Complex sentence: Sommer was influenced by his studies on environmental psychology with Dr. Humphry Osmond, a psychiatrist who researched Hallucinogens, developing the term psychedelic, and who also worked in mental hospitals researching social environments and how they affect recovery.
Split into simpler sentences: Sommer was influenced by his studies on environmental psychology with Dr. Humphry Osmond, a psychiatrist who researched Hallucinogens. Osmond developed the term psychedelic and also worked in mental hospitals researching social environments and how they affect recovery.