Endel Tulving: An Appreciation of His Scientific Contributions.

We review Endel Tulving's primary scientific accomplishments. The first section, by Roediger, covers the period from 1957 to 1975, during which Tulving introduced the concepts and phenomena of subjective organization, the availability and accessibility of memories, the power of retrieval cues, the recognition failure of recallable words, the encoding specificity principle, and the distinction between episodic and semantic memory. In the second section, Schacter describes Tulving's growing interest in neuropsychology, his studies of amnesic patient K.C., and his involvement in the development of the Unit for Memory Disorders at the University of Toronto. During this time, Tulving introduced the concept of mental time travel and the idea that memory for the past underlies thoughts of the future. In the third section, Craik describes Tulving's discoveries using brain-imaging techniques, first employing positron emission tomography (PET) and then functional magnetic resonance imaging (fMRI). He describes research that gave rise to Tulving's idea that encoding of memories relies on the left prefrontal cortex and retrieval of memories on the right prefrontal cortex (the HERA theory, for Hemispheric Encoding Retrieval Asymmetry). Craik also briefly discusses the status of the HERA model and other aspects of Tulving's work later in his life. We conclude by noting Tulving's impact on the authors and the field, as well as a selective review of the awards Tulving received for his research.