Goro MAEHARA and Ken GORYO¹

Graduate School of Science and Technology, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan
¹Faculty of Letters, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan

(Received November 1, 2004; Accepted December 27, 2004)

It has been reported that a quadratic summation rule can account for threshold versus masker contrast (TvC) functions for binocular, monocular and dichoptic masking. However, the present study suggests that inputs from two eyes are summed in different ways. Foley's model was revised to describe TvC functions for binocular, monocular and dichoptic masking. The revised model has the following two characteristics. First, the revised model receives two monocular inputs. Secondly, excitations and inhibitory signals are subjected to nonlinear transducer functions before and after summation of the monocular signals. A two-alternative forced-choice procedure was used to measure contrast thresholds for Gaussian windowed sine-wave gratings (target) in the presence of sine-wave gratings (masker). Thresholds were measured for 11 masker contrasts and the three masking conditions. It was shown that this revised model fitted the data reasonably well. The revised model indicates how monocular inputs are summed in contrast processing.

Key words: binocular vision, binocular summation, contrast, masking, detection