From the Renaissance to the mid-19th century, painting evolved to mimic the appearance of things in the real world ever more convincingly. But Modernism dispensed with the requirement of imitating nature and treated paintings as objects of pure contemplation.

In Double-take: The Poetics of Illusion and Light, a lovely exhibition of painting, sculpture, photography and video at the Contemporary Museum, three artists invite us to contemplate the act of looking at artworks as an end in itself.

Before we can understand what any artwork means, we have to look at it and then interpret what we see.

Some paintings offer lots of clues: the woman in blue holding a baby is usually the Virgin Mary; the callow youth ogling three nude female deities is probably Paris of Troy, whose choice of Venus as the most beautiful led to his city's destruction; the bearded geezer hurling thunderbolts is surely Jupiter, ruler of gods and men.

But other artworks deliberately attempt to confuse us. William Hartnett's eye-deceiving still lifes of musical instruments seem so tangible it takes a minute to realize they're just painted images. Giuseppe Arcimboldo's portrait busts look like real people until you catch on that they're all clever collages of fruits, vegetables and other edibles.

So what to make of the subtle shadows of trees in Mary Temple's Southwest Corner, Northeast Light (2007)? It takes a minute to even see them when you enter the museum's darkened rear gallery, but that's not unusual; we often don't notice shadows cast by sunlight streaming through a window on an opposite wall.

Except in this case, there are no windows. Closer inspection reveals that the "shadows" are actually drawn on the wall, and the impression of sunlight filling the space around them is likewise merely a painted illusion.

Still, we've all seen such shadows before, hovering just on the edge of perceptual awareness, and it takes a deliberate act of will not to feel warmed by the "sunlight" on the wall or imagine those ghostly branches gently swaying in the breeze outside.

Here it's our memories of past experiences that are telling our eyes what to see, even though our minds know it's all a visual sleight of hand.

Bernhard Hildenbrandt's photographs of his monochrome enamel paintings, displayed side-by-side with the originals, offer a similar lesson in perceptual ambiguity.

The glossy, mirrorlike surface of Hildenbrandt's paintings reflect the outlines of nearby objects in the gallery. Normally we aren't aware of these vestigial reflections when we look at paintings.

The unblinking eye of the camera, however, sees and records everything - paintings and reflections as well as any stray beams of light bouncing around.

As a result, when a painting by Hildenbrandt and his photograph of it are placed next to each other, they seem like completely different artworks - one a pristine object rendered in a single, uniform color, the other a mad jumble of painted ground, reflected images and streaks of colored light.

Thus does the artist convince us that even when we make the effort to look carefully - as people generally do in museums - we still end up mostly seeing only what we choose to.

The show, which includes wire sculpture and custom wallpaper by Alexandra Grant, runs through May 11 at the Contemporary Museum, 100 W. Centre St. Call 410-783-5720 or go to contemporary.org. glenn.mcnatt@baltsun.com