Capsule reviews of current area art exhibitions.    Lifeboxes --
Keep in mind one phrase when viewing this enigmatic but powerful
exhibit by Cleveland artist Susan Umbenhour: "politics of
space." That's the key to these heavily conceptual wooden
"sketches" and sculptures, most of which underscore the subtly
discriminatory effects of everyday architecture. Mother of a
child with cerebral palsy, Umbenhour is keenly attuned to
inconsiderate design, to structures like stairways and narrow
aisles that assist the able-bodied but impede the physically
handicapped. Similarly, she also objects to gated communities,
whose borders warmly envelop some but exclude most others.
Regarding the first topic, Umbenhour flips the tables in four
sinuous, smooth, paper-thin cutouts of birch and maple
blueprints that, if realized in three dimensions, would
crystallize the matter for everyone. One, called "Closed
Seating," would be accessible only by the able-bodied, while the
others would cater primarily to the wheelchair-bound. A