Nonspatial attributes of stimuli can influence spatial limitations of attentional control

Abstract

Work from a variety of approaches suggests that the selection and representation of visual information is subject to fairly severe spatial limitations. These limitations are believed to reflect the structure and function of basic visual information-processing mechanisms, including the formation and individuation of coherent object representations (see, e.g., Cavanagh, 2001; C. W. Eriksen & Hoffman, 1973;He, Cavanagh, & Intriligator, 1996Intriligator & Cavanagh, 2001;Pelli, Palomares, & Majaj, 2004). Here we report evidence that the spatial control of attention can be modulated by nonspatial features (such as color and luminance) of the stimuli.Intriligator and Cavanagh (2001) used the term "attentional resolution" to define the smallest possible interitem distance that still allows observers to successfully shift attention from one item to another. They measured attentional resolution using a task that we will refer to as the attentional walk. In one condition, displays consisted of circular arrays of identical disks that varied in density and eccentricity. While observers fixated a central point, one of the disks briefly changed color, indicating that attention should be shifted to that disk. Following this cue, a series of verbal commands instructed the observers to move attention one disk to the left or to the right of the disk they were currently attending (e.g., "left, left, right, left," etc.). At the end of a five-to seven-step series of commands, another disk was probed by having it change colors. The observers' task was to indicate whether or not the probed disk was the end point of the attentional walk. The logic was that if the observers were able to reliably shift their attention within the array, then they would be able to follow the walk and indicate correctly where it ended. If, however, the density of the array was beyond the resolution of attentional control, then the observers would be unable to move through the array successfully and therefore unable to indicate where the walk ended. Notice that performance in the attentional walk task reflected not only the observers' ability to select an individual item, but also their ability to use that information to successfully shift attention from one item to another within arrays of items; these abilities may be separable processing limitations (Moore, Lanagan-Leitzel, & Fine, 2007). Using the attentional walk task, Intriligator and Cavanagh (2001) found that observers could easily perceive individual items within a broad range of display densities, yet they could not reliably report the end point of an attentional walk. In addition, they found that attentional resolution, as measured using the attentional walk, tended to be coarser in the upper visual field than in the lower visual field (see also He et al., 1996), and that it tended to be coarser with increasing eccentricity. These findings are consistent with the idea that spatial attention is spatially limited.In conceptualizing the limitations of attentional resolution, Intriligator and Cavanagh...

Distinguishing between the precision of attentional localization and attentional resolution

“…In particular, it forces observers to rely on spatial location more than they might if the items differed in other attributes as well (e.g., color). Consistent with this possibility, we have found that attentional walks can be executed more reliably in dense arrays when the disks are heterogeneously colored than when they are identical (Moore, Lanagan-Leitzel, Chen, Halterman, & Fine, 2007).…”

Limited influence of perceptual organization on the precision of attentional control

“…could conduct an attentional walk from red item to red item, thereby effectively halving the density of the display. If, however, performance in the walk task does not reflect attention being allocated within an organized representation of the display but, instead, depends only on the local (image level) distinctiveness of items, then, although there may be some advantage for the organized display over a completely homogeneous array, similar to that found by Moore et al (2007), it is unlikely that it would effectively halve the display density.…”

“…In an earlier study (Moore et al, 2007), we showed that performance in the attentional walk task is better when the array in which the attentional walk occurs consists of heterogeneously colored disks than when it consists of identical (gray) disks. Note that this would not be expected if the walk task reflected only limitations of attentional resolution.…”

“…In several recent articles (Moore, Lanagan-Leitzel, Chen, Halterman, & Fine, 2007;Moore, Lanagan-Leitzel, & Fine, 2008), we have presented evidence that the attentional walk task reflects limitations on the precision with which attention can be targeted, rather than (only) a minimal size of the attentional selection area. If we adopt the spotlight metaphor for expository purposes, the distinction between a limited minimal size for attentional se- Figure 1.…”

Investigating temporal properties of covert shifts of visual attention using the attentional walk task

“…The density of the array is varied from sparse, where reliable shifts of attention are easily achieved, to dense, where reliable shifts of attention are difficult or impossible. Previous work has shown that performance in the attentional walk task reflects limitations in the precision with which attention can be localized within an array of items (Moore, Lanagan-Leitzel, Chen, Halterman, & Fine, 2007;Moore, Lanagan-Leitzel, & Fine, 2008). In particular, rather than reflecting only the spatial resolution of selection, which can be thought of as the size of the metaphoric spotlight of attention (Cave & Bichot, 1999), it seems to reflect the spatial uncertainty with which attention can be focused, which can be thought of as the tremor, so to speak, that occurs while the metaphoric spotlight is moved from one point of focus to another.…”