Hand preferences in sign-learning students with autistic disorder

Can cerebral lateralisation explain heterogeneity in language and increased non-right handedness in autism? A literature review

BACKGROUND

Autism is characterised by phenotypic variability, particularly in the domains of language and handedness. However, the source of this heterogeneity is currently unclear.

AIMS

To synthesise findings regarding the relationship between language, handedness, and cerebral lateralisation in autistic people and consider how future research should be conducted in order to progress our understanding of phenotypic variability.

METHODS AND PROCEDURES

Following a literature search and selection process, 19 papers were included in this literature review. Studies using behavioural, structural, and functional measures of lateralisation are reviewed.

OUTCOMES AND RESULTS

The studies reviewed provided consistent evidence of differential cerebral lateralisation in autistic people, and this appears to be related to between-group differences in language. Evidence relating this to handedness was less consistent. Many of the studies did not include heterogeneous samples, and/or did not specify the language process they investigated.

CONCLUSIONS AND IMPLICATIONS

This review suggests that further research is needed to fully understand the relationship between cerebral lateralisation and phenotypic variability within autism. It is crucial that future studies in this area include heterogeneous samples, specify the language process they are investigating, and consider taking developmental trajectories into account.

Learning an Embodied Visual Language: Four Imitation Strategies Available to Sign Learners

The parts of the body that are used to produce and perceive signed languages (the hands, face, and visual system) differ from those used to produce and perceive spoken languages (the vocal tract and auditory system). In this paper we address two factors that have important consequences for sign language acquisition. First, there are three types of lexical signs: one-handed, two-handed symmetrical, and two-handed asymmetrical. Natural variation in hand dominance in the population leads to varied input to children learning sign. Children must learn that signs are not specified for the right or left hand but for dominant and non-dominant. Second, we posit that children have at least four imitation strategies available for imitating signs: anatomical (Activate the same muscles as the sign model), which could lead learners to inappropriately use their non-dominant hand; mirroring (Produce a mirror image of the modeled sign), which could lead learners to produce lateral movement reversal errors or to use the non-dominant hand; visual matching (Reproduce what you see from your perspective), which could lead learners to produce inward–outward movement and palm orientation reversals; and reversing (Reproduce what the sign model would see from his/her perspective). This last strategy is the only one that always yields correct phonological forms in signed languages. To test our hypotheses, we turn to evidence from typical and atypical hearing and deaf children as well as from typical adults; the data come from studies of both sign acquisition and gesture imitation. Specifically, we posit that all children initially use a visual matching strategy but typical children switch to a mirroring strategy sometime in the second year of life; typical adults tend to use a mirroring strategy in learning signs and imitating gestures. By contrast, children and adults with autism spectrum disorder (ASD) appear to use the visual matching strategy well into childhood or even adulthood. Finally, we present evidence that sign language exposure changes how adults imitate gestures, switching from a mirroring strategy to the correct reversal strategy. These four strategies for imitation do not exist in speech and as such constitute a unique problem for research in language acquisition.