Psychological studies of amnesia
- Key People:
- Théodule-Armand Ribot
Short-term memory
The so-called short-term memory is typically intact among those who experience amnesia. Such individuals usually can repeat a short phrase or a series of words or numbers from immediate memory as adequately as anyone of comparable age and intelligence. Such an amnesic person can retain the gist of a question or request long enough to respond appropriately, unless, of course, there is enough delay in performance or attention is diverted. Evidently the ability to register information is intact, if this means availability of data in short-term memory. Thus, experimental psychologists who favor a sharp distinction between short-term and long-term storage systems contend that the primary deficit in amnesia is an inability to transfer information from short-term to long-term storage.
Associative learning
It has been argued that the basic deficit in the amnesic state is a loss of learning ability. In a series of experiments with amnesic patients, using, for the most part, verbal material, the subjects evidenced failure to link new with old associations, rapid fading of new associations, and great difficulty in reproducing whatever associations might have been formed. These findings have been amply confirmed. In one view, however, the weakness resides less in the failure to establish new associations than in their rapid decay (i.e., accelerated forgetting). On the other hand, it has often been noticed that if a Korsakoff patient can once succeed in learning an item, the patient may be able to reproduce it correctly after an appreciable interval of time. Further experiments, using a variety of techniques for assessing learning and retention, have suggested that retrieval rather than learning is at fault.
Motor skill
It has been noted that the fact that the acquisition of manual skill in Korsakoff patients is less impaired than either verbal learning or the solution of puzzles or mazes. This is confirmed in the observation that a severely amnesic patient who had undergone an extensive operation on the temporal lobes could perform rotary-pursuit and tracking tasks at a level not greatly inferior to that of healthy subjects. A second case of the same kind has been described, in which memory for motor tasks such as maze learning or the rendering of new compositions on the piano is said to have been completely preserved. These observations suggest that the acquisition of motor skill may remain relatively unaffected by lesions that give rise to a severe condition of general memory. Such global or generalized memory irregularity may, therefore, become increasingly subject to fractionation.
Residual learning capacity
Korsakov himself pointed out that a patient who consistently denies having seen a doctor before does not necessarily react to that doctor on each successive encounter as a total stranger. It thus appears that, despite gross amnesia, some learning, perhaps implicit, can still take place. This view has gained much support from clinical and experimental studies. About 1900 it was reported that even severely affected Korsakoff patients show appreciable savings in relearning verbal material after an interval of several hours or days, thus indicating minimal retention. Some Korsakoff patients, in spite of gross amnesia, eventually learn their way about the hospital. Again, some patients who disown any knowledge of their whereabouts may nevertheless give the correct name of the hospital, when asked to guess or to select it from a list containing the names of several hospitals. Thus, while learning capacity is seldom, if ever, wholly destroyed, there is failure to integrate new knowledge within the total personality. It is apparently a lack of mental cohesion that lies at the basis of Korsakoff psychosis.
Forgetting
Although some clinicians have attributed memory reduction largely to declines in registration of experience (i.e., failure to form memory traces), the widely accepted view is that it results primarily from a greatly increased rapidity of forgetting (i.e., rapid decay of memory traces). This view has also been held by the great majority of experimental psychologists who have worked with amnesic people. The consensus is that amnesia patients characteristically lose much of the memory they once had. This conclusion finds support in the very rapid extinction of conditioned eyeblink responses to a buzzer. It is notable that, in Korsakoff states, forgetting appears to be due to the passage of time (oblivescence) rather than to retroactive inhibition or some kindred interference effect.
Time disorders
Estimation of time is typically poor in amnesic states. Amnesic patients are prone to underestimate grossly the time in which they have been engaged in any particular activity. Conversely, they may equally grossly overestimate the time that has elapsed since a particular event (e.g., the visit of a relative) of which they have preserved some recollection. Indeed, amnesic patients exhibit a remarkable want of coherence in their thought processes, suggesting that a lack of temporal synthesis underlies, and may indeed in large part explain, the decline of memory. Yet, although difficulties in dating particular past events and in building a coherent time framework are characteristic of amnesic states and may persist after otherwise good recovery, an explanation couched wholly in terms of time disturbance is scarcely convincing.
