Abstract
In an fMRI study, Williams et al. (2008) discovered a foveal feedback mechanism that supports peripheral discrimination of objects. Subsequent behavioural studies confirmed that asynchronously presented foveal noise disrupts peripheral discrimination of objects. However, the majority of previous studies employed the same or similar peripheral objects to investigate this effect. Therefore, it is not clear if the observed effect is limited to high-level objects or applies to other types of stimuli such as letters. Despite using similar objects and tasks, the reported time window for the foveal feedback mechanism varies across studies. One explanation could be the lack of consistency in foveal noise ranging from dynamic black and white noise to static broadband colored noise. Hence, we investigated if the foveal feedback effect occurs also for the highly overtrained stimulus class of letters and if the disruption of foveal feedback depends on the spatial frequency of the foveal noise. To this end, we tested the foveal feedback effect in peripheral letter discrimination by using three types of foveal noise at spatial frequency bands of 0.9, 3.6, and 12.5 c/letter-width that were presented at a random SOA between 25-360 ms. At the beginning of each session, a QUEST procedure was used to determine letter contrast that yields 75% peripheral discrimination performance without noise. Following the calibration measurement, observers performed the peripheral letter discrimination task at the designated letter contrast with or without a foveal noise. Our results suggest that the foveal feedback mechanism not only supports the peripheral discrimination of high-level objects and natural scenes but also letters. We observed a tendency of a greater reduction in peripheral letter discrimination performance by the medium noise compared to the other noise types. Therefore, the relationship between peripheral targets and foveal noise properties might modulate the disruption of the foveal feedback mechanism.