The strength of the orienting response during Pavlovian conditioning.

The strength of orienting toward a light that signaled food was studied in five experiments. Experiment 1 demonstrated that this response declined in strength during conditioning but was temporarily restored during extinction. In Experiment 2 the light was again paired immediately with the unconditioned stimulus (US), whereas in Experiments 3 and 4 it signaled a tone which in turn signaled the US. In these three experiments we again found that continuous reinforcement resulted in a decline in the strength of light orientation. These studies also revealed that under conditions of partial reinforcement, orientation to the light was sustained. Experiment 5 demonstrated that the decline in light orientation with a continuous reinforcement procedure can be retarded either by preexposing the light for a number of trials prior to conditioning or by intermixing reinforced light trials with nonreinforced presentations of a tone. This experiment also revealed that reversing the reinforcement contingency associated with the tone restored orientation to the light. This pattern of results can be most readily explained by the proposal that the strength of orientation toward the light is inversely related to the predictive accuracy of this stimulus.