The Bender Gestalt and Symbol Digit Modalities Tests as Cerebral Dysfunction Screening Instruments :a Comparative Evaluation

Problem One of the problems confronting the psychologist in an institutional setting is the selection of appropriate instruments for the screening and diagnosis of a variety of psychological problems. Among the more subtle and yet far-reaching problems of this sort are those associated with disease, trauma, or congenital defect of the central nervous system. It was the purpose of this study to evaluate the usefulness of two well-known psychological tests as screening instruments for neurological dysfunction in a large and varied institutional population. Method The Bender Visual-Motor Gestalt Test (BGT) and Symbol Digit Modalities Test (SDMT) were administered to one hundred incarcerated males from four institutions operated by the Michigan Department of Corrections. The attending neurologist at the prison hospital had diagnosed thirty-five subjects as having intracranial lesions, closed head trauma, or chronic cerebral disease process, and sixty-five as free from significant central nervous system disorder. Scores obtained from the SDMT and from the BGT scored with the Hain criteria were compared to optimum cut-off scores provided by the test and scoring method authors to determine presence or absence of brain damage in the sample subjects. The frequencies of correct diagnoses for both tests, and for the combination of the two tests by adding the scores together, were compared by means of the Chi-square statistic for correlated samples. Results The two tests proved to be virtually opposite in their sensitivity. The SDMT was significantly more sensitive to the presence of brain damage in the sample subjects, while the BGT was significantly more sensitive to the absence of brain damage. Administration of the two tests together, and addition of their scores made no significant improvement in the frequency of correct diagnosis of the absence of brain damage in the study sample, and only a slight, statistically insignificant, improvement in the diagnosis of the presence of brain damage in the study sample. Conclusions The extent to which the two tests assess common neuro-behavioral functions appears to be significantly less than was expected. The BGT demonstrated a higher overall percentage of correct diagnoses, but by virtue of its greater sensitivity to the absence of brain damage in the sample, also produced a higher frequency of false positive diagnoses. From the data obtained, it appears that the greatest diagnostic accuracy can be obtained with the SDMT alone, or used in conjunction with other, more carefully constructed and standardized tests of visuo-grapho-motor neuropsychological functions than the Bender Visual-Motor Gestalt Test