Graham J. Hitch

Toward a network model of the articulatory loop

The basic features of verbal short-term memory for serially ordered lists are reviewed. A feed-forward network model based on Baddeleys concept of an “articulatory loop” is presented. One of its aims was to explore mechanisms for the storage of serial order information in the articulatory loop. Information is represented locally, learning is by “one-shot” Hebbian adjustment of weighted connections, corresponding to item-item and item-context associations, which decay with time. Items are modeled at the level of phonemes and phonemic output is fed back to the next phonemic input. At recall, items are selected serially by “competitive queuing.” Noisy activation values are used, resulting in errors during recall. Simulations of recall showed good agreement with human performance with respect to memory span, phonemic similarity, word length, and patterns of error. There was good but incomplete agreement on the shape of the serial position curve and on the effects of articulatory suppression. A simple modification is shown to produce the correct serial position curve. However, the model was unable to simulate human memory for sequences containing mixtures of phonemically similar and dissimilar items. A suggested modification which retains the central idea of using competitive queuing to select among noisy activation values is described.

Visual working memory in young children

Five experiments investigated immediate memory for drawings of familiar objects in children of different ages. The aims were to demonstrate younger children’s greater dependence on visual working memory and to explore the nature of this memory system. Experiment 1 showed that visual similarity of drawings impaired recall in young (5-year-old) children but not in older (10-year-old) children. Experiment 2 showed that younger and older children were affected in contrasting ways when the temporal order of recall was manipulated. Experiment 3 explored a recency effect found in backward recall and investigated its sensitivity to the presentation modality of materials used to produce retroactive interference (RI). For younger children, recency was reduced by visual but not by auditory-verbal RI; for older children, recency was more sensitive to auditoryverbal RI. Experiment 4 confirmed the effect of visual RI on visual recency in young children and showed that the same RI had little effect on their recall of spoken words. These results confirm younger children’s dependence on visual working memory. A final experiment showed that the effects of visual similarity and visual RI are additive, suggesting that they reflect different modes of accessing stored visuospatial information. Implications of these findings for developmental issues and for the nature of visual working memory are discussed.

Visual and phonological components of working memory in children

Previous studies have shown that young children’s immediate memory for a short series of drawings of objects is mediated by a visual component of working memory, whereas older children rely chiefly upon a phonological component. Three experiments investigated the hypothesis that older children rely also, but to a lesser extent, on visual working memory. Experiment 1 confirmed previous evidence that Tl-year-olds’ memory is disrupted by phonemic similarity of object names, but is unaffected by visual similarity of the objects themselves. However, when articulatory suppression was used to prevent phonological coding, levels of recall were sensitive to visual rather than phonemic similarity. Experiment 2 compared the effects of interpolating an auditory-verbal or a visual postlist task on memory for drawings viewed either with or without suppression. The visual task had a clear disruptive effect only in the suppression condition, where it interfered selectively with recall of the most recent item. Experiment 3 compared the effects of interpolating an auditory-verbal or a mixed-modality (visual-auditory) postlist task when subjects were not required to suppress. There was greater interference from the mixed-modality task, and this effect was confined to the last item presented. These experiments are taken as confirming the presence of a small but reliable contribution from visual working memory in Ll-year-old children’s recall. As in younger children, visual working memory in Ll-year-olds is sensitive to visual similarity and is responsible for a final-item visual recency effect. The results also show that older children’s use of visual working memory is usually masked by the more pervasive phonological component of recall. Some implications for the structure of working memory and its development are discussed.

Influence of short-term memory codes on visual image processing : evidence from image transformation tasks

Three experiments showed that phonological recording of visual stimuli in short-term memory (STM) affects coding in long-term memory (LTM) and therefore performance on tasks involving generation and manipulation of visual images of the stimuli. An image transformation task was devised. It consists of mentally subtracting a part of an image to discover in the remainder another object. In Experiment 1, Ss were required to learn a set of easily nameable visual stimuli and then perform the subtraction task on images retrieved from LTM. Performance was significantly better when initial learning was accompanied by articulatory suppression (AS). Experiment 2 confirmed that AS had no effect when the task was performed on an image of a just-presented stimulus. In Experiment 3, the nameability of the stimuli was manipulated. The results replicated the effect of AS for items that were easy to name but showed no effect of AS for stimuli that were difficult to name.

