4 MECHANISM MODEL FOR THRESHOLD SPATIAL VISION

Data on the threshold visibility of spatially localized, aperiodic patterns are used to derive the properties of a general model for threshold spatial vision. The model consists of four different size-tuned mechanisms centered at each eccentricity, each with a center-surround sensitivity profile described by the difference of two Gaussian functions. The two smaller mechanisms show relatively sustained temporal characteristics, while the larger two exhibit transient properties. All four mechanisms increase linearly in size with eccentricity. Mechanism responses are combined through spatial probability summation to predict visual thresholds. The model quantitatively predicts the spatial modulation transfer function (cosine grating thresholds) under both sustained and transient conditions with no free parameters. © 1979.