Reasons for the growth of traditional memory span across age

Three studies, covering together the age range from 3 to 16 years, show the relationships between age, short-term memory span, and language abilities. The growth of the traditional memory span in childhood is systematically related to a concomitant growth of language abilities as tested with CELF-3 Screening, two tests of word knowledge, a test of reception of grammar (TROG-2), and the British Picture Vocabulary Test (BPVS). Linear regression and ANCOVA analyses show that the growth of memory span is fully explained by the growth of language abilities in the three studies that covered different subsamples of children. In a confirmatory factor analysis a two-factor model fits the data well and shows that a “crystallised” language factor is strongly related to age, whereas a “fluid” short-term memory factor is unrelated to age. The two-factor model gives support to Baddeley's multicomponent model of working memory, and the current data suggest that the capacity of the phonological store is fully developed in children younger than 4 years old. The authors hold that chunking capacity, highly dependent on language abilities, is a major source of memory span growth with age. Rather than an increase in the number of chunks, or episodes retained in short-term memory (=chunk span), it is argued that childhood memory span development reflects an increase in the size of each chunk (=chunking capacity).