Content Addressable Memory

In a symbolic system information is stored in an external mechanism. In the example of the computer it is stored in files on the disks. As the information has been encoded in some form of file system in order to retrieve that information one must know the index system of the files -- the addresses of the files. In other words, data is "address adressable".

In contrast, data in a connectionist system is stored in what is called content addressable memory (Bechtel & Abrahamsen, 2002). In content addressable memory, information is not retrieved by knowing a (content-less) address, but instead by using some of the content as a cue to retrieve the remainder of the information. For instance, using a single fact as a cue can retrieve other related facts (i.e., activities of units) that results in a whole pattern of information being reconstructed.

This type of memory has the advantage of allowing greater flexibility of recall and is more robust. This distributed memory is able to work its way around errors by reconstructing information that may have been lesioned from the system. Such memory systems can also be used to model many of the charateristics of human memory (e.g. Hinton & Anderson, 1981).

References:

1. Bechtel, W., & Abrahamsen, A. A. (2002). Connectionism And The Mind : Parallel Processing, Dynamics, And Evolution In Networks (2nd ed.). Malden, MA: Blackwell.
2. Hinton, G. E., & Anderson, J. A. (1981). Parallel Models Of Associative Memory. Hillsdale, NJ: Lawrence Erlbaum Associates.

(Revised December 2009)