Spatial attention alters visual appearance

Abstract

It is well established that attention improves performance on many visual tasks. However, for more than 100 years, psychologists, philosophers, and neurophysiologists have debated its phenomenology-whether attention actually changes one's subjective experience. Here, we show that it is possible to objectively and quantitatively investigate the effects of attention on subjective experience. First, we review evidence showing that attention alters the appearance of many static and dynamic basic visual dimensions, which mediate changes in appearance of higher-level perceptual aspects. Then, we summarize current views on how attention alters appearance. These findings have implications for our understanding of perception and attention, illustrating that attention affects not only how we perform in visual tasks, but actually alters our experience of the visual world.

Figure 1.

Visual appearance varies across the visual field. (a) An original photograph of the Brunnen der Lebensfreude in Rostock, Germany (left image). Using a pooling model, synthetic images (right image) can be generated to appear nearly identical to the original when viewed with fixation at the center (red dot), despite gross distortions in the periphery. Adapted from [14]. (b,c) Visual information appears different across isoeccentric locations; both perceived contrast and perceived spatial frequency are higher along the horizontal than the vertical meridian, and at lower than upper locations along the vertical meridian. Consequently, when viewed with fixation at the center cross, signals of different contrast (b) or different spatial frequency (c) appear to be identical [see 8,12,18]. Given that these effects depend on eccentricity, these figures illustrate qualitative differences.

Figure 2.

Exogenous attention alters appearance. (a) Trial sequence: exogenous attention is manipulated using brief, non-informative precues at either both locations (distributed, neutral) or at one location (test cued or standard cued). Observers have to report the orientation of the stimulus with higher contrast. (b) When plotting the proportion of time the test stimulus is chosen as being higher contrast than the standard stimulus (e.g., 20% reference contrast), cueing the test or standard stimulus location shifts the curve leftward (lower PSE) and rightward (higher PSE), respectively. (c) Control conditions: No change is observed when postcues or longer inter-stimulus intervals (ISI) are used. (d) Exogenous attention changes how we subjectively perceive various visual dimensions, except for hue; upper row: stimuli match physical stimuli under neutral condition; bottom row: perceived stimuli change under attention condition.

Figure 3.

Endogenous attention alters appearance. (a) Trial sequence: Observers are asked to report whether a target letter ‘X’ was present in one of two rapid serial visual presentation (RSVP) streams. Endogenous attention was manipulated using symbolic precues at fixation indicating one (cued) or both (distributed/neutral) RSVP streams in which the target letter could be presented. In trials in which observers did not see a RSVP target, they were asked to do an appearance task. By varying the delay between the two tasks, we can ensure that voluntary attention is still sustained at the cued location when the stimuli for the appearance task are presented. (b) Similar to exogenous attention, cueing the test or standard stimulus location shifts the curve leftward (lower PSE) and rightward (higher PSE), respectively. (c) Reverse instructions: in addition to other control conditions in which no effect is observed (e.g., lengthened delay), reversing the instructions in the appearance task usually shows changes consistent with an appearance change, rather than a response bias. (d) Endogenous attention changes how we subjectively perceive various visual dimensions; upper row: stimuli match physical stimuli under neutral condition; bottom row: perceived stimuli change under attention condition. For the perceived brightness illustration, maintain fixation on any of the fixation spots while shifting attention from one disk to another. You should notice that the attended disk appears to darken [69].