Arts exposes one to different kinds of social sciences like sociology,anthropology,history,philosophy,economics,psychology etc.
While selecting a major subject for your final year you need to delve deeper into the subjects that you have studied in 12th, and get as much as information about the various careers that the subject has to offer. You can also talk to various professionals inorder to get first-hand information on the industry.
While you say that psychology is one of the subject that interests you the most, you can log on to
http://www.youngbuzz.com/careers/careerdetail/psychologist-career for more information on the career,its scope, prospectus, remuneration, opportunities etc.
This will surely help.