Associative Memory Models

Introduction:-An associative memory is a system which stores mappings of specific input representations to specific output representations.

• An associative memory "associates" two patterns such that when one is encountered, the other can be reliably recalled.
• Most associative memory implementations are realized as connectionist networks.

The simplest associative memory model is linear associator, which is a feed-forward type of network. It has very low memory capacity and therefore not much used. The popular models are Hopfield Model and Bi-directional AssociativeMemory (BAM) model.

The simplest and among the first studied associative memory models is Linear associator. It is a feed-forward type of network where the output is produced in a single feed-forward computation. It can be used as an auto-associator as well as a hetero-associator, but it possesses a very low memory capacity and therefore not much used. The popular associative memory models are Hopfield Model and Bi-directional Associative Memory (BAM) model.

• The Hopfield model is an auto-associative memory, proposed by John Hopfield in 1982. It is an ensemble of simple processing units that has a fairly complex collective computational abilities and behavior. The Hopfield model computes its output recursively in time until the system becomes stable. Hopfield networks are designed using bipolar units and a learning procedure.
• The Bi-directional associative memory (BAM) model is similar to linear associator, but the connections are bi-directional and therefore allow forward and backward flow of information between the layers. The BAM model can perform both auto-associative and hetero-associative recall of stored information.

The neural associative memory models follow different neural network architectures to memorize information. The network architectures are either single layer or two layers.

• The Linear associator model, is a feed forward type network, consists, two layers of processing units, one serving as the input layer while the other as the output layer.
• The Hopfield model is a single layer of processing elements where each unit is connected to every other unit in the network other than itself.
• The Bi-directional associative memory (BAM) model is similar to that of linear associator but the connections are bidirectional.