Exploring the nature of verbal short-term memory in Down syndrome and developing potential routes for intervention

Down syndrome (DS) is associated with a specific verbal short-term memory (STM) deficit. Given the strong association between verbal STM and the development of vocabulary and comprehension, it is important that this deficit is understood and addressed. The first part of this thesis sought to highlight the basis of verbal STM problems in those with DS, exploring key components of STM performance (Experiments 1, 2, 3, 4a, 4b and 4c). I also investigated effects upon item and order memory respectively (Experiments 3, 4a, 4b and 4c), using process dissociation. Individuals with DS and vocabulary matched typically developing (TD) children experienced significant serial recall improvements as a result of temporal grouping, semantic relation, visual presentation, item frequency, and pre-exposure to items. Both groups also showed evidence of phonological coding of verbal input. However, significantly poorer verbal STM performance was observed in those with DS across all comparisons with TD children, and the findings consistently indicated that this deficit reflected both item and order memory difficulties. Those with DS also displayed limitations processing the temporal context of purely verbal input, and displayed a reduced semantic relation benefit, relative to TD comparison children. These findings theoretically informed the design of a subsequent trammg experiment (Experiment 5), focussing on the use of phonological and semantic associations to support recall of items, and visuospatial support to enhance order memory. Individuals with DS experienced difficulties retrieving the correct associated items. However, vi suo spatial SUppOlt resulted in significant improvements in serial recall performance in those with DS. A follow up experiment revealed that spatial support plays a significant role at encoding (Experiment 6), but benefits appear to be bigger if a spatial component is present throughout encoding and recall (Experiment 5). This thesis shows that, whilst memory performance in DS and TD individuals is moderated by some common factors, there are distinct patterns of deficits shown in DS individuals. The findings highlight suitable areas to target in future training studies, and potential approaches to incorporate in interventions.