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Contrast response functions (CFs) produced by the hyperbolic ratio model (Eq. 12) on a linear contrast axis. Positions of maximal slopes of the CFs are indicated by arrowheads. A: CFs with 3 different values of the exponent parameter nHB. B: CFs with 3 different values of the semisaturation contrast parameter αHB. A stimulus with contrast αHB elicits one-half of the saturation level MHB. (αHB = 0.1 for A; nHB = 2 for B.)
