hypothesis testing and focusing behavior during ... - Science Direct

Neuropsychologia,

1973. Vol. 11, PD. IY I

to i98.

Pergamon Press. Printed in England.

HYPOTHESIS TESTING AND FOCUSING BEHAVIOR DURING CONCEPT FORMATION BY AMNESIC KORSAKOFF PATIENTS* MARLENE OSCAR-BERMAN Neurology Department, Boston University School of Medicine, and Aphasia Research Center, Boston V. A. Hospital, Boston, Mass., U.S.A. (Received 9 October 1972)

with Korsakoff’s syndrome were compared to brain-damaged and neurologically intact control subjects on visual discrimination tasks designed to evaluate hypothesis testing and focusing behavior. Results show that Korsakoffs can formulate and use hypotheses, but that their strategies are not leading to correct solution. Rather, they perseverate with one strategy even after indications of its inappropriateness. Furthermore, that this pattern of results occurs in the presence of memory aids, suggests that Korsakoffs may have impaired

Abstract-Patients

cognitive functioning independent

of their retention deficits.

INTRODUCTION ETIOLOGY of Korsakoff’s syndrome is most frequently related to polyneuropathy of chronic alcoholism, e.g. [l], and critical brain lesions are thought to include the mammillary bodies of the hypothalamus, and/or medial thalamic nuclei [2, 3, 41. Damage to these or to other regions of the brain (hippocampus, fornix, anterior thalamus), which are part of the classic interconnected circuit of PAPEZ [5], has been associated with a clinical memory impairment. Clinical symptoms of KorsakofYs disease include severe anterograde amnesia for recent events, and some retrograde amnesia for events prior to hospitalization [6, 71. In addition to the Korsakoff’s severe memory problems, several investigators have suggested that these patients have impaired cognitive functioning (e.g. perseverative tendencies) which may be independent of their retention deficits [6, 81. The present study was aimed at exploring the Korsakoff cognitive and memory impairments more thoroughly. Performance of patients with Korsakoff’s syndrome was compared with that of braindamaged controls (aphasic patients) and neurologically intact controls (normal subjects or alcoholic patients) on tests of concept learning previously found helpful in describing cognitive impairments in syndromes associated with basal ganglia disease [9]. Many recent theories of concept learning [e.g. 10, 11, 121 assume that subjects test hypotheses about the relevance of particular stimulus dimensions (e.g. color, size, form and position) to problem solution. According to these theories, the subject obeys a “winstay, lose-shift” rule of behavior. That is, he selects one hypothesis (from a defined set of THE

*This study was supported in part by National Institutes of Health Grants NS 06209 and NS 10577-01 to Boston University, and NS 07615 to Clark University. Results were reported at the American Psychological Association Convention, Honolulu, 1972. Thanks are due to Harold Goodglass and T. S. Greatrex for their continued and invaluable support. Reprint requests may be sent to M. Oscar-Berman, V. A. Hospital, 150 So. Huntington Ave., Boston, Mass. 02130. 191

Boston

MARLENE OSCAR-BERMAN

192

hypotheses) at the start of a trial, and he responds on that trial in a manner consistent with his hypothesis; on subsequent trials, he will change his hypothesis only when he receives information that it is incorrect. In this manner, the subject continues to select hypotheses until one of them is correct consistently, and the solution to that problem is obtained. A relatively simple method has been devised by LEVINE [ll] for the study of hypothesis behavior in a problem-solving situation such as that just described. With his method, Levine was able to indicate which hypotheses were being used by normal adults during visual learning. He also found, as predicted, that his subjects were able to eliminate irrelevant hypotheses in a systematic manner (referred to as focusing), to arrive at the correct solution of a problem. More recently, several investigators have used the Levinian procedure to describe the development of hypothesis formation in children, and the extent to which focusing improves developmentally [13, 141. In the present study, we used the Levinian technique to assess the same phenomena in patients with Korsakoff’s syndrome. Specifically, we attempted to determine (a) whether or not Korsakoffs were able to adopt definite strategies (hypotheses) during the learning of two-choice visual discrimination problems, (b) if they were able to focus normally on the correct solution, or if instead, they would perseverate with one hypothesis even though detrimental to correct solution, and (c) whether any deficits might be reduced by the use of “memory aids” as described and used by EIMAS [15], to eliminate the necessity of remembering outcome information essential to problem solution. METHOD Subjects There were four groups of subjects from the Boston V. A. Hospital: (1) eleven male Korsakoff patients, diagnosed by the neurology services of the Boston and Brockton V. A. Hospitals; (2) ten male left-hemisphere brain-damaged controls from the aphasia ward; (3) ten male alcoholic controls from the medical, surgical or psychiatric wards, with no clinical signs of Korsakoff’s disease; (4) a normal control group consisting of ten staff members or neurologically intact hospital patients. The Wechsler Adult Intelligence Scale and four subtests of the Wechsler Memory Scale (information, orientation, digit span and pairedassociate learning) were given to the Korsakoff patients to insure that their IQ’s and digit spans were within normal range, and the Wechsler Memory Scale was given to the alcoholics to substantiate the clinical evaluation of no memory impairment. More detailed information on these two groups is presented in Table 1. The mean age of the Korsakoffs was 53 years (range 42-66), and the etiology of the syndrome in Table 1. Comparison

Grouvs

of Korsakoffs and Alcoholic controls Wechsler Memory Scale

Information

Alcoholics Korsakoffs *Significantly

Orientation

5.2 2.4* different

Subtests Paired Associates

5.0 2.9* from

Alcoholic

11.9 68* controls

on subtests of the

Digit span Forward Backward 6.4 6.5 (Mann-Whitney

48 3.8 U-test,

p