An automated version of the digit symbol substitution test (DSST)

Abstract

An automated version of the Digit Symbol Substitution Test is described that employs a relatively inexpensive, commercially available microcomputer to present and score the task. Advantages of the automated DSST include: (1) objective scoring of both speed and accuracy of test performance, (2) printed copies of test scores, (3) convenient administration under standardized test conditions, and (4) the capacity for repeated assessment of an individual's performance over time. Task performance data for individual subjects following doses of pentobarbital are presented; these data illustrate both the stability of task performance under constant conditions and the within-subjects sensitivity of task performance to experimental manipulations.The Digit Symbol Substitution Test (DSST), a component of the Wechsler Adult Intelligence Scale (Wechsler, 1958), is frequently used to measure associative ability. The DSST is also a popular instrument for the assessment of performance following administration of pharmacological agents. Indeed, it appears to be one of the more sensitive tasks used for this purpose (Hindmarch, 1980; McNair, 1973;Wittenborn, 1979).The DSST typically is administered as a paper-andpencil task. A subject is given a digit-symbol code in which each of nine digits is paired with a different symbol. On the same page (located below the code), a series of digits, selected from those in the code, is presented in an irregular order. The subject is instructed to draw the symbol that is appropriate for each digit in the space below each digit and to draw as many correct symbols as possible within a 90-sec test period.The present paper describes an automated version of the DSST that can be implemented easily on a commercially available personal microcomputer. This computerized version of the task offers advantages over the traditional pencil-and-paper version in terms of conve- nience, objective scoring, repeated measurement, and experimental control. METHODWith the automated DSST, the digit-symbol code is constantly displayed at the top of the video screen and the test digits are presented, one at a time, in the center of the screen. The subject's task is to enter, on the microcomputer keyboard, the geometric pattern of keypresses, shown in the digit-symbol code, which corresponds to the test digit. The microcomputer controls each 90-sec test session, scores the test, and stores the results; there is no need for a test administrator to be present during the test session.To implement the DSST program that controls the procedures described below, we use a TRS-80® Model I or Model III microcomputer (Radio Shack) with Level II BASIC and numeric key pad, a cassette tape recorder to load and save the program, and a peripheral interface package manufactured by the LVB Corporation (Lehigh Valley, Pennsylvania). The interface package includes a 1080-54 programmable timer card, 1080-01 bus extension, and a 1081-72 daisy chain cable. A Quick Printer II® (Radio Shack) is a useful system addition for providing printed rec...

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