Abstract
Temporal feature binding is the ability to distinguish a combination of features shown simultaneously from other binding possibilities. Temporal binding is vital because visual scenes are often dynamic and people constantly move their eyes. In the current study, we investigated properties of binding spatially separated features. In the first experiment, we found that binding spatially separated color and orientation is faster in the fovea than in the periphery. The stimulus was a disk. Half of the disk was spatially uniform but alternated in color over time (e.g., red and green) and the other half contained gratings alternating in time between two orientations (e.g., 45° and 135°). The disk was shown either at fixation or 10° below fixation (suitably scaled in size). For a given trial, one color-orientation pair alternated with another color-orientation pair. Noise maskers preceded and followed the stimuli. Subjects responded by indicating the correct pairing of color and orientation. Subjects could better detect the color and orientation combination when the stimulus was presented in central vision than peripheral vision. (About 10% greater accuracy in central vision at all three alternation frequencies.) In the second experiment, two circular disks each containing either color or orientation features were separated by 8 deg. We found that when the two features were placed in the left and right hemifields, subjects were more accurate in detecting the feature pairings compared to when they were placed in the same hemifield (at the same eccentricity and with the same spatial separation). This observation indicates that binding spatially separate features requires central resources (e.g., attention) which are more available across two hemifields than within one hemifield. Together, the foveal advantage and cross hemifield advantage support the idea that binding spatially separate color and orientation features is achieved at a high level in the visual pathway.