Procedural learning deficits in specific language impairment (SLI): a meta-analysis of serial reaction time task performance

Abstract

Meta-analysis and meta-regression were used to evaluate whether evidence to date demonstrates deficits in procedural memory in individuals with specific language impairment (SLI), and to examine reasons for inconsistencies of findings across studies. The Procedural Deficit Hypothesis (PDH) proposes that SLI is largely explained by abnormal functioning of the frontal-basal ganglia circuits that support procedural memory. It has also been suggested that declarative memory can compensate for at least some of the problems observed in individuals with SLI. A number of studies have used Serial Reaction Time (SRT) tasks to investigate procedural learning in SLI. In this report, results from eight studies that collectively examined 186 participants with SLI and 203 typically-developing peers were submitted to a meta-analysis. The average mean effect size was .328 (CI95: .071, .584) and was significant. This suggests SLI is associated with impairments of procedural learning as measured by the SRT task. Differences among individual study effect sizes, examined with meta-regression, indicated that smaller effect sizes were found in studies with older participants, and in studies that had a larger number of trials on the SRT task. The contributions of age and SRT task characteristics to learning are discussed with respect to impaired and compensatory neural mechanisms in SLI.

Keywords: Meta-analysis; Procedural Deficit Hypothesis (PDH); Procedural memory; Serial reaction time (SRT) task; Specific language impairment (SLI).

Fig. 1

PRISMA flowchart showing the process of article identification.

Fig. 2

Funnel plot showing SMD plotted against standard error (which measures study precision). Note that effect sizes are symmetrically distributed when standard errors are high (i.e., study precision is low). Less variability in effect sizes is observed at higher levels of study precision.

Fig. 3

Forest plot showing study level and average weighted effect sizes for individuals with SLI and control individuals.

Fig. 4

Forest plot showing average effect sizes for study's using Keyboard/Response Boxes and Touchscreens as the input device on the SRT Task.

Fig. 5

Predicted study effect sizes from model reported in Table 2, plotted against observed effect sizes. Departures from the diagonal line are residuals. Data points are proportionally sized according to their weight in the model.