it is likely that the perpetrator had secretly obtained the object sometime earlier and waited for an opportunity to fling it, even from outside the room—thus supposedly proving he or she was innocent. According to research in anomalistic psychology, claims of poltergeist activity can be explained by psychological factors such as illusion, memory lapses, and wishful thinking. A study (Lange and Houran, 1998) wrote that poltergeist experiences are delusions "resulting from the affective and cognitive dynamics of percipients' interpretation of ambiguous stimuli". Psychologist Donovan Rawcliffe has written that almost all poltergeist cases that have been investigated turned out to be based on trickery, whilst the rest are attributable to psychological factors such as hallucinations. Attempts have also been made to scientifically explain poltergeist disturbances that have not been traced to fraud or psychological factors. Skeptic and magician Milbourne Christopher found that some cases of poltergeist activity can be attributed to unusual air currents, such as a 1957 case on Cape Cod where downdrafts from an uncovered chimney became strong enough to blow a mirror off of a wall, overturn chairs and knock things off shelves. Unverified natural phenomena In the 1950s, Guy William Lambert proposed that reported poltergeist phenomena could be explained by the movement of underground water causing stress on houses. He suggested that water turbulence could cause strange sounds or structural movement of the property, possibly causing the house to vibrate and move objects. Later researchers, such as Alan Gauld and Tony Cornell, tested Lambert's hypothesis by placing specific objects in different rooms and subjecting the house to strong mechanical vibrations. They discovered that although the structure of the building had been damaged, only a few of the objects moved a very short distance. The skeptic Trevor H. Hall criticized the hypothesis claiming if it was true "the building would almost certainly fall into ruins." According to Richard Wiseman the hypothesis has not held up to scrutiny. Michael Persinger has theorized that seismic activity could cause poltergeist phenomena. However, Persinger's claims regarding the effects of environmental geomagnetic activity on paranormal experiences have not been independently replicated and, like his findings regarding the God helmet, may simply be explained by the suggestibility of participants. David Turner, a retired physical chemist, suggested that ball lightning might cause the "spooky movement of objects blamed on poltergeists." Paranormal Parapsychologists Nandor Fodor and William G. Roll suggested that poltergeist activity can be explained