Memory and motor skill components of the WAIS-III Digit Symbol-Coding subtest

Area of Science:

• Neuropsychology
• Cognitive Psychology
• Psychometrics

Background:

• The Digit Symbol-Coding subtest is a common measure of cognitive function.
• Previous research suggests age-related declines in this subtest are primarily due to motor skills rather than memory.
• These findings were based on non-clinical samples and earlier versions of the intelligence scale.

Purpose of the Study:

• To investigate the contributions of motor skill and memory to Digit Symbol-Coding performance in a clinical sample.
• To validate previous findings using the Wechsler Adult Intelligence Scale-II (WAIS-II).

Main Methods:

• Examined motor skill (Copy scores) and memory (Incidental Learning scores) components of the WAIS-II Digit Symbol-Coding subtest.
• Utilized Wechsler Memory Scale-II (WMS-II) indexes (Immediate Memory and General Memory) as independent memory measures.
• Statistical analysis to determine the variance explained by motor and memory components.

Main Results:

• Copy scores significantly explained a large proportion of the variance in Digit Symbol-Coding scores, even when controlling for Incidental Learning scores.
• Incidental Learning scores explained minimal additional variance when Copy scores were already accounted for.
• This pattern held true when using WMS-II memory indexes, indicating motor ability's dominant role.

Conclusions:

• Motor ability is a primary determinant of Digit Symbol-Coding performance in clinical samples, consistent with prior research.
• Memory components, as measured by Incidental Learning or WMS-II indexes, contribute little to the variance in this subtest once motor skills are considered.
• The findings underscore the importance of assessing motor function when interpreting Digit Symbol-Coding results, particularly in clinical contexts.