How Attention Affects Spatial Resolution

Abstract

We summarize and discuss a series of psychophysical studies on the effects of spatial covert attention on spatial resolution, our ability to discriminate fine patterns. Heightened resolution is beneficial in most, but not all, visual tasks. We show how endogenous attention (voluntary, goal driven) and exogenous attention (involuntary, stimulus driven) affect performance on a variety of tasks mediated by spatial resolution, such as visual search, crowding, acuity, and texture segmentation. Exogenous attention is an automatic mechanism that increases resolution regardless of whether it helps or hinders performance. In contrast, endogenous attention flexibly adjusts resolution to optimize performance according to task demands. We illustrate how psychophysical studies can reveal the underlying mechanisms of these effects and allow us to draw linking hypotheses with known neurophysiological effects of attention.

Figure 1

Cumulative numbers of publications reported by PubMed since 1970 containing the key word “visual attention” in either the title or the abstract.

Figure 2

Schematic depiction of (A) receptive field (RF) size and (B) population receptive field (pRF) size as a function of eccentricity based on physiological measurements in macaque areas V1, V2, and V4, and fMRI measurements in human areas V1, V3, and hV4. The center of each array corresponds to the fovea. The size of each circle is proportional to its eccentricity, based on the corresponding scaling parameters. At a given eccentricity, a larger scaling parameter implies larger receptive fields. (A, Reprinted by permission from Macmillan Publishers Ltd. from Freeman and Simoncelli 2011; B, reproduced with the permission of Jonathan Winawer and Hiroshi Horiguchi; https://archive.nyu.edu/handle/2451/33887.)

Figure 3

Summary of the effects of exogenous and endogenous attention on spatial resolution tasks described in this paper.

Figure 4

Effects of attention in visual search tasks. (A) Performance in conjunction visual search decreases with eccentricity, as depicted by slower reaction times and higher error rates. Adjusting stimulus size according to the cortical magnification factor at a given eccentricity eliminates the eccentricity effect in visual search, indicating that spatial resolution constrains performance. (B) Manipulating exogenous attention has a similar effect to cortical magnification, strongly reducing the eccentricity effect. These results support the idea that attention increases resolution at the attended location, restoring visual search performance in the periphery where low resolution is a limiting factor. (A, Adapted from Carrasco and Frieder 1997; B, adapted from Carrasco and Yeshurun 1998.)

Figure 5

Effects of attention in acuity tasks. (A) Attention improves performance in acuity tasks in both humans and non-human primates (macaques), resulting in lower acuity thresholds with attention. (B) For human observers, both exogenous and endogenous attention trade-off acuity, increasing acuity at the attended location at the cost of decreased acuity at unattended locations. (A, Adapted from Golla et al. 2004; B, adapted from Montagna et al. 2009.)

Figure 6

(A) Lincoln in Dalivision (1977) by Salvador Dalí. Depending on the dominance of high- or low-spatial frequency content of the image, the observer will perceive Gala’s body or Lincoln’s face (note small inserts on the lower left). (B) Texture segmentation task used in the studies described. Note that performance peaks at perifoveal locations and decreases at central locations (central performance drop; CPD), where resolution is too high for the task, as well as at peripheral locations, where resolution is too low.

Figure 7

Effects of attention in texture segmentation tasks. (A) Exogenous attention automatically increases spatial resolution, improving texture segmentation performance in the periphery where the resolution is too low and impairing performance at central locations where the resolution is already too high, for the scale of the texture. The vertical dashed lines indicate the eccentricity of the performance peak. The blue overlay shows a range of eccentricity in which exogenous attention has opposite effects improving performance (left) or impairing performance (right), depending on the scale of the texture. (B) Endogenous attention benefits performance across eccentricities, regardless of whether performance is limited by the resolution being too low or too high. The vertical dashed lines indicate the eccentricity of the performance peak. (A, Adapted from Yeshurun and Carrasco 1998; B, adapted from Yeshurun et al. 2008.)

Figure 8

Changes in resolution with attention along the vertical meridian (VM). (A) Changes in texture segmentation along the vertical meridian and with exogenous attention. Spatial resolution is higher in the lower VM than the upper VM, resulting in higher performance in the periphery where resolution is too low and worse performance at central locations where resolution is too high for the scale of the texture. Similarly, by enhancing resolution, exogenous attention impairs and improves performance at central and peripheral locations, respectively. (B) Effects of exogenous attention on texture segmentation along the upper and lower VM. Exogenous attention impairs and improves performance across eccentricity consistent with enhanced resolution. Note that the attentional crossover (indicated by the colored area) occurs closer to the fovea along the upper (lower resolution) than the lower (higher resolution) VM, consistent with the idea that increasing resolution impairs or improves performance according to resolution constraints. (Adapted from Talgar and Carrasco 2002, with kind permission from Springer Science+Business Media.)

Figure 9

Schematic depiction of the effects of spatial frequency adaptation on texture segmentation performance and visual attention effects. (A) Effects of selective adaptation to spatial frequencies (SF) at central locations on texture segmentation. Adapting to high-SF shifts sensitivity toward lower SF, reducing the CPD and shifting the peak closer to the fovea, similar to a decrease in resolution. Conversely, adapting to low-SF shifts sensitivity toward higher-SF, increasing the CPD and shifting the peak toward the periphery similar to an increase in resolution. (B) Adapting to high SF, but not low SF, reduces the effects of exogenous attention at central locations, suggesting that exogenous attention enhances resolution by increasing the contribution of the high-SF filters. (C,D) Endogenous attention may benefit performance at central locations either by (C) enhancing activity in the low-SF filters or (D) suppressing activity in the high-SF filters. Adapting to high SF, but not to low SF, reduced the attentional benefits supporting a mechanism that can either boost or suppress the high SF to optimize resolution to the task demands.