Riesenhuber and Poggio supplied a seminal model of object recognition in 1999. It derived a lot of its power from sheer simplicity. With just a few mathematical operations it seemed to model the entirety of the ventral stream, the area of the brain dedicated to processing “What” information, i.e. information about the identity of an object. It starts with a layer of Gaussian-tuned `simple’ or S cells, which respond to particular line orientations. That is, a particular S cell might respond to a diagonal line in a particular spot in an image. Then, all S cells of the same orientation feed to a ‘complex’ or C cell, which represents the maximally activated S cell. In CS terms, they take an argmax over a local neighborhood.

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