Child Neuropsychology, 2015 Vol. 21, No. 4, 481–489, http://dx.doi.org/10.1080/09297049.2014.913557
Spatial-simultaneous working memory and selective interference in Down syndrome Silvia Lanfranchi1, Irene C. Mammarella1, and Barbara Carretti2 1
Department of Developmental Psychology and Socialization, University of Padova, Padova, Italy 2 Department of General Psychology, University of Padova, Padova, Italy Several studies have suggested that individuals with Down syndrome (DS) have impairments in some aspects of the visuospatial domain. It has been reported that they are particularly impaired in the spatial-simultaneous working memory (WM) even in advantageous conditions such as when information is grouped to form a configuration. This study aimed to assess the performance of individuals with DS carrying out a spatial-simultaneous WM task in single and dual selective interference conditions in order to better explore the characteristics of their impairment in this area. Groups of individuals with DS and mentally age-matched typically developing (TD) children were asked to carry out a spatial-simultaneous WM task in a single- and in two dual-task conditions. In the single condition, the participants were required to recall an increasing number of positions of red squares presented simultaneously in a matrix. In the dual-task conditions, together with the spatialsimultaneous WM task, the participants were asked to carry out an articulatory suppression task or a tapping task. As has already been shown in other studies, individuals with DS were found to be impaired in carrying out a spatial-simultaneous WM task and showed a worse performance with respect to the TD group in both the conditions. These findings indicate that individuals with DS use the same coding modality as TD children of the same mental age. Just as the TD children, they performed lower in the dual- than in the single-task condition and there was no difference between the verbal and visuospatial conditions. Keywords: Working memory; Down syndrome; Visuospatial memory; Intellectual disability; Interference.
Down syndrome (DS) is due to abnormalities on Chromosome 21 and it is the most common cause of intellectual disability (Kittler, Krinsky-McHale, & Devenny, 2008). The cognitive profile of this syndrome is characterized by a relative weakness in verbal abilities, while visuospatial skills seem to be relatively preserved (Dykens, Hodapp, & Finucane, 2000). This work was supported by Grant CPDA 127939 awarded by the University of Padova to SL. We thank all children who participated in this study and their families. Moreover we are grateful to Arianna Ferrara and Laura Valle who collected the data. Address correspondence to Silvia Lanfranchi, Department of Developmental and Socialization Psychology, University of Padova, Via Venezia, 8, 35131 Padova, Italy. E-mail: [email protected]
© 2014 Taylor & Francis
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Several studies have analyzed working memory (WM) in individuals with DS. In particular, it has been found that children (Jarrold & Baddeley, 1997), adolescents (Hulme & Mackenzie, 1992; Marcell & Weeks, 1988), and adults (Kittler, Krinsky-McHale, & Devenny, 2004; Kittler et al., 2008; Numminen, Service, Ahonen, & Ruoppila, 2001) with DS have a weaker verbal WM than typically developing (TD) children with the same mental age and than individuals with severe intellectual disabilities with similar mental age as well. Performance on visuospatial working memory (VSWM) tasks is, instead, usually considered a point of strength for individuals with DS. In fact, several investigators have reported that their performance is comparable to that of TD children matched for mental age. There are, however, some data indicating that the profile of individuals with DS is not homogeneous with regard to the visuospatial domain. Lanfranchi, Carretti, Spanò, and Cornoldi (2009), for example, reported that performance in spatial-simultaneous tasks was lower in a DS group with respect to a TD cohort but comparable when a spatial-sequential task was considered. Lanfranchi et al. (2009) explained their findings on the basis of Pazzaglia and Cornoldi’s (1999, see also Cornoldi & Vecchi, 2003) hypothesis, according to which the visuospatial sketchpad originally included in Baddeley and Hitch’s model (1974) can be divided into separate components. Pazzaglia and Cornoldi (1999; see also Mammarella, Pazzaglia, & Cornoldi, 2008), in fact, suggested that VSWM can be divided into three components: a visual component in charge of processing shapes and colors and two kinds of spatial components, both involved in memorizing patterns of spatial locations but presenting them in different formats and consequently using different spatial processes, simultaneous in one case, sequential in the other. Data gathered from various groups of children have, in fact, supported the hypothesis that there is a distinction between visual and spatial-simultaneous processes (Mammarella, Cornoldi, & Donadello, 2003) just as there is between spatial-simultaneous and spatial-sequential processes (Mammarella et al., 2006). Subsequent studies attempting to clarify the impairment in spatial-simultaneous tasks in individuals with DS by analyzing situations that could reduce the performance gap came across unexpected difficulties (Carretti & Lanfranchi, 2010; Carretti, Lanfranchi, & Mammarella, 2013). Carretti and Lanfranchi, who analyzed the advantage associated to a structured pattern in spatial-simultaneous tasks, demonstrated that, although a pattern condition led to a better performance also in the DS group, it did not reduce the difference in performance with the TD group. Instead the gap between the two groups was wider than in the random condition. In accordance with these results, Carretti et al., who compared the advantage associated to structured material both in spatialsimultaneous and in spatial-sequential tasks, reported that it led to a marked difference between groups in the former but not in the latter tasks. The paradoxical effect of configuration on individuals with DS could be explained in more than one manner from more basic difficulties in pattern recognition to a different way of encoding the to-be-remembered information to high-order level difficulties in the strategic use of pattern for recall. In the current study, we explored whether individuals with DS are comparable to TD children in terms of encoding spatial items simultaneously presented. To evaluate this, participants were asked to carry out a spatial-simultaneous task in three conditions: a single one and two dual tasks in which participants were required to process information needing to be recalled in two selective interference conditions, an articulatory suppression one, in which verbal components of the working memory were loaded and a tapping one, loading on spatial components of the working memory. If individuals with DS use a verbal
