Parapsychology refers only to the study of psychokinesis (PK) and extrasensory perception (ESP). Psychokinesis refers to the ability physically to affect objects or events by mental influence alone, known popularly as 'mind over matter'. In practice, however, the term parapsychology is often used more widely to refer to the study of any paranormal events. A milestone in parapsychological investigation was the establishment in 1935 by Joseph Banks Rhine of the Parapsychology Laboratory at Duke University. Rhine carried out studies of PK, in which subjects would attempt to influence the roll of a dice, and studies of ESP using a special pack of cards, known as a Zener pack. Rhine's early research appeared to demonstrate that subjects could perform on both ESP and PK tasks at a level far higher than could be explained simply on the basis of chance expectation.