Mental retardation general intelligence and modularity

Estimating the level of functional ability of children identified as likely to have an intellectual disability

Screening tools can provide an indication of whether a child may have an intellectual disability (ID). Item response theory (IRT) analyses can be used to assess whether the statistical properties of the tools are such that their utility extends beyond their use as a screen for ID. We used non-parametric IRT scaling analyses to investigate whether the Child and Adolescent Intellectual Disability Screening Questionnaire (CAIDS-Q) possessed the statistical properties that would suggest its use could be extended to estimate levels of functional ability and to estimate which (if any) features associated with intellectual impairment are consistently indicative of lower or higher levels of functional ability. The validity of the two proposed applications was assessed by evaluating whether the CAIDS-Q conformed to the properties of the Monotone Homogeneity Model (MHM), characterised by uni-dimensionality, local independence and latent monotonicity and the Double Monotone Model (DMM), characterised by the assumptions of the MHM and, in addition, of non-intersecting item response functions. We analysed these models using CAIDS-Q data from 319 people referred to child clinical services. Of these, 148 had a diagnosis of ID. The CAIDS-Q was found to conform to the properties of the MHM but not the DMM. In practice, this means that the CAIDS-Q total scores can be used to quickly estimate the level of a person's functional ability. However, items of the CAIDS-Q did not show invariant item ordering, precluding the use of individual items in isolation as accurate indices of a person's level of functional ability.

Pathways to language: a naturalistic study of children with Williams syndrome and children with Down syndrome

This is a naturalistic study of the development of language in Hebrew-speaking children with Williams syndrome (WS) and children with Down syndrome (DS), whose MLU extended from 1·0 to 4·4. Developmental curves over the entire span of data collection revealed minor differences between children with WS, children with DS, and typically developing (TD) controls of similar MLU. Development within one calendar year showed remarkable synchrony among the variables. However, age of language onset and pace of acquisition departed significantly from normal timing. It is argued that in view of the centrality of genetic timing and the network properties of cognition, normal schedules are crucial determinants of intact development. Consequently, with respect to neurodevelopmental syndromes, the so-called 'language delay' is indicative of deviance that is likely to impact development in critical ways.

The mind of the mnemonists: an MEG and neuropsychological study of autistic memory savants

About 10% of autistic individuals exhibit some form of islets of abilities in the face of serious intellectual or mental disability ("savant syndrome"). The aim of this study was to investigate brain mechanisms in a sample of autistic subjects with outstanding memory. We investigated seven mnemonist savants with high-functioning autism spectrum disorder and seven matched controls with 151-channel whole-head magnetencephalography in a continuous old-new paradigm. They were presented with 300 pseudowords and 300 shapes and had to indicate by button press, whether the presented stimulus had been shown before. Unexpectedly, mnemonist savants did not perform better than controls, but were outperformed in the recognition of pseudowords. Accordingly, event-related magnetic fields elicited by pseudowords showed widespread old-new effects in controls, but not in savants. A source analysis of its early components revealed right occipital activation in savants, but left parietal activation in controls. This might be related to a visual processing style in mnemonist savants that proved to be inefficient in this task. During the possibly familiarity-based recognition of shapes, there were earlier and more widespread bilateral old-new effects in mnemonist savants, what might reflect their experience with figural material. In a neuropsychological test battery, mnemonist savants performed comparably to autistic people without special memory skills. However, a different factor structure of these tests pointed to a different organization of memory in mnemonist savants compared to controls that is characterized by its relative independence of general intelligence.

Uncovering Knowledge of Core Syntactic and Semantic Principles in Individuals With Williams Syndrome

We investigate knowledge of core syntactic and semantic principles in individuals with Williams Syndrome (WS). Our study focuses on the logico-syntactic properties of negation and disjunction (or) and tests knowledge of (a) core syntactic relations (scope and c-command), (b) core semantic relations (entailment relations and DeMorgan's laws of propositional logic), and (c) the relationship between (a) and (b). We examine the performance of individuals with WS, children matched for mental age (MA), and typical adult native speakers of English. Performance on all conditions suggests that knowledge of (a-c) is present and engaged in all three groups. Results also indicate slightly depressed performance on (c) for the WS group, compared to MA, consistent with limitation in processing resources. Implications of these results for competing accounts of language development in WS, as well as for the relevance of WS to the study of cognitive architecture and development are discussed.

Melody and Pitch Processing in Five Musical Savants with Congenital Blindness

We examined absolute-pitch (AP) and short-term musical memory abilities of five musical savants with congenital blindness, seven musicians, and seven non-musicians with good vision and normal intelligence in two experiments. In the first, short-term memory for musical phrases was tested and the savants and musicians performed statistically indistinguishably, both significantly outperforming the non-musicians and remembering more material from the C major scale sequences than random trials. In the second experiment, participants learnt associations between four pitches and four objects using a non-verbal paradigm. This experiment approximates to testing AP ability. Low statistical power meant the savants were not statistically better than the musicians, although only the savants scored statistically higher than the non-musicians. The results are evidence for a musical module, separate from general intelligence; they also support the anecdotal reporting of AP in musical savants, which is thought to be necessary for the development of musical-savant skill.

