Preschool, second-, and sixth-grade children performed developmentally gradated, easy and difficult visual discrimination tasks in a quiet room or with one of two levels of extraneous auditory stimulation. Subjects' errors, response latencies, and glances away from the task were recorded. (Author/RH)

In recent research, two qualitatively different classes of mental operations have been identified. The performance of one type of cognitive task requires attention, in the sense of mental effort, for its execution, while the second type can be performed automatically, independent of attentional control. Further research has shown that automatic…