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Low inhibitory control (IC) is sometimes associated with enhanced problem-solving amongst adults, yet for young children high IC is primarily framed as inherently better than low IC. Here, we explore associations between IC and performance on a novel problem-solving task, amongst 102 English 2- and 3-year-olds (Study 1) and 84 Swedish children, seen at 18-months and 4-years (Study 2). Generativity during problem-solving was negatively associated with IC, as measured by prohibition-compliance (Study 1, both ages, Study 2 longitudinally from 18-months). High parent-reported IC was associated with poorer overall problem-solving success, and greater perseveration (Study 1, 3-year-olds only). Benefits of high parent-reported IC on persistence could be accounted for by developmental level. No concurrent association was observed between problem-solving performance and IC as measured with a Delay-of-Gratification task (Study 2, concurrent associations at 4-years). We suggest that, for young children, high IC may confer burden on insight- and analytic-aspects of problem-solving.

Typically developing (TD) infants adapt to the social world in part by shifting the focus of their processing resources to the relevant aspects of a visual scene. Any impairment in visual orienting may therefore constrain learning and development in domains such as language. However, although something is known about visual orienting in infants at risk of autism, very little is known about it in infants/toddlers with other neurodevelopmental disorders. This is partly because previous studies focused on older children and rarely compared the children to "both" chronological age (CA)- and mental age (MA)-matched TD controls. Yet, if visual orienting is important for learning and development, then it is imperative to investigate it "early in development" and ascertain whether it relates to higher level cognitive functions such as language. We used eye-tracking technology to directly compare visual orienting in infants/toddlers with one of three neurodevelopmental disorders--Down syndrome (DS), fragile X syndrome (FXS) and Williams syndrome (WS)--matched on CA or MA to TD controls (~15 months). We also measured language ability using the Mullen Scales of Early Learning (MSEL). We found that the ability to "disengage" attention from a visual stimulus in order to shift it to another visual stimulus is related to language ability in infants/toddlers irrespective of group affiliation. We also found that, contrary to the literature, infants and toddlers with DS (but not WS) are slow at disengaging attention. Our data suggest that orienting attention constrains language development and is impaired in DS.

Background: Studies in Down syndrome (DS) and Williams syndrome (WS) have suggested that mathematical abilities are impaired. However, it is unclear which domain-general or domain-specific abilities impact on mathematical development in these developmental disorders. Method: The current study examined the foundations of mathematical development across participants with WS (n = 24) and DS (n = 26) compared to typically developing (TD) children (n = 26) in relation to domain-general (i.e., general intelligence and visuospatial abilities) and domain-specific abilities (non-symbolic and symbolic number abilities). Results: Developmental trajectories showed that mathematical abilities were delayed in line with overall mental age in DS and WS. Whilst visuospatial abilities predicted performance for DS and TD participants, this was not the case for the WS group, instead Approximate Number Sense abilities predicted mathematical development. Conclusions: These findings suggest that those with DS and WS may benefit from different mathematical intervention programmes.

It has been reported that approximate number sense (ANS) task performance is impaired in individuals with Williams syndrome (WS) and Down syndrome (DS). Research with infants has suggested this impairment is caused by sticky fixation in WS and sustained attention deficits for those with DS. This study examined looking patterns of older children and adults with WS (n = 24) and DS (n = 23) during an ANS task compared to typically developing controls matched for chronological age and those matched for mental age. Results showed that, although there were no group differences, looking patterns changed with chronological age for both the WS and DS groups. Looking behaviour related to ANS performance only in the WS group. Implications for interventions are discussed.

