The performance of human infants on a measure of frontal cortex function, the delayed response task

The Delayed Response task is the best-established marker of frontal lobe function in nonhuman primates. This article reports the developmental progression of human infants on that task. It is proposed that maturation of prefrontal cortex may make possible these age-related improvements in Delayed Response performance. This would suggest the importance of prefrontal cortex functioning very early in life. Twelve infants (6 male, 6 female) were tested longitudinally every two weeks from 6-12 months of age. Another 36 infants (18 male, 18 female) were tested only once: 12 each at 8, 10, and 12 months. We predicted that infants would improve on Delayed Response over these ages because infants' performance on AB improves during this time, and Delayed Response is very similar to AB. The AB task, devised by Piaget, is used to study cognitive development in infants. The ages over which AB performance improves are well established. In both AB and Delayed Response, the subject watches as the experimenter hides a desired object in one of two identical wells. After a brief delay, the subject is allowed to reach. In AB, the object is hidden in the same well on subsequent trials until the subject reaches to the correct well; then side of hiding is reversed and the procedure repeated. In Delayed Response, side of hiding is varied randomly over trials. In the present study of Delayed Response each testing session consisted of 16 trials (eight to the right, eight to the left). We found: (1) the developmental progression for Delayed Response is almost identical to that for AB. (2) Infants of 7 1/2-9 months fail Delayed Response under the same conditions and in the same ways as do monkeys with lesions of dorsolateral prefrontal cortex. It is therefore suggested that AB and Delayed Response require the same cognitive abilities, and that improved performance on these tasks provides an index of maturation of frontal cortex function.