Answer:
D. fixed-ratio; variable-ratio.
Explanation:
In Operant Conditioning, the highest rates of responding occurred when rats reinforced for pressing a bar were placed on fixed-ratio and variable-ratio schedules of reinforcement. A fixed-ratio schedule, is reinforcement after a set number of responses have been provided. In the fixed-ratio schedule, the reward is predictable and produces high levels of responses. In the variable-ratio schedule, the reinforcement is provided after a varying set of responses. The reward is unpredictable and it produces a steady rate of responses.
