Academic journal article Perception and Psychophysics

Distinguishing between the Precision of Attentional Localization and Attentional Resolution

Academic journal article Perception and Psychophysics

Distinguishing between the Precision of Attentional Localization and Attentional Resolution

Article excerpt

Attentional resolution is a construct that refers to the minimal separation that allows one stimulus to be attended separately from nearby stimuli. The attentional walk task, which requires a series of covert shifts of attention within variably dense arrays of stimuli, was introduced as a method of measuring attentional resolution. Using a cuing task, we show that individual items within arrays that are too dense to support an attentional walk can nonetheless be attended. We note that the precision with which attention can be localized is, in principle, a limitation separate from attentional resolution and conclude that performance in the attentional walk task is better suited for measuring this limitation than for measuring attentional resolution per se.

Numerous metaphors have been used to discuss visual attention (see Fernandez-Duque & Johnson, 1999, for a review). These include visual attention as a spotlight (e.g., Posner, 1980; Posner, Snyder, & Davidson, 1980), as a zoom lens (e.g., Eriksen & St. James, 1986; Eriksen & Yeh, 1985), as a gradient filter (e.g., LaBerge & Brown, 1989), and as a nonlinear filter (e.g., Cutzu & Tsotsos, 2003; Tsotsos et al., 1995). All of these metaphors characterize mechanisms by which visual information can be processed selectively. They also share the property of attributing a spatial extent to the area over which visual attention can be focused. Reflecting this property, researchers have asked about limitations of the spatial extent of focused attention; specifically, how narrowly can attention be focused and how does it vary across conditions, such as location within the visual field?

This question, which has been characterized as the question of attentional resolution (He, Cavanagh, & Intriligator, 1996, 1997; Intriligator & Cavanagh, 2001), has been addressed in a variety of ways. For example, using the flankers task, in which observers identify a central target letter that is flanked by distractor letters, Eriksen and Huffman (1972) estimated the extent of selection to be about 1° of visual angle. Others, using probe detection and related methods, have proposed a gradient area of selection extending as much as 19° from a cued location (e.g., Downing & Pinker, 1985; Henderson & Macquistan, 1993; LaBerge & Brown, 1986). Still others, using methods involving many distractors and, sometimes, multiple targets separated by variable distances, have suggested that the area of selection has a facilitatory-center-inhibitory-surround profile with a spatial extent that is as large as 6° and as small as 1° (e.g., Bahcall & Kowler, 1999; Cutzu & Tsotsos, 2003; Mounts, 2000a, 2000b; Steinman, Steinman, & Lehmkuhle, 1995). Finally, others have suggested that the spatial extent and shape of selection varies with the task and characteristics of the stimuli (e.g., Eriksen & St. James, 1986; Juola, Bouwhuis, Cooper, & Warner, 1991; LaBerge, 1983; LaBerge & Brown, 1986), as well as with the location of stimuli within the visual field (e.g., He et al., 1996, 1997; Sagi & Julesz, 1986).

Citing concern regarding the heterogeneity of the approaches and findings, Intriligator and Cavanagh (2001) introduced the attentional walk task as a method for measuring attentional resolution. In this task, observers are shown arrays of identical disks similar to those shown in Figure 1 that vary in density and eccentricity. Observers fixate the central point, and a short time later, one of the disks briefly changes color, indicating that attention (but not fixation) should be shifted to that disk. Following this cue, a series of instructions is given directing the observer to shift attention one disk to the left or to the right of the currently attended disk (e.g., "left," "left," "right," "left," etc.). At the end of a five- to seven-step series of commands, observers are probed with another disk that changes color. The task is to indicate whether or not the final probe disk marks the end point of the attentional walk. …

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