Is the phonological loop responsible for intelligence-related differences in forward digit span?

Children with mild mental retardation were compared with CA-matched and verbal-age-matched children without mental retardation on a forward digit span task. Forward digit span is typically used as a measure of the phonological loop (Baddeley, 1986). We hypothesized that intelligence-related differences in forward digit span are largely due to central executive functioning rather than phonological loop functioning. Results showed that the highly significant group difference in forward digit span was reduced to nonsignificance when a measure of central executive functioning was covaried out.