Abstract
We recently reported that the pattern of fMRI response across foveal retinotopic cortex contains position-invariant information about objects presented in the periphery, and further that this object information is correlated with object discrimination performance (Williams et al, 2008). This finding suggests that during perception of peripherally-presented objects, higher cortical areas feed information back to foveal retinotopic cortex, improving performance, a phenomenon inconsistent with most theories of object recognition, retinotopic cortex, and the role of feedback in visual processing. In order to better understand this surprising phenomenon, we tested its generality across new tasks and stimuli. Specifically, we asked whether the effect occurs only when two stimuli are compared (by testing individual peripheral stimulus categorization), and only for complex stimuli (by testing oriented Gabors instead of objects). On each trial, a single Gabor was briefly presented in a peripheral location. In separate sessions, subjects performed either a color or orientation discrimination task on the Gabor while maintaining fixation. Subjects were asked either to 1) discriminate between two shades of either red or blue, or 2) determine whether the Gabor tilted slightly right or left of the vertical axis, or slightly above or below the horizontal axis. The results show that the pattern of fMRI response in foveal retinotopic cortex contains information about the orientation (vertical vs. horizontal) of the Gabor presented in the periphery. These findings indicate that information about peripheral stimuli is found in foveal retinotopic cortex not only for object shape, but also for orientation, and not only for a simultaneous comparison task, but also for categorization of individually-presented stimuli. However, foveal information about peripheral colors is weak, and foveal information about orientations is apparently less position-invariant than information about objects, providing some clues about the boundary conditions and hence functional significance of this phenomenon.
Supported by EY 13455 to NK.