Experiments with a theory of visual texture segmentation using modulation/demodulation processes

The receptive field profiles of certain simple cells in the visual cortex have recently been shown to approximate the 2-D Gabor functions, which are Gaussian-modulated sinusoidal gratings in the space domain, and shifted Gaussians in the frequency domain (Marcelja 1980; Daugman 1980,1985). The 2-D Gabor functions minimize the space-frequency uncertainty principle, and hence can be defined with narrow frequency and orientation responses while maintaining spatial localization. Physiological evidence indicates that the Gabor receptive fields are often arranged in quadrature pairs (Pollen and Ronner 1981) allowing a novel interpretation of early visual processing whereby highly frequency- or orientation-specific information can be recovered from the ampUtude or phase envelopes of a set of Gabor-filtered images. In particular, this leads to an interpretation of texture as a surface code from which physical information can be derived via appropriate filtering/ demodulation processes.