Academic journal article Attention, Perception and Psychophysics

The Source of Dual-Task Limitations: Serial or Parallel Processing of Multiple Response Selections?

Academic journal article Attention, Perception and Psychophysics

The Source of Dual-Task Limitations: Serial or Parallel Processing of Multiple Response Selections?

Article excerpt

Published online: 18 July 2013

© Psychonomic Society, Inc. 2013

Abstract Although it is generally recognized that the concurrent performance of two tasks incurs costs, the sources of these dual-task costs remain controversial. The serial bottleneck model suggests that serial postponement of task performance in dual-task conditions results from a central stage of response selection that can only process one task at a time. Cognitive-control models, by contrast, propose that multiple response selections can proceed in parallel, but that serial processing of task performance is predominantly adopted because its processing efficiency is higher than that of parallel processing. In the present study, we empirically tested this proposition by examining whether parallel processing would occur when it was more efficient and financially rewarded. The results indicated that even when parallel processing was more efficient and was incentivized by financial reward, participants still failed to process tasks in parallel. We conclude that central information processing is limited by a serial bottleneck.

Keywords Dual-task performance · Attention · Psychological refractory period (PRP)

When we attempt to carry out two arbitrary sensory--motor tasks in rapid succession, the response to the second task is almost invariably delayed (Welford, 1952), a phenomenon known as the psychological refractory period (PRP). Why do we show such severe limitations in performing dual tasks?

According to the serial bottleneck model (Pashler, 1984, 1994a, 1994b), this dual-task cost originates from the presence of a central bottleneck of information processing that allows only a single response selection operation to proceed at a time, thereby inducing serial postponement of response selection for the second task. By contrast, a broad range of "cognitive-control" models propose that multiple response selections can proceed in parallel (Meyer & Kieras, 1997; Miller, Ulich, & Rolke, 2009; Tombu & Jolicoeur, 2003), and that serial postponement of task performance is simply the result of individuals adopting a serial processing strategy.

Which classes of model best capture the source(s) of dual-task limitations? The cognitive control models make a simple prediction that would disconfirm the serial bottleneck model: If multitask performance is under control, it should be possible to execute two tasks in parallel. However, participants in dual-task conditions overwhelmingly exhibit a serial mode of information processing (Tombu & Jolicoeur, 2003). Some cognitive control proponents have attributed this finding to insufficient practice with the task conditions for developing the appropriate cognitive control necessary to perform tasks in parallel (e.g., Schumacher et al., 2001). However, whereas extensive practice may virtually eliminate dual-task costs (Schumacher et al., 2001; but see Tombu & Jolicoeur, 2004), it does not logically follow that this training effect results from the development of parallel processing of multiple response selections (Ruthruff, Johnston, & Remington, 2009). Practice could just as well lead to faster processing speed of each task, which could dramatically reduce the time that the second of the two tasks is postponed until it gets access to the bottleneck stage of response selection. Indeed, although recent behavioral, neuroimaging, and modeling work is consistent with the latter possibility (e.g., Dux et al., 2009; Kamienkowski, Pashler, Dehaene, & Sigman, 2011; Ruthruff, Johnston, & Van Selst, 2001), no direct evidence for the former has been found.

Although several previous studies have claimed that extensive practice should not only facilitate processing of each task, but also allow one to perform two tasks in parallel (Maquestiaux, Laguë-Beauvais, Bherer, & Ruthruff, 2008; Ruthruff, Hazeltine, & Remington, 2006), these studies cannot address whether parallel processing is possible at the response selection stage because the practice effects were claimed to result from bypassing the capacity-limited response selection stage (i. …

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