Visual Arts/Reviewed: Ma, Douglas Hyde Gallery, Dublin, until July 7th (01-6081116), Vija Celmins, Douglas Hyde Gallery, Dublin, until July 7th (01-6081116), Heaven In Earth, Cross Gallery, Dublin, until June 16th (01-4738978) Rita Duffy, Hillsboro Gallery, Dublin, ends tomorrow (01-6777905)

Ma is a Japanese word that translates as "space" or "time". The exhibition of that name at the Douglas Hyde Gallery combines the disparate work of Yoshihiro Suda and Takehito Koganezawa. In fact, it is almost as if there are three artists in the show, given the further disparity between the latter's live-action and animated videos.

The live-action piece, Sex Without Sex (For Men), features pairs of men jostling and pushing each other, with that recognisable air of simmering aggression that threatens to boil over in to full-scale fighting but more often than not doesn't. It's physical and direct, and there is an obviously jokey, comical element to Koganezawa's idea, as well as something darker implied in that link between aggression and sexuality.

By comparison, his animated videos and related drawings are mellow and relaxed to the point of indolence. They subject simple, coloured, drawn forms, linear or blobbily amorphous, to movements through implied spatial expanses, forming and re-forming like cartoon baby universes - but that cosmic reference makes them sound more ambitious or involved than they are.

In the event, they're agreeable and playful but curiously slack and inconsequential, and they don't look particularly well made. To say, as the accompanying note does, that the work is linked to the idea of nothingness doesn't really help much.

It does, though, in the case of Suda, whose work has featured in the gallery before. He makes intricate, painted carved-wood sculptures of individual flowers and weeds. At least, we are told that's what they are. They are so finely done that the petals of clematis and morning glory are paper thin, and they look so convincingly real that it's hard to believe they are made of wood.

Suda plays on the tensions between perception and reality, truth and illusion. His single plants and stems seem to sprout from the massed concrete slabs of the Hyde's walls, usually incongruously but, in the case of one tiny weed, quite plausibly.

In all cases, although they are diminutive presences in proportion to the cavernous gallery, they manage to redefine, and in a sense dominate, the space around them. There is an epiphanic quality to the way these self-effacing representations compel us to look anew at ordinary things, and to look at ourselves looking. Suda's work amounts to something distinctive and valuable within the extensive field of realistic sculpture. His drawings, which also feature, are altogether consistent with his carvings.

It isn't always the case, but the show in the Hyde's small, adjacent Gallery 2 complements Ma.

Vija Celmins's five prints have a gentle, velvety softness of surface. All have a nocturnal feeling, most obviously three views of the night sky, crammed with stars and other celestial objects, but two of the images are reversed, like photographic negatives, so it's as if the points of light burn in to the plate.

The others are views of spider webs, pale linear networks against darkness. Although the prints obviously evoke space very effectively, in a very subtle way they also convey a profound sense of time.

Siobhán McDonald's paintings, in Heaven In Earth at the Cross Gallery, are better in reality than in reproduction. Although they are gestural pieces, made with great vigour and energy, they are also very subtle, built up from many layers of different media, including charcoal, ink, beeswax, marble dust and oil paint, and much of their effect depends on the overlapping and often translucent interplay of these materials.

The paintings are rooted in landscape, but in a very particular way. In their impassioned lyricism they come across as celebrating an intense bond with the earth.

The title Goddess Peak is indicative of a sacred sense of place; others, including Journey and Destination, suggest the idea of a pilgrimage. There is nothing cloying or precious about the way all this is conveyed.

The soaring, symbolic presence of a mountain is generally there. McDonald places an emphasis on that soaring. She tries to engender a sense of a physical presence that is at once substantial and ethereal, beyond and above the foreground, earthly plain, a pictorial framework used most explicitly, and very successfully, in one large piece, Earth And Man.

At times the freedom of her treatment is too loose - in a couple of the larger pieces, for example - and a picture will float away, so to speak. But she has more hits than misses.

A few years ago Rita Duffy was involved in a project at the disused women's prison in Armagh. One of the pieces she made involved using several cell doors to define an internal space, visible only through the peepholes in the doors, in which were gathered the tears of former inmates. That format dominates the work in her Hillsboro Gallery show, which is composed of mixed-media paintings.

Small windows are cut out of panels armoured with lead. These pictures within heavily textured pictures afford views in to bright interior spaces inhabited by single female, almost doll-like figures. There is a voyeuristic element to the format, yet for the most part these naked, playful figures, engaged in various workaday activities, do not come across as being incarcerated or vulnerable. Rather they seem to be brash, confident, allegorical presences set on exploring their sense of self.

The fact that the windows are often mediated by frames of stitching bolsters a benign, curative interpretation, as does the other, related work in the show.