Mark Swidler. ‘30 Styrofoam Cups’ (detail), 1990s; styrofoam cups. Private Collection. (Jill Fannon)

True visionaries need no explanation. This seems to be the main message behind “All Things Round: Galaxies, Eyeballs & Karma,” the 17th annual themed exhibition at the American Visionary Museum in Baltimore. It’s a show that’s chockablock with jaw-dropping oddities created by artists from all over the world, using all manner of unlikely materials. It’s visually dense, but light on continuity and context. Visitors should expect to be wowed and bewildered in equal measure.

In their relentless pursuit of singular weirdness, AVM director and founder Rebecca Hoffberger and co-curator Mary Ellen Veh­low have cast a wide net, pulling in artists with wildly different backgrounds and working methods. “All Things Round” includes pieces made from vacuum tubes, toothpicks, embroidered sock thread, melted plastic, paper plates, bottle caps and plastic foam cups. Objects here range in age from about 1200 years to less than 6 months old and are hung floor-to-ceiling and cheek-to-jowl against brightly colored walls. Never mind the white cube environment of most art museums: The Visionary Museum cultivates a distinctive fun-house-meets-cabinet-of-curiosities aesthetic.

One wall in the show’s first room features pencil drawings created circa World War I by seminal Swiss outsider artist (and institutionalized psychotic) Adolf Woelfli. These mesmerizing pieces are full of unconventional musical notations, masklike faces and spirals, all rendered with obsessive-compulsive care.

Another wall is crowded with abstract sculptural reliefs by Candy Cummings, a Maryland-based art school dropout who inherited the contents of her father’s electronic service company a decade ago. Since then, she’s been using those transistors, capacitors and circuit boards to assemble dozens of inexplicable retro-futuristic-looking contraptions.

Around the corner from these are tiny, roughly 2.5-by-3-inch embroidered images by Ray Materson, a self-taught artist who began stitching richly detailed miniatures out of sock thread to pass the time while serving a 15-year prison sentence. His subjects range far from his prison environment — daydreams of Katie Couric, the Mars Exploration Rover and a castle on the Crimean Peninsula.

’Rolling Through the Bay,’ by Scott Weaver, 1974-2008, toothpicks. Collection of the artist. (Photo by Exploratorium's Tinkering Studio)

These three artists live in completely disparate universes, and it’s hard to imagine any one theme that would tie them together. Instead, Hoffberger and Vehlow spin “All Things Round” into a series of tangential subtopics: from manifestations of the Divine Feminine, to pieces based on the Mayan calendar and circular conceptions of time, to works that reuse or recycle castoff consumer goods.

Hoffberger’s oft-stated objective is to keep the museum as “un-museum-y” as possible. In pursuing this goal, she has eschewed curatorial orthodoxies and transformed the institution itself into the main artwork on view. All of the pieces included in a show here seem to become interchangeable supporting players. The Visionary Museum is the real star.

This transformation becomes problematic when applied to art from other cultures. The section of the show about cyclical time, for example, features aboriginal funerary memorials from Australia and Huichol Indian yarn paintings from Mexico. Can such artifacts by anonymous artists, representing rich, long-standing cultural practices, really be equated with, say, whimsical paintings of outer space created by an amateur astronomer living in Maryland? Does a giant, wall-filling mandala made entirely from cut paper plates by Wendy Brackman this year help the viewer appreciate the bronze Bala Krishna statue displayed nearby?

The universalist, difference-eroding attitude toward all art glimpsed in this show hearkens back to a time when all cultures were viewed through the lens of Western tradition — when Henri Rousseau, the famed self-taught modern painter, created fantasy images of jungles at the edges of France’s empire base on nothing more than taxidermied animals and colonialist fever-dreams. It’s a romantic, exoticizing approach that is bound to lead to misunderstandings and over-simplifications.

An ancient Mayan codex and a bunny rabbit made entirely out of bottle caps don’t exist for the same reasons.

And, yet, despite this broad-brush approach to all art everywhere, there’s no denying the appeal of Hoffberger’s infectious energy and the bold, distinctive aesthetics of the museum’s displays. Many of the artworks on view look perfectly at home in this environment — and it’s hard to imagine them functioning anywhere else.

Scott Weaver’s “Rolling Through the Bay,” for example, is a marvelous misfit object: It’s a nine-foot-tall, eight-foot-wide, roughly-three-foot-deep sculpture made entirely out of toothpicks and Elmer’s glue. Weaver has been working on the piece for at least 34 years — starting when he was 14.

’Flustered Rustics,’ by J.J. Cromer, 2007, mixed media. Permanent Collection of the American Visionary Art Museum, Gift of J.J. and Mary Cromer. (Photo by Dan Meyers )

The piece is intensely autobiographical and serves as a love letter to the artist’s home town — San Francisco. Every aspect of the city’s skyline and surrounding landscape is represented somewhere in the tangle of spires, bridges and houses.

The piece was designed with 11 entry points where table tennis balls can be inserted so that they descend long, snaking ramps; the balls take various tours through all of the sculpture’s zones, winding their way to the bottom over the course of a minute or more. Windmills and ferris wheels actually turn as the balls pass through features such as the Palace of Fine Arts in the Marina District, BART trains and the buildings of Chinatown. All of these sites are lovingly rendered, hidden within the labyrinthine sculpture.

Part boardwalk attraction, part lifelong obsession, part hermit tinkerer’s secret pride and joy, “Rolling Through the Bay” is unclassifiable. Yet the day it arrived at the Visionary Museum, having been driven cross-country by the artist himself, it had come home. Whatever unresolved issues regarding the definition and proper presentation of outsider art are raised by the Visionary Museum’s practices, the experiences it offers simply cannot be found anywhere else.

All Things Round: Galaxies, Eyeballs & Karma

Through Sept. 2, 2012, at the American Visionary Art Museum, 800 Key Hwy., Baltimore, MD. More information at www.avam.org.