Exogenously cued attention triggers competitive selection of surfaces

AbstractIt has been reported that when an endogenous cue directs attention to a brief translation of one of two superimposed surfaces, observers reliably report the direction of that translation as well as the direction of a second translation of the cued surface. In contrast, if the uncued surface translates second, direction judgments are severely impaired for several hundred milliseconds. We replicated this result, but found that the impairment survived the removal of the endogenous cue. The impairment is therefore not due to endogenously cued attention. Instead, a brief translation of one surface acts as an exogenous cue that triggers an automatic selection mechanism, which suppresses processing of the other surface. This study provides a clear case of exogenous cueing of surface-based attention. We relate these results to identified competitive selection mechanisms in visual cortex

Attentional selection of superimposed surfaces cannot be explained by modulation of the gain of color channels

AbstractWhen two differently colored, superimposed patterns of dots rotate in opposite directions, this yields the percept of two superimposed transparent surfaces. If observers are cued to attend to one set of dots, they are impaired in making judgments about the other set. Since the two sets of dots are overlapping, the cueing effect cannot be explained by spatial attention. This has led to the interpretation that the impairment reflects surface-based attentional selection. However, recent single-unit recording studies in monkeys have found that attention can modulate the gain of neurons tuned for features such as color. Thus, rather than reflecting the selection of a surface, the behavioral effects might simply reflect a reduction in the gain of color channels selective for the color of the uncued set of dots (feature-based attention), as if viewing the surfaces through a colored filter. If so, then the impairment should be eliminated when the two surfaces are made the same color. Instead, we find that the impairment persists with no reduction in strength. Our findings thus rule out the color gain explanation

Object-based attention determines dominance in binocular rivalry

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Neural Correlate of Object-Based Selection in Area V4

Single unit studies of attention in monkeys have identified competitive circuits in extrastriate cortex that could mediate selection of one stimulus over another. While these studies show that attention operates by resolving competition, they used stimuli atseparate locations, confounding selection of objects with selection of spatial locations. To resolve this, we recorded responses of V4 neurons to two spatially superimposed transparent surfaces, one of which was delayed in onset. The surfaces were defined by patterns of dots that rotated rigidly around a common center. One set of dots was of the neuron's preferred color and the other was of an isoluminant non-preferred color. Human psychophysics using the same type of stimuli found that the delayed onset of one surface exogenously cues attention to that surface and suppresses processing of the other surface for several hundred milliseconds. Consistent with this, neurons in area V4 were preferentially driven by the delayed surface. Using superimposed surfaces ruled out spatial selection. But is this selection object-based? If it is, the selection should survive moving the superimposed surfaces through space. When the appearance of one of the two surfaces was delayed outside the neuron's receptive field and both surfaces then moved into the RF, the pair response was still preferentially driven by the delayed surface. Neurophysiological and functional imaging studies have shown that endogenously directing attention to the color or motion of a stimulus preferentially processes it throughout the visual field. We tested for feature-based selection by using placing two surfaces within the RF and two outside of the RF. When the delayed surface appeared within the RF, the results were similar to the first experiment, i.e. the delayed surface was preferentially processed. If this effect were the result of global color-based selection, thenthe same effect should be seen when the delayed surface appeared outside the RF. This effect was not seen, hence the selection was not of the color of the surface but of the surface itself. These results show that competitive circuits in V4 are not limited to mediating competition between spatial locations, but also select objects. These circuits are a likely neural substrate for object-based attention

Occlusion and the Interpretation of Visual Motion: Perceptual and Neuronal Effects of Context

ion perception; psychophysics; neurophysiology; binocular disparity; extrastriate; monkey The locally measured motion of a one-dimensional visual image feature, such as an edge, is ambiguous (Wohlgemuth, 1911; Wallach, 1935; Marr and Ullman, 1981). This is known as the "aperture problem." This ambiguity can, in principle, be overcome by measuring the unambiguous motion of a two-dimensional visual image feature, such as where two edges of a surface meet to form a corner. Many two-dimensional visual image features, however, occur where edges from two different but overlapping surfaces meet. Such compound features are "intrinsic" to neither surface and have been termed "extrinsic" (Nakayama et al., 1989). Shimojo et al. (1989) demonstrated that human observers differentiate intrinsic and extrinsic features on the basis of depth-ordering cues that exist at occlusion boundaries. Furthermore, these investigators discovered that intrinsic features are used to overcome the aperture p