1. An optical neural net memory, comprising: a spatial light modulator including an array of modulator elements arranged in a plurality of rows and one or more columns, each element comprising an input aperture, an exit aperture, and means for modulating a property of light received at the input aperture to produce modulated light at the exit aperture; optical feedback means for combining, for each column, the light exiting from the exit apertures of the elements in the column to produce an optical feedback signal for the column; optical input means for receiving one or mor optical signals and one or more optical feedback signals and for conveying each input and feedback signal to the input apertures of the elements of an associated row such that each input and feedback signal is associated with a different row; and output means for providing one or more output signals, each output signal having a magnitude corresponding to the intensity of a different one of the feedback signals.