Visual Arts: Aidan Dunnereviews Dark Portraits by John Gerrard, The Garden Room & New Landscapes by Jacqueline Stanley, The Anatomy of Territory by Leonard Sheil and Threshold by Siobhan McDonald

• Dark Portraits John Gerrard, Royal Hibernian Academy until Jan 7 (01-6612558)
• The Garden Room & New Landscapes Jacqueline Stanley, Hallward Gallery until Dec 6 (01-6621482)
• The Anatomy of Territory, Leonard Sheil, Paul Kane Gallery until Dec 2 (087-6478423)
• Threshold Siobhan McDonald, Cross Gallery until Dec 2 (01-4738978)

John Gerrard's work usually attracts intense interest from viewers, and Dark Portraits at the Royal Hibernian Academy - the show occupies all three galleries there - should be no exception. Gerrard, who was born in Dublin and is in his early 30s, makes "virtual sculptures", using digital technologies with remarkable flair and proficiency. Numerous artists routinely use elements of the vast arsenal of imaging technologies now available, but most of them do so in a fairly routine, passive way. The technology gives an impression of competence even when none is there. In this context it's worth pointing out that Gerrard is very, very good at using technology to his own ends, and his technical abilities are such that he operates at the edges of what is possible.

One problem with work that foregrounds technology is that technical effects can become an end in themselves and eclipse other considerations. In the field of video art, the pre-eminent example of someone who has managed to combine cutting edge technology with challenging content is Bill Viola, though opinion is sharply divided about the direction his work has taken over the last 10 years or so.

Viola is a valid point of reference for Gerrard. The work of both is characterised by an almost startling level of visual clarity, an enhanced reality. But this interest in outward appearances is balanced by a concern for inner life and imperceptible transformations.

The Dark Portraits are but one element of the RHA show. These intense portrait images are made by placing their subjects in a darkened room. Illuminated and photographed without warning, the individuals are captured as if in a space apart. As a strategy for getting around the strictures of conventional portraiture, it is very effective, and though it does recall Rineke Dijkstra's various approaches to exactly the same problem, Gerrard's images are really compelling and convincing. His concern with building in real-time change is evident in another portrait piece, a profile programmed to smile once a year.

Two large-scale projected video installations take up a gallery apiece. Smoke Tree is, as the title implies, an endless, circular tracking shot around the central image of an oak tree, its foliage continually transforming itself into smoke: a portrait of a carbon footprint? It's a close-to-biblical image that allows several lines of interpretation, and it is hypnotically engaging, as is the extraordinary One Thousand Year Dawn, in which a man stands at the edge of the sea as the sun rises.

The water laps at the sand, but otherwise the scene is perfectly, eerily still. Yet not quite - we are told the slowed-down sunrise will be completed a thousand years hence. As with a great deal of contemporary photographic and video art, Gerrard's work is clearly related to aspects of painting. He very successfully uses the possibilities of a new technological era to incorporate not only movement but also the controlled use of time and change in ways that are intriguing and provocative. His work must be seen at first hand and you should grab this opportunity to do so.

Jacqueline Stanley's The Garden Room & New Landscapes at the Hallward Gallery is an outstanding, spirited show.

Drawing is the backbone of Stanley's art. Her compositions are object lessons in the use of line as a means to highly energized, rhythmic patterning, and there is tremendous verve and attack in this body of work, which actually encompasses a broad range of subject matter, all related to landscape in one way or another. It includes tributes to the late Christopher Lloyd in studies of his garden at Great Dixter, many fine accounts of the west Cork coastline, luxuriant blue pools and sinuous descriptions of bare winter vegetation.

Just as her line abstracts, making clear the underlying structure and trend of things, so too her colour is lifted out of a naturalistic register in the interests of conveying a heightened sense of a scene.

There is perhaps a darker note running through the work in this show than usual. From the elegiac nod towards Lloyd to a schematic rendering of a calamitous lightning strike at a copper mine, or Winter grass with hawk, which recalls Tony O'Malley's tribute to Peter Lanyon after his death in a gliding accident, or the magpies scavenging in a winter garden - a certain ominous or foreboding quality is evident. Enjoyable overall, many of the individual works in the show are real gems.

Both Leonard Sheil and Siobhan McDonald are textural painters. In much of the work in The Anatomy of Territory at the Paul Kane Gallery, Sheil moves inland from his usual source of inspiration, the sea. Largely based on residencies in Austria, the paintings draw on the idea of the Danube working its way eastwards.

The rigorous cut and thrust of the layered paintings equate to the processes of flow and erosion that mark the interaction of land and water, together with the huge degree of human input that is a feature of Europe's great rivers. Sheil throws himself into the process with exemplary commitment, and most of the paintings have a rugged, durable quality, as though they have been weathered and aged into their configurations by natural forces. Striking a different note, with their intense colour and boxlike format, a few pieces incongruously suggest the influence of Howard Hodgkin.

McDonald's work in Threshold is based on landscape, but always with an eye to both atmospherics and metaphysics. It is as if each painting builds towards a state of epiphany and transcendence. Waves of energy wash across the picture surface in successive layers until a point of buoyant equilibrium is reached.

Sometimes, however, it is as if the pictures are not pushed as far as they might be. A certain air of contrivance creeps in, as though McDonald is holding back, being overly cautious, not following the logic of the painting process. Often a particular piece will feature substantial passages of lovely painting only to end up being tied too neatly into a pictorial package.