Visual attention: The past 25 years

We summarize the various strands of research on peripheral vision and relate them to theories of form perception. After a historical overview, we describe quantifications of the cortical magnification hypothesis, including an extension of Schwartz's cortical mapping function. The merits of this concept are considered across a wide range of psychophysical tasks, followed by a discussion of its limitations and the need for non-spatial scaling. We also review the eccentricity dependence of other low-level functions including reaction time, temporal resolution, and spatial summation, as well as perimetric methods. A central topic is then the recognition of characters in peripheral vision, both at low and high levels of contrast, and the impact of surrounding contours known as crowding. We demonstrate how Bouma's law, specifying the critical distance for the onset of crowding, can be stated in terms of the retinocortical mapping. The recognition of more complex stimuli, like textures, faces, and scenes, reveals a substantial impact of mid-level vision and cognitive factors. We further consider eccentricity-dependent limitations of learning, both at the level of perceptual learning and pattern category learning. Generic limitations of extrafoveal vision are observed for the latter in categorization tasks involving multiple stimulus classes. Finally, models of peripheral form vision are discussed. We report that peripheral vision is limited with regard to pattern categorization by a distinctly lower representational complexity and processing speed. Taken together, the limitations of cognitive processing in peripheral vision appear to be as significant as those imposed on low-level functions and by way of crowding.

Peripheral vision and pattern recognition: a review.

Covert attention, the selective processing of visual information at a given location in the absence of eye movements, improves performance in several tasks, such as visual search and detection of luminance and vernier targets1,2,3,4,5,6 An important unsettled issue is whether this improvement is due to a reduction in noise (internal or external)6,7,8,9, a change in decisional criteria10,11, or signal enhancement3,5,12 Here we show that attention can affect performance by signal enhancement For a texture segregation task in which performance is actually diminished when spatial resolution is too high, we observed that attention improved performance at peripheral locations where spatial resolution was too low, but impaired performance at central locations where spatial resolution was too high4,5,6,7,8,9,10,11,12 The counterintuitive impairment of performance that we found at the central retinal locations appears to have only one possible explanation: attention enhances spatial resolution

Attention improves or impairs visual performance by enhancing spatial resolution

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.

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Attentional enhancement of spatial resolution: linking behavioural and neurophysiological evidence

Transient attention is the automatic and short-lasting preferential processing of an area in visual space initiated by sudden stimulation in the same vicinity. Transient attention enhances early visual processing in a variety of dimensions, increasing contrast sensitivity, spatial resolution, and acuity. A recent study established that the increase in contrast sensitivity is accompanied by an increase in apparent contrast. In the present study, we investigated whether the effects of transient attention on spatial resolution and acuity are accompanied by corresponding phenomenological changes in these dimensions. The data indicate that transient attention increases the apparent spatial frequency of Gabor stimuli (Experiment 1) and increases apparent gap size in a Landolt-square acuity task (Experiment 2). Transient attention not only affects basic visual processing-it changes what one experiences.

Attention Alters the Appearance of Spatial Frequency and Gap Size

In 3 experiments, subjects were required to detect the presence of a small region of disparate texture embedded in a larger background at a range of eccentricities. Detection performance always peaked several degrees from fixation. Experiment 1 showed that the location of the peak was not retinally specific; scaling the display changed the location of the performance peak. Experiment 2 showed that poor foveal performance could not be explained by cross-frequency interference; filtering out high spatial frequencies did not lead to improved foveal performance. Experiment 3 showed that the effect is not unique to textures comprising left and right oblique line segments. A parsimonious account of these data is that, at the fovea, there is a mismatch between the scale of the texture and the scale of the mechanisms responsible for encoding texture differences. This mismatch diminishes as the textures are moved further into the periphery. Language: en

Duncan Day

Papers

Texture segmentation along the horizontal meridian: nonmonotonic changes in performance with eccentricity.