Abstract

The model consists of discrete units, both spatial and temporal. The outputs are also restricted to discrete values and are nonlinear functions of the input. Units are arranged in three levels: (1) analogous to the photoreceptors, the image is sampled by a hexagonal array of units; (2) analogous to the center-surround-type cells, each unit is excited by nearby receptor units and inhibited by more distant units; (3) analogous to simple cells in the visual cortex, the units receive excitatory input from a band of center-surround units and inhibitory input from adjacent bands to produce a series of six orientation selective units. An important feature at level (3) is connectivity between the orientation selective units. In a local region of space excitatory connections exist between similarly oriented units and inhibitory connections between orthogonally oriented units. Consequently the properties of level (3) units are modified as the system iterates. The effect of this position-orientation interaction is to sharpen the tuning curves for both orientation and spatial frequency selectivity. The outputs of the units in level (3) may also serve as a basis for simple texture discrimination.

© 1987 Optical Society of America