Handedness in Childhood Autism Shows a Dissociation of Skill and Preference

Abstract

Hand preference and hand skill were assessed in 20 children with autism, 20 normal controls and 12 children with mental retardation. 90% of the normal controls and 92% of the children with mental retardation showed concordance for hand preference and hand skill (i.e. the preferred hand was also the more skillful), whereas only 50% of the children with autism showed concordance of preference and skill, the remaining 50% preferring to use the hand which was less skillful. Children with autism also showed a lesser degree of handedness and a lesser degree of consistency than the other groups, although this was unrelated to the discordance of skill and asymmetry. A developmental model of handedness is proposed in which the development of handedness as preference is ontogenetically prior to the development of handedness as skill asymmetry, such that in normal children the development of skill asymmetry occurs as a secondary consequence of the establishment of preference. The causal sequence is disrupted in autism, so that although preference is established, it does not subsequently result in concordant skill asymmetry.

Hand preference and hand skill in children with autism

“…Consistency of hand preference was calculated across all pairs of replications of each item (lst with 2nd, 2nd with 3rd, 1st with 3rd), two tasks were considered consistent only if the right hand was preferred on both occasions or the left hand was preferred on both occasions. Since in the present paper only 10 items were scored, whereas in McManus et al (1992), 13 items were scored, there are minor differences in the results shown in Table I from those reported previously. It should be noted here that since, particularly among the younger subjects, a moderate number of bilateral or mixed preferences were given, the result is that laterality scores can take any value in the range 0-100%; this is in distinction to the slightly different definition used by McManus et al (1992), where of necessity scores are constrained to the range 33-100%.…”

“…A review by Satz, Green, and Lyon (1989) estimated that AH accounts for approximately 40% of the handedness observed in individuals with autism and individuals with learning difficulties but is relatively rare in normal populations above the age of 4 years. However, in a study by McManus et al (1992), AH was significantly increased in children with autism compared to a mentally retarded control group and normal control group, even when degree of handedness, age, and mental age were taken into account. It should also be noted that differences in hand preference (be they direction, degree, or consistency) and assessed typically by reaching, should not be confused with differences in hand skill, assessed typically by a task such as the Annett Pegboard, and in which one can also assess the direction of the more skillful hand, and the degree of difference ~between the hands.…”

“…The present study consists of a development and an extension of the work of McManus et al (1992); in particular additional groups of subjects were tested and then combined with the original subjects of McManus et al (1992) to allow a more comprehensive analysis.…”

“…A third anomaly of handedness recently reported in children with autism is a dissociation between hand skill and hand preference (McManus et aL, 1992). Children with autism demonstrated a high level of discordance between hand preference and hand skill, 50% of them preferring to use the hand which was actually less skilled on the Annett Pegboard task (Annett, 1970).…”

“…AH refers to reduced consistency of hand preference within tasks (e.g., preferring to carry out task A with the right hand on one occasion and with the left hand on a second occasion), and should not be confused with reduced degree of hand preference between tasks, in which one hand is preferred for task A and the other hand preferred for task B. The two are however partially confounded statistically (McManus, 1996;McManus, Murray, Doyle, & Baron-Cohen, 1992). According to Soper et al (1986); AH is distinct from PLH and probably resuits from early bilateral hemisphere deficit rendering neither hemisphere sufficient for manual dominance.…”