Episodic Memory

Memory is important for all cognitive agents. One unique form of memory is episodic memory, which attempts to capture information such as “what”, “when” and “where” [Clayton and Dickinson, 1998] [Nyberg, et al., 1996]. It is this memory structure that remembers events that are observed through experience [Nuxoll and Laird, 2004]. In its simplest form, episodic memory can be considered somewhat analogous to a snapshot from one’s past experience. More complicated episodes can, however, be compared to entire reels of footage stored within the mind. [Tulving, 1983] originally described episodic memory as a record of a person’s experience that held temporally dated information and spatio-temporal relations.

One of the main features ascribed to episodic memory by Tulving is that it, in essence, allows an agent to “travel back in time” [Tulving, 2002]. This concept is based on the supposition that episodic memory allows an agent to be consciously aware of a re-experience. Therefore, an agent retrieving an episode from episodic memory should not confuse the feelings of the re-experience with their ordinary, real-time, awareness of the situation. In other words, recalling an episode may cause an agent to internally experience some of the sensations present during that previous experience, but this is not confused with the current perception of the environment (i.e. recalling an experience of eating an unpleasant food does not make the hamburger a person is currently eating taste unpleasant). This ability to recall provides the agent with a means of associating previous feelings with current situations.

At the Center for Intelligent Systems we have begun researching, developing, and implementing episodic memory for a cognitive robot [Dodd, 2005], [Dodd and Gutierrez, 2005], and [Ratanawasd, et al., 2006]. Episodes are created by the CEA from contents in working memory and the Self Agent, as shown in Figure 1 [Dodd and Gutierrez, 2005].

Figure 1: Creation of Episodes in Episodic Memory

The episodic long-term memory (LTM) provides several key functions for ISAC. The first key function is to enable ISAC to recall specific past experience to solve a current problem. This is analogous to classical case-based reasoning techniques. A second key function is to indirectly influence task execution by influencing the information that is placed in working memory. For example, when presented with a new situation episodic memory enables associations to be created between the current, forming episode and stored episodes. These associations are used to trigger which information is placed in working memory. This is analogous to the associative memory mechanisms used in [Anderson, 1983] and [Anderson and Lebiere, 1998]. A third key function of episodic memory is to determine situation similarity and to cross-associate internal state information. Based on ISAC’s unique past experience of success and failure in different situations, episodic memory enables ISAC to derive preferences in new situations. These preferences are used by ISAC’s deliberative processes to influence goal and task switching.

Finally, another key function of episodic memory that is just beginning to receive research focus with ISAC is the idea proposed in [Baddeley, 2000] in which an episodic buffer interacts with working memory and alleviates the problems associated with binding information. In Baddeley’s episodic buffer, information from separate conscious memory channels (such as, visuo-spatial sketchpad and phonological loop) are integrated into single memory chunks and used as the buffering mechanism between working memory and long-term memory. ISAC’s working memory system does not currently use separate memory channels, as in Baddeley’s and Hitch’s model [Baddeley and Hitch, 1974], however, the use of episodic memory to bind incoming sensory information is being explored.


[Anderson, 1983] J.R. Anderson, The Architecture of Cognition, Harvard University Press, Cambridge, 1983

[Anderson and Lebiere, 1998] J.R. Anderson and C. Lebiere, The Atomic Components of Thought, Lawrence Erlbaum Associates, 1998

[Baddeley, 2000] A.D. Baddeley, "The Episodic Buffer: A New Component to Working Memory?", Trends in Cognitive Science, Vol. 4, No. 11, 2000

[Baddeley and Hitch, 1974] A.D. Baddeley and G.J. Hitch, "Working Memory", In G.A. Bower (Ed.), Recent Advances in Learning and Motivation, Vol. 8, pp. 47-90, Academic Press, New York, NY., 1974

[Clayton and Dickinson, 1998] N.S. Clayton and A. Dickinson, “What, Where, and When: Episodic-Like Memory During Cache Recovery by Scrub Jays”, Nature, Vol. 395, pp. 272-274

[Dodd, 2005] W. Dodd, The Design of Procedural, Semantic, and Episodic Memory Systems for a Cognitive Robot, Master's Thesis, Vanderbilt University, August 2005

[Dodd and Gutierrez, 2005] W. Dodd and R. Gutierrez, “The Role of Episodic Memory and Emotion in a Cognitive Robot”, Proceedings of 14th Annual IEEE International Workshop on Robot and Human Interactive Communication (RO-MAN), Nashville, TN, August 13-15, 2005, pp 692-697, 2005
[Nuxoll and Laird, 2004] A. Nuxoll and J. Laird “A Cognitive Model of Episodic Memory Integrated With a General Cognitive Architecture”, International Conference on Cognitive Modeling, 2004

[Nyberg, et al., 1996] L. Nyberg, A.R. McIntosh, R. Cabeza, R. Habeb, and E. Tulving, “General and Specific Brain Regions Involved in Encoding and Retrieval of Events: What, Where, and When”, Proc. of National Academy Of Science, Vol. 93, pp. 11280-11285, 1996

[Ratanaswasd, et al., 2006] P. Ratanaswasd, C. Garber, and A. Lauf, “Situation-Based Stimuli Response in a Humanoid Robot”, Proc. from 5th Int’l Conf on Development and Learning, Bloomington, IN, June 2006

[Tulving, 1983] E. Tulving, Elements of Episodic Memory, Oxford University Press, New York, 1983

[Tulving, 2002] E. Tulving, “Episodic Memory: From Mind to Brain”, Annual Review of Psychology, Vol. 53, pp. 1-25, 2002