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Goro Maehara, Ken Goryo; A Processing Model of Binocular Summation: An Extension of Foley's Model for Binocular, Monocular and Dichoptic Masking. Journal of Vision 2004;4(8):784. doi: https://doi.org/10.1167/4.8.784.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study is to investigate how monocular inputs are summed in contrast processing. For this purpose the present study is concerned with binocular, monocular and dichoptic masking. A two-alternative forced-choice 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 three masking conditions (binocular, monocular and dichoptic). For binocular and monocular masking, threshold vs. masker contrast (TvC) functions had the dipper-shape. That is, the target contrast thresholds decrease and then increase as masker contrast increases. Target contrast thresholds were lower for binocular masking than for monocular masking at a range of low masker contrasts. For dichoptic masking, there was threshold elevation as much as for binocular and monocular masking. But dichoptic masking produced little facilitation at a range of low masker contrasts. Moreover, target contrast thresholds were usually higher for dichoptic masking than for binocular and monocular masking. These results were consistent with Legge's study (1984a, 1984b). We extended Foley's model (Foley, 1994; Foley & Chen, 1999) to account for binocular, monocular and dichoptic masking. Although Foley's model has been used to account for a variety of masking data, his model cannot be applied to the data of monocular and dichoptic masking because inputs from two eyes are not separate in his model. We revised Foley's model to receive two monocular inputs. Linear operators are applied to the stimulus patterns presented to two eyes respectively. Outputs of linear operators are half-wave rectified and subjected to nonlinear transducer function. These two monocular signals are summed to yield a binocular signal. A binocular signal is subjected to nonlinear transducer function and then divisive inhibition. It was proved that this revised model fitted the data reasonably well.
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