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strategy to encode configured material, their performance should decrease when a verbal task is combined with a standard memory condition. If, instead, they use a visual encoding strategy, their performance should be worse when the task is combined with a spatial tapping task. METHOD Participants Twenty individuals with DS took part in the study. Their mean chronological age was 14 years and 2 months (SD = 29 months, range 9 years and 5 months to 17 years and 11 months), and their mean mental age was 5 years and 2 months (SD = 25 months). A control group was made up of 20 TD children with a mean chronological age of 5 years and 5 months (SD = 5 months). The two groups were matched one to one on the raw scores they obtained on the Peabody Picture Vocabulary Test—Revised (PPVT-R; Dunn & Dunn, 1997) (see Table 1). In addition, since usually individuals with DS show a discrepancy between their verbal and nonverbal abilities, Raven’s Coloured Progressive Matrices (CPM; Raven, Court, & Raven, 1998) were administered to both groups to measure their nonverbal abilities. The two groups’ performance on both the PPTV-R (F < 1) and Raven’s Matrices F(1, 39) = 1.12, p = .29 was comparable.
Materials Spatial-Simultaneous Memory Task. The task consisted of recalling the position of an increasing number of red squares in a matrix presented on a computer screen. The size of the matrices varied on the basis of items to be recalled (3 × 4 matrices for two, three, and four items to be recalled; 4 × 4 matrices for five, six, and seven items to be recalled; and 4 × 5 matrices for eight items to be recalled). The visuospatial memory task was presented in two different configurations: (1) Pattern configuration, in which the red squares were presented as a visual configuration (or pattern); (2) Random configuration, in which the red squares were presented in random locations. The presence/absence of a pattern was defined on the basis of the proximity among the red squares in the matrices. Moreover, the two versions were presented in both singleand dual-task conditions. Table 1 Participants’ Characteristics. Down Syndrome
PPVT-R CPM
Raw score Mental age Raw score Mental age
Typically Developing
M
SD
M
SD
56.20 61.9 14.05 59.7
24.38 25.55 4.20 16.41
58.00 61.75 15.15 64.2
18.85 19.87 1.98 7.46
Note. PPTV-R: Peabody Picture Vocabulary Test—Revised; CPM = Raven’s Colored Matrices.
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Figure 1 Examples of matrixes used during the spatial-simultaneous task. An example of a pattern configuration is shown on the left and a random one on the right.
In the single condition (see Figure 1), each matrix was displayed on the computer screen for 5 s, then removed, and, just after, the participants were asked to recall where the red squares were positioned by pointing on an empty matrix. Two trials for each level of difficulty were presented from the shortest lists (containing two positions to recall) to the longest (containing eight positions to recall). To avoid frustration, the task was terminated if a participant failed on both trials at the same level, and it was assumed that the remaining items would not be recalled correctly. In the dual task, participants carried the basic task in conjunction with one of the following tasks. In the verbal interference (i.e., articulatory suppression), the single condition was combined with a verbal task. In particular, while the participant looked at the stimulus matrix he or she was asked to repeat continuously the syllable “la la la la.” In the dual task with visuospatial interference (i.e., tapping), the single condition was combined with a visuospatial task. Specifically, while the participant looked at the stimulus matrix he or she was asked to tap his or her hand on the table. Of course, those concurrent tasks were not “pure” verbal and visuospatial tasks, but since individuals with DS have well-documented problems in performing dual tasks (e.g., Kittler et al., 2004; Lanfranchi, Baddeley, Gathercole, & Vianello, 2012; Lanfranchi, Cornoldi, & Vianello, 2004), they seemed easy enough to avoid a floor effect. The number of correct trials was considered as the dependent variable for all the conditions. The maximum score was 16. Procedure The study consisted of three sessions held approximately a week apart from one another with each session lasting approximately 25 minutes. The participants completed the CPM test and PPVT-R during the first session. The raw score that the individuals with DS obtained on the latter was used to identify the matching child in the control group, while the CPM scores were used as a measure of the two groups’ nonverbal abilities. The VSWM tasks were administered individually during the second and third sessions and the presentation order of the tasks was counterbalanced across the participants. RESULTS A 2 × 3 × 2 mixed-design analysis of variance (ANOVA) with Group (DS vs. TD group) as a between-group variable and Condition (control, tapping, articulatory suppression) and Configuration (pattern vs. random) as the within-group variables in the number
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of correct trials (see Figure 2) showed a significant main effect of group, F(1, 38) = 5.21, ƞ2p = .12, p < .05, with TD children outperforming (M = 7.75, SE = 0.54) the DS group (M = 6.00, SE = 0.54). A significant effect of condition was also found, F(2, 76) = 5.11, ƞ2p = .12, p < .01. Subsequent post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction showed better performance in the control condition (M = 7.36, SE = 0.28) than in the two interference ones (visuospatial interference: M = 6.62, SE = 0.39, p < .05; verbal interference: M = 6.63, SE = 0.46 p < .01), but performance in the latter conditions was not different. Finally, a significant effect of configuration was also found, F(1,38) = 259.72, ƞ2p = .87, p < .001, with better performance in the pattern (M = 9.00, SE = 0.44) than in the random condition (M = 4.75, SE = 0.37). A significant interaction Group × Configuration was found, F(1, 38) = 19.02, ƞ2p = .33, p < .001; subsequent post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction indicated that the TD children (M = 10.45, SE = 0.63) outperformed the participants with DS (M = 5.05, SE = 0.52) when the squares were presented as a pattern (p < .001); this was not the case in the random condition (p = .41). In addition, both groups showed better performance when the squares were presented as a pattern (DS: M = 5.05, SE = 0.52; TD: M = 10.45, SE = 0.62) with respect to the random condition (DS: M = 4.45, SE = 0.52; TD: M = 7.55, SE = 0.63). No other significant interactions were found. We subsequently calculated the dimension of the differences between groups in the pattern conditions by using the Cohen’s d. In the control condition, the difference between the TD and DS groups was .91, while in the tapping condition it was .64, and in the articulatory suppression condition, it was 1.17.
