Self-paced vs. externally paced motor tracking by retarded and nonretarded persons.

An expectancy hypothesis of the psychological refractory period (PRP) was tested as an alternative to an arousal hypothesis to explain retarded persons' longer reaction times. Retarded adolescents, CA-matched nonretarded adolescents, and MA-matched nonretarded children tracked light stimuli presented under self-paced and externally paced conditions. Response latencies under both conditions were longer for the retarded and MA-matched groups, and all groups decreased latencies from the self-paced to externally paced conditions. Neither hypothesis was supported. We suggested that group differences were due to differences in the central delay effect of the PRP.