The accessibility of spatial channels for stereo and motion

Using fractal noise images, we measured the dependence of Dmin on the spatial passband (spatial frequency and orientation) over which information was correlated either between the eyes for stereo or between sequential frames for motion. Without affecting the amplitude spectrum of the noise stimulus we used idealized filters to scramble the phase of components outside a pre-defined passband. Using a simple Gaussian model in which performance depends on the signal/noise within a restricted spatial region, we obtained estimates of the bandwidth of the narrowest underlying spatial frequency and orientation spectral region subserving these two comparable tasks. Spatial bandwidths varied with peak spatial frequency but were very broad approximating the spectrum of the stimulus itself. Orientation properties of the underlying mechanisms were isotropic. These results suggest that the independent activity of individual narrowband spatial channels is not perceptually accessible for these tasks.