Associative memory in neural networks

An associative memory retrieves a stored pattern from a related cue. An incomplete cue supplies only some coordinates; a corrupted cue supplies some wrong coordinates. A Hopfield network implements retrieval by making intended patterns stable states with surrounding basins of attraction. This turns correction into a collective computation: no unit needs to know the entire desired answer. A cue outside the appropriate basin of attraction can retrieve another pattern or an unintended stable state.

Reinstatement of a stored representation from an incomplete or degraded cue. Recurrent autoassociative memory provides one mechanism; its success depends on the cue entering the correct basin of attraction. Partial-cue deficits after CA3-targeted NMDA receptor deletion support a hippocampal role without identifying a unique weight-update rule.^[ref]

A transformation that makes representations of similar inputs less overlapping, helping reduce interference between stored events. It must retain enough information for useful downstream learning and retrieval. The dentate gyrus is a proposed substrate, with quantitative input–output evidence from spatial cue-conflict experiments.^[ref]

A memory retrieves a stored pattern from a partial or corrupted version of that pattern. A recurrent Hopfield network supplies a precise idealization through stored attractors and their basins of attraction. Retrieval can fail through interference, ambiguous cues or spurious stable states.

A learned map retrieves an associated output pattern that need not equal its input cue. With normalized cue vectors $x^{\mu }$ and targets $t^{\mu }$, Hebbian learning gives $W={\sum }_{\mu }{t}^{\mu }(x^{\mu }{)}^{\mathsf{T}}$. For orthonormal cues, $W{x}^{\nu }=t^{\nu }$; taking the matrix product proves exact retrieval. Nonorthogonal cues add interference ${\sum }_{\mu \ne \nu }{t}^{\mu }((x^{\mu }{)}^{\mathsf{T}}{x}^{\nu })$. Additional context is required if one identical cue should select different outputs on different occasions.