Figure 2 Performance of individuals with DS and TD children as a function of condition (random vs. pattern) and type of task (standard, dual with verbal interference, dual with visuospatial interference). Error bars represent standard errors of the mean.
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Figure 3 Performance on the spatial-simultaneous task according to group and condition.
The difference in performance across the memory-load levels was also analyzed separately for the pattern and random conditions (see Figure 3). The 2 × 3 × 7 ANOVA on the performance in the pattern condition, with Group (DS vs TD group) as between-group factor and Conditions (control, tapping, articulatory suppression) and Memory Load (2 vs. 3 vs. 4 vs. 5 vs. 6 vs. 7 vs. 8) as within-group factors, showed a main effect of Group F(1, 38) = 10.76, ƞ2p = .22, p < .001, with TD children (M = 1.49, SE = 0.089) outperforming the DS group (M = 1.08, SE = 0.089), as well as of Condition, F(2, 76) = 3.33, ƞ2p = .08, p < .05. Subsequent post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction showed better performance under the control (M = 1.38, SE = 0.07) than in the tapping condition (M = 1.23, SE = 0.08 p < .05). The performance in interference conditions was not different. The main effect of Memory load was also significant F(6, 228) = 100.05, ƞ2p = .73, p < .001, showing a stable performance until Level 3 (with no differences in performance) and a continuous decrease in the other levels (for all the comparisons p < .001, with the exception of the difference between Levels 4 and 5; p < .05). The interaction Group × Memory load was significant F(6, 228) = 3.26, ƞ2p = .08, p < .01; post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction showed that the performance of the two groups differed from Level 4 onward (Level 4 p < .01, Level 5 p < .05, Level 6 p < .01, Levels 7 and 8 p < .05). With respect to the intragroup comparisons, post hoc comparisons with regard to the DS group showed no differences between the three initial levels, between Levels 4 and 5, Levels 6 and 7, and finally between Levels 7 and 8; all the other comparisons were significant for p < .001 with a decrease associated to an increase in memory load. No
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differences emerged between Levels 4 and 5, p = .38. For the TD group, performance did not change until Level 5; no differences emerged between Levels 5 and 6; all the remaining comparisons were significant for p < .01 with a decrease associated to an increase in memory load. No other effects were significant. When the random condition was considered, only the effect of Memory load was significant F(6, 228) = 154.45, ƞ2p = .80, p < .001, no differences emerged when Levels 6, 7, and 8 were compared. All the other comparisons were significant for p < .001. DISCUSSION This study aimed to analyze the performance of individuals with DS on a spatialsimultaneous task in which squares could be randomly arranged or grouped together to form a pattern. While the visuospatial domain is usually considered a strength in DS (see, e.g., Lanfranchi et al., 2004, or, for a review, Baddeley & Jarrold, 2007), recent studies suggest that their performance is not homogeneous and that they have a specific impairment in the spatial-simultaneous component of VSWM (Lanfranchi et al., 2009). This result has been found even in conditions in which the information to be recalled was grouped to form a pattern, therefore, in theory, in a more advantageous mode for recall (see Carretti & Lanfranchi, 2010; Carretti et al., 2013). In view of those results, the current study explored the possibility that impairment on spatial-simultaneous tasks can depend on the use of different encoding modalities. Individuals with DS and TD children, matched on verbal and nonverbal mental age, carried out a spatial-simultaneous task in both single- and dual-task (i.e., verbal and visuospatial) conditions, in order to explore whether a concurrent task would disrupt the performance in the main task. The effect of concurrent tasks would therefore inform us of the type of encoding modality used by individuals with DS and TD children for processing spatial-simultaneous material. Results showed that in the single-task condition, individuals with DS performed worse than TD children of the same mental age, confirming that spatial-simultaneous WM is a relatively weak area in the cognitive profile of individuals with DS (see, e.g., Carretti & Lanfranchi, 2010; Carretti et al., 2013; Lanfranchi et al., 2009). Moreover, consistent with Carretti and Lanfranchi’s and Carretti et al. findings, individuals with DS were found to be less