Sleep plays a key role in the consolidation of newly acquired information and skills into long term memory. Children with Down syndrome (DS) and Williams syndrome (WS) frequently experience sleep problems, abnormal sleep architecture, and difficulties with learning; thus, we predicted that children from these clinical populations would demonstrate impairments in sleep-dependent memory consolidation relative to children with typical development (TD) on a cognitive procedural task: The Tower of Hanoi. Children with DS (n = 17), WS (n = 22) and TD (n = 34) completed the Tower of Hanoi task. They were trained on the task either in the morning or evening, then completed it again following counterbalanced retention intervals of daytime wake and night time sleep. Children with TD and with WS benefitted from sleep for enhanced memory consolidation and improved their performance on the task by reducing the number of moves taken to completion, and by making fewer rule violations. We did not find any large effects of sleep on learning in children with DS, suggesting that these children are not only delayed, but atypical in their learning strategies. Importantly, our findings have implications for educational strategies for all children, specifically considering circadian influences on new learning and the role of children's night time sleep as an aid to learning.

It has been reported that approximate number sense (ANS) task performance is impaired in individuals with Williams syndrome (WS) and Down syndrome (DS). Research with infants has suggested this impairment is caused by sticky fixation in WS and sustained attention deficits for those with DS. This study examined looking patterns of older children and adults with WS (n = 24) and DS (n = 23) during an ANS task compared to typically developing controls matched for chronological age and those matched for mental age. Results showed that, although there were no group differences, looking patterns changed with chronological age for both the WS and DS groups. Looking behaviour related to ANS performance only in the WS group. Implications for interventions are discussed., Author(s): Jo Van Herwegen [sup.1] , Erica Ranzato [sup.2] , Annette Karmiloff-Smith, Victoria Simms [sup.3] Author Affiliations: (Aff1) 0000000121901201, grid.83440.3b, Department of Psychology and Human Development, UCL Institute of Education, [...]

In executing purposeful actions, adults select sufficient and necessary limbs. But infants often move goal-irrelevant limbs, suggesting a developmental process of motor specialization. Two experiments with 9- and 12-month-olds revealed gradual decreases in extraneous movements in non-acting limbs during unimanual actions. In Experiment 1, 9-month-olds produced more extraneous movements in the non-acting hand/arm and feet/legs than 12-month-olds. In Experiment 2, analysis of the spatiotemporal dynamics of infants' movements revealed developmental declines in the spatiotemporal coupling of movements between acting and non-acting arms. We also showed that the degree of specialization in infants' unimanual actions is associated with individual differences in motor experience and visual attention, indicating the experience-dependent and broad functional nature of these developmental changes. Our study provides important new insights into motor development: as in cognitive domains, motor behaviours are initially broadly tuned to their goal, becoming progressively specialized during the first year of life.

In order to understand how language abilities emerge in typically and atypically developing infants and toddlers, it is important to embrace complexity in development. In this paper, we describe evidence that early language development is an experience-dependent process, shaped by diverse, interconnected, interdependent developmental mechanisms, processes, and abilities (e.g. statistical learning, sampling, functional specialization, visual attention, social interaction, motor ability). We also present evidence from our studies on neurodevelopmental disorders (e.g. Down syndrome, fragile X syndrome, Williams syndrome) that variations in these factors significantly contribute to language delay. Finally, we discuss how embracing complexity, which involves integrating data from different domains and levels of description across developmental time, may lead to a better understanding of language development and, critically, lead to more effective interventions for cases when language develops atypically.

Sleep plays an active role in memory consolidation. Because children with Down syndrome (DS) and Williams syndrome (WS) experience significant problems with sleep and also with learning, we predicted that sleep-dependent memory consolidation would be impaired in these children when compared to typically developing (TD) children. This is the first study to provide a cross-syndrome comparison of sleep-dependent learning in school-aged children. Children with DS (n = 20) and WS (n = 22) and TD children (n = 33) were trained on the novel Animal Names task where they were taught pseudo-words as the personal names of ten farm and domestic animals, e.g. Basco the cat, with the aid of animal picture flashcards. They were retested following counterbalanced retention intervals of wake and sleep. Overall, TD children remembered significantly more words than both the DS and WS groups. In addition, their performance improved following night-time sleep, whereas performance over the wake retention interval remained stable, indicating an active role of sleep for memory consolidation. Task performance of children with DS did not significantly change following wake or sleep periods. However, children with DS who were initially trained in the morning continued to improve on the task at the following retests, so that performance on the final test was greater for children who had initially trained in the morning than those who trained in the evening. Children with WS improved on the task between training and the first retest, regardless of whether sleep or wake occurred during the retention interval. This suggests time-dependent rather than sleep-dependent learning in children with WS, or tiredness at the end of the first session and better performance once refreshed at the start of the second session, irrespective of the time of day. Contrary to expectations, sleep-dependent learning was not related to baseline level of performance. The findings have significant implications for educational strategies, and suggest that children with DS should be taught more important or difficult information in the morning when they are better able to learn, whilst children with WS should be allowed a time delay between learning phases to allow for time-dependent memory consolidation, and frequent breaks from learning so that they are refreshed and able to perform at their best.

