Timing of bimanual rhythmic finger tapping in adolescents with mental retardation or autism

An experiment was conducted to examine timing control of bimanual rhythmic finger-tapping sequences in adolescents with mental retardation or autism. Firstly, we examined the serial information processing of bimanual alternating finger-tapping sequences (required intertap intervals of 200, 400 and 800ms). At the shorter target intervals of 200 and 400ms, strong negative correlations between adjacent between-hand intervals were observed for adolescents with autism or mental retardation, suggesting that this might be accounted for by two coupled Wing-Kristofferson timing systems with left and right clock intervals kept in appropriate relative phase by corrections involving the previously preceding produced intervals. While the group with autism made faster tapping movements than the normal group over the three conditions, the group with mental retardation produced faster tapping movements than the other two groups only in the 800ms condition. This indicated that while adolescents with mental retardation or autism appeared to produce two taps with alternate hands as a chunk, they were unable to spontaneously reproduce the required target intertap intervals. Next, we examined the motor organisation strategy adopted by participants in a bimanual finger-tapping task of a 3:2 polyrhythm. Because strong negative correlations between between-hand taps were observed for participants with mental retardation, and further, their slow-hand movements were subordinate to the movements of the fast hand, they adopted a hierarchical integrated organisation.