Wait a minute. Was that here yesterday?

Now you see it, now you don’t. Or did you just forget?

Through April 11, artist Justin Stadel is playing mind games along Glendale Boulevard across from Echo Park with “Still Life in Memory,” his ever-changing art installation involving a daisy-sprouting bench, a mirrored trash receptacle and a 300-foot metal retaining wall.

Some days, the bench is covered in perky yellow flowers; at other times it’s plain. Sometimes the trash container looks ordinary; then the next day it’s clad in mirrors. And while you are sleeping, both pieces are likely to shift position, even as the wall behind them gets an ever-changing coat of paint.

To the Bureau of Engineering, part of the Los Angeles Department of Public Works, the bench is a “nonstandard item placed in the right of way.” You need a permit for that. To Stadel, an Echo Park resident who spent six months cutting red tape to get the permit, the bench and its surroundings represent an exercise in collective memory. It’s art about what people notice, what they forget and what they retain.

Since mid-March, between 4 and 7 a.m. and before heading out for his day job as a preparator at UCLA Hammer Museum, Stadel, 25, has been painting the retaining wall, originally white, a burnt orange color, 10 feet in from each end -- for a total of 20 feet a day. When he reached the middle, he began painting the wall white again, this time moving outward, 20 feet a day.

Each day, this shyly affable man with wavy hair approximately the color of the orange paint also alters the bench and trash container. Sometimes one or the other is missing from the sidewalk. Or the flowered bench appears with the mirrored trash container, or it’s flowered bench / absent container, or absent bench / mirrored container.... You get the idea.

And remember: Like the painting process on the wall, the bench and the trash receptacle have all this time been moving, first closer together, then farther apart.

To bedeck the bench, which he bought and placed on the sidewalk for the project, Stadel removes its six slats and replaces each with a special slat holding 75 daisies, each in a vial of water, for a total of 450 blooms. He considered using roses, but “they’d get jacked.”

At the end of the 30-day project, the wall will be back to its original white, the bench and trash receptacle will be gone, and “it will be as if the project was never there,” Stadel says.

“I think art schools, and art in general, work off history rather than memory,” adds Stadel, a University of Oregon art grad who moved to Los Angeles two years ago. “I am trying to push in the other direction by working off people’s personal memories.”

And, he says, “I wanted to address car culture in some way. There was a purposefulness in doing this in a way that people would stop and look at it, but only for the time they are in traffic.”

Says Wesley Tanijiri, a civil engineer in the city’s Bureau of Engineering who helped Stadel get his permit: “We thought he might lose interest with all the paperwork that he had to go through, but he got it done -- I have to give him that. Personally, I don’t really understand it, but that’s what he wants to do.”

How do passers-by react?

One woman volunteered to help paint, Stadel says, and vowed to show up at 4 a.m. The artist brought two brushes, but the woman never showed.

One day, a group of kids hauled the flower-covered bench up onto some concrete stairs on the hillside. Stadel guesses that it became part of a skateboarding stunt.

He says that in the early days of the project, people would trash the daisies, but as time has gone on, they seem to be developing a respect for the bench -- or else they’ve stopped noticing.

“They’re doing less to it, not taking the flowers off it,” he says.

Although there was this: “One day I found a piece of barbecued chicken between the flowers. Apparently someone just sat on the bench and ate lunch.”