Abstract
Recent fMRI studies have shown that the representation of peripheral objects is also available in the area of the cortex that corresponds to the fovea, suggesting a new form of cortical feedback. This feedback process can be perturbed: peripheral performance deteriorates when noise is presented foveally delayed by 50-250 ms. It was proposed that this feedback process occurs only when participants had to discriminate fine spatial details of high level, complex objects. Here, we show that similar effects also occur with low level stimuli. Participants reported the offset direction (left/right) of a peripheral vernier. In the first experiment, a foveal colored dynamic noise patch was presented in addition to the vernier, while in the second experiment two vertical lines were presented. The lines are very different from a mask, but they are known to interfere with vernier performance in crowding. Our results show a peak reduction in performance for noise presented in the fovea 50 ms after stimulus onset in experiment 1, and 50-150 ms in experiment 2. This time window is consistent with previous studies of high-level object discrimination (~100 ms). As opposed to what was previously hypothesized, thus, foveal feedback seems to be involved not only in high-level visual features processing, but also lower ones. Interestingly, varying the noise characteristics (i.e., presenting a simpler object like two vertical lines) did not alter the effect but led to a larger temporal window (the reduction in performance was also present at 150 ms). Our results suggest that foveal feedback is not specific to processing of high-level objects and that its temporal properties may depend on target and/or noise characteristics.