Materials
A plastic doorbell button, approximately 3 inches tall, and a dome light, approximately
5 inches in diameter, were mounted on a wall in the testing room (attached with
Velcro). The objects were mounted 30 inches high so that infants could easily
manipulate them. When pressed, the doorbell button chimed through a speaker
located in the wall (triggered by the experimenter). The dome light, when pressed,
became illuminated.