Knowledge of results and counting of sequential light flashes by retarded and intellectually normal children

12 adolescent retarded boys and 12 younger third-grade boys of equivalent mental age observed sequential flashes of light and made judgements of numerosity. Durations of successive flashes were 300, 500, 700, and 900 msec. in trains of 1 to 15 flashes. Over six daily sessions, subgroups receiving information about accuracy after each trial made fewer errors, and subgroups receiving none made more errors. The linear trend interaction of knowledge of results with IQ was significant, with performance of the nonretarded boys decreasing to the level of the retarded boys in the no-feedback condition. With feedback, the rate of decrease in error over sessions was similiar for both levels of IQ. The results indicate a substantial effect of knowledge of results in improving accuracy of counting by retarded and nonretarded children, this effect being relatively greater for the latter group.