Psychophysically disrupting the delayed feedback signal to foveal retinotopic cortex selectively impairs extra-foveal object perception

Abstract

Previous neuroimaging and TMS studies (Williams et al, 2008; Chambers et al, 2013) suggest that object information from peripherally presented images was available in foveal retinotopic cortex and is functionally relevant, presumably due to feedback signals from high-level object sensitive cortex. In this study, we further investigated the behavioral significance and timing of this potential feedback signal. Two objects with fine details similar to the ones used in Williams and colleagues’ study were presented for 100 ms in diagonal quadrants on two sides of the fixation point and subjects were asked to make a same/different decision. A dynamic noise patch was presented for 80 ms in the fovea region at five different SOAs, at 50, 150, 250, 350, and 450 ms after the onset of the object images. The results showed that subjects’ ability to discriminate object images was severely impaired at the SOAs of 50 ms and 250 ms, mildly at 150 ms, but not at other SOAs. At 50 ms SOA, the fovea noise overlapped with the peripheral objects in time, and presumably attracted attention away from the object images. The severe dip in performance at SOA of 250 ms is more interesting and is unlikely due to a simple masking effect in the feedforward sweep, given that performance was only mildly affected at the SOA of 150 ms. However, the foveal noise-induced temporally selective impairment at 250ms was not found in a control condition in which subjects performed a motion speed comparison task at the same peripheral locations. Presumably processing of motion speed in the periphery does not benefit from feedback signals to foveal cortex. Our results support a task-dependent and temporally specific feedback signal from high-level cortex to foveal retinotopic cortex that plays an important role in processing spatially detailed object information.

Meeting abstract presented at VSS 2015