The rules for the task were as follows: Immediately after the experimenter tapped once with a wooden dowel (22.5 cm long, 2.5 cm in diameter), the child was to tap twice with the dowel. Immediately after the experimenter tapped twice, the child was to tap once.
Each session consisted of a pseudorandom series of 16 trials; each trial was composed of the experimenter’s tap(s) and the subject’s response. The experimenter tapped, then handed the dowel to the child for a response, after which the child returned the dowel to the experimenter. Experimenters were carefully trained to avoid influencing the child’s response by reaching for the dowel too early or by leaving it with the child too long. For example, experimenters were trained not to reach too quickly after a response of one tap in case the child might tap again. We used only one dowel for both the experimenter and child so that neither the child nor experimenter would begin tapping before the other had finished. (author abstract)