able than TD children to take advantage from the possibility of chunking the items into a pattern. Analysis on performance distinguishing by memory load showed that the TD children were able to maintain a high performance up until Level 3, whereas the performance of DS individuals dropped significantly already at Level 2. With regard to the study’s main aim, the results seem to suggest that individuals with DS use the same encoding modality as do the TD children of the same mental age. In fact, just as the TD children, their performance was worse on both dual-task conditions than on the single-task one, with no differences between verbal and visuospatial concurrent task conditions. On the basis of these findings, it could be hypothesized that both the TD and DS children use both verbal and visuospatial modality to encode positions simultaneously presented. According to Palmer (2000), after an initial period in which children prefer using a visual modality to encode visually presented material, they switch to a dual code—verbal and visuospatial—and finally, at about the age of 7, they use only a verbal one. The modality used by the DS individuals studied here in encoding spatialsimultaneous items was consistent with their mental age. Similar results have been reported with regard to the visual working memory (Lanfranchi, Toffanin, Zilli, &
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Vianello, 2013). In fact, in a memory task using visually presented nameable items and exploring word-length effect, phonological similarity effect and visual similarity effect, the performance of individuals with DS was similar to that of TD children of the same mental age, suggesting that both groups use a visual modality to encode visually presented items. Again, these results suggest that the modality used by individuals with DS is consistent with their mental age. It is worth noting that matching participants is a difficult question when children with intellectual disability are studied. Results should be interpreted with a degree of caution due to the fact that, matching individuals with DS and TD children on the basis of mental age, we are comparing younger TD children with older children with DS, therefore, introducing a possible source of confounding. In fact, the performance of this second group could be affected, for example, by their longer life experience or maturation time. However, although individuals with DS were older than TD children, they still had lower performance in VSWM tasks. Moreover, since this study focused on working memory, we believe that considering two groups with the same general cognitive level was a prerogative to compare individuals with DS and TD children. Of course, future studies are needed to better explore the effect of experience variables on the performance of individuals with DS in working memory. In conclusion, our results indicate that, although individuals with DS encode spatialsimultaneous information as do TD children, they are still not as proficient in taking advantage from structured material and show worse performance in the pattern condition. This could suggest that the difficulties in the spatial-simultaneous task encountered by the DS group are not due to encoding problems but maybe to more basic perceptual difficulties in pattern recognition. Further studies should explore this hypothesis. Original manuscript received December 2, 2013 Revised manuscript accepted April 6, 2014 First published online May 12, 2014
REFERENCES Baddeley, A. D., & Hitch, G. J. (1974). Working memory. In G. H. Bower (Ed.), The psychology of learning and motivation (Vol. 8, pp. 47–89). New York, NY: Academic Press. doi:10.1016/ S0079-7421(08)60452-1 Baddeley, A., & Jarrold, C. (2007). Working memory and Down syndrome. Journal of Intellectual Disabilities Research, 51, 925–931. Carretti, B., & Lanfranchi, S. (2010). The effect of configuration on VSWM performance of Down syndrome individuals. Journal of Intellectual Disability Research, 54, 1058–1066. doi:10.1111/ j.1365-2788.2010.01334.x Carretti, B., Lanfranchi, S., & Mammarella, I. C. (2013). Spatial-simultaneous and spatial-sequential working memory in individuals with Down syndrome: The effect of configuration. Research in Developmental Disabilities, 34, 669–675. doi:10.1016/j.ridd.2012.09.011 Cornoldi, C., & Vecchi, T. (2003). Visuo-spatial working memory and individual differences. Hove: Psychological Press. Dunn, L. M., & Dunn, L. M. (1997). Peabody picture vocabulary test (3rd ed.). Circle Pines, MN: American Guidance Service. Dykens, E. M., Hodapp, R. M., & Finucane, B. M. (2000). Genetics and mental retardation syndromes. New York, NY: Paul H. Brookes.