This article outlines the "over-pruning hypothesis" of autism. The hypothesis originates in a neurocomputational model of the regressive sub-type (Thomas, Knowland & Karmiloff-Smith, 2011a, 2011b). Here we develop a more general version of the over-pruning hypothesis to address heterogeneity in the timing of manifestation of ASD, including new computer simulations which reconcile the different observed developmental trajectories (early onset, late onset, regression) via a single underlying atypical mechanism; and which show how unaffected siblings of individuals with ASD may differ from controls either by inheriting a milder version of the pathological mechanism or by co-inheriting the risk factors without the pathological mechanism. The proposed atypical mechanism involves overly aggressive synaptic pruning in infancy and early childhood, an exaggeration of a normal phase of brain development. We show how the hypothesis generates novel predictions that differ from existing theories of ASD including that (1) the first few months of development in ASD will be indistinguishable from typical, and (2) the earliest atypicalities in ASD will be sensory and motor rather than social. Both predictions gain cautious support from emerging longitudinal studies of infants at-risk of ASD. We review evidence consistent with the over-pruning hypothesis, its relation to other current theories (including C. Frith's under-pruning proposal; C. Frith, 2003, 2004), as well as inconsistent data and current limitations. The hypothesis situates causal accounts of ASD within a framework of protective and risk factors (Newschaffer et al., 2012); clarifies different versions of the broader autism phenotype (i.e. the implication of observed similarities between individuals with autism and their family members); and integrates data from multiple disciplines, including behavioural studies, neuroscience studies, genetics, and intervention studies.

Being able to see a talking face confers a considerable advantage for speech perception in adulthood. However, behavioural data currently suggest that children fail to make full use of these available visual speech cues until age 8 or 9. This is particularly surprising given the potential utility of multiple informational cues during language learning. We therefore explored this at the neural level. The event-related potential (ERP) technique has been used to assess the mechanisms of audio-visual speech perception in adults, with visual cues reliably modulating auditory ERP responses to speech. Previous work has shown congruence-dependent shortening of auditory N1/P2 latency and congruence-independent attenuation of amplitude in the presence of auditory and visual speech signals, compared to auditory alone. The aim of this study was to chart the development of these well-established modulatory effects over mid-to-late childhood. Experiment 1 employed an adult sample to validate a child-friendly stimulus set and paradigm by replicating previously observed effects of N1/P2 amplitude and latency modulation by visual speech cues; it also revealed greater attenuation of component amplitude given incongruent audio-visual stimuli, pointing to a new interpretation of the amplitude modulation effect. Experiment 2 used the same paradigm to map cross-sectional developmental change in these ERP responses between 6 and 11 years of age. The effect of amplitude modulation by visual cues emerged over development, while the effect of latency modulation was stable over the child sample. These data suggest that auditory ERP modulation by visual speech represents separable underlying cognitive processes, some of which show earlier maturation than others over the course of development.

