**8. Conclusion**

32 Advances in Object Recognition Systems

Fig. 1. A diagram of the episodic-like memory trial used in our study. An example of a possible configuration for the rst exposure phase (a), second exposure phase (b), and test phase (c). Shading indicates a different floor colour (i.e., different context). The black circle

indicates the novel object/location/context in the test phase of this trial.

Fig. 2. A pig interacting with an object during episodic-like memory test.

The above findings indicate that the formation of a tripartite code of either "what/where/when" or "what/where/which" seems to be within the compass of animals when species-typical preferences are taken into account. While the what/where/when model of Clayton and Dickinson (1998) is an elegant demonstration of episodic-like memory, its usefulness may be restricted due to the limited number of animals that cache food. While some researchers, notably Babb and Crystal (2006), have attempted to modify this task with rodents it requires a significant amount of pre-training because it does not use behaviours that naturally exist within the repertoire of some species. The recent findings from object exploration indicate that this may be a powerful way to study the formation of a tripartite code in animals. The paradigm allows for the testing of a tripartite code of what/where/which but not what/where/when memory (Eacott & Norman, 2004). It takes advantage of the tendency to explore novel objects, seen in many species, to demonstrate spontaneous recall (Menzel, 1999). It tests an animal's recall of an event when the test is not expected (Zentall et al., 2001) and may even allow for a test of past events over a long period of time (Schwartz & Evans, 2001) although no such long term tests have yet been carried out.

While a model of episodic memory based on object recognition is applicable to a greater variety of animals than a model based on food caching behaviour, we acknowledge that many of the criticisms that have been lodged against the what/where/when model (e.g., Suddendorf & Busby, 2003) also apply to the what/where/which model. For example, evidence for future planning and mental time travel would greatly improve both models of episodic-like memory. Clayton et al., (2003a) have recognized that their basic what/where/when criteria no longer adequately define the evolving concept of episodiclike memory. In response, they have refined their definition of episodic-like memory to include three particular behavioural criteria. Specifically, they state that a solid demonstration of episodic-like memory requires *content* (what/where/when details of a specific past event), *structure* (integration of the what/where/when details into a consolidated memory), and *flexibility* (ability to change how information gained from an episodic-like memory is used). Eacott et al. (2005) have argued that these three criteria are also met in their modified task examining recall of objects.

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If we are willing to accept that the what/where/which model of episodic memory is a *model* of human episodic memory, and therefore, concede that it does not encompass the human characteristics of consciousness and mental time travel, then we can use this model to investigate the tripartite what/where/which code. One of the main strengths of this model is that it allows for episodic-like memory to be studied in a wide range of species. Comparative work should focus on the ability of other animals, including pigs, to recall information without the stimuli being re-presented on test (similar to that of Eacott et al., 2005) and to determine if this ability is long-lasting.
