Abstract

The effect that induced gratings [ Vision Res. 22, 119 ( 1982)] exert on the perceived contrast of standard gratings situated within a 0.5° test field was assessed for two observers by a contrast-matching procedure. Five levels of inducing-grating contrast, C_I, ranged from 0.0 to 0.75. Functions relating matching contrast, C_M, to standard-grating contrast, C_S, were obtained at four levels of inducing-grating contrast across a range of standard contrasts, −0.90 ≤ Cs ≤ +0.90, where the sign denotes the spatial phase of the standard relative to the inducing grating. The matching functions possessed three distinct limbs separated by two inflection points; the limb between the inflection points represents a region of high contrast gain. Another measure, canceling contrast, was obtained at the four levels of inducing contrast by variation of C_S until the test field appeared spatially homogeneous. Induction magnitude measured in terms of canceling contrast, C_C, grew approximately linearly with C_I, such that C_C = 0.819 (C_I). Induction magnitude determined from matching-contrast data obtained for homogeneous test fields (i.e., C_M for C_S = 0.0) grew as a decelerating function of inducing-grating contrast, such that C_M = 0.308(C_I)^1.8/([C_I]^1.8 + 0.096), effectively asymptoting at a contrast of approximately 0.275 for C_I ≥ 0.50. When the difference between the absolute values of matching and standard contrast, |C_M| − |C_S|, is plotted against the ratio of standard to inducing-grating contrast, C_S/C_I, the resulting functions are generally biphasic, revealing regions of both contrast overmatching (i.e., |C_M| > |C_S|) and contrast under-matching, |C_M| < C_S|. A four-parameter model is presented that accounts for many features of the raw matching functions and that is mathematically similar to Semmelroth’s account of the crispening effect in brightness matching [ J. Opt. Soc. Am. 60, 1685 ( 1970)]. The model describes matching contrast, C_M, as the weighted sum of two nonlinear contrast-response functions whose inputs are C_S and C_S − C_I The results are discussed relative to the crispening effect (the effect of contrast adaptation on perceived contrast) and to similarities and differences in luminance and contrast-domain visual processing.

© 1994 Optical Society of America

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