Psychological research on the principles of learning has most directly influenced the development of

Answer: Behaviour therapy

Explanation: Behaviour therapy based on research of learning principles is directly linked to the treatment of disorders and symptoms in patients by training patients to respond appropriately to stimuli. Such therapy has the effect of modifying the behaviour of patients because by adequately altered, therefore, trained behaviours, they respond adequately to the different range of disorders treated with this therapy, from depression through anorexia and many others. Such therapy treats or modifies behaviours in patients that are the result of or are the cause of these disorders.