I walked across the hall to a gallery of early Ellsworth Kellys. While I was considering post-war Paris as a link between abstract painting and minimalism, I heard another voice: "Tuesday." This time it seemed to come from up near the ceiling. I looked up and there was nothing there, no workman on a ladder, no speaker, no nothing. This was getting weird.

Finally, a few minutes later, I entered the gallery pictured here and I understood. Roberta Smith described this installation as "like paintings by Robert Ryman hanging on Fred Sandback's string sculptures," a mash-up on which I cannot improve. Those white squares are wafer-thin speakers. Each speaker projects voices reciting the days of the week. The orders in which the days are spoken varies. The speakers are both men and women, adults and children. (See here for another picture.)

The piece I was hearing -- and only later seeing -- was Bruce Nauman's Days, which was part of Nauman's Philadelphia Museum-curated, Golden Lion-winning presentation at last year's Venice Biennale. (The Italian-language version of the piece, Giorni, is installed across the street from the PMA's Beaux Arts HQ, in its Richard Gluckman-designed Perelman Building.) The Naumans are installed at the PMA through April 4.

Inside the gallery, the recitation of the days of the week flow at the listener, one after the other after the other. But as I discovered while looking at Matisse and Kelly, Days also turns the surrounding galleries into an audio funhouse. One minute you're looking at a painting and a "Monday" pops up. Then you hear nothing else for 10 minutes... and then another day of the week comes out of nowhere. I found that the barrage of information was projected at me so consistently, so insistently and incessantly, that the words lost their meaning. After an hour in the PMA's galleries I had to really, really focus hard in order to remember what day of the week it really was.

While it's easy to think of Days as witty and whimsical, it's dark art. Consider Days Nauman's latest exploration of torture. First installed last year in a prominent national pavilion in a major international exhibition at a time when America's torture of detainees was a major international issue, the artwork serves as a metaphor for confusion and dislocation enabled by the pro-torture policies of the second Bush Administration. (Nauman has made torture a key subject of his work ever since 1981.)

Days recalls a passage from the International Committee of the Red Cross' 2007 report on American torture, a report that detailed how Americans used sound and noise to torture detainees. (The report was not leaked to the media until April, 2009, but details that were in the report were reported in Jane Mayer's 2008 book The Dark Side.):

One detainee who did not wish his name to be transmitted to the authorities alleged that loud music played for twenty-four hours a day throughout the one year period he believed he was held in Afghanistan. He reported that during the last month it changed to sounds of wind, waves and birds.

Nauman seems to be reminding us that even the simple and banal can be harnessed in a way that can confound and discomfort. Days may be the most important contemporary artwork on view in an American museum.

Related: Nauman's Double Steel Cage Piece, Nauman begins to explore torture, Nauman's hanging chairs.