Receptive Fields for the Determination of Textured Surface Inclination

The image of a uniformly textured inclined surface exhibits systematic distortions which affect the projection of the spatial frequencies of which the texture is composed. Using a set of filters having suitable spatial, frequency and orientation resolution, the inclination angle of the textured surface may be estimated from the resulting spatial frequency gradients. Psychophysical experiments suggest that, in absence of other cues, humans perceive surface inclination from perspective distortions, suggesting the possibility of a specific neuronal mechanism in the visual system. Beginning with a low level filter model found to be an accurate and economical model for simple cell receptive fields, we have developed both algorithmic machine vision and neural network models to investigate physiologically plausible mechanisms for this behavior. The two models are related through a new class of receptive field formed in the hidden layer of a neural network which "learned" to solve the problem. This receptive field can also be described analytically from the analysis developed for the algorithmic study. This paper, then, offers a prediction for a new type of receptive field in cortex which may be involved in the perception of inclined textured surfaces.