Abstract
Li and Atick (1994) presented a theory of efficient binocular encoding in which the two eyes’ signals are combined using separately adaptable binocular summation and differencing channels. We designed a dichoptic test stimulus for which the summation channel sees a grating tilted in one direction (clockwise or anticlockwise of horizontal), and the differencing channel sees a grating tilted in the opposite direction. The observer’s perceived direction of tilt (summation or difference direction) should depend on the relative sensitivities of the two channels. We manipulated channel
sensitivity using adaptation. In correlated adaptation, each eye received the same image, which selectively adapted the summation channel; in anticorrelated adaptation, each eye received the
photographic negative of the other eye’s image, which selectively adapted the differencing channel.
These adaptation stimuli had equal energy at all orientations. Despite being isotropic, the adaptors influenced perceived tilt: The test stimulus usually appeared tilted in the difference direction after correlated adaptation, and usually appeared tilted in the summation direction after anticorrelated
adaptation. This counterintuitive finding of a tilt aftereffect from isotropic adaptors is analogous to May, Zhaoping and Hibbard’s (2012) finding of a motion aftereffect from static adaptors. These two results strongly support Li and Atick’s theory.