Retrograde amnesia
Since retrograde amnesia relates to memory for events that took place when brain function was unimpaired, it clearly cannot be ascribed to failure of registration—with the exception, perhaps, of the very brief permanent amnesias following electroconvulsive shock or head injury. Retrograde amnesia otherwise would appear to be wholly due to a failure of retrieval, though this failure is evidently selective. That recent memories are generally harder to evoke than those more remote is usually explained on the basis of consolidation—i.e., progressive strengthening of memory traces with the passage of time. Yet recency is not the only factor, and in some cases memory for a relatively recent event may still be preserved while that for one more remote is inaccessible. Much depends, too, on the method used to test retrieval; e.g., recognition may succeed when voluntary recall entirely fails. By and large, the availability of information in memory would seem to depend to a considerable extent on its relation to the person’s current interests and preoccupations. When these are severely curtailed by an amnesic state, the links connecting present and past are severed, with a consequent failure of reproduction.
Psychogenic amnesia
Some forms of amnesia appear to be quite different from those associated with detectable injury or disease of the brain. These comprise, first, amnesias that can be induced in apparently normal individuals by means of suggestion under hypnosis; and, second, amnesias that arise spontaneously in reaction to acute conflict or stress. Such amnesias are reversible and have been explained wholly in psychological terms. Nevertheless, organic factors are not infrequently involved to some extent, and the distinction between organic and psychogenic amnesia may turn out to be far less absolute than has been supposed.
Hypnotic amnesia
Memory of a hypnotic trance is often vague and fragmentary, as in awakening from an ordinary dream. This may be due in part to a reduction of registration during the period of altered consciousness. At the same time, very much more complete posthypnotic amnesia can be induced if hypnotized individuals are told that, upon waking, they will remember nothing of what went on during the period of hypnosis. This is clearly a psychogenic phenomenon; memory is fully regained if a patient is rehypnotized and an appropriate countersuggestion given. It may also be regained if a person is persistently interrogated in the waking state, again suggesting that the amnesia is apparent rather than real. This observation led Freud to seek access to ostensibly forgotten (repressed) memories in his patients without the use of hypnosis.
Amnesia affecting specific memories
Amnesia that affects specific memories can involve the failure to recall particular past events or events falling within a particular period of the patient’s life. This is essentially retrograde amnesia, but it does not appear to depend upon an actual brain disorder, past or present. There also may be a failure to register—and, accordingly, later to recollect—current events in the patient’s ongoing life. This is essentially anterograde amnesia and, as an ostensibly psychogenic phenomenon, would appear to be rather rare and almost always encountered in cases in which there has been a preexisting amnesia of organic origin. Rarely, amnesia appears to cover the patient’s entire life, extending even to the person’s own identity and all particulars of the patient’s whereabouts and circumstances. Although most dramatic, such cases are extremely rare and seldom wholly convincing. They usually clear up with relative rapidity, with or without psychotherapy.
Amnesia of specific events or periods of time differs from organic amnesia in important respects. As a rule it is sharply bounded, relating only to particular memories, or groups of memories, often of direct or indirect emotional significance. It is also usually motivated in that it can be understood in terms of the patient’s needs or conflicts—e.g., the need to seek financial compensation after a road accident causing a mild head injury or to escape the memory of an exceptionally distressing or frightening event. It also may extend to basic school knowledge, such as spelling or arithmetic, which is never seen in organic amnesia unless there is concomitant aphasia or a very advanced state of dementia. A most distinctive feature of amnesia relating to specific memories is that it can almost always be relieved by such procedures as hypnosis. Although distinguishing organic from psychogenic amnesia is not always easy, it can usually be achieved on the basis of such criteria, especially when there is no reason to suspect actual brain damage.
Fugue states
The fugue is a condition in which an individual wanders from home or a place of work for periods of hours, days, or even weeks. One celebrated case was that of the Rev. Ansell Bourne, described by American psychologist William James. This clergyman wandered from home for two months and acquired a new identity. On his return, he was found to have no memory of the period of absence, though it was eventually restored under hypnosis. In not all cases, however, is the basis of the fugue so manifestly psychogenic. Indeed, close observation in some instances may reveal minor alterations in consciousness and behavior that suggest an organic basis, probably epileptic. According to one view, pathological wandering with subsequent amnesia is due to a constellation of factors, among which are a tendency toward periodic depression, history of trauma in childhood, and predisposition to states of altered consciousness, even in the absence of organic brain lesion. Psychoanalysts, on the other hand, see in the fugue a symbolic escape from severe emotional conflict.