Socioeconomic status (SES) impacts on both structural and functional brain development in childhood, but how early its effects can be demonstrated is unknown. In this study we measured resting baseline EEG activity in the gamma frequency range in awake 6-9-month-olds from areas of East London with high socioeconomic deprivation. Between-subject comparisons of infants from low-and high-income families revealed significantly lower frontal gamma power in infants from low-income homes. Similar power differences were found when comparing infants according to maternal occupation, with lower occupational status groups yielding lower power. Infant sleep, maternal education, length of gestation, and birth weight, as well as smoke exposure and bilingualism, did not explain these differences. Our results show that the effects of socioeconomic disparities on brain activity can already be detected in early infancy, potentially pointing to very early risk for language and attention difficulties. This is the first study to reveal region-selective differences in functional brain development associated with early infancy in low-income families.

Background: In typical development, early reading is underpinned by language skills, like vocabulary and phonological awareness (PA), as well as taught skills like letter knowledge. Less is understood about how early reading develops in children with neurodevelopmental disorders who display specific profiles of linguistic strengths and weaknesses, such as Down syndrome (DS) and Williams syndrome (WS). Methods: Early reading, letter knowledge, rhyme matching, phoneme matching and receptive vocabulary were assessed in 26 children with DS and 26 children with WS between 4 and 8 years, as well as in two groups of typically developing (TD) children matched on nonverbal mental age (NVMA controls) or reading (RA controls). Reading was also measured 1 year later in DS, WS and RA controls to assess reading growth and its longitudinal predictors. Results: Despite poor PA and vocabulary, children with DS displayed good reading and letter knowledge, compared with NVMA controls. Performance of children with WS was equivalent to RA controls and superior to NVMA controls on all tasks. Longitudinal delays emerged in reading in both DS and WS compared with RA controls. Vocabulary was a significant longitudinal predictor of reading growth for all children, but, for both children with DS and WS, and unlike RA controls, letter knowledge and PA were not. Conclusions: Children with DS and WS display atypical developmental patterns in the earliest stages of reading, further underlining the importance of cross-syndrome, longitudinal research, which tracks all levels of development in neurodevelopmental disorders. Identifying early syndrome-specific profiles of strengths and weaknesses underlying literacy development is critical for planning intervention programmes. (Contains 4 tables and 1 figure.)

Based on previous findings of frequent sleep problems in children with Down syndrome (DS) and Williams syndrome (WS), the present study aimed to expand our knowledge by using parent report and actigraphy to define sleep problems more precisely in these groups. Twenty-two school-aged children with DS, 24 with WS and 52 typically developing (TD) children took part in the study. Each child wore an actiwatch for a minimum of four nights and parents completed the Children's Sleep Habits Questionnaire (CSHQ). Sleep problems were common in both developmental disorders. Children with DS had the greatest sleep disruption, with frequent and longer night wakings as well as restlessness. Parents reported symptoms of sleep-disordered breathing and a range of other problems including grinding teeth, bedtime resistance and sleep anxiety. Children with WS had problems initiating sleep and parents also reported bed-wetting and body pain. Despite these problems, the mean actual sleep time, as measured by actigraphy, did not differ between the three groups. CSHQ reports were in agreement with actigraphy for children's sleep duration, but this was not the case for sleep latency, restlessness and the night wakings variables. Sleep problems in DS and WS are common and appear to be syndrome-specific. Due to the inaccuracy of parent report, it is recommended that children at risk undergo objective measures of sleep assessment. (Contains 2 figures and 6 tables.)

Previous research into face processing in autism spectrum disorder (ASD) has revealed atypical biases toward particular facial information during identity recognition. Specifically, a focus on features (or high spatial frequencies [HSFs]) has been reported for both face and nonface processing in ASD. The current study investigated the development of spatial frequency biases in face recognition in children and adolescents with and without ASD, using nonverbal mental age to assess changes in biases over developmental time. Using this measure, the control group showed a gradual specialization over time toward middle spatial frequencies (MSFs), which are thought to provide the optimal information for face recognition in adults. By contrast, individuals with ASD did not show a bias to one spatial frequency band at any stage of development. These data suggest that the "midband bias" emerges through increasing face-specific experience and that atypical face recognition performance may be related to reduced specialization toward optimal spatial frequencies in ASD.

