In 1970, the physicist David Simpson and his colleague Norman Foxwell performed an experiment involving a group of UFO buffs in England. On a Saturday evening about thirty of these individuals had gathered on a remote hilltop where they thought there was a good chance of sighting a UFO. Simpson positioned himself on another hilltop, about three-quarters of a mile away, and he pointed a purple spotlight, connected to a 12-volt battery, in the direction of the group. At 11:00 p.m. he switched on the light for 5 seconds, and after a 5-second pause he switched it on again for 25 seconds. Mr. Foxwell, Simpson's accomplice, was stationed among the observers, and to enhance the emotional effect, shortly after the purple light was sighted, Foxwell switched on a buzzer that was attached to a bogus magnetic-field sensor. According to UFO lore, UFOs are supposed to generate intense magnetic fields, so the buzzer signaled to the crowd that a UFO was operating nearby. To further enhance the effect, Foxwell had loaded a camera with a roll of film, two frames of which had been doctored with a fake latent image of a UFO. Foxwell proceeded to take two additional snapshots in the general direction of the purple light (which by then had been turned off), and he then gave the film to one of the members of the group for processing.

When the film was developed, sure enough, a tiny image of what appeared to be a UFO was visible on two frames. But those two frames (which were taken a year earlier) also contained geographic features that were inconsistent with the other two (genuine) frames. These inconsistencies were so glaring that anyone who examined all four frames closely would detect that at least two of them had been faked. However, when the photographs were examined in the laboratory of the Flying Saucer Review, an international publication devoted to UFO sightings, the experts announced that the negatives were "genuine beyond all doubt." Later, the director of research at the Astrophysical Institute of the French National Centre for Scientific Research published a "tentative interpretation" of the photographs, stating "In my opinion there is no question of the object photographed being in any possible way the result of faking."

Four months after the sighting, a report of the incident was published in the Flying Saucer Review. As you read the following selection from the report, remember that the purple light was turned on for a total of 30 seconds, that it was absolutely stationary, and that it was located on the horizon, at zero degrees of elevation from the observers:

At 11:02 P.M. an object was seen at an elevation of approximately 20 degrees in the eastern sky. The object appeared very suddenly as if it came through the clouds, and appeared to the eye as a very bright ovoid light-purple in colour with a periphery of white. Two members of my group who observed the object through binoculars both remarked they could see a crimson light in the centre; this was also attested to by witnesses with good vision.

The object remained stationary for approximately 30 seconds, during which time Mr. Foxwell was able to take the first of his photographs. The object then moved slowly to the right-towards the town-and lost a little altitude in the process. At one stage in the movement it dimmed considerably as though obscured by a low cloud. The object continued moving for approximately 20 to 30 seconds, and then stopped again. The light then increased considerably in intensity, though we could not be sure if the object was moving directly toward the observation point, or if it remained stationary. At this point the alarm of a detector sounded and a witness ran to switch it off. After 10 to 20 seconds the light dimmed and went out as though concealed by a cloud. However we were all certain that the object had not moved once more. The sighting had lasted for approximately one to one and a half minutes.

Why do you think the observers saw the purple light move? Was it because they associated the light with the faked UFO images (the second of which appeared slightly below and to the right of the first)? Why did the observers see the light as elevated 20 degrees off the horizon? (The faked UFO images appeared approximately on the horizon.) Do you think that the expectations of the observers affected what they reportedly saw? Do you think that confabulation played a role in the report? How about the autokinetic effect? Or perceptual sets? Why do you think the specialists who examined the photographs failed to detect the inconsistencies? Could emotions have played a role in this oversight? (From "A Controlled UFO Hoax: Some Lessons," by David I. Simpson, in Frazier, 1981.)