My first class Freshman year of college we were given a lengthy speech by our professor. His forty minute speech basically summarized how difficult earning his doctorate in archaeology was and that it would be highly inappropriate to belittle this by calling him "Professor Lastname." This scared me into calling all of my professors (with doctorates) Dr. and those who I were not sure had their doctorates or not or only had masters, I always called Professor just to be safe. Three years later, I'm horrified to learn that Professor is considered a higher distinction. Granted, I am a Psychology student, so the majority of my professors are clinical psychologists and are referred to as "Dr." not only in their academic circles, but sometimes by patients as well. (Although the psych profs who have been in their field awhile actually introduce themselves by their first names.... and Ive never had a therapist insist I use Dr. Lastname.)
Going by the rules in the States, because I know the UK has different rules, how should I address my professors with doctorates?
It may be important to note that we still have full-time, non-adjunct professors at my university with masters degrees.