Academic journal article Attention, Perception and Psychophysics

Timing Divided Attention

Academic journal article Attention, Perception and Psychophysics

Timing Divided Attention

Article excerpt

Visual attention can be divided over multiple objects or locations. However, there is no single theoretical framework within which the effects of dividing attention can be interpreted. In order to develop such a model, here we manipulated the stage of visual processing at which attention was divided, while simultaneously probing the costs of dividing attention on two dimensions. We show that dividing attention incurs dissociable time and precision costs, which depend on whether attention is divided during monitoring or during access. Dividing attention during monitoring resulted in progressively delayed access to attended locations as additional locations were monitored, as well as a one-off precision cost. When dividing attention during access, time costs were systematically lower at one of the accessed locations than at the other, indicating that divided attention during access, in fact, involves rapid sequential allocation of undivided attention. We propose a model in which divided attention is understood as the simultaneous parallel preparation and subsequent sequential execution of multiple shifts of undivided attention. This interpretation has the potential to bring together diverse findings from both the divided-attention and saccade preparation literature and provides a framework within which to integrate the broad spectrum of divided-attention methodologies.

Attention enhances the processing of selected visual information. A fundamental capacity of visual attention is that it can be concurrently allocated to multiple objects or locations (e.g., Castiello & Umiltà, 1992; Kramer & Hahn, 1995; McMains & Somers, 2004). However, the mechanism(s) underlying this ability have been the topic of substantial debate. Among the contested aspects are very fundamental questions, including the maximum number of attentional foci that can be maintained (e.g., Alvarez & Cavanagh, 2005) and the limits on their spatial resolution (e.g., Gobell, Tseng, & Sperling, 2004; Intriligator & Cavanagh, 2001), the degree to which these foci are independent (e.g., Yantis, 1992), and the flexibility with which attention can be allocated to the different foci (e.g., Castiello & Umiltà, 1992; McCormick, Klein, & Johnston, 1998). Furthermore, it remains disputed whether attention is divided over locations, objects, or features (e.g., Bichot, Cave, & Pashler, 1999; Scholl, Pylyshyn, & Feldman, 2001) and how the spatiotemporal properties of attentional allocation to multiple foci are best understood (e.g., Kramer & Hahn, 1995; VanRullen, Carlson, & Cavanagh, 2007; Wolfe, 1998). To date, no single theoretical framework of divided attention has been able to incorporate all the lines of evidence provided by the wide range of experimental paradigms with which it has been studied.

Stages of Visual Processing: Monitoring Versus Access

Attention can be divided into (at least) two stages of visual processing (Pashler, 1998). In general, accounts of perception and attention distinguish between an early preattentive system in which a limited subset of visual features (such as color, orientation, etc.) are processed rap- idly and in parallel and a later capacity-limited attentive system in which additional features (such as the identity of a character or the gender of a face) and feature combinations are analyzed in greater depth (e.g., Palmer, 1995; Treisman & Gelade, 1980; Shiffrin, Gardner, & Allmeyer, 1973; Wolfe, 1994). A filter mechanism restricts the information that is transferred from the first to the second stage (e.g., Broadbent, 1958).

Attention might be divided during the first stage, which we will call monitoring: the anticipatory allocation of attention to a specific region of the visual field. In a cuing task, for example, a subset of potential target locations is attended in preparation for the appearance of a target (e.g., Awh & Pashler, 2000; Castiello & Umiltà, 1992; Kramer & Hahn, 1995). …

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