Speed and memory in WAIS-R-NI Digit Symbol performance among healthy older adults

Date of Completion

January 2000

Keywords

Psychology, Clinical|Psychology, Cognitive

Degree

Ph.D.

Abstract

The Digit Symbol test has been an integral part of the Wechsler intelligence scales since their inception. Although a relatively weak predictor of IQ, Digit Symbol has received considerable research attention owing to its remarkable value as a neuropsychological screening test, yet the cognitive operations required for successful performance of the test remain poorly understood. Roles have been proposed for both graphomotor speed and learning in the execution of Digit Symbol. The WAIS-R-NI (Kaplan, Fein, Morris, & Delis, 1991), a neuropsychologically informed extension of the Wechsler scales, attempts to evaluate these components separately. Unfortunately, few data have been available concerning performance across the adult lifespan on the Symbol Copy, paired-associates, or free recall measures derived from Digit Symbol and recommended in the WAIS-R-NI. We report findings on 177 healthy older adults (ages 50–90), providing normative data by age group, education level, and gender. Digit Symbol scores decline steeply with age (r = −.64). Symbol Copy speed declines almost as steeply (r = −.58). Incidental learning, however, declines only modestly (r = −.26 on both paired-associates and free recall measures), and only among the less well educated participants. Symbol Copy speed is a far more powerful predictor of Digit Symbol (r = .72) than are paired-associates or free recall memory scores (r = .26 and r = .28, respectively). Scores on the two incidental learning measures do, however, offer valuable supplementary information as part of a comprehensive individual assessment. When low Digit Symbol scores are produced by slowing on Symbol Copy, further evaluation of perceptual and motor speed and dexterity are indicated. When low incidental learning scores are obtained, further evaluation of memory is warranted. Qualitative analysis of errors produced on the two incidental learning tests may provide additional information. For example, rotations of symbols (which increase slightly in frequency with age) may indicate subtle visuoperceptual disturbances. In summary, these data increase our theoretical understanding of the Digit Symbol test and expand the interpretive value of the test in applied settings. ^

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