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Daisuke Hayashi, Ikuya Murakami; Collinear facilitation by flankers with invisible orientation. Journal of Vision 2012;12(9):98. doi: 10.1167/12.9.98.
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The detectability of a Gabor patch (target) in the fovea is improved by two high contrast, aligned, flanking Gabor patches (flankers). This effect is termed collinear facilitation (Polat & Sagi, 1993). Despite a lot of psychophysical and physiological studies about the characteristics of this facilitation, the processing stage that is responsible for this facilitation has not been identified. In this study, we psychophysically approached to the mechanism of collinear facilitation by investigating the influence of the orientation information and perceptual appearance of the flankers. For this purpose, we used D2 patterns (Motoyoshi & Nishida, 2001). The D2 pattern has specific orientation, and linear summation of two orthogonal D2 patterns is equal to an isotropic Laplacian. This means we can test conditions in which flankers contain orientation information that is consciously invisible. The target was a vertical D2 pattern, and two flankers were presented above and below the target, so facilitation should occur when the flankers were vertical. We measured the detection threshold of the target by two-interval forced choice. Three flanker types were tested: a vertical D2 pattern, a horizontal D2 pattern, and an isotropic Laplacian. The facilitation effect was greatest with the vertical D2 flankers, as expected. To our surprise, a smaller but robust facilitation also occurred with the isotropic Laplacian flankers. Facilitation did not occur with the horizontal D2 flankers. This pattern of results indicates that an invisible vertical orientation contained in the isotropic pattern looking like a bull's eye is sufficient for producing collinear facilitation, and that a degree of facilitation is further enhanced by the perceptual appearance of flankers that is consistent with collinearity. We argue that lateral interactions of orientation-selective units in an early stage of visual processing and feedback from a higher stage of visual processing are both involved in collinear facilitation.
Meeting abstract presented at VSS 2012
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