The legendary American-Hungarian stage magician and escape artist Harry Houdini (1874–1926) was hostile to spiritualism, and wrote books about his debunking of mediums. 

James Houran is an American psychologist and parapsychologist whose research interests include the study of transliminality, ghostly phenomena and paranormal belief.  

Anthropologist, writer and teacher, with particular research interests in mediumship and trance phenomena. He is author of Greening the Paranormal (2019) and editor of Paranthropology

American psychologist, amateur magician and leading critic of parapsychology, co-founder of the Committee for the Scientific Inquiry (CSI).

James Hervey Hyslop (1854-1920) was a professor of philosophy, a psychologist, and, during the last fifteen years of his life, a dedicated psychical researcher.

Irish journalist, author and broadcaster (1916-1993), whose many published works include books about psychical research.

Robert Jahn was a plasma physicist who made notable contributions to the science of rocket propulsion and founded  the PEAR anomalies research laboratory, specializing in the study of mind-machine interaction.

The American philosopher and psychologist William James (1842-1910) is one of the most eminent academic figures to have been involved in psi research.

CEM Joad  (1891-1953) was a British philosopher and television personality with an active interest in psychical research.

Cambridge zoologist (1860-1940) who played a significant role as researcher and administrator in the early years of the Society for Psychical Research.