Final answer:
The detailed observations of a man with synesthesia would constitute a case study in psychological research, providing significant insights into this unique condition but with limited ability to generalize the findings.
Step-by-step explanation:
The type of research that involves detailed observations of the abilities and behaviors of a man with synesthesia is a case study. This method is similar to the approach taken by Sigmund Freud in developing his theory of human personality. In psychology, case studies allow researchers to collect a wealth of information about a unique individual or a small group of people. This approach, however, has the limitation of difficulty in generalizing the findings to a larger population due to the specificity and rarity of the cases observed.
Observational study is a broader term for nonexperimental research where the investigator records naturally occurring behaviors without manipulation or intervention. Naturalistic observation is a specific type of observational study that requires recording behavior in its natural setting, and while it provides honest data in a realistic environment, the subjects might not behave naturally if they are aware they are being observed.