Imitatieproblemen bij kinderen met autismespectrumstoornissen: Onderzoek naar de aard, klinische relevantie en bruikbaarheid voor de diagnose.

摘要

Imitation is the natural aptitude to replicate an observed action, which plays a pivotal role in the development of a child. It involves the ability to transform perceptual information into a motor copy. Basically, imitation results from the interaction of selection and correspondence processes. Children’s imitation can be divided in two main levels depending on the content of the observed action and the means/ends structure: action- and program-level imitation.When young children do not understand the overall reason for a demonstrator's behaviour, as young children often do, they will be more likely to imitate on action-level. Action-level imitation is the faithful and detailed copying of the directly observable motor organisation of the demonstrator’s action by replicating the movement itself and the movement effect. Young children do this to demonstrate to the adult that they are ‘in tune’ about the current situation and to join the social dance. By copying faithfully and conservatively children learn subtle new behaviours, such as culture dependent communicative gestures, new techniques and specific ways to most effectively manipulate tools. Young children learn to understand the novel actions through imitation. The fidelity to the perceived actions or the accuracy of imitation performance is an important criterion for the child’s aptitude to learn new social and non-social skills. Imitation on action-level can only be explained by a direct route of imitation, which transforms visuospatial characteristics directly into motor representations. In terms of human brain activity, action-level imitation may be supported by activation of areas belonging to the dorsal stream. When young children do recognise and understand the overall meaning, goal and intention of the demonstrator's behaviour, they may imitate on program-level. Program-level imitation is the copying of the non-observable, but inferable higher organisational structure of the demonstrator’s action by replicating the mental representation of the demonstrator’s desired end result and the mental representation of the means, the demonstrator has chosen to achieve the desired end result. Program-level imitation is founded on the ability to recognise in motor terms goal directed transitive actions with real or imaginary objects and the meaning of intransitive actions. Children imitate on program-level because they understand the observed actions. The imitation on program-level relies on the indirect semantic-related route of imitation. In terms of human brain activity, program-level imitation may be supported by activation of areas belonging to the ventral stream. However, goal directed and meaningful actions can be imitated along both the direct and indirect route of imitation. When assessing imitation development in an elicited test condition, these levels of imitation and these routes should be considered. Since existing imitation tests for young children are one-dimensional constructs, we developed the Preschool Imitation and Praxis Scale (PIPS). The PIPS was designed to assess the accuracy of bodily and procedural imitation performances in young children. To construct the PIPS, we chose action types with different effects (salient environmental and internal), representational levels (meaningful, and non-meaningful; goal directed and non-goal directed), temporal complexities (single and sequential) and visual monitoring possibilities (transparent and opaque) to cover the full range of possible imitation mechanisms. We selected imitation tasks, which are possible to be performed by young children, but unlikely to be exhibited spontaneously. Findings in typically developing preschoolers revealed that the tasks elicited more frequently imitative behaviour than non-imitative behaviour, including end-state emulation. Exploratory factor analysis on the PIPS scores of 498 typically developing preschoolers (1y-4.9y) disclosed four dimensions in the scale, labelled: goal directed versus non-goal directed procedural imitation and single versus sequential bodily imitation. PIPS scale and subscale scores have high internal consistency and demonstrate acceptable intra- and interrater reliability. Results of test-retest analysis suggest that the imitation score is stable over time. All PIPS scores are strongly related to age, suggesting that the PIPS measures core dimensions of imitation development in typically developing preschoolers. The PIPS was administered to 654 typically developing children to obtain imitation age-equivalent scores.Pervasive Developmental Disorders are neurodevelopmental disorders characterised by qualitative impairment in social interaction, communication skills and behaviour, which is restricted and repetitive. These behavioural features are manifest before the age of three years. In this dissertation the term autism spectrum disorders encompasses autistic disorder, Asperger’s disorder and Pervasive Developmental Disorder Not Otherwise Specified. Young children with autism spectrum disorders have difficulties to use and understand social-communicative gestures and facial expressions and to learn culture dependent skills. A growing body of evidence indicates imitation problems in young children with autism spectrum disorders. The main aim of our research was to investigate the nature of imitation problems in young children with autism spectrum disorders, in conjunction with their clinical utility to the diagnosis. Studies in this dissertation have addressed the question if imitation problems are broad, specific, universal and unique to autism spectrum disorders. To investigate these criteria for a core deficit, we compared imitation aptitude of school-aged children with autistic disorder with this of non-autistic controls and of preschoolers with autism spectrum disorders compared to non-autistic peers who have previously been suspected of autism. Although we found evidence of broad imitation problems in children with autism spectrum disorders, we did not find convincing evidence that these problems are specific, universal and unique to autism. We found in school-aged children with autistic disorder that gestural imitation problems may be partially explained by motor problems. In preschoolers with autism spectrum disorders, both bodily and procedural imitation retardation are to some extent part of the children’s cognitive and motor impairment. With increasing cognitive abilities, imitation problems seem to become more specific to autism. Much research has diverted towards the nature of imitation problems in young children with autism spectrum disorders. However, for the time being, conclusions regarding the underlying mechanisms of this imitation deficit are elusive. Our findings in school-aged children with autistic disorder support the notion that mainly an impaired correspondence mechanism in the visuomotor mapping system causes autism imitation problems. We found no evidence for selection problems. Tentatively we conclude that autism imitation problems rely primarily on a weak perceptual motor translation of an observed act to perform a similar act, termed as action-level imitation. We found evidence for a delayed rather than deviant development of this perceptual motor ability. This finding suggests that the primary problem relies on an impairment of the direct route of imitation. However, the finding that in preschoolers with autism spectrum disorders imitation problems are apparent regardless of the representational level of the observed actions may indicate that in the beginning both routes of imitation are involved in autism imitation problems. We speculate that the primary problem relies on an impairment of the direct route of imitation or action-level imitation and in addition, that the young child with autism spectrum disorders is not yet capable to use the indirect route of imitation or program-level imitation to overcome its motor difficulties to imitate. Consequently, the young child with autism spectrum disorders will be incapable to imitate precisely to learn implicitly through imitation the meaning and goal of an observed behaviour, which are central in culture dependent communicative gestures and specific tool use. With increasing mental age and growing experience, and probably also thanks to a huge amount of explicit information from parents and other caregivers, the child with autism spectrum disorders may recognise the content, meaning, goal of the observed actions and may develop the indirect route of imitation and accordingly program-level imitation. This problem may obviously contribute to the social impairment of young children with autism. From this point of view, the young child with autism engages less well in social interactions, joins the social dance less well, because he or she lacks the effortless, ever-present, intrinsically rewarding imitation ability and implicit learning aptitude. It is not evident to isolate a single symptom from the heterogeneous picture of social and non-social characteristics seen in autism. We conducted a cohort type diagnostic accuracy study to investigate the utility of imitation assessment for the diagnosis of autism spectrum disorders at preschool age. For this purpose, we have applied the Preschool Imitation and Praxis Scale (PIPS) in a consecutively referral group suspected of autism. We found some evidence, although no convincing one, that a procedural imitation retardation that goes beyond the children’s nonverbal mental retardation may predict the diagnosis of autism. Since these findings are new to the literature, they should be interpreted with caution until the study is replicated in other research samples and recruitment settings. At this moment, imitation assessment may primarily offer meaningful information about imitation development itself in preschoolers suspected of autism spectrum disorders. This information may provide insight in the future learning capacity of the children and accordingly their possible response to treatment.