What process involves reducing sensitivity to stimuli over time?

Desensitization is a process aimed at gradually reducing an individual's sensitivity to certain stimuli through controlled exposure over time. This technique is commonly used in a Fear Free framework to help animals that exhibit anxiety or fear responses to various triggers, such as veterinary visits or specific handling procedures. By presenting the stimulus at a low intensity that does not elicit a fearful response, and gradually increasing the intensity while pairing it with positive reinforcement, the animal learns to associate the once frightening stimulus with positive experiences. This approach effectively helps in building the animal's tolerance and confidence in the presence of previously feared situations.

In contrast, reinforcement refers to the process of encouraging or increasing certain behaviors through rewards but does not specifically focus on the gradual reduction of fear or sensitivity. Conditioning involves learning associations between stimuli but encompasses a wider range of learning processes beyond just desensitization. Negative CER (Conditioned Emotional Response) specifically relates to reducing negative emotions but lacks the defined structure of gradual exposure that desensitization provides. Thus, desensitization is distinctly tailored to systematically lessen sensitivity to stimuli, making it the correct answer.