Abstract
It is well known that the apparent contrast of a luminance-modulated (LM) test grating is reduced in the presence of a surrounding LM grating, a phenomenon sometimes termed “contrast-contrast”. Rather less is known about surround induction with texture gratings. In particular one might expect that with texture gratings that are defined by modulations in local orientation, termed orientation-modulated (OM) gratings, the perceived amplitude of a test might be enhanced by surround gratings lower in amplitude, on the grounds that OM amplitude might be encoded through OM amplitude-selective channels. We tested this idea using vertically oriented 0.5 cpd square-wave OM gratings constructed from dense arrays of 6.0 cpd Gabor micropatterns. The surrounds were 12 deg and the central tests 4 deg in diameter, resulting in respectively 6 and 2 cycles of modulation. We tested both in-phase and opposite-phase spatial test-surround relationships with various combinations of surround and test amplitudes. A two-interval-forced-choice procedure was employed to determine the point-of-subjective equality between the test amplitude and an adjustable matching pattern with a zero-amplitude surround. When the surrounds were higher in amplitude than the test, we found that perceived test amplitude was suppressed, as with luminance contrast grating. However, we found very little evidence of enhancement of tests higher in amplitude that their surrounds. We conclude that OM amplitude is likely encoded as a scalar dimension like luminance contrast and as with luminance contrast is subject to inhibition from surrounding OM gratings.