Visual Pattern Recognition, Neural Networks, and Household Chores
2009
The visual field of each eye is split in half. Approximately half of the axons from each eye cross over so that the left hemisphere of the brain processes the right half of the visual fields while the right hemisphere processes the left half. The optic nerves lead to the lateral geniculate nuclei and then proceed to the primary visual (striate) cortex. Here, according to the research of Hubel and Wiesel, groups of neurons are organized into short lines that fire when an edge, corresponding to that particular orientation, enters the visual field. Half of the neurons process signals that originated in the left eye (L layers) and the other half process signals from the right eye (R layers); the Land R layers are interleaved. The visual image is thus dissected into many short edges, the first step in the hierarchical buildup of more complex geometrical shapes. All possible edge orientations are detected by a layer of simple (S) cells; these feed a layer of complex (C) cells which bestow invariance with respect to lateral displacement. A one-dimensional model is presented in which a to-element visual signal is analyzed by an S 1 C 1 pair of layers feeding an S 2 C 2 pair. The model looks at (1) a white strip gradually lowered over a black background; (2) a white bar moving downward; and (3) a white bar that expands until it covers the entire black background. Some rules for designing one-dimensional pattern-recognition models are derived. Self-organization of the cortex is considered. A scheme is presented by which one cell in a group of cells captures the input for itself and suppresses all of the other neurons. A somewhat more complicated neural network is examined as it goes through learning, organizing, and testing phases. Because the same techniq ues are common to real and artificial neural networks (ANNs), a section is devoted to ANNs. Associative memory, the task-assignment problem, and back propagation are considered. Various ?>household chores ?> associated with vision are also discussed as follows: the constant jerky movements of the eye (saccadic motion) and compensation for it; control of the lens opening (pupillary reflex); distance accommodation; and binocular convergence.