Similar Neural Representations of the Target for Saccades and Perception during Search

Abstract

Are the body's actions and the mind's perceptions the result of shared neural processing, or are they performed largely independently? The brain has two major processing streams, and some have proposed that this division segregates visual processing for action and perception. The ventral pathway is claimed to support conscious experience (perception), whereas the dorsal pathway is claimed to support the control of movement (action). Others have argued that perception and action share much of their visual processing within the primate cortex. During visual search, the brain performs a sophisticated deployment of eye movements (saccadic actions) to gather information to subserve perceptual judgments. The relationship between the neural mechanisms mediating perception and action in visual search remains unexplored. Here, we investigate the visual representation of target information in the human brain, both for perceptual decisions and for saccadic actions during visual search. We use classification image analysis, a form of reverse correlation, to estimate the behavioral receptive fields of the visual mechanisms responsible for saccadic and perceptual responses during the same visual search task. Results show that the behavioral receptive fields mediating the perceptual decisions are indistinguishable from those driving the oculomotor decisions, suggesting that similar neural mechanisms are responsible for both perception and oculomotor action during search. Diverging target representations would result in an inefficient coupling between eye movement planning and perceptual judgments. Thus, a common target representation would be more optimal and might be expected to have evolved through natural selection in the neural systems responsible for visual search.

Constrained sampling experiments reveal principles of detection in natural scenes

“…For example, results from classification image experiments strongly suggest that the human visual system uses image features that deviate from those of the MT observer (33)(34)(35). Thus, it is unlikely that the subjects in our experiments are carrying out a computation directly equivalent to applying a matched template.…”

A Single Route to Action? The Common Representation of Perceptual and Saccade Targets

“…In an article published recently in the Journal of Neuroscience, Eckstein et al (2007) address this question in human subjects with a novel method that avoids some of the problems of equating similar performance with a common mechanism. Rather than comparing performance, the authors propose a classification image (CI) analysis.…”

“…The task proposed by Eckstein et al (2007) is a five-alternative forced choice (5-AFC) visual search task: participants must detect a brighter Gaussian-shaped target among four distracters. Spatially uncorrelated Gaussian noise is added to the stimuli.…”

“…Then, the CIs were again averaged over pixels of equal radius from the center. The apparent radial symmetry of the CIs [Eckstein et al (2007), their Fig. 2 (http://www.jneurosci.org/cgi/content/ full/27/6/1266/F2)] suggests that this is a good way to reduce the degrees of freedom in the data without losing important features.…”

“…2 (http://www.jneurosci.org/cgi/content/ full/27/6/1266/F2)] suggests that this is a good way to reduce the degrees of freedom in the data without losing important features. The radial profiles are shown in Eckstein et al (2007), their Fig. 3 (http:// www.jneurosci.org/cgi/content/full/27/6/ 1266/F3).…”