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Digit span forward is thought to measure short-term memory, whereas digit span backward measures working memory because it imposes both storage and processing demands. However, several speech-language pathologists have observed the unexpected pattern of better digit backward than forward performance for some children assessed on the Test of Integrated Language and Literacy Skills (TILLS). Our goal was to understand this pattern of performance by reanalyzing the TILLS normative sample (n = 1258). Percentile ranks are sparsely estimated for the digit span subtests relative to most subtests, which could lead to larger score discrepancies. Consistent with the SLPs observations, higher digit backward than forward standard scores and percentiles were observed. Even when standard scores and percentiles were higher for the backward than forward subtest, however, this often corresponded to higher raw scores and longer span length for the forward task. Results suggest that standard scores and percentiles should not be considered to reflect comparative strengths in forward or backward digit recall. Thus, we caution against overinterpreting individual task performance.
We thank the authors of the TILLS for providing the normative sample. |
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