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Transcript
A perceptron implementing the Hubel-Wiesel model of selectivity and invariance. The network in Figure E–2C can be extended to grids of many cells by specifying synaptic connectivity at all locations in the visual field. The resulting network can be repeated four times, one for each preferred orientation (horizontal, vertical, and two diagonals). This yields four retinotopically organized grids of simple cells, one for each preferred orientation, as well as four grids of complex cells. Each grid is called a feature map. Throughout the network the responses to two slightly different images of the numeral 2 are superimposed for comparison. A yellow pixel indicates a neuron that responds to both stimuli. A red pixel indicates a neuron that responds to one of the stimuli, and a green pixel indicates a neuron that responds to the other. Source: Neural Networks, Principles of Neural Science, Fifth Editon In the LGN layer the difference between the two stimuli is evident (see red and green pixels at the top of the numeral). In the simple cell layer the bottom Citation: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S. Principles of Neural Science, Fifth Editon; 2012 Available two feature maps show different responses to the images (red and green pixels), but the top two are the same (all yellow pixels). Finally, the responses of at: http://mhmedical.com/ Accessed: June 11, 2017 the complex cells are the same for both images (all yellow pixels). Thus invariance and selectivity occur together in one network, although the invariance is Copyright © 2017 McGraw-Hill Education. All rights reserved limited (it does not hold for all distortions) and the selectivity is fairly simple.