Mental time travel in animals

Twelve years on from Suddendorf and Corballis's mental time travel (MTT) hypothesis, the debate as to whether episodic cognition is unique to humans remains unresolved. In this article, we review the evidence for mental time travel in nonhuman animals and the empirical methods used in this field. Investigation of episodic-likememory has been dominated by 'What-Where-When' paradigms, with limited success outside of food-caching corvids, and with only scrub-jays meeting Clayton and colleagues' more specific description of the underlying mnemonics. The recent emergence of an 'unexpected question' paradigm tapping recall of unattended aspects of episodes provides a promising new avenue for future studies. Falsification of the Bischof-Kohler hypothesis, that acting to satisfy a future motivational state is beyond the scope of nonhuman animals, has been the 'holy grail' of animal future planning research, spawning a plethora of studies. We argue that although the criterion proposed by this hypothesis provides a test for an explicit representation of a future time, it does nothing to get at whether planning for this future is mediated by semantic or episodic processes. (C) 2010 John Wiley & Sons, Ltd. WIREs Cogn Sci 2010 1 915-930