Food-deprived golden hamsters in a large enclosure received food every 30 sec contingent on lever pressing, or free while their behavior was continuously recorded in terms of an exhaustive classification of motor patterns. As with other species in other situations, behavior became organized into two main classes. One (terminal behaviors) increased in probability throughout interfood intervals; the other (interim behaviors) peaked earlier in interfood intervals. Which class an activity belonged to was independent of whether food was contingent on lever pressing. When food was omitted on some of the intervals (thwarting), the terminal activities began sooner in the next interval, and different interim activities changed in different ways. The interim activities did not appear to be schedule-induced in the usual sense. Rather, the hamsters left the area of the feeder when food was not due and engaged in activities they would normally perform in the experimental environment.
