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Tests of handedness were carried out with 34 autistic children aged from 4 years 10 months to 18 years 11 months, and with sex-, age-, and IQ-matched retardates and sex- and age-matched normals. There were no significant differences between the groups on frequency of handedness, degree of righthand usage, or degree of dominant-hand usage. There was however a significant increase in the variance of dominant-hand usage from normals and retardates to autistics. These results were taken to indicate that earlier reports of handedness differences in young autistic children may reflect a developmental lag rather than a specific etiology of autism. Some support for this hypothesis was found from a comparison of age-trends between the groups. The relationship of such a developmental delay to the etiology of autism was discussed.

Experiment 1 examined changes in respiratory period, peripheral pulse amplitude and cephalic pulse amplitude in autistic, retarded and normal children as a function of stimulus novelty. The respiratory measure showed habituation in the retardates and normals but not in the autistic group. Measures of peripheral and cephalic pulse amplitude showed no habituation in any group, but a higher mean response level for autistics. Autistic children thus differed from both retarded and normal children in two respects: a failure to habituate phasic respiratory responses, and enhanced response magnitude in the vascular systems. This experiment was replicated using groups of preschool children and university students. Results indicated significant age effects in the vascular systems, with preschoolers showing enhanced response magnitude. It was thus argued that autistics may display a general developmental lag in phasic vascular response measures, and an additional specific deficit indicated by failure to habituate respiratory responses. The implications of these group differences were discussed in relation to the etiology of autistic psychopathology.