Episodic-like memory in common bottlenose dolphins

Abstract

Episodic memory involves the conscious recollection of personally experienced events, which has often been argued to be a uniquely human ability.1-5 However, evidence for conscious episodic recall in humans is centered around language-based reports. With no agreed upon non-linguistic behavioral makers of consciousness,6 episodic-like memory7 therefore represents the behavioral characteristics of human episodic memory, in the absence of evidence for subjective experience during recall. Here, we provide compelling evidence for episodic-like memory in common bottlenose dolphins (Tursiops truncatus), based on the incidental encoding and unexpected question paradigm.8 This methodology aims to capture the incidental encoding characteristic of human episodic memory, in that when we recall an experience, we remember information that was trivial at the time of encoding, but was encoded automatically.9 We show that dolphins are able to use incidentally encoded spatial ("where") and social ("who") information to solve an unexpected memory task, using only a single test trial per test type, which ensured that the dolphins did not have the opportunity to semantically learn "rules" to pass the test. All participating dolphins made correct choices in both the "where" and "who" tests. These results suggest that dolphins are capable of encoding, recalling, and accessing incidental information within remembered events, which is an ability indicative of episodic memory in humans. We argue that the complex socio-ecological background of dolphins may have selected for the ability to recall both spatial and social information in an episodic-like manner.