This was published in 1964. What is interesting is an earlier 1962 study by Oscar Janiger on 194 people from the general public without religious setting or strong interest in religion/spirituality, found that only 24% had religious experiences, revealing the importance of "set and setting".

Timothy Leary had a similar study of 69 religious professionals in a religious setting, finding that three fourths of them had religious experiences.

Thats the Superman curl :)

William Richards, in Sacred Knowledge, points out the tendency for people to have mystical experiences in forms from outside their religious traditions, occasionally ones that are unknown to them. I had a client who saw God as a bird, and weeks later recognized it as Horus - the Egyptian deity.