BOOK REVIEW / Invited out to lunch by little grey aliens: Abduction: Human Encounters With Aliens; John E Mack, Simon & Schuster, pounds 16.99

THEY have dark eyes like bottomless pits, and grey bodies about four feet in height, with large triangular heads bulging at the top. They have three or four fingers on each hand, at the ends of spindly arms, and they abduct humans.

John Mack, the Professor of Psychiatry at Harvard Medical School, has treated more than 80 people who believe they have been taken by aliens. Their experiences consist mostly of memories obtained under hypnosis. Reading the details of these accounts, and just as importantly the extreme emotional reactions exhibited by the patients, one can understand the professor's point of view. The physical details of the aliens and their experiments display a remarkable uniformity. The vast majority of abductees have almost identical intrusive procedures carried out on their bodies. They are wafted aboard spaceships on beams of light. The females are penetrated by metallic probes which extract something from their ovaries. The males have sperm samples taken.

Some are convinced they have parallel identities, half alien, half human. Others see evidence of a breeding program producing alien-human hybrids. Whether it is scientific prurience, alien concern for our future or a plot to take over the world is not, however, clear.

As Mack implies, all this places a strain on our credulity: 'I was dealing with a phenomenon that I felt could not be explained psychiatrically, yet was simply not possible within the framework of the Western scientific worldview.' Mack is fond of phrases such as 'ontological parameters' and magic words of para-psychobabble. Once invoked, they suspend the standard rules of scientific methodology - which is necessary if we are to accept that the aliens can make themselves and their vessels invisible to all but the abductee.

Tell-tale signs, we learn, include small wounds on the body, waking up in a position other than that in which one fell asleep, having one's pyjamas on backwards, having a headache, soreness in the genital regions, and having unaccountable memory loss. A sceptic might dismiss all this as a hangover, yet the vividness of the experience under hypnotic regression suggests something more profound.

Memories elicited in this manner, however, are by no means universally accepted as genuine. Mack counters the 'critics and sceptics': such experimentally induced false memories, he says, related to 'events that were of peripheral significance to the subject'. Abductees, however, 'are highly motivated to remember accurately intense occurrences that are of the most vital importance to them.' They are true because they are important. They are important because they are true. Yet many, if not all, of the patients underwent their hypnosis sessions after some weeks at abductees' support groups. It is scarcely surprising that their accounts tally.

The science fiction of alien abduction has become a new religion available to anyone doubting the meaningfulness of life. But the hypothesis is not supportable by either science or logic. The aliens can walk through walls and carry people through buildings on light beams, yet they still need crude and painful methods of incision to extract samples. They can erase conscious memories, yet forget about the deep memories that may be elicited under hypnosis. Sloppy work, chaps.

This is a deeply disturbing book, not for its implications about the motivations of beings from another dimension, but for the view it provides of one aspect of psychiatry. Believe it if you like, but I'm afraid this all belongs in a world where the ontological pigs are unrestrained by a non-flying parameter.