Binocular vision enhances phase discrimination by filtering the background

Previous studies have shown that the detectability of a noise-masked target can be enhanced under stereoscopic viewing when the target's interocular d isparity differs from that of the noise. This enhanced detectability can be accounted for by a model postulating that the binocular system linearly su ms the left-eye and right-eye views of a visual scene. This model also pred icts enhanced phase discrimination under specifiable interocular disparitie s of target and noise. Two experiments were conducted in which subjects wer e asked to discriminate between two luminance patterns (target and foil) th at differed only in phase. The target patterns were constructed by summatin g two vertical sinusoidal gratings in which the phase difference between th e higher and the lower spatial frequency gratings was 45 degrees. The foils contained the same two component frequencies, with a phase difference of - 45 degrees. Thus, targets and foils were mirror images of one another. The ability of subjects to discriminate between these stereoscopically viewed m irror-image patterns was investigated under two sets of interocular dispari ties: those that, according to our model, would unmask one or both spatial frequency components, and those that would leave both components masked by the noise. Phase discrimination was enhanced only when both component frequ encies of the target and foil were unmasked. The implications of these find ings for template-matching and phase-discrimination models of pattern discr imination are considered.