Techniquely its possiblle though hard it might be.
Actully the basic requirements for a PhD. in certain area differ from school to school. But you have to pass the test on that subject at least.
this is the admission requirements of Graduate study in Psychology for the univerisity of Columbia in New York.
http://www.columbia.edu/cu/psycholog...plication.html
hope it helps.
p.s
checking out that kind of information on the official website of a univerisity is really tough work
take it easy lol