Phase selectivity of spatial frequency channels.

The phase selectivity of spatial frequency channels was measured, using an adaptation technique. Subjects first adapted to a grating of a given spatial frequency; subsequent threshold measurements were made at various spatial frequencies and phase shifts. Changes in the phase relationship between the test and adaptation gratings due to eye movements were circumvented by viewing the grating through an image stabilization apparatus. Local retinal adaptation was minimized by using an adaptation grating whose contrast flickered sinusoidally as a function of time. We were able to demonstrate channel-like frequency tuning for all conditions studied, but the threshold elevations following adaptation were always independent of the phase shift between the test and adaptation gratings. Our results imply that the channels which are selectively tuned to spatial frequency are not selectively tuned to spatial phase.