Attention is construed as multicomponential, but the roles of its distinct subfunctions in shaping the broader developing cognitive landscape are poorly understood. The current study assessed 3- to 6-year-olds (N = 83) to: (a) trace developmental trajectories of attentional processes and their structure in early childhood and (b) measure the impact of distinct attention subfunctions on concurrent and longitudinal abilities related to literacy and numeracy. Distinct trajectories across attention measures revealed the emergence of 2 attentional factors, encompassing "executive" and "sustained-selective" processes. Executive attention predicted concurrent abilities across domains at Time 1, whereas sustained-selective attention predicted basic numeracy 1 year later. These "concurrent" and "longitudinal" constraints cast a broader light on the unfolding relations between domain-general and domain-specific processes over early childhood. (Contains 5 tables.)

Loss of previously established behaviors in early childhood constitutes a markedly atypical developmental trajectory. It is found almost uniquely in autism and its cause is currently unknown (Baird et al., 2008). We present an artificial neural network model of developmental regression, exploring the hypothesis that regression is caused by overaggressive synaptic pruning and identifying the mechanisms involved. We used a novel population-modeling technique to investigate developmental deficits, in which both neurocomputational parameters and the learning environment were varied across a large number of simulated individuals. Regression was generated by the atypical setting of a single pruning-related parameter. We observed a probabilistic relationship between the atypical pruning parameter and the presence of regression, as well as variability in the onset, severity, behavioral specificity, and recovery from regression. Other neurocomputational parameters that varied across the population modulated the risk that an individual would show regression. We considered a further hypothesis that behavioral regression may index an underlying anomaly characterizing the broader autism phenotype. If this is the case, we show how the model also accounts for several additional findings: shared gene variants between autism and language impairment (Vernes et al., 2008); larger brain size in autism but only in early development (Redcay & Courchesne, 2005); and the possibility of quasi-autism, caused by extreme environmental deprivation (Rutter et al., 1999). We make a novel prediction that the earliest developmental symptoms in the emergence of autism should be sensory and motor rather than social and review empirical data offering preliminary support for this prediction. (Contains 3 tables, 7 figures and 3 footnotes.)

The current study investigated whether contrasting face recognition abilities in autism and Williams syndrome could be explained by different spatial frequency biases over developmental time. Typically-developing children and groups with Williams syndrome and autism were asked to recognise faces in which low, middle and high spatial frequency bands were masked. All three groups demonstrated a gradual specialisation toward the mid-band. However, while the use of high spatial frequencies decreased in control and autism groups over development, the Williams syndrome group did not display a bias toward this band at any point. These data demonstrate that typical outcomes can be achieved through atypical developmental processes, and confirm the importance of cross-syndrome studies in the investigation of developmental disorders.

The aims of this study were to investigate whether specific linguistic difficulties in preterm children persist at eight years and to examine the interrelationships between language and literacy in this population, compared with a control group of full-term children. Sixty-eight monolingual Italian preterms and 26 chronologically matched controls were recruited. Language (grammar comprehension, lexical production and phonological awareness), literacy (reading comprehension, reading and writing) and general cognitive development were investigated. Results showed no general delay in preterms, but slight difficulties in specific linguistic abilities (grammar, lexicon, phoneme synthesis and deletion of the first syllable), more difficulties in literacy (speed in reading and accuracy in writing) and certain correlations among competencies turning out to be different from the control group. In conclusion, our study established that a partially atypical trajectory emerged in preterms, showing specific long-term effects of preterm birth on language and literacy development.

Previous research has suggested that a mid-band of spatial frequencies is critical to face recognition in adults, but few studies have explored the development of this bias in children. We present a paradigm adapted from the adult literature to test spatial frequency biases throughout development. Faces were presented on a screen with particular spatial frequencies blocked out by noise masks. A mid-band bias was found in adults and 9- and 10-year-olds for upright faces but not for inverted faces, suggesting a face-sensitive effect. However, 7- and 8-year-olds did not demonstrate the mid-band bias for upright faces but rather processed upright and inverted faces similarly. This suggests that specialization toward the mid-band for upright face recognition develops gradually during childhood and may relate to an advanced level of face expertise. (Contains 2 figures.)

