Abstract
Central vision, the fovea, is thought to be processed differently from the peripheral parts of the visual field, relying on different physiological streams. However, because usually both fovea and periphery are simultaneously stimulated, one would expect mutual modulations between the two representations in order to achieve a unified percept. We measured ERP responses to different sizes of Gabor patches, occupying from strictly foveal (0.4 degrees) to a combined foveal and peripheral parts of the visual field (up to 14 degrees). Annuli (rings produced from a Gabor with the foveal opening filled with mean-luminance background) were used to stimulate the surround. The results show 3 main components representing the foveal and the peripheral processing. 1) P1-amplitude increased with increasing absolute area of stimuli, similarly to our findings for increasing contrasts. Moreover, it reflected a linear summation of sensory representation of complementary center and surround stimuli. However, surprisingly, the latency showed a faster processing in periphery than in the fovea. 2) P2-amplitude showed no linear summation between the two parts. However, latency showed significant additional gains in the speed of processing for the combination of center and surround, compared to the parts in isolation, suggesting that the periphery accelerates the processing of the fovea. 3) N2-amplitude showed no linear summation, but a step change from the strictly foveal to peripheral stimulation, despite the linear shortening of latencies with increasing stimulation area. Moreover, the difference in the amplitude for the peripheral stimulus vs. the one combining both fovea and periphery support our earlier suggestions that N2 reflects lateral interactions from the fovea. Surprisingly, stimulation of periphery increases the speed of foveal processing. Our results suggest interactions between the representation of the fovea and the periphery, rather than an independent representation. Thus, faster peripheral processing compensates for spatial distance, resulting in a coherent percept.
Supported by grants from the National Institute for Psychobiology in Israel, funded by the Charles E. Smith Family and the Israel Science Foundation.