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Hulme, C., & Mackenzie, S. (1992). Working memory and severe learning difficulties. Hove: Lawrence Erlbaum Associates. Jarrold, C., & Baddeley, A. D. (1997). Short-term memory for verbal and visuospatial information in Down’s syndrome. Cognitive Neuropsychiatry, 2, 101–122. doi:10.1080/135468097396351 Kittler, P. M., Krinsky-McHale, S. J., & Devenny, D. A. (2004). Semantic and phonological loop effects on verbal working memory in middle-age adults with mental retardation. American Journal on Mental Retardation, 109(6), 467–480. doi:10.1352/0895-8017(2004)109 2.0.CO;2 Kittler, P. M., Krinsky-McHale, S. J., & Devenny, D. A. (2008). Dual-task processing as a measure of executive function: A comparison between adults with Williams and Down syndromes. American Journal on Mental Retardation, 113(2), 117–132. doi:10.1352/0895-8017(2008)113 [117:DPAAMO]2.0.CO;2 Lanfranchi, S., Baddeley, A., Gathercole, S., & Vianello, R. (2012). Working memory in Down syndrome: Is there a dual task deficit? Journal of Intellectual Disability Research, 56, 157–166. doi:10.1111/j.1365-2788.2011.01444.x Lanfranchi, S., Carretti, B., Spanò, G., & Cornoldi, C. (2009). A specific deficit in visuospatial simultaneous working memory in Down syndrome. Journal of Intellectual Disability Research, 53, 474–483. doi:10.1111/j.1365-2788.2009.01165.x Lanfranchi, S., Cornoldi, C., & Vianello, R. (2004). Verbal and visuospatial working memory deficits in children with Down syndrome. American Journal on Mental Retardation, 109, 456–466. doi:10.1352/0895-8017(2004)109 2.0.CO;2 Lanfranchi, S., Toffanin, E., Zilli, S., & Vianello, R. (2013). Memory coding in children with Down syndrome. Child Neuropsychology. Advance online publication. doi:10.1080/ 09297049.2013.856396 Mammarella, N., Cornoldi, C., & Donadello, E. (2003). Visual but not spatial working memory deficit in children with spina bifida. Brain and Cognition, 53, 311–314. doi:10.1016/S02782626(03)00132-5 Mammarella, I. C., Cornoldi, C., Pazzaglia, F., Toso, C., Grimoldi, M., & Vio, C. (2006). Evidence for a double dissociation between spatial-simultaneous and spatial-sequential working memory in visuospatial (nonverbal) learning-disabled children. Brain and Cognition, 62, 58–67. doi:10.1016/j.bandc.2006.03.007 Mammarella, I. C., Pazzaglia, F., & Cornoldi, C. (2008). Evidence for different components in children’s visuospatial working memory. British Journal of Developmental Psychology, 26, 337–355. doi:10.1348/026151007X236061 Marcell, M. M., & Weeks, S. L. (1988). Short-term memory difficulties and Down’s syndrome. Journal of Mental Deficiency Research, 32, 153–162. Numminen, H., Service, E., Ahonen, T., & Ruoppila, I. (2001). Working memory and everyday cognition in adults with Down’s syndrome. Journal of Intellectual Disability Research, 45, 157–168. doi:10.1046/j.1365-2788.2001.00298.x Palmer, S. (2000). Working memory: A developmental study of phonological recoding. Memory, 8, 179–193. doi:10.1080/096582100387597 Pazzaglia, F., & Cornoldi, C. (1999). The role of distinct components of visuo-spatial working memory in the processing of texts. Memory, 7, 19–41. doi:10.1080/741943715 Raven, J. C., Court, J. H., & Raven, J. (1998). Manual for Raven’s progressive matrices. Oxford: Oxford Psychologists Press.
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Spatial-simultaneous working memory and selective interference in Down syndrome Silvia Lanfranchi1, Irene C. Mammarella1, and Barbara Carretti2 1
Department of Developmental Psychology and Socialization, University of Padova, Padova, Italy 2 Department of General Psychology, University of Padova, Padova, Italy Several studies have suggested that individuals with Down syndrome (DS) have impairments in some aspects of the visuospatial domain. It has been reported that they are particularly impaired in the spatial-simultaneous working memory (WM) even in advantageous conditions such as when information is grouped to form a configuration. This study aimed to assess the performance of individuals with DS carrying out a spatial-simultaneous WM task in single and dual selective interference conditions in order to better explore the characteristics of their impairment in this area. Groups of individuals with DS and mentally age-matched typically developing (TD) children were asked to carry out a spatial-simultaneous WM task in a single- and in two dual-task conditions. In the single condition, the participants were required to recall an increasing number of positions of red squares presented simultaneously in a matrix. In the dual-task conditions, together with the spatialsimultaneous WM task, the participants were asked to carry out an articulatory suppression task or a tapping task. As has already been shown in other studies, individuals with DS were found to be impaired in carrying out a spatial-simultaneous WM task and showed a worse performance with respect to the TD group in both the conditions. These findings indicate that individuals with DS use the same coding modality as TD children of the same mental age. Just as the TD children, they performed lower in the dual- than in the single-task condition and there was no difference between the verbal and visuospatial conditions. Keywords: Working memory; Down syndrome; Visuospatial memory; Intellectual disability; Interference.