We examined auditory perception in Williams syndrome by investigating strategies used in organizing sound patterns into coherent units. In Experiment 1, we investigated the streaming of sound sequences into perceptual units, on the basis of pitch cues, in a group of children and adults with Williams syndrome compared to typical controls. We showed that individuals with Williams syndrome were sensitive to the same pitch cues as typical children and adults when streaming these patterns. In Experiment 2, we evaluated differences in reliance on pitch and contour cues in unfamiliar melody perception in a group of adults with Williams syndrome relative to typical control children and adults. Unlike controls who demonstrated greater proficiency when contour cues were available, adults with Williams syndrome showed no such advantage.

Most studies of infant cognition focus on group data from single domains. Yet, without the multi-domain testing of the same infants longitudinally, such data cannot be used to evaluate whether the timing of cognitive change occurs in a domain-general or a domain-specific way. We present the results of a longitudinal study pooling data from three European laboratories set up identically. Over 100 healthy, monolingual infants each underwent multi-domain testing at 6 and again at 10 months in six experimental tasks (speech processing, face processing, and action/event processing), as well as a videotaped 3-minute recording of mother/infant dyads in a play session with an identical set of toys. Previous research examined the effects of maternal sensitivity only on general intelligence measures, but our approach is novel in that it assessed dyadic effects on specific cognitive domains, attempting to pinpoint in finer detail the effects of mother-infant dyadic interaction on the timing of cognitive change. Our findings highlight the importance of a multi-domain approach, in that unlike the assumptions drawn from cross-sectional data, our longitudinal study yielded different developmental timing across domains within the same infants. Our results also highlight a crucial difference: at the group level 6- and 10-month-olds display the expected effects found in previous research, but when re-analysed according to mother-child interaction ratings, the quality of dyadic interaction style turned out to subtly foster or delay development in domain-specific and age-specific ways, contributing to the range of individual differences in timing that we observe in cognitive development over the first year of life.

We report a cross-syndrome comparison of the development of holistic processing in face recognition in school-aged children with developmental disorders: autism, Down syndrome, and Williams syndrome. The autism group was split into two groups: one with high-functioning children and one with low-functioning children. The latter group has rarely been studied in this context. The four disorder groups were compared with typically developing children. Cross-sectional trajectory analyses were used to compare development in a modified version of Tanaka and Farah's part-whole task. Trajectories were constructed linking part-whole performance either to chronological age or to several measures of mental age (receptive vocabulary, visuospatial construction, and the Benton Facial Recognition Test). In addition to variable delays in onset and rate of development, we found an atypical profile in all disorder groups. These profiles were atypical in different ways, indicating multiple pathways to, and variable outcomes in, the development of face recognition. We discuss the implications for theories of face recognition in both atypical and typical development, including the idea that part-whole and rotation manipulations may tap different aspects of holistic and/or configural processing. (Contains 5 figures and 3 tables.)

This article argues that one dominant position in psychology, linguistics, neuroscience, and philosophy about how genetic disorders point to the innate specification of dissociated modules in the human brain should be replaced by a dynamic, neuroconstructivist approach in which genes, brain, cognition, and environment interact multidirectionally. The article challenges current thinking about a series of questions: (a) Do significantly better scores in one domain necessarily indicate an intact module? (b) What do scores in the normal range suggest? (c) What is wrong with mental-age matching? (d) Why is the notion of an intact module unlikely? (e) Do developmental disorders suggest associations rather than dissociations? (f) Is the environment the same for atypically developing individuals? The article concludes by examining the implications of taking a neuroconstructivist approach and by arguing that human intelligence is not a state (i.e., not a collection of static, built-in modules that can be intact or impaired) but a process (i.e., the emergent property over developmental time of dynamic, multidirectional interactions between genes, brain, cognition, behavior, and environment) with domain-specific outcomes impossible without the process of development.

