Convergent Algorithm for Sensory Receptive Field Development

An unsupervised developmental algorithm for linear maps is derived which reduces the pixel-entropy (using the measure introduced in previous work) at every update and thus removes pairwise correlations between pixels. Since the measure of pixel-entropy has only a global minimum the algorithm is guaranteed to converge to the minimum entropy map. Such optimal maps have recently been shown to possess cognitively desirable properties and are likely to be used by the nervous system to organize sensory information. The algorithm derived here turns out to be one proposed by Goodall for pairwise decorrelation. It is biologically plausible since in a neural network implementation it requires only data available locally to a neuron. In training over ensembles of two-dimensional input signals with the same spatial power spectrum as natural scenes, networks develop output neurons with center-surround receptive fields similar to those of ganglion cells in the retina. Some technical issues pertinent to developmental algorithms of this sort, such as “symmetry fixing,” are also discussed.