Our contact with the world is through perception, and therefore the
study of the process is of obvious importance and signi?cance. For much
of its long history, the study of perception has been con?ned to
natural- tic observation. Nonetheless, the phenomena considered worthy
of note have not been those that nurture our survival--the veridical
features of perception--but the oddities or departures from the common
and c- monplace accuracies of perception. With the move from the natural
world to the laboratory the oddities of perception multiplied, and they
received ever more detailed scrutiny. My general intention is to examine
the interpretations of the perc- tual process and its errors throughout
history. The emphasis on errors of perception might appear to be a
narrow approach, but in fact it enc- passes virtually all perceptual
research from the ancients until the present. The constancies of
perception have been taken for granted whereas - partures from
constancies (errors or illusions) have fostered fascination.