[2] Evidence for implicit memory arises in priming, a process whereby subjects are measured by how they have improved their performance on tasks for which they have been subconsciously prepared.
Similar effects have been found with studies where participants made judgments about difficulty of anagrams and recognized famous names.
This study shows that people implicitly make a strong associative connection between a song's tune and its lyrics that they can't separate later.
Some clues as to the anatomical basis of implicit memory have emanated from recent studies comparing different forms of dementia.
This possible double dissociation involving HD and DAT patients suggests that different implicit memory tasks are mediated by distinct neural systems and that these tasks can be used to differentiate some of the so-called "cortical" (e.g., DAT) from "subcortical" (e.g., HD) dementias (Cummings and Benson, 1984).
[10] A more recent contribution to the study of implicit memory comes from the experiments with a spatial organization computer game on amnesic patients (Stickgold et al., 2000).
This observation is interesting as it shows that learning can be memorized without the contribution of explicit memory, which requires the activation of the hippocampus and of the temporal and basal cortex.
Modern discoveries in neuropsychology concerning the organization of memory allow us to hypothesize that some synaptical cortical and subcortical circuits form the seat of unconscious mental functions.
This depends on a presupposition: that the experiences, emotions, phantasies, and defences that help organize an individual's unconscious psychic reality, from birth throughout life, are stored in the nervous structures concerning memory, both implicit and explicit.
This is, after all, in line with Freud's conviction: 'latent conceptions, if we have any reason to suppose that they exist in the mind—as we had in the case of memory—let them be denoted by the term "unconscious"' (1912, p. 260).
This approach is dependent on many independent variables that affect the response of a person's implicit and explicit memory.
Since procedural memory is based on automatic responses to certain stimuli, amnesic patients are not affected by their disability when behaving habitually.
The critical development during the past decade has been the systematic demonstration, exploration, and attempted explanation of dissociations between explicit and implicit memory.
In 1962, the severely impaired amnesic patient H. M. was reported to be capable of day-to-day improvement in a hand–eye coordination skill, despite having no memory for the practice sessions (Milner, 1962).
Amnesia was considered to impair memory globally, with the recognition that an exception should be made for motor skills.
[18] The illusion-of-truth effect shows in some ways the potential dangers of implicit memory as it can lead to unconscious decisions about a statement's veracity.
Procedural memory lets us perform some actions (such as writing or riding a bike) even if we are not consciously thinking about it.
In one experiment two groups of people, one composed of amnesic patients with heavily impaired long-term memory, and the other composed by healthy subjects, were asked several times to solve a Tower of Hanoi puzzle (a complex problem-solving game that requires thirty-one steps to complete).
This shows that there appears to be an implicit, procedural memory that subconsciously links the sickness and the drink flavor.
The strongest evidence that suggests a separation of implicit and explicit memory focuses on studies of amnesic patients.
For example, amnesic patients and a control group showed similar improvements in word completion as a result of priming, even if they had no memory of being involved in a previous test.
In addition, the idea that the hippocampus might be involved in only one kind of memory appeared independently in the animal literature, on the basis of the selective effects of limbic lesions (Gaffan, 1974; Hirsch, 1974; O'Keefe & Nadel, 1978; Olton et al., 1979).
The sections that follow suggest that the findings from humans and experimental animals, including rats and monkeys, are now in substantial agreement about the kind of memory that depends specifically on the hippocampus and related structures.
This premise led investigators to create different functional neural components that seek to explain the activation of memory (explicit and implicit) in the human brain.
[28] Neuropsychology has used imaging techniques such as PET (positron emission tomography) and MRI (magnetic resonance imaging) to study brain-injured patients, and has shown that explicit memory relies on the integrity of the medial temporal lobe (rhinal, perirhinal and parahippocampal cortex), the frontal–basal areas and the bilateral functionality of the hippocampus.
It presides over the learning of various skills: a) priming, which is the ability of an individual to choose an object to which he has previously been exposed subliminally; b) procedural memory, which concerns cognitive and sensorimotor experiences such as motor skills learning, everyday activities, playing instruments or playing certain sports: c) emotive and affective memory, which concerns emotional experiences, as well as the phantasies and defences linked to the first relations of the child with the environment and in particular with the mother.
In this case, there was little decline in the priming effect when patients were tested explicitly by merely being asked whether they recognized hearing the word in the first part of the experiment.
[6] Both implicit and explicit memory experiences can be present in transference, influencing each other just as they do in the normal development of the infantile mind (Siegel, 1999).
This finding was observed initially with a word-identification task, which requires subjects to identify words from extremely brief presentations (Jacoby & Dallas, 1981), and has since been demonstrated with various other implicit memory tests.
Finally, it has also been demonstrated that elaborative versus nonelaborative processing activities have little or no influence on priming effects in a lexical decision task (Carroll & Kirsner, 1982).