Measuring working memory span with WAIS-IV: Digit sequence is the superior span test.

Area of Science:

• Neuropsychology
• Cognitive Psychology
• Psychometrics

Background:

• The Digit Span test is a long-standing component of Wechsler intelligence scales.
• Recent versions (WAIS-IV) introduced the Digit Span Sequencing (DSS) subtest, with future versions (WAIS-5) including visual working memory span.
• Previous research has questioned the sensitivity of traditional Digit Span measures to working memory impairments.

Purpose of the Study:

• To evaluate the sensitivity of WAIS-IV Digit Span Forwards (DSF), Digit Span Backwards (DSB), Letter-Number Span (LNS), and WMS-III Spatial Span (SS) in identifying working memory deficits.
• To compare the performance of these measures against the D-KEFS Trail Making Test-4 (TMT-4) as a criterion for working memory impairment.
• To investigate the diagnostic utility of DSS compared to LNS in a mixed clinical sample.

Main Methods:

• A mixed clinical sample was assessed using WAIS-IV Digit Span (DSF, DSB), LNS, WMS-III Spatial Span (SS), and D-KEFS TMT-4.
• Performance was analyzed in relation to normative data and TMT-4 scores indicative of working memory impairment (≤1 SD below mean).
• Regression analyses were conducted using LNS and TMT-4 as criterion measures of working memory (WM).

Main Results:

• DSF scores were above average, DSB scores were around the average.
• SS and LNS showed slight impairment, while DSS was significantly impaired, mirroring TMT-4 impairment levels.
• Regression analyses indicated no unique contribution of DSF to the variance in LNS and TMT-4, suggesting limited sensitivity.
• A double dissociation was noted between DSF and SS performance in individuals with language versus non-verbal learning disorders.

Conclusions:

• The Digit Span Sequencing subtest (DSS) is more sensitive to working memory impairments than the Letter-Number Span (LNS) and the traditional Digit Span measures.
• Critiques regarding the composite Digit Span measure's sensitivity are supported by these findings.
• The study highlights the importance of specific subtests, like DSS, for accurately assessing working memory capacity in clinical populations.