Attentional enhancement of spatial resolution: linking behavioural and neurophysiological evidence

Abstract

Attention allows us to select relevant sensory information for preferential processing. Behaviourally, it improves performance in various visual tasks. One prominent effect of attention is the modulation of performance in tasks that involve the visual system's spatial resolution. Physiologically, attention modulates neuronal responses and alters the profile and position of receptive fields near the attended location. Here, we develop a hypothesis linking the behavioural and electrophysiological evidence. The proposed framework seeks to explain how these receptive field changes enhance the visual system's effective spatial resolution and how the same mechanisms may also underlie attentional effects on the representation of spatial information.

Figure 1. Allocation of spatial attention

a | Overt attention. We shift our gaze to the location of interest (the name tag). b | Covert voluntary (endogenous) attention. We shift attention covertly to the location of interest while keeping our gaze somewhere else (at the person’s face). c | Covert involuntary (exogenous) attention. While we keep our gaze straight ahead, an external event (the falling coffee cup) leads to an involuntary shift of attention to the location of the event.

Figure 2. Behavioural evidence of attention effects on spatial resolution

a | Typical search task display for feature and conjunction search. In a feature search, observers report a target that is defined by a single feature (for example, a vertical line among tilted lines), whereas in a conjunction search, the target is defined by a combination of features (for example, a purple vertical line among purple tilted lines and green vertical lines). b | When the number of distractors (set-size) increases, there are more possible target locations at farther eccentricities. Performance deteriorates with eccentricity and thus with set-size. Attention improves performance (both speed and accuracy) and reduces both the eccentricity and the set-size effect. c | Possible mechanism for effects of attention in a visual search task: without attention, information from the target and distractors is integrated where spatial resolution is low. Attention effects could be mediated by a reduction of the integration area (orange) so that the influence of distractors is diminished. d | Attention improves acuity as a function of eccentricity. Attention could improve performance by reducing spatial integration, so that the visual system is better able to resolve the gap in the Landolt stimulus (insets). e | Texture segmentation performance typically peaks at mid-peripheral locations and drops at nearer as well as farther eccentricities (blue line). Attention modulates performance (red line) consistent with a change in optimal filter size; performance improves where resolution is too low (in the periphery) but declines where resolution is too high (centrally). f | Texture stimulus with filters (orange) that are too small, optimal or too large depending on target eccentricity (top panels). Attention may reduce the filter size so that the eccentricity at which the filter size is optimal shifts to farther eccentricities (bottom panels). Part b is modified, with permission, from REF. © (1998) American Psychological Association. Part d is modified from REF. © (2002) Association for Research in Vision and Ophthalmology. Part e is modified, with permission, from REF. © (1998) Macmillan Publishers Ltd. All rights reserved.

Figure 3. Attention alters perception of spatial stimulus features

a | The same physical stimulus appears to have higher spatial frequency with attention (right panel) than without attention (left panel) allocated to it. b | Attention may modulate perceived spatial frequency by a shift of sensitivity to higher spatial frequencies. Spatial frequency tuning curves of a set of neurons with different preferred spatial frequencies without attention are shown in blue. Horizontal dashed lines indicate the response of two example neurons to a stimulus of a particular spatial frequency (vertical black line). Spatial frequency tuning curves and response levels of the same set of neurons after attention has selectively up-modulated those neurons tuned for higher spatial frequencies are shown in red. The same stimulus now elicits a higher response from the example neurons (red dashed lines) and others tuned for the higher spatial frequency (shown as darker red curves on the right side of the graph) and the population response is biased towards higher spatial frequencies. c | Attention increases perceived offset between two lines of a Vernier stimulus after a pair of cues are flashed diagonally (for example, in the upper left and lower right quadrant of the middle panel), which is consistent with perceptual repulsion (indicated by arrows) of the lines away from the cues. d | The same physical stimulus appears larger (indicated by arrows) after attention has been drawn to its centre. e | The same oval stimulus appears either stretched out along the vertical or horizontal dimension after a pair of cues is either flashed inside or outside the contour, consistent with perceptual repulsion of the line away from the cues. f | Illustration of how RF shifts could mediate an increase in perceived size. Without attention, a regular grid of receptive fields (RFs) covers the visual scene (middle left panel). Attention shifts RFs towards the focus of attention, in this case the centre of a banana piece (middle right panel). The shift is accompanied by a shrinkage at the attentional focus and an expansion around it. Because RFs are still labelled with their original position, stimuli are perceptually pulled away from the centre of the attentional focus, so that the banana appears larger (far right panel). Note that the effect sizes depicted here are exaggerated for clarity. Part a is modified, with permission, from REF. © (2005) Sage. Part b is modified from REF. © (2010) Springer. Part c is modified, with permission, from REF. © (1997) American Psychological Association. Part d is modified from REF. © (2007) Association for Research in Vision and Ophthalmology. Part e is modified, with permission, from REF. © (2011) Springer. The images in part f are courtesy of K.A.-E.

Figure 4. Attention alters receptive field profiles

a | The left panel shows that responses to a preferred stimulus (represented by a purple vertical bar) and a non-preferred stimulus (represented by a green horizontal bar) presented simultaneously inside a neuron’s receptive field (RF; represented by a black line) reflect an average between the neuron’s response to the preferred stimulus presented alone (light purple line) and the response to the non-preferred stimulus presented alone (light green line). Attention biases this average response in favour of the attended stimulus. Attention on the preferred stimulus enhances the response (dark purple line), whereas attention on the non-preferred stimulus reduces the response (dark green line). The panels on the right show hypothetical changes in RF profile (indicated by orange shading). The results are consistent with a shrinkage of the RF around the attended stimulus as well as a shift towards the attended stimulus. b | Attention on a stimulus inside the RF (red dot) shifts and shrinks the RF towards and around the attended stimulus (right panel) compared with the same stimulus configuration when attention is allocated elsewhere (left panel). c | Attention on a stimulus near (but not inside) the RF shifts and expands the RF towards the attended stimulus (red dot in the right panel) compared with the same stimulus configuration when attention is allocated elsewhere (left panel). Part a is modified, with permission, from REF. © (1999) Society for Neuroscience. Part b is modified, with permission, from REF. © (2006) Macmillan Publishers Ltd. All rights reserved. Part c is modified from REF. .