Researchers have found that Parkinson's disease is related to deficiencies in the production of...?

All of them would for different reasons depending on their individual field of study. In the case of experimental and physiological, that information would be critical to the development of new drugs and different ways to understand the underlying components of the disease. Clinical psychologists would want to know this to refer to psychiatrists who can write appropriate prescriptions and know how best to counsel their clients with Parkinson's on disease management and coping mechanisms. Psychometric psychologists would find a way to measure psychological dysfunction because of the Parkinson's and use it to measure rate of decline. If I had to choose one, though, it would be most helpful for the experimental psychologist who would need more specific biochemical information to aid their research.