Two experiments on the development of subvocal rehearsal in short-term memory (STM) are reported in this study. According to the articulatory loop model of adult performance, rehearsing the names of visually presented stimuli involves extra mental operations compared with rehearsing items that are heard. We used this analysis to predict that rehearsal will appear later in the development of STM for pictured objects than for spoken words. To provide an indication of rehearsal, we manipulated the word length of these two types of stimuli. Experiment 1 tested children's ability to recall sequences of fixed length, while Expt 2 used a memory span procedure. The results supported our prediction in that STM for spoken words was sensitive to word length at all ages from 4 years upwards, while STM for pictured objects showed equivalent effects only in children aged over 8 years.Subsidiary analysis of the relation between recall of spoken words and speech rate confirmed previous evidence that the capacity of the articulatory loop remains approximately constant during development. We conclude that this rehearsal system is present from an early age, and that development involves a broadening of the range of stimuli which can gain access to it.It is widely accepted that very young children do not rehearse in STM tasks and that the development of rehearsal strategies contributes to the increase in performance with age (see Kail, 1984). One line of evidence comes from studies of lip movements. Using namable pictorial stimuli, Flavell, Beach & Chinsky (1966) found that rehearsal was regularly present only in children aged 7 years or over. A less direct method is to examine the development of speech-based coding by testing for the phonemic similarity effect. This effect is well established in adult subjects and is the tendency for short-term recall to be poorer for phonemically similar items (e.g. Baddeley, 1966). In an influential study, Conrad (1971) found that introducing phonemic similarity among the names of pictorial stimuli had no effect on STM in children aged under about 6 years. Thus there is some convergence between different kinds of evidence about the development of rehearsal.A further method is to study the development of the word length effect: the tendency for adult subjects to be able to recall fewer long words than short words *Requests for reprints.

No abstract

It is frequently assumed that the development of children’s abilities in short-term memory reflects changes in a unitary short-term store. This approach makes only poor contact with recent research on adults, which suggests the idea of a more complex ‘ working memory ’ system consisting of a limited-capacity central processor controlling a number of special-purpose stores. Two such stores are (i) the articulatory loop, a subsystem involved in subvocal rehearsal and associated with memory span, and (ii) the visuo-spatial scratch-pad, involved in imagery. This paper considers the applicability of the working memory framework to the study of children’s memory. In adults, memory span for words is affected by their length, varying linearly with the rate at which they can be articulated, and thus presumably rehearsed. Studies of the developmental growth of memory span in children show that the same linear relation describes performance, with older children’s better memory associated with faster rates of articulation. It appears from this that developmental change corresponds to an increase in the efficiency of subvocal rehearsal, with the decay characteristic of the articulatory loop remaining constant. However, although this simple developmental pattern is observed in memory for sequences of spoken words it is not present when the items are nameable pictures. Further investigation shows that older children use the articulatory loop to remember picture names: their performance is sensitive to phonemic similarity of the names and articulatory interference. However, younger children’s performance is not affected by either of these factors but is sensitive to visual similarity. It is suggested that such children may be storing material in the visuo-spatial scratch-pad. An additional aspect of working memory is that separate mechanisms are thought to be involved in memory span and the ‘recency effect’, the tendency for recent items in a list to be remembered well in unordered recall. A review of evidence obtained with children suggests that age differences in these two phenomena are independent. In general, therefore, it seems difficult to interpret the developmental changes reported here in terms of a unitary short-term store, and it is concluded that working memory provides a more promising approach.

No abstract

According to the working memory model of Baddeley and Hitch (1974), the sensitivity of memory span to word length arises from the time taken to rehearse items in a speech-based “articulatory loop”. Alternatively, it has been suggested that the word-length effect may result from differences in the speed of perceptual processes of item identification. Changes in the speed of rehearsal and of item identification have also been claimed to contribute to the growth of memory span that is seen in development. In order to compare these two variables directly, groups of children aged 8 and 11 were assessed on memory span for words of one, two, and three syllables; span under articulatory suppression; rehearsal rate; and item identification time. Span was found to be a linear function of rehearsal rate across differences in both word length and age. The word-length effect was unrelated to item identification time and was diminished by articulatory suppression. These results show that the word-length effect reflects rehearsal and not item identification processes. However, the results also suggest that changes in item identification time contribute to developmental differences in span when articulation is suppressed. A distinction between item identification and rehearsal effects can be readily interpreted in terms of the working memory model if it is assumed that they indicate the efficiency of different subsystems involved in span.