Without a pianist at the bench, pianos can foray into wildly perplexing terrain. The rollicking automated upright in a saloon spools show tunes from that essential absence, while the avant-garde has made hay with unmanned grands since George Antheil synchronized player-pianos and airplane propellers for Ballet Mecanique in 1924. (A rare realization of that piece, including eight Yamaha Disklaviers, was performed downtown last year by the League of Electronic Musical Urban Robots.) Conlon Nancarrow punched dazzling intricacies into piano rolls just before the electronic music era, then artists such as Nam June Paik put the instrument’s very existence on the line.

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In the hands of Céleste Boursier-Mougenot—or out of his hands, as it were—the piano may be left most fully to its own devices. His latest exhibition at the Paula Cooper Gallery includes index, in which the composer’s delicate, persistent music resonates from a Pleyel piano with its keyboard cover shut. In the skylit gallery, the visitor pays mind to the sound of the music, not its action. And index ups the ante by turning the very notion of a musical score inside out, with an unsettling grace that’s a hallmark of Boursier-Mougenot’s work. What’s tickling the unseen ivories is generated by daily computer tasks across the street in Cooper’s offices.

That’s right: Those lofting gems of sound are not eked from the composer’s pen. Beguiling, to be sure, but index is perpetuated by utterly pedestrian activity. If Boursier-Mougenot’s system is a jest, however, it’s a loaded one that’s made even richer once one knows the punch line. There’s a stimulating warm-up available online at analogues.fr/indexinprogress, where the program that filters the gallery’s office output “plays” excerpts from a monograph on the composer and his works, published last year and available at the Cooper Gallery. Boursier-Mougenot doesn’t release CDs, so listening to the online excerpt is in effect reversing the function of his art. What’s exposed, though, is the extraordinary flexibility of his pieces, because it’s hard not to hear the online music as through-composed. Then again, the exhibition’s canny visual presence won’t mask the limpid, dancing impression with which a visitor departs—in a word, its music. Created by a composer whose science can seem as leavened by Jacques Tati’s discoveries as by those of John Cage.

“The piano is a very reactive instrument,” Boursier-Mougenot said on the phone from the Mediterranean harbor town of Sete, days after the birth of his first son. “I wanted a piano that is not played by people, by fingers, yet they play.” By mainlining the computerized Pleyel (piano maker of choice for Frederic Chopin) into the office, the composer marries the workhorse of virtuosic indulgence to that least musical of arenas. “You’re not going to play piano because you’re working,” he said, “but you’re playing piano because you’re on the computer. My idea is to extract a segment that can be used as a line of notes, or a dynamic or other musical indication. When one person is at work, it will be like a breath; with many people working it is not more active.”

“Up to 130 text elements could become notes, and out of a page of text, more than sixty percent could work to give information to the program, including nomenclature like ‘p’ for piano, ‘pp’ for pianissimo, or forte or fortissimo.” To fluently skirt shifting workloads, the program selects among inputs rather than becoming “over-actioned” when several people are at their keyboards. “I did some extensions, also, for instance with a paragraph that’s less rich in its terms,” Boursier-Mougenot added, “a kind of extrapolation to decide what I’d like to use.”

“I wanted to have chords sometimes, for example. If a word has more than three [pitch] inputs—say, an A, an E, and a D—that word contains a chord.” The individual notes are sounded, “and when you push the space bar, it will play the chord, the accumulated notes.” The results call to mind Morton Feldman’s solo piano vistas such as Palais de Mari, which mine both a sensation of stasis and incredible worlds within individual tones and their relations. But where Feldman precisely notated patterns into evolving textures, index operates with an elusive indifference, challenging the listener’s impressions of what dictates the heart of the musical matter.

Analogues’ catalog of Bousier-Mougenot’s works, replete with images of his music-generating pieces, is in its own way a coup du théâtre. What you see may be what you get, yet the images on pages and spreads are standing in for vibrant sonic environments, laden with surprise and discovery. (The finches in the cover image aren’t just whistling “Dixie,” suggests the fat black amp cable dangling from the Les Paul they’re perched on.) Essays include a Q&A that establishes the term dispositif as a spatial presentation, “with an implication of a productive principle,” which the installation genre can lack. Boursier-Mougenot then specifies his dispositifs as “a place or a situation correspond[ing] to what other musicians achieve when they perform or make recordings.”

His compositional work moved in this direction in the mid-1990s, then in 1997 he presented his first pieces in New York City, including and you’ll get breakfast…, where a toaster, juicer, and egg cooker were activated by visitors singing (or, in the case of this writer, prolonged yowling). Two years later, his aviary for finches that twitter and light in a subtly miