Abstract
The detectability of a Gabor patch (target) at the fovea is improved by two high contrast, aligned, flanking Gabor patches (flankers). This effect is termed collinear facilitation (Polat & Sagi, 1993). Hayashi & Murakami (VSS2012) tested collinear facilitation with a vertically oriented pattern as a target and concentric Laplacians shown above and below as flankers, demonstrating that such flankers with no predominant orientation can also facilitate the target detection. However, the amount of facilitation was smaller than that obtained using conventional oriented flankers, suggesting the visibility of flanker orientation playing some role. In the present study, we further examined the influence of the flankers' visibility by making use of a method called continuous flash suppression (CFS) (Tsuchiya & Koch, 2005). The target was a vertical D2 pattern, and two flankers were presented above and below the target. All of them were presented monocularly. We measured the detection threshold of the target by two-interval forced choice. Three flanker types were tested: a vertical pattern, a horizontal pattern, and an isotropic concentric Laplacian. These flankers were made invisible by CFS due to dynamic maskers presented to the other eye throughout the experiment. The vertical flankers still caused significant facilitation whereas the horizontal flankers and the Laplacian flankers did not. These results indicate two things. First, facilitation with vertical flankers does not require the awareness of the flankers, which means that the collinearity that is necessary for facilitation is only a neural one established by lateral interactions of orientation-selective units in an early, unconscious stage of visual processing. Second, facilitation with isotropic Laplacian flankers requires the awareness of the flankers, which means that the mechanism of this facilitation is different from that of conventional collinear facilitation and the responsible stage for this facilitation may be located in a higher stage of visual processing.
Meeting abstract presented at VSS 2013