Academic journal article Cognitive, Affective and Behavioral Neuroscience

Evidence for a Fixed Capacity Limit in Attending Multiple Locations

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Evidence for a Fixed Capacity Limit in Attending Multiple Locations

Article excerpt

Published online: 12 November 2013

© Psychonomic Society, Inc. 2013

Abstract A classic question concerns whether humans can attend multiple locations or objects at once. Although it is generally agreed that the answer to this question is "yes," the limits on this ability are subject to extensive debate. According to one view, attentional resources can be flexibly allocated to a variable number of locations, with an inverse relationship between the number of selected locations and the quality of information processing at each location. Alternatively, these resources might be quantized in a "discrete" fashion that enables concurrent access to a small number of locations. Here, we report a series of experiments comparing these alternatives. In each experiment, we cued participants to attend a variable number of spatial locations and asked them to report the orientation of a single, briefly presented target. In all experiments, participants' orientation report errors were well-described by a model that assumes a fixed upper limit in the number of locations that can be attended. Conversely, report errors were poorly described by a flexible-resource model that assumes no fixed limit on the number of locations that can be attended. Critically, we showed that these discrete limits were predicted by cue-evoked neural activity elicited before the onset of the target array, suggesting that performance was limited by selection processes that began prior to subsequent encoding and memory storage. Together, these findings constitute novel evidence supporting the hypothesis that human observers can attend only a small number of discrete locations at an instant.

Keywords Attention · Working memory · ERP

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As a doctoral student in the laboratory that was codirected by Edward E. Smith and John Jonides, the senior author of this article was introduced to the field of cognitive neuroscience when it was still an emerging trend rather than the dominant approach for understanding cognition. Ed Smith was the perfect advisor during this exciting time. He had always been celebrated for his ability to see the broad conceptual connections between different domains of psychology, and that same vision fostered his transition from an eminent career in traditional cognitive psychology to a prominent place in the field of cognitive neuroscience. As a thesis committee member, Ed Smith had a substantial influence on E.A.'sdoctoralwork examining the links between working memory and attention. Indeed, a core theme of that work is still evident in this article: We report that-as with visual working memory-capacity limits in visual selective attention are best described by discrete rather than flexible resource allocation. Moreover, we show that capacity limits for internal storage in working memory are strongly correlated with the number of positions to which covert attention could be allocated. We are grateful to have benefited from Ed Smith's lasting and powerful contributions to psychology and neuroscience, and we hope that this work can serve as a small token of our gratitude for his guidance, energy, and vision.

The human visual system has a limited processing capacity. Consequently, mechanisms of selective attention are needed to prioritize stimuli that are relevant to the current behavioral goals. Converging evidence from behavioral (e.g., Alvarez & Cavanagh, 2005; Alvarez, Gill, & Cavanagh, 2012; Awh & Pashler, 2000; Franconeri, Alvarez, & Enns, 2007; Kramer & Hahn, 1995), electrophysiological (e.g., Anderson, Vogel, & Awh, 2011, 2013;Drew&Vogel, 2008;Ester,Drew,Klee,Vogel,&Awh,2012; Malinowski, Fuchs, & Müller, 2007; Müller, Malinowski, Grube, & Hillyard, 2003), and neuroimaging (e.g., McMains & Somers, 2004, 2005) studies have suggested that human observers can select at least two noncontiguous locations at once. Although it is generally agreed that there is some limit in the number of locations or stimuli that can be concurrently attended, the nature of this limit is unclear. …

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