Answer: Relying mostly on animal ( excluding humans) subjects whose experience can be controlled.
Explanation: the behaviour of all animals can be controlled, when we study and observe what tends to cause that behaviour. Using the cause to cure. But human behaviour is always more difficult when compared to other animals, because humans tend to have a more developed brain. Our experience in life always seems to control our behaviour. But with the study of animal behaviours, how past experience plays a significant role, and how it can be controlled from prior experience, it has been easy for phycologist to control humans behaviour from prior experience.
Using dog as a case study: Ring a bell and give the dog food, when you repeat that many times, when ever the dog hears the sound of a bell he will start salivating for food. But to control this, ring the bell and flog the dog, repeat this many times, when ever the dog hears the sound of a bell he will hide, to avoid being floged. The same approach has been used to control humans behaviour from prior experience.