Down syndrome (DS) is due to abnormalities on Chromosome 21 and it is the most common cause of intellectual disability (Kittler, Krinsky-McHale, & Devenny, 2008). The cognitive profile of this syndrome is characterized by a relative weakness in verbal abilities, while visuospatial skills seem to be relatively preserved (Dykens, Hodapp, & Finucane, 2000). This work was supported by Grant CPDA 127939 awarded by the University of Padova to SL. We thank all children who participated in this study and their families. Moreover we are grateful to Arianna Ferrara and Laura Valle who collected the data. Address correspondence to Silvia Lanfranchi, Department of Developmental and Socialization Psychology, University of Padova, Via Venezia, 8, 35131 Padova, Italy. E-mail: [email protected]
© 2014 Taylor & Francis
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Several studies have analyzed working memory (WM) in individuals with DS. In particular, it has been found that children (Jarrold & Baddeley, 1997), adolescents (Hulme & Mackenzie, 1992; Marcell & Weeks, 1988), and adults (Kittler, Krinsky-McHale, & Devenny, 2004; Kittler et al., 2008; Numminen, Service, Ahonen, & Ruoppila, 2001) with DS have a weaker verbal WM than typically developing (TD) children with the same mental age and than individuals with severe intellectual disabilities with similar mental age as well. Performance on visuospatial working memory (VSWM) tasks is, instead, usually considered a point of strength for individuals with DS. In fact, several investigators have reported that their performance is comparable to that of TD children matched for mental age. There are, however, some data indicating that the profile of individuals with DS is not homogeneous with regard to the visuospatial domain. Lanfranchi, Carretti, Spanò, and Cornoldi (2009), for example, reported that performance in spatial-simultaneous tasks was lower in a DS group with respect to a TD cohort but comparable when a spatial-sequential task was considered. Lanfranchi et al. (2009) explained their findings on the basis of Pazzaglia and Cornoldi’s (1999, see also Cornoldi & Vecchi, 2003) hypothesis, according to which the visuospatial sketchpad originally included in Baddeley and Hitch’s model (1974) can be divided into separate components. Pazzaglia and Cornoldi (1999; see also Mammarella, Pazzaglia, & Cornoldi, 2008), in fact, suggested that VSWM can be divided into three components: a visual component in charge of processing shapes and colors and two kinds of spatial components, both involved in memorizing patterns of spatial locations but presenting them in different formats and consequently using different spatial processes, simultaneous in one case, sequential in the other. Data gathered from various groups of children have, in fact, supported the hypothesis that there is a distinction between visual and spatial-simultaneous processes (Mammarella, Cornoldi, & Donadello, 2003) just as there is between spatial-simultaneous and spatial-sequential processes (Mammarella et al., 2006). Subsequent studies attempting to clarify the impairment in spatial-simultaneous tasks in individuals with DS by analyzing situations that could reduce the performance gap came across unexpected difficulties (Carretti & Lanfranchi, 2010; Carretti, Lanfranchi, & Mammarella, 2013). Carretti and Lanfranchi, who analyzed the advantage associated to a structured pattern in spatial-simultaneous tasks, demonstrated that, although a pattern condition led to a better performance also in the DS group, it did not reduce the difference in performance with the TD group. Instead the gap between the two groups was wider than in the random condition. In accordance with these results, Carretti et al., who compared the advantage associated to structured material both in spatialsimultaneous and in spatial-sequential tasks, reported that it led to a marked difference between groups in the former but not in the latter tasks. The paradoxical effect of configuration on individuals with DS could be explained in more than one manner from more basic difficulties in pattern recognition to a different way of encoding the to-be-remembered information to high-order level difficulties in the strategic use of pattern for recall. In the current study, we explored whether individuals with DS are comparable to TD children in terms of encoding spatial items simultaneously presented. To evaluate this, participants were asked to carry out a spatial-simultaneous task in three conditions: a single one and two dual tasks in which participants were required to process information needing to be recalled in two selective interference conditions, an articulatory suppression one, in which verbal components of the working memory were loaded and a tapping one, loading on spatial components of the working memory. If individuals with DS use a verbal
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strategy to encode configured material, their performance should decrease when a verbal task is combined with a standard memory condition. If, instead, they use a visual encoding strategy, their performance should be worse when the task is combined with a spatial tapping task. METHOD Participants Twenty individuals with DS took part in the study. Their mean chronological age was 14 years and 2 months (SD = 29 months, range 9 years and 5 months to 17 years and 11 months), and their mean mental age was 5 years and 2 months (SD = 25 months). A control group was made up of 20 TD children with a mean chronological age of 5 years and 5 months (SD = 5 months). The two groups were matched one to one on the raw scores they obtained on the Peabody Picture Vocabulary Test—Revised (PPVT-R; Dunn & Dunn, 1997) (see Table 1). In addition, since usually individuals with DS show a discrepancy between their verbal and nonverbal abilities, Raven’s Coloured Progressive Matrices (CPM; Raven, Court, & Raven, 1998) were administered to both groups to measure their nonverbal abilities. The two groups’ performance on both the PPTV-R (F < 1) and Raven’s Matrices F(1, 39) = 1.12, p = .29 was comparable.
Materials Spatial-Simultaneous Memory Task. The task consisted of recalling the position of an increasing number of red squares in a matrix presented on a computer screen. The size of the matrices varied on the basis of items to be recalled (3 × 4 matrices for two, three, and four items to be recalled; 4 × 4 matrices for five, six, and seven items to be recalled; and 4 × 5 matrices for eight items to be recalled). The visuospatial memory task was presented in two different configurations: (1) Pattern configuration, in which the red squares were presented as a visual configuration (or pattern); (2) Random configuration, in which the red squares were presented in random locations. The presence/absence of a pattern was defined on the basis of the proximity among the red squares in the matrices. Moreover, the two versions were presented in both singleand dual-task conditions. Table 1 Participants’ Characteristics. Down Syndrome
PPVT-R CPM
Raw score Mental age Raw score Mental age
Typically Developing
M
SD
M
SD
56.20 61.9 14.05 59.7
24.38 25.55 4.20 16.41
58.00 61.75 15.15 64.2
18.85 19.87 1.98 7.46
Note. PPTV-R: Peabody Picture Vocabulary Test—Revised; CPM = Raven’s Colored Matrices.
