believed to be hemisphere-specific. The authors conclude that response selection represents a central bottleneck that cannot operate simultaneously and independently in the two cerebral hemispheres. This finding challenges the hypothesis that the hemispheres possess mutually inaccessible resource pools that can mitigate dual-task interference. Instead, it supports the view that the bottleneck is a central, unitary mechanism shared by both hemispheres. The study implies that previous evidence for hemispheric independence in dual-task performance likely stemmed from tasks that did not involve the critical response-selection stage. Consequently, the paper argues for a reconciliation of the two approaches by asserting that while hemispheric specialization exists, it does not bypass the central bottleneck inherent in response selection.

Key finding

Dual-task interference in response selection is not reduced by manipulating tasks to rely on separate cerebral hemispheres, indicating that response selection is a central bottleneck that cannot operate independently in both hemispheres.

Methodology

lab_experiment

Provenance

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Topics

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• dual task multitasking
• dual task performance