Intra-Individual Variability of Normal and Educable Mentally Retarded Children on a Coincidence Timing Task

A visual coincidence timing task was used to compare the level of performance (constant error) and the intra-individual variability of 100 normal and 100 educable mentally retarded children. The mean performance of the intellectually normal children on this task was significantly superior to that of the retarded children, and the intra-individual variability of the latter was significantly greater than that of the former. The hypothesis that high intra-individual variability and depressed level of performance are closely associated was not supported.