Spiritus, at the Douglas Hyde Gallery, is a thematic group show from Sweden, writes Aidan Dunne.

It is by no means exclusively Scandinavian, featuring pieces by nine international contemporary artists and a documentary strand. This strand consists of a disparate group of photographs of seances, dating from the early 20th century, together with a report on a seance from a 1928 issue of the International Psychic Gazette and an essay by Marina Warner. She writes about the strange phenomenon of ectoplasm, a supposedly other-worldly substance sometimes produced during mediumistic trances. It features in several of the photographs. All of which sets the thematic agenda and, presumably, provides a comparative context of some kind within which to view the contemporary work.

Except that, having jump-started the project with this intriguing and very specific idea, the curators decide that they are going to broaden things out considerably when it comes to their selection of present-day artists.

"Spiritus," they write, "addresses altered states of consciousness, ecstasy, rituals and parallel worlds . . . Our aim has been to display work that relates to the exhibition's thematic on an associative rather than illustrative level."

But, flexibly interpreted, pretty much any contemporary work could be bundled into that particular box.

As it happens, there is an Irish artist, Susan McWilliam, who has made a sizeable body of strong work, mostly in the form of film or video installation, that is not just thematically relevant in a vague, associative sense, but directly and, dare one say, almost uncannily relevant to Spiritus. So much so that if you are familiar with those particular pieces of hers the show comes to seem haunted by their absence.

Not that Spiritus is bad, as group shows go; it's actually very good. The one real disappointment is that Ann Veronica Janssen's Blue, Red and Yellow, a small room that promises to disorientate you with a little help from a smoke machine, is out of order and looks a bit sad, a big plastic cube parked in a corner of the gallery like a broken toy. Otherwise there is a diverting and, on occasion, modestly interactive mix.

The documentary images are extraordinary. They come across as being clumsily staged and obviously unreal. But the vogue for occult phenomena drew in all sorts of notionally reasonable and rational people, and seances dependent on third-rate conjuring tricks were observed with a kind of pompous, mock-scientific rigour and an apparent absence of common sense. Not that we can afford to feel superior when it comes to levels of credulity.

What comes across from Warner's essay is not only the willed self-delusion involved, the desperate desire to believe that something paranormal was really going on. There was also the disturbing obsession with monitoring the mediums, and with ectoplasm, this pliable, amorphous stuff - synthetic lining material, Warner rather anticlimactically reports in the case of a preserved sample - issuing from the various orifices of mediums' bodies. All of which related to an anxiety about maintaining control of women's bodies and, further, anxiety over what might be going on in women's heads.

Mutaflor, by the Swiss artist, Pipilotti Rist, known for her snappy, upbeat videos, takes us on a fast, vivid, roller-coaster ride through her own body, plunging into her mouth and tearing through the highways and byways of her digestive system and out again.

Perhaps there is a correspondence between ectoplasm and the vicarious body fluids that Paul McCarthy employs to such effect in his pantomime of domestic abuse. A demented cross between a cookery programme and a psychotic soap opera, what makes it really disturbing, as with most of his work, is that McCarthy, apparently fallen into a trance-like state, just keeps on going, muttering away to himself.

Others, including Ceal Floyer and Marine Hugonnier, aim to capture a more subtle sense of the uncanny, the former with her evocation of a space beyond a doorway, the latter with a candle that anticipates its own extinction - a little too subtle, perhaps.

There is also an uncanny quality to Carsten Holler's stroll through a forest, but not enough of one. Mention of The Blair Witch Project as a point of comparison merely underlines that fact that his effort really just peters out inconsequentially.

Dan Graham's Rock My Religion is a self- indulgently long, rambling, but still compelling documentary, an exercise in analogy that parallels the ecstatic rituals of American puritanical religious movements with the logically antithetical abandonment that characterises rock 'n' roll and the 1960s youth movement. There is cringe-making footage of people being very silly indeed under the influence of chemical stimulants and rock music.

Sigalit Landau seems to refer to ecstatic religious rituals involving pain and blood- letting in her video, Barbed Hula. As the title suggests she literally twirls a hula-hoop fashioned from barbed wire, apparently oblivious to the way it cuts into her flesh. But as the camera zooms in we become aware that her "wounds" are actually cosmetic.

You can lie down on Doug Aitken's wooden platform and feel the amplified reverberations of someone breathing, which can be a bit disconcerting. But then the least you can expect from a show with altered states of consciousness on its agenda is that it will be disconcerting.

Runs until August 2nd.