Discrimination of spatial phase shows a qualitative difference between foveal and peripheral processing

Detection and discrimination of compound grating stimuli were examined in foveal and peripheral vision. At the fovea, stimuli containing two components (spatial frequencies F and 3 F) can be discriminated on the basis of their relative spatial phase when the 3 F component is at a contrast below its independent detection threshold. This is no longer the case at increasing retinal eccentricity, where phase discrimination thresholds fall off much more steeply than simple detection thresholds. This relative fall-off in discrimination performance is still present for stimuli scaled for the cortical magnification factor, and is not attributable to fading of peripheral images due to the Troxler effect. The results therefore must imply a qualitative change in the processing of phase information between foveal and peripheral vision.