Subvocalization rate versus other predictors of the memory span

Two experiments were performed to determine how accurately the immediate memory span may be predicted from the subject's subvocalization rate, as compared with other subject and stimulus variables. In the first, span and free-recall measures were obtained for 24 subjects, each tested with four types of spoken material (nonsense syllables, random words, fourth-order approximations to English, and normal prose). Silent subvocalization rate, whispered subvocalization rate, speaking rate, and silent reading rate were also measured for each subject. The span (3.9-14 items) showed the highest zero-order correlation with silent subvocalization rate: r = .80. Multiple regression analysis confirmed this as the span's best predictor, partial r = .31. Similar results were found for free-recall scores. In Exp. 2 the digit span was correlated against measures of age, intelligence, subvocalization rate, perceptual speed, and memory search rate, for 40 subjects aged 7 to 17 yr. The best zero-order predictor was age (.62), followed by subvocalization rate (.57) and intelligence (.39). Multiple regression analysis indicated that the span was best predicted by age, partial r = .37, and subvocalization rate, partial r = .29. The span appears more closely related to subjects' internal speech rate than to other cognitive functions.