Collinear facilitation and suppression at the periphery.

Collinear facilitation is a common phenomenon in the fovea, but it has been recently challenged at the human periphery. Since physiological studies show that facilitation is found at the periphery but only from outside the receptive field, our hypothesis was that facilitation at the periphery exists but from larger target-flanker separations than the fovea. Here, we applied a recent paradigm (Polat & Sagi, 2007) to probe facilitation at the periphery. We used a Yes/No detection task by measuring the false-positive reports (false-alarm, pfa) and hit-rate (phit) for a low-contrast Gabor target (between two flankers) that appeared randomly at the fovea or at the periphery (2° or 4°) to the right or left side. We used different target-flanker separations and orientations at the fovea and at the periphery. Importantly, we found that phit is affected by the target-flanker separations and orientations. Short distances show a suppression effect, but the range of suppression increases with increasing eccentricity. A facilitation effect was found for collinear configuration outside of the suppression range. A similar effect was found for the decisional criterion (Cr), which was correlated with suppression (positive) and facilitation (negative). All together, our results indicate that facilitation exists at the periphery when the target-flanker distance is properly scaled. Thus, our results indicate that collinear facilitation is a common phenomenon that exists in both the periphery and fovea. The suppression range indicates that the perceptual receptive field increases with increasing eccentricity. Our results provide a working hypothesis that explains the functional differences found between the fovea and the periphery. This supports the basic phenomena underlying visual perception, such as collinear facilitation, visual crowding, and backward masking.