The common stereotype that memory gets worse in old age actually is true for episodic memory but is not true for semantic memory or priming. Literally hundreds of laboratory studies have documented age differences in episodic memory tasks (e.g., memory for linguistic material such as words, sentences, paragraphs, and stories, and memory for visual material such as pictures, objects, faces, and scenes). Remember that these materials are presented for study and subsequently tested for retention by means of recall (e.g., write down all the words you can remember from list) or recognition tests. More recently, these age differences have been documented outside the laboratory as well (e.g., faces and names, hiding valuable objects, etc.).

These types of memory tasks are episodic because subjects are asked to remember items experienced during a personally experienced episode. In a recent review of scientific studies (1993), I found that healthy older adults remembered an average of 32 percent less than young adults. This difference occurred even though memory was tested with picture recognition, probably the easiest episodic test (age differences are typically greater for free recall tests, in which no retrieval cues are provided). Thus, healthy elderly adults can be characterized on a group basisas having a measurable, quantitative loss of retrieval from episodic memory. (Robin West and her colleagues at the University of Florida have also found that age-related decline is the primary factor in “everyday memory performance.”) The quantitative aspect is emphasized because the manner in which healthy older adults remember is not qualitatively different from younger adults.

In contrast, the episodic memory deficit in Alzheimer’s disease patients is definitely qualitative. For starters, these patients certainly remember less information. In a number of studies, dementia patients consistently recalled considerably less information compared to healthy elderly of the same age. But even more importantly, the way in which Alzheimer’s disease patients recall information is very different from healthy older adults. A couple of examples from my own research will illustrate this point. This research was conducted when was at Duke University, in collaboration with Reed Hunt (University of North Carolina at Greensboro) and Frederick Schmitt.

In one study, we asked subjects to read a number of sentences. Some of the sentences were complete, such as “The gentleman opened the door.” Other sentences were incomplete and the subject was asked to supply the missing word, as in “The teacher taught the —.” Later, we provided each person with the subject of each sentence (e.g., gentleman and teacher) and asked them to recall the object (last word) of that sentence (e.g., door for the first sentence, class, student, etc., for the second sample sentence, depending on the word generated).

Even though older adults recalled less information, both young and older healthy adults memory benefited from generating their own words. Words they thought of themselves (for incomplete sentences) were better remembered than words they read in the complete sentences. This phenomenon is known as the generation effect. The magnitude of this effect is plotted in figure as the difference between generated minus read words. The Alzheimer patients, in contrast, did not benefit from the generation effect, they recalled words poorly regardless of whether those.

Mean size of the generation effect (number of generated minus read words recalled) in young and older healthy adults and Alzheimer patients (adapted from Mitchell, Hunt, and Schmitt, 1986). Note that normal aging does not diminish the memory advantage of self-generated information, but that Alzheimer patients memory demonstrates virtually no benefit from generation.

Another episodic memory task we investigated was reality monitoring, which involves discriminating memory for internal thoughts from external perceptions or actions. For instance, as you drive to work one morning, you wonder if you actually turned off your electric coffee maker or only thought about unplugging it. Did you actually take your medicine or only think about taking it? We showed subjects all the complete and incomplete sentences they had seen earlier, with the incomplete sentences filled in with their own words. They were asked to decide which sentences were ones they had read, and which ones they had generated (completed). It is evident that healthy older adults were just slightly worse than young adults-a quantitative difference-but Alzheimer

Mean reality monitoring scores in young and older healthy adults and Alzheimer patients (adapted from Mitchell. Hunt, and Schmitt, 1986). Note that the ability to discriminate previously generated words from previously read words is only slightly impaired with normal aging, whereas Alzheimer patients have lost this ability. Patients performed much worse than either of the other groups. In fact, the Alzheimer patients’ performance was no different from chance (50 percent), which is qualitatively different from the healthy older adults. This result parallels anecdotes about Alzheimer victims who have written the same check a few times, or who have left the range on.

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