At least since the time of Plato's Allegory of the Cave, humans have questioned what constitutes reality. Is it merely appearances or something else?

Walker Art Center's compelling exhibition "Lifelike" asks us to contemplate, if not dive in with abandon, the shape-shifting nature of reality. For Plato, reality was not an actual object, but some sort of essence that could only be apprehended intellectually. In "Lifelike" we not only confront objects' visual reality, but also their conceptual essence and then some.

International and multi-generational in scope, "Lifelike" -- organized by Walker curator Siri Engberg and headed to museums in New Orleans, San Diego and Austin, Texas, after its debut here -- features 90-plus works by more than 50 artists who explore ideas of verisimilitude -- what it means to make a work of art look real. In our curiosity, if not amazement, we are forced to question our assumptions about reality.

As in Alice's Wonderland, an object's scale may be too large or too small, throwing us perceptually off balance. Robert Therrien's impeccably conceived card table and chairs is large enough to walk under, while Maurizio Cattelan's untitled installation of a pair of perfectly functioning elevators is not even knee-high.

Largely shunning technology, the show includes painting, sculpture, photography, drawing and three-dimensional installations, such as Keith Edmier's "Bremen Towne," a meticulous re-creation of his childhood kitchen in suburban Chicago.

Even the videos are less about technology than a test of our observational acumen. As Thomas Demand says about his video "Rain/Regen," which masquerades as raindrops hitting the pavement, "there is nothing either wet or moving" in this video. It's a clever simulation -- a stop-motion animation of candy wrappers doubling as raindrops and frying eggs providing the sound of rain.

The ghost of Duchamp treads lightly but everywhere, whether it is his painting "Nude Descending the Staircase," seen by extension in Sam Taylor-Wood's 2001 time-based video "Still Life" of decaying fruit, or his urinal "Fountain," given ironic new life in Charles Ray's 1989 cast-iron tub "Bath," which is installed vertically into the wall, water and all.

Reality: what a concept

The show's starting point is the 1960s, a time dominated by notions of the real as evoked in Pop art, such as Warhol's 1964 "White Brillo Box" (the earliest work on view), and slick Photo Realist paintings.

But artists also were beginning to investigate the conceptual underpinnings of making work that looked real. And this is precisely the distinction that "Lifelike" makes. These works are not concerned with reproducing generic brands or critiquing contemporary culture but rather investigating the artist's conceptual motivations and the centuries-old attraction to making something that looks real.

In addition to Warhol, works by Jasper Johns, Ed Ruscha and Sylvia Plimack Mangold set the stage. Alex Hay's gargantuan 1966 "Cash Register Slip" and 1968 "Paper Bag" are objects of amazement and beauty.

From here "Lifelike" moves forward with objects made over the past four decades, some commissioned for the exhibit. There is not a loser in the bunch. On a gallery floor lays Gavin Turk's "Nomad," a blue nylon sleeping bag obviously sheltering a body. That it is painted bronze confuses our perceptual powers.

Paul Winstanley's painting "Utopia 1" depicts a stark, airless corporate interior that is so real as to be otherworldly. Gerhard Richter, a recognized trickster of the real, is represented by four works including his iconic 1982 "Candle (Kerze)."

One of the most beautiful works is Tauba Auerbach's painting "Untitled (Fold)," made specifically for "Lifelike." Auerbach folded the canvas, airbrushed it in a range of jewel-toned hues, unfolded it and touched it up, and then stretched it. The folds are real.

Another defining aspect of "Lifelike" is the elemental labor-intensive, handmade, process-driven foundation of each work. Kaz Oshiro's "Sony Bookshelf Speakers," a wall-mounted stack of speakers à la Donald Judd's minimalist boxes, are constructed from individual paintings assembled into box form.

The electrical outlets throughout the galleries are small paintings by Minnesota's David Lefkowitz. And any ashtrays, butts and all, scattered about the museum are by Minneapolis artist Ruben Nusz.

To its credit, the conceptually tight "Lifelike" never becomes didactic, clichéd or trendy. Rather, its intellectual chops nicely give balance to the visually loaded, Wonderland environment we tumble into.