ABSTRACT
It is well established that memory is not a unitary system. This idea has a long and rich history. For example, the distinction between knowing and remembering, that is, between knowledge and memory, can be traced back to ancient Greek philosophers, including Aristotle. In more recent times, the hypothesis that the acquisition and retrieval of different kinds of information depend on distinct mechanisms characterized by different properties has been articulated by several philosophers and scientists, including Bergson (1896), Gall (1835), Maine de Biran (1804, trans. 1929), James (1890), Ribot (1882), Claparède (1911), Korsakoff (1889), Husserl (1950), and Sartre (1943) among others. After World War II, a number of hypotheses concerning multiple forms of memory were put forward. A key breakthrough in this issue is due to what can truly be called an accident. William Scoville, a neurosurgeon, and Brenda Milner, a neuropsychologist, described the case of a young man, known by the initials H.M., who had undergone a complete bilateral resection of the medial temporal lobes for relief of intractable epilepsy (Scoville & Milner, 1957). H.M. showed severe anterograde and retrograde amnesia, even though his overall level of intelligence remained above average and other cognitive functions were unaffected. A few years later, Warrington and Weiskrantz (1968) showed that amnesic patients can learn implicitly information that they cannot recall explicitly, that is, on a conscious basis. This implicit form of learning, known since then as the priming effect, led to an explosion of experimental studies in the following decades. However, although many theoretical and empirical dissociations within memory have been proposed for many centuries, the notion that memory is organized in different systems is quite recent and can be traced back to the distinction between episodic and semantic memory proposed by Tulving in 1972.