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Figure 1 Examples of matrixes used during the spatial-simultaneous task. An example of a pattern configuration is shown on the left and a random one on the right.
In the single condition (see Figure 1), each matrix was displayed on the computer screen for 5 s, then removed, and, just after, the participants were asked to recall where the red squares were positioned by pointing on an empty matrix. Two trials for each level of difficulty were presented from the shortest lists (containing two positions to recall) to the longest (containing eight positions to recall). To avoid frustration, the task was terminated if a participant failed on both trials at the same level, and it was assumed that the remaining items would not be recalled correctly. In the dual task, participants carried the basic task in conjunction with one of the following tasks. In the verbal interference (i.e., articulatory suppression), the single condition was combined with a verbal task. In particular, while the participant looked at the stimulus matrix he or she was asked to repeat continuously the syllable “la la la la.” In the dual task with visuospatial interference (i.e., tapping), the single condition was combined with a visuospatial task. Specifically, while the participant looked at the stimulus matrix he or she was asked to tap his or her hand on the table. Of course, those concurrent tasks were not “pure” verbal and visuospatial tasks, but since individuals with DS have well-documented problems in performing dual tasks (e.g., Kittler et al., 2004; Lanfranchi, Baddeley, Gathercole, & Vianello, 2012; Lanfranchi, Cornoldi, & Vianello, 2004), they seemed easy enough to avoid a floor effect. The number of correct trials was considered as the dependent variable for all the conditions. The maximum score was 16. Procedure The study consisted of three sessions held approximately a week apart from one another with each session lasting approximately 25 minutes. The participants completed the CPM test and PPVT-R during the first session. The raw score that the individuals with DS obtained on the latter was used to identify the matching child in the control group, while the CPM scores were used as a measure of the two groups’ nonverbal abilities. The VSWM tasks were administered individually during the second and third sessions and the presentation order of the tasks was counterbalanced across the participants. RESULTS A 2 × 3 × 2 mixed-design analysis of variance (ANOVA) with Group (DS vs. TD group) as a between-group variable and Condition (control, tapping, articulatory suppression) and Configuration (pattern vs. random) as the within-group variables in the number
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of correct trials (see Figure 2) showed a significant main effect of group, F(1, 38) = 5.21, ƞ2p = .12, p < .05, with TD children outperforming (M = 7.75, SE = 0.54) the DS group (M = 6.00, SE = 0.54). A significant effect of condition was also found, F(2, 76) = 5.11, ƞ2p = .12, p < .01. Subsequent post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction showed better performance in the control condition (M = 7.36, SE = 0.28) than in the two interference ones (visuospatial interference: M = 6.62, SE = 0.39, p < .05; verbal interference: M = 6.63, SE = 0.46 p < .01), but performance in the latter conditions was not different. Finally, a significant effect of configuration was also found, F(1,38) = 259.72, ƞ2p = .87, p < .001, with better performance in the pattern (M = 9.00, SE = 0.44) than in the random condition (M = 4.75, SE = 0.37). A significant interaction Group × Configuration was found, F(1, 38) = 19.02, ƞ2p = .33, p < .001; subsequent post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction indicated that the TD children (M = 10.45, SE = 0.63) outperformed the participants with DS (M = 5.05, SE = 0.52) when the squares were presented as a pattern (p < .001); this was not the case in the random condition (p = .41). In addition, both groups showed better performance when the squares were presented as a pattern (DS: M = 5.05, SE = 0.52; TD: M = 10.45, SE = 0.62) with respect to the random condition (DS: M = 4.45, SE = 0.52; TD: M = 7.55, SE = 0.63). No other significant interactions were found. We subsequently calculated the dimension of the differences between groups in the pattern conditions by using the Cohen’s d. In the control condition, the difference between the TD and DS groups was .91, while in the tapping condition it was .64, and in the articulatory suppression condition, it was 1.17.
Figure 2 Performance of individuals with DS and TD children as a function of condition (random vs. pattern) and type of task (standard, dual with verbal interference, dual with visuospatial interference). Error bars represent standard errors of the mean.
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Figure 3 Performance on the spatial-simultaneous task according to group and condition.
