Implicit memory appears to be the most basic memory system, and recent evidence suggests that it continues to function normally in old age, in amnesics, and perhaps in patients with Alzheimer’s disease. Remember that some stimulus must be presented to the subject in order to elicit a response. Either the accuracy of the response (e.g., a subject completes a word fragment) or the speed of the response (e.g., a previously seen item is named faster) reveals the functioning of implicit memory. An implicit memory task that have used involves measuring how long it takes people to name pictures of common objects, such as line drawings of a dog, trumpet, banana, or a chest of drawers, etc. Naming time is measured in milliseconds from the moment a picture comes up on a computer monitor until an individual speaks into a microphone. Only naming times for names successfully retrieved are used in the analysis. When people are asked to name pictures a second time, their naming times are faster than on the first presentation indicating implicit memory for those pictures. This is true even for pictures that people cannot consciously recollect.

Frederick Schmitt and employed this task with three groups of subjects young and old healthy adults and Alzheimer patients. We asked them to name sixty pictures, half of the pictures were presented a second time a few minutes later. Average naming times (not shown) were fastest in young adults, somewhat slower in healthy older adults, and slowest in Alzheimer patients. In spite of the group differences in overall naming speed, the three groups showed equivalent increases in name retrieval speed on the second occurrence (or repetition) of a picture. This phenomenon is called priming and is assumed to reflect the operation of implicit memory. Thus, neither normal aging nor Alzheimer’s disease seems to disrupt the functioning of implicit memory. However, many researchers are actively investigating a variety of priming tasks, because while most of these tasks reveal preserved functioning in patients with Alzheimer’s disease, some do not.

A related finding has been reported by Laura Monti and John Gabrieli and colleagues at the Rush Alzheimer’s Disease Center in Chicago. These investigators asked patients to read passages many times. Their Alzheimer patients showed normal implicit memory as evidenced by increased reading speed for identical passages on subsequent tests. This priming effect was equivalent for a group of normal elderly and the Alzheimer patients, in spite of the latter group’s very poor performance on episodic (recognition) memory tests for the same passages.

Jason Brandt and his colleagues at Johns Hopkins University have employed another priming memory task. In this task, subjects are initially shown a list of words. Later, subjects see a longer list of words, some of which are related to the original list. Subjects are asked simply to say the first word that comes to mind-thus, it is not presented as a memory task. Both Alzheimer patients and normal elderly (mostly patients’ spouses) revealed memory for the original words, in that their word associates to the new list tended to be the original words, at a greater-than-chance level. This priming memory equivalence held in spite of the Alzheimer patients’ poor episodic recall (about 37 percent of the level of healthy older adults).

Daniel Schacter, at Harvard University, published a very interesting example of intact implicit memory in a patient (MT) diagnosed with Alzheimer’s disease. Schacter took MT (an experienced “duffer” in his own words) out for a couple of rounds of golf. MT’s memory for the location of his last shot-episodic memory was quite poor (only 35 percent correct). Likewise, his episodic memory for playing golf with Schactel’ was severely impaired, as he denied having played at all when asked about it a week after the fact. In contrast, his playing ability, and knowledge of etiquette, rules, strategies, and jargon demonstrated remarkable preservation of his semantic and priming memories. In light of the research discussed above, M.T. ‘s priming memory is not surprising. His semantic memory functioning, however, is unusually good compared to the average Alzheimer patient, but is in line with his laboratory measures, which show his vocabulary and information skills to be intact. His semantic memory functioning suggests that he is only in the mild stage at this point. It would not be surprising if his golf skills (i.e., priming memory) remain intact for some time after his naming and vocabulary abilities deteriorate in the course of the disease.

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