Final answer:
A behaviorist psychologist studies observable actions by focusing on direct, measurable behaviors and often uses conditioning principles for research.
Step-by-step explanation:
The type of psychologist who studies observable actions is known as a behaviorist psychologist. Behaviorist psychologists, like Ivan Pavlov and John B. Watson, focus on studying behaviors that can be directly seen and measured. They emphasize objective, observable environmental influences on overt behavior, and they often utilize principles such as conditioning to understand the learning process. This field contrasts with areas like cognitive psychology, which involves the study of mental processes and inner experiences.