Visuospatial support for verbal short-term memory in individuals with Down syndrome
Highlights
► Visuospatial support can improve verbal span performance in DS individuals. ► When a spatial code is used, DS individuals can better remember the location of verbal information. ► Research differentiating visual and spatial abilities within STM in DS individuals is needed.
Introduction
Short-term memory (STM) refers to the ability to maintain a limited amount of information activated in mind for a short period of time. It is the memory that we use, for example, when we are to make a phone call; the numerical sequence is activated in our mind until we reach the telephone and dial the number, and then, the information fades away.
Separate systems are thought to deal with short-term storage of verbal and visuospatial information (Baddeley & Hitch, 1974). Individuals with Down syndrome (DS), for instance, tend to have impaired verbal STM with relatively preserved visuospatial STM (Baddeley and Jarrold, 2007, Jarrold and Baddeley, 2001).
In general, verbal STM is assessed by means of a digit span (or word span) task, in which the examinee must repeat a list of numbers (or words) in the same order provided by the examiner. Visuospatial STM, on the other hand, is commonly assessed by the Corsi span task, in which the examiner taps blocks arranged visuospatially in random sequence and participants must reproduce the block tapping in the same order. DS children and adolescents show impairment in digit span but not in Corsi span tasks, when compared to typically developing children (Azari et al., 1994, Jarrold and Baddeley, 1997, Jarrold et al., 2000).
DS individual's impairment in digit span tasks persists even when visual support is provided to complete the task. In other words, verbal STM deficits are not reduced when digits or words are presented visually (Broadley et al., 1995, Marcell et al., 1988), or when response to the task is given by pointing numbers or pictures representing the digits or words listened, eliminating the need to provide a verbal response (Brock and Jarrold, 2005, Marcell and Weeks, 1988).
On dealing with nameable pictures, e.g. drawings, typically developing children between the ages of 5 and 8 progress from using no obvious strategy to using visual encoding, then to the use of both visual and verbal codes, and finally to a mature state where more efficient verbal encoding is preferred (Palmer, 2000). However, there are no similar studies on individuals with DS. One might expect that visual strategies could be used to compensate for the marked verbal STM deficit; however, the above mentioned studies do not support this hypothesis whereas performance in verbal tests does not improve when either input or output is visual.
To our knowledge, no study has investigated whether spatial strategies can compensate for verbal STM deficits in DS. Recent studies show that this might be the case: Laws (2002) demonstrated that visual STM is only minimally preserved in individuals with DS, and discussed that the unimpaired Corsi span performance found in this population might be due to the spatial component of the task, rather than the visual one. Moreover, there are indications that the visuospatial ability preserved in DS individuals is their capacity for spatial sequencing (Lanfranchi, Carretti, Spanò, & Cornoldi, 2009).
Verbal STM is crucial for language development and vocabulary acquisition (Baddeley, Gathercole, & Papagno, 1998) and is important for day-to-day activities by keeping task goals actively in mind (Miyake, Emerson, Padilla, & Ahn, 2004). Intervention programs for individuals with DS commonly focus on training verbal STM in order to increase verbal span (Broadley and MacDonald, 1993, Conners et al., 2008, Conners et al., 2001).
Therefore, finding ways to improve verbal span can be useful for efficient intervention. This study investigated whether visuospatial support, rather than just visual support, could compensate for the verbal STM deficits encountered in individuals with DS. Five word span tasks, using the same words – or drawings to represent the words – were created. Four of the five tasks varied in terms of input and output, which could be either verbal and/or visual; the fifth test contained a spatial component in addition to the visual input and output.
The aim of this experiment was to understand the interaction among different input/output modalities in verbal STM tasks for each group of individuals, with and without DS.
Section snippets
Participants
Twenty-five individuals (9 girls) diagnosed with Down syndrome (DSGROUP), who used verbal language as means of communication, were evaluated and compared with two different groups of typically developing children (MENTALAGE and VOCAB), containing 25 individuals each.
Sixteen participants from the DSGROUP were enrolled in regular schools and nine in special-needs schools. DSGROUP and MENTALAGE were paired by mental age, as derived from their intelligence quotient (IQ) and chronological age;
Results
Mental age, IQ and PPVT scores for each group are summarized in Table 1. DSGROUP and MENTALAGE did not differ in terms of mental age (t = .02, p = .9) and DSGROUP group had lower total IQ (t = −21.7, p < .001, η2 = .93), verbal IQ (t = −21.9, p < .001, η2 = .92) and execution IQ (t = −15.8, p < .001, η2 = .84) than MENTALAGE. There was a group effect for performance on PPVT (F2,72 = 51.5; p < .001): MENTALAGE had higher scores than the other two groups (with p < .05), but DSGROUP and VOCAB did not differ.
Table 2
Discussion
The purpose of this study was to investigate whether visuospatial support in verbal STM tasks could compensate for the verbal STM deficit exhibited by individuals with DS. Standard STM tasks, e.g. digit and Corsi span, and novel verbal STM tasks, varying in terms of modality of input and output – verbal, visual or visuospatial – were administered in individuals with DS and in typically developing children.
Results for the standard STM tasks showed that individuals with DS performed worse than
Funding
MackPesquisa and CNPq.
Acknowledgments
We would like to thank all participants and the institutions that allowed us to carry out this study.
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