Relation between self-paced and synchronized movement in persons with mental retardation

The relation between self-paced and synchronized tapping in 64 persons with mental retardation whose mental ages ranged from 2 to 11 years and chronological ages from 13 to 23 years was investigated. In a self-paced tapping task no stimulus was presented, and subjects' easy and spontaneous tapping was measured. In a synchronized tapping task their synchronous tapping with an auditory stimulus present at a quick or slow tempo was measured. Under both tempo conditions, the lower the subjects' mental age, the larger the errors in the intertap interval they made. The subjects of low mental age showed significantly larger errors in the intertap interval in the Slow than in the Quick Tempo condition and tended to tap at a rate near the self-paced tapping. These results may suggest that ability to adjust one's self pace is one of the key factors in the development of motor synchronization in persons with mental retardation.