SPATIAL INTERACTIONS MODULATE STEREOSCOPIC PROCESSING OF HORIZONTAL AND VERTICAL DISPARITIES

Stereoscopic processing of horizontal and vertical disparities was ass essed by measuring how the stereoscopic appearance of test dots near t he fixation point was influenced by inducing stimuli in the near perip hery. The inducing stimuli were differentially magnified in the two ey es and varied in horizontal eccentricity. As expected, when the induce rs were horizontally magnified, the test dots exhibited depth contrast , slanting in depth in a direction opposite the slant of the inducing dots. When the inducers were vertically magnified, the test dots slant ed in depth around a vertical axis toward the eye with the larger vert ical image (the induced-size effect). However, two lines of evidence s uggested that an eccentricity-dependent weighted average of horizontal and vertical components of inducer-dot magnification determined the s lant of the test dots. First, as the horizontal eccentricity of the in ducing dots was varied, the trend of test-dot slants measured with ver tical inducer magnifications was predicted by the trend of test-dot sl ants measured with horizontal inducer magnifications. Second, test-dot slants measured with a combination of both horizontal and vertical in ducer magnification could be predicted by simply adding test-dot slant s measured with either horizontal or vertical inducer magnification al one.