The difference in performance across the memory-load levels was also analyzed separately for the pattern and random conditions (see Figure 3). The 2 × 3 × 7 ANOVA on the performance in the pattern condition, with Group (DS vs TD group) as between-group factor and Conditions (control, tapping, articulatory suppression) and Memory Load (2 vs. 3 vs. 4 vs. 5 vs. 6 vs. 7 vs. 8) as within-group factors, showed a main effect of Group F(1, 38) = 10.76, ƞ2p = .22, p < .001, with TD children (M = 1.49, SE = 0.089) outperforming the DS group (M = 1.08, SE = 0.089), as well as of Condition, F(2, 76) = 3.33, ƞ2p = .08, p < .05. Subsequent post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction showed better performance under the control (M = 1.38, SE = 0.07) than in the tapping condition (M = 1.23, SE = 0.08 p < .05). The performance in interference conditions was not different. The main effect of Memory load was also significant F(6, 228) = 100.05, ƞ2p = .73, p < .001, showing a stable performance until Level 3 (with no differences in performance) and a continuous decrease in the other levels (for all the comparisons p < .001, with the exception of the difference between Levels 4 and 5; p < .05). The interaction Group × Memory load was significant F(6, 228) = 3.26, ƞ2p = .08, p < .01; post hoc comparisons with the Tukey method adjusted for multiple comparisons with Bonferroni correction showed that the performance of the two groups differed from Level 4 onward (Level 4 p < .01, Level 5 p < .05, Level 6 p < .01, Levels 7 and 8 p < .05). With respect to the intragroup comparisons, post hoc comparisons with regard to the DS group showed no differences between the three initial levels, between Levels 4 and 5, Levels 6 and 7, and finally between Levels 7 and 8; all the other comparisons were significant for p < .001 with a decrease associated to an increase in memory load. No
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differences emerged between Levels 4 and 5, p = .38. For the TD group, performance did not change until Level 5; no differences emerged between Levels 5 and 6; all the remaining comparisons were significant for p < .01 with a decrease associated to an increase in memory load. No other effects were significant. When the random condition was considered, only the effect of Memory load was significant F(6, 228) = 154.45, ƞ2p = .80, p < .001, no differences emerged when Levels 6, 7, and 8 were compared. All the other comparisons were significant for p < .001. DISCUSSION This study aimed to analyze the performance of individuals with DS on a spatialsimultaneous task in which squares could be randomly arranged or grouped together to form a pattern. While the visuospatial domain is usually considered a strength in DS (see, e.g., Lanfranchi et al., 2004, or, for a review, Baddeley & Jarrold, 2007), recent studies suggest that their performance is not homogeneous and that they have a specific impairment in the spatial-simultaneous component of VSWM (Lanfranchi et al., 2009). This result has been found even in conditions in which the information to be recalled was grouped to form a pattern, therefore, in theory, in a more advantageous mode for recall (see Carretti & Lanfranchi, 2010; Carretti et al., 2013). In view of those results, the current study explored the possibility that impairment on spatial-simultaneous tasks can depend on the use of different encoding modalities. Individuals with DS and TD children, matched on verbal and nonverbal mental age, carried out a spatial-simultaneous task in both single- and dual-task (i.e., verbal and visuospatial) conditions, in order to explore whether a concurrent task would disrupt the performance in the main task. The effect of concurrent tasks would therefore inform us of the type of encoding modality used by individuals with DS and TD children for processing spatial-simultaneous material. Results showed that in the single-task condition, individuals with DS performed worse than TD children of the same mental age, confirming that spatial-simultaneous WM is a relatively weak area in the cognitive profile of individuals with DS (see, e.g., Carretti & Lanfranchi, 2010; Carretti et al., 2013; Lanfranchi et al., 2009). Moreover, consistent with Carretti and Lanfranchi’s and Carretti et al. findings, individuals with DS were found to be less able than TD children to take advantage from the possibility of chunking the items into a pattern. Analysis on performance distinguishing by memory load showed that the TD children were able to maintain a high performance up until Level 3, whereas the performance of DS individuals dropped significantly already at Level 2. With regard to the study’s main aim, the results seem to suggest that individuals with DS use the same encoding modality as do the TD children of the same mental age. In fact, just as the TD children, their performance was worse on both dual-task conditions than on the single-task one, with no differences between verbal and visuospatial concurrent task conditions. On the basis of these findings, it could be hypothesized that both the TD and DS children use both verbal and visuospatial modality to encode positions simultaneously presented. According to Palmer (2000), after an initial period in which children prefer using a visual modality to encode visually presented material, they switch to a dual code—verbal and visuospatial—and finally, at about the age of 7, they use only a verbal one. The modality used by the DS individuals studied here in encoding spatialsimultaneous items was consistent with their mental age. Similar results have been reported with regard to the visual working memory (Lanfranchi, Toffanin, Zilli, &
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Vianello, 2013). In fact, in a memory task using visually presented nameable items and exploring word-length effect, phonological similarity effect and visual similarity effect, the performance of individuals with DS was similar to that of TD children of the same mental age, suggesting that both groups use a visual modality to encode visually presented items. Again, these results suggest that the modality used by individuals with DS is consistent with their mental age. It is worth noting that matching participants is a difficult question when children with intellectual disability are studied. Results should be interpreted with a degree of caution due to the fact that, matching individuals with DS and TD children on the basis of mental age, we are comparing younger TD children with older children with DS, therefore, introducing a possible source of confounding. In fact, the performance of this second group could be affected, for example, by their longer life experience or maturation time. However, although individuals with DS were older than TD children, they still had lower performance in VSWM tasks. Moreover, since this study focused on working memory, we believe that considering two groups with the same general cognitive level was a prerogative to compare individuals with DS and TD children. Of course, future studies are needed to better explore the effect of experience variables on the performance of individuals with DS in working memory. In conclusion, our results indicate that, although individuals with DS encode spatialsimultaneous information as do TD children, they are still not as proficient in taking advantage from structured material and show worse performance in the pattern condition. This could suggest that the difficulties in the spatial-simultaneous task encountered by the DS group are not due to encoding problems but maybe to more basic perceptual difficulties in pattern recognition. Further studies should explore this hypothesis. Original manuscript received December 2, 2013 Revised manuscript accepted April 6, 2014 First published online May 12, 2014
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