Item Identification Time and Rehearsal Rate as Predictors of Memory Span in Children

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.

Speech, “inner speech,” and the development of short-term memory: Effects of picture-labeling on recall

Three experiments explored the effect of overt speech on childrens use of inner speech in short-term memory (STM). Experiments 1 and 2 compared recall of a series of pictured objects when 5- and 11-year-olds either labeled stimuli at presentation or remained silent. Use of inner speech was assessed by manipulating word length of the picture names (Experiment 1) or phonemic similarity (Experiment 2). Word length and phonemic similarity had greater effects in the older children and when pictures were labeled at presentation. These tendencies were such that 5-year-olds were sensitive to word length and phonemic similarity only with labeling. Experiment 3 compared labeling by the child with labeling by the experimenter in 5-year-olds. There were no significant differences with respect to overall performance or effects of word length and phonemic similarity. It is suggested that speaking or listening to speech activates and internal articulatory loop, and that such activation is especially important when the childs ability to use inner speech in STM has not fully developed.

Verbal short-term memory in children: The role of the articulator loop

Abstract Three experiments investigated immediate memory for drawings of familiar objects in children of different ages. The aim was to investigate the effect of articulatory suppression on word length and phonemic similarity effects. Experiment 1 showed that, with pictorial presentation, 11-year-old children showed word length effects in memory span which were abolished by suppression, whereas 5-year-olds did not. Experiment 2 provided similar results in relation to the phonemic similarity effect. Experiment 3 showed that the absence of word length and phonemic similarity effects in the younger children was not due to a floor effect, because similar results were obtained in the serial recall of lists of fixed length. In all three experiments the processing demands of the suppression task were controlled for by comparing it with a simple motor task involving tapping. In the younger children, suppression and tapping had the same effect; in the older children, tapping reduced performance but did not abolish...

Manipulation of visual mental images in children and adults

Recently, there has been a debate on whether visual patterns can be transformed and reinterpreted in mental imagery. In the present study, task demands and age of subjects were manipulated to see whether children and adults were able to discover a novel visual pattern after transforming a mental image. Two tasks, called combination and subtraction, were devised. They consist of either compounding or taking away parts of images to discover a new construal. Results indicate that not only adults, but also children aged 6 and 10, are able to transform a mental image so as to yield another image with a different interpretation. Task demands had a greater effect on children than adults, consistent with the suggestion that the ease of manipulating mental images is a function of the efficiency of control processes.

Magnitude comparisons by children with specific language impairments: evidence of unimpaired symbolic processing.

A size judgement task was used to investigate number processing skills in children with specific language impairments (SLI). Previous work with unimpaired adults and children has shown that when comparing the size of written numbers and other ordinal stimuli, there is a symbolic distance effect (SDE) such that decision time decreases with the size distance between items. This study examined the ability of children to judge stimulus pairs which were varied to contrast the processing of symbolic material against direct perceptual judgement and to test processing of numeric versus non-numeric material. Children with SLI were compared with a control group matched on verbal comprehension level. The children with SLI responded faster than the control subjects. The SLI and control groups showed similar SDE and a similar pattern of response across materials. No indication was found in the SLI data of any selective deficit in processing symbolic information. Findings are discussed in relation to theories of numeracy acquisition which acknowledge the importance of non-verbal representation of number meanings.

Prospective memory for future intentions: Some comparisons with memory for past events

Abstract Memory for future intentions was compared with memory for past activities by asking members of a film society to retrieve names of films they intended to see later on in a Season and films they had seen earlier. Memory for films that had been seen showed the usual recency effect, while retrieval of films to be seen showed an analogous proximity effect in that films to be seen sooner were more accessible. It was also found that recall of past films was inversely related to the total number of such films, but was unrelated to the average time interval since they were seen. In a similar fashion, retrievability of future films was inversely related to the total number of such films and was unrelated to when they were to be seen. There was a small but significant correlation between an individuals ability to retrieve the names of past and future films. Taken together, these correspondences suggest that similar empirical laws may govern the retrieval of stored information about past events and future ...