Attention: Divided

For experienced drivers, talking on a cell phone while driving seems relatively easy. From a processing perspective, however, it requires the concurrent perception, analysis, decision making, and response selection of multiple stimuli from different sensory modalities. Research on the efficiency of such concurrent perceptual and cognitive processing of multiple stimuli or tasks comes under the heading of divided attention. The degree to which performance deteriorates under such conditions has been studied to characterize limitations on real-world human performance, as well as to inform theoretical models of the functional architecture of the human perceptual-cognitive system. Theories of divided attention have proposed that limitations on multitask performance can be attributed to competition for processing resources as well as to competition for processing mechanisms.

Laboratory research on divided attention typically involves dual-task methodology, in which performance on a given task performed alone is compared with performance when the same task is performed in combination with another task, whose difficulty is often systematically varied. Deterioration under dual-task conditions is assumed to reflect limitations on divided attention, whereas the lack of any decline in performance is assumed to reflect successful division of limited cognitive resources. For example, despite the apparent ease with which one can talk on a cell phone and drive, laboratory studies reveal significant impairment in driving performance with cell phone use. This is true even with hands-free phones, suggesting that attentional resources cannot be effectively divided between the two tasks.

Not all dual-task decrements necessarily reflect a failure of divided attention. For example, deterioration in certain combinations of tasks or stimuli may reflect structural limitations on sensory processing rather than attentional limits. Thus, the [Page 85]need to look at one's cell phone to dial a number may produce a decrement in concurrent driving performance simply because one's eyes are no longer “on the road.” Such a decrement would not be considered an attentional limitation. This entry describes theories of divided attention and effects of practice on the ability to perform multiple tasks simultaneously.