Rat's anticipation of diurnal and a-diurnal feeding.

Rats, confined either to Skinner boxes or to activity wheels, were fed at regularly scheduled feeding times which were either diurnal, i.e., every 24 hr., or a-diurnal, i.e., every 19 or 29 hr. Even though the a-diurnal Ss had been born, reared, and tested under 19or 29-hr, schedules to provide further support for the anticipation of feeding, they failed to show such an effect. The fact that the diurnal Ss showed both increased running and increased bar pressing in the hours just before feeding indicates that when such an anticipation occurs, it is governed by a 24-hr, biological clock rather than being based upon deprivation produced stimuli.