Comprehension of spatial language in Williams syndrome: evidence for impaired spatial representation of verbal descriptions

Individuals with the rare genetic disorder, Williams syndrome, have an unusual cognitive profile with relatively good language abilities but poor non-verbal and spatial skills. This study explored the interaction between linguistic and spatial functioning in Williams syndrome by investigating individuals' comprehension of spatial language. A group of 17 individuals with Williams syndrome and a control group of typically developing children were given two types of picture-matching task in which they were asked to select a picture to match a spoken sentence describing the spatial relation between two items. In the first task this matching could be done on the basis of existing semantic knowledge. In the second, we argue that a mental representation of the spatial relations was required. Results demonstrated that individuals with Williams syndrome were selectively impaired on the second task relative to controls. The study therefore provides support for previous work demonstrating impaired comprehension of spatial language in this population. Furthermore, the results suggest that such impairments reflect a fundamental problem with processing spatial descriptions rather than merely a poor understanding of the semantics of spatial terms, which in turn has implications for the interaction between spatial abilities and language processing in general.

Language abilities in Williams syndrome: a critical review

Williams syndrome is a rare genetic disorder in which, it is claimed, language abilities are relatively strong despite mild to moderate mental retardation. Such claims have, in turn, been interpreted as evidence either for modular preservation of language or for atypical constraints on cognitive development. However, this review demonstrates that there is, in fact, little evidence that syntax, morphology, phonology, or pragmatics are any better than predicted by nonverbal ability, although performance on receptive vocabulary tests is relatively good. Similarly, claims of an imbalance between good phonology and impaired or atypical lexical semantics are without strong support. There is, nevertheless, consistent evidence for specific deficits in spatial language that mirror difficulties in nonverbal spatial cognition, as well as some tentative evidence that early language acquisition proceeds atypically. Implications for modular and neuroconstructivist accounts of language development are discussed.

Annotation: the savant syndrome

BACKGROUND

Whilst interest has focused on the origin and nature of the savant syndrome for over a century, it is only within the past two decades that empirical group studies have been carried out.

METHODS

The following annotation briefly reviews relevant research and also attempts to address outstanding issues in this research area. Traditionally, savants have been defined as intellectually impaired individuals who nevertheless display exceptional skills within specific domains. However, within the extant literature, cases of savants with developmental and other clinical disorders, but with average intellectual functioning, are increasingly reported.

RESULTS

We thus propose that focus should diverge away from IQ scores to encompass discrepancies between functional impairments and unexpected skills. It has long been observed that savant skills are more prevalent in individuals with autism than in those with other disorders. Therefore, in this annotation we seek to explore the parameters of the savant syndrome by considering these skills within the context of neuropsychological accounts of autism. A striking finding amongst those with savant skills, but without the diagnosis of autism, is the presence of cognitive features and behavioural traits associated with the disorder.

CONCLUSIONS

We thus conclude that autism (or autistic traits) and savant skills are inextricably linked and we should therefore look to autism in our quest to solve the puzzle of the savant syndrome.

Longitudinal outcomes of very low birth weight: neuropsychological findings

To investigate the effects of very low birth weight (VLBW, &1500 g) on the development of neuropsychological skills, we assessed 67 children with birth weight <750 g, 64 with birth weight 750-1499 g, and 67 term-born controls. Growth modeling of raw scores from mean ages 7-14 years revealed persistent VLBW sequelae. Even when adjusting for IQ, the <750 g group scored more poorly than the term-born group on measures of language processing, verbal list learning, and perceptual-motor and organizational abilities. This group also made slower age-related progress than the control group on tests of perceptual-motor and executive functions. Environmental factors moderated group differences in change on other cognitive measures. These results revealed further evidence for slower skill development in both VLBW groups relative to controls, as well as"catch-up" growth in the 750-1499 g group on some measures. The findings suggest age-related changes in the cognitive sequelae of VLBW that depend on the skill assessed, the degree of VLBW, and environmental factors.

The structure of language abilities at 4 years: a twin study

Normal language development was studied in 310 pairs of 4-year-old twins born in the United Kingdom in 1994. Twins were assessed individually in their homes on a diverse battery of language and nonverbal measures. Rotated factor analyses indicated the presence of a general Language factor (L) as well as a general Nonverbal (NV) factor. Moderate genetic influence was found for both L and NV abilities. Bivariate genetic analysis estimated a genetic correlation of .63 between L and NV abilities, implying that over half of the genetic influence on L overlaps with genetic influence on NV. These results suggest that at age 4, genetic influences on individual differences in language overlap substantially with genetic influences on individual differences in other cognitive abilities, although perhaps less so than later in development.

Heuristic and analytic processing: age trends and associations with cognitive ability and cognitive styles

Developmental and individual differences in the tendency to favor analytic responses over heuristic responses were examined in children of two different ages (10- and 11-year-olds versus 13-year-olds), and of widely varying cognitive ability. Three tasks were examined that all required analytic processing to override heuristic processing: inductive reasoning, deductive reasoning under conditions of belief bias, and probabilistic reasoning. Significant increases in analytic responding with development were observed on the first two tasks. Cognitive ability was associated with analytic responding on all three tasks. Cognitive style measures such as actively open-minded thinking and need for cognition explained variance in analytic responding on the tasks after variance shared with cognitive ability had been controlled. The implications for dual-process theories of cognition and cognitive development are discussed.