Background: Figurative language, such as metaphor and metonymy, is very common in daily language use. Its underlying cognitive processes are sometimes viewed as lying at the interface of language and thought. Williams syndrome, which is a rare genetic developmental disorder, provides an opportunity to study this interface because individuals with this disorder have relative strengths in vocabulary and syntax against a background of low general cognitive ability. Few studies have investigated metaphor comprehension in Williams syndrome and none has investigated metonymy. Aims: This is the first study to investigate metaphor and metonymy comprehension in Williams syndrome and to compare their performance with a group of typically developing children. Methods & Procedures: Ten children with Williams syndrome were compared with eleven typically developing children in a novel metaphor-metonymy comprehension task. Cross-sectional trajectory analyses were used to compare the development of metaphor and metonymy using a child-friendly story picture task. Trajectories were constructed linking task performance either to chronological age or to measures of mental age (receptive vocabulary, visuospatial construction). Outcomes & Results: The performance of children with Williams syndrome was significantly poorer than the typically developing group. The comprehension of metonyms was in line with receptive vocabulary, but comprehension of metaphors fell below this level. Conclusions & Implications: Metonyms may be part of vocabulary and treated as synonyms in Williams syndrome, while metaphor engages additional cognitive mechanisms outside language that develop atypically in this disorder. Despite earlier reports that emphasize good language skills, the Williams syndrome language system shows anomalies compared with typical development. (Contains 1 table, 4 figures, and 1 note.)

Grouping by luminance and shape similarity has previously been demonstrated in neonates and at 4 months, respectively. By contrast, grouping by proximity has hitherto not been investigated in infancy. This is also the first study to chart the developmental emergence of perceptual grouping longitudinally. Sixty-one infants were presented with a matrix of local stimuli grouped horizontally or vertically by luminance, shape or proximity at 2, 4, and 6 months. Infants were exposed to each set of stimuli for three presentation durations. Grouping was demonstrated for luminance similarity at the earliest testing age, 2 months, by shape similarity at 4 months, but was not observed for grouping by proximity. Grouping by shape similarity showed a distinctive pattern of grouping ability across exposure durations, which reflected familiarity preferences followed by novelty preferences. This remained stable across age. No link was found between the emergence of perceptual grouping ability and the exposure duration required to elicit grouping. We conclude by stressing the importance of longitudinal studies of infant development in furthering our understanding of human cognition, rather than relying on assumptions from the adult endstate.

Perceptual grouping by luminance similarity and by proximity was investigated in infants with Williams syndrome (WS) aged between 6 and 36 months (visit 1, N=29). WS infants who were still under 36 months old, 8 months later, repeated the testing procedure (visit 2, N=15). Performance was compared to typically developing (TD) infants aged from 2 to 20 months (N=63). Consistent with the literature, TD participants showed grouping by luminance at the youngest testing age, 2 months. Grouping by proximity had not previous been charted in typical development: this study showed grouping by proximity at 8 months. Infants with WS could group by luminance. Developmental progression of the WS group showed some similarities to typical development, although further investigation is required to further address this in more depth. In contrast, infants with WS were not able to group by proximity. This pattern of emergence and development of grouping abilities is considered in relation to the pattern of grouping abilities observed in adults with WS.

It is becoming increasingly clear that little in development is predetermined or permanently fixed. Rather, gene expression is activity dependent, and epigenesis is probabilistic. So, the study of genetic disorders needs to change from the still widely held view that developmental disorders can be accounted for in terms of intact versus impaired modules, to one which takes serious account of the fact that the infant cortex passes from an initial state of high regional interconnectivity to a subsequent state of increasing specialization and localization of function. With such early interconnectivity in mind, developmental neuroscientists must consider the possibility that an early deficit in one part of the brain may have subtle effects on other parts of the developing brain, even when scores fall "in the normal range". In studying developmental disorders, it is thus crucial to examine not only domains of clear-cut deficit, but also domains of behavioural proficiency. Atypical epigenesis may often involve a lack of specialization and localization of brain function over developmental time, even in cases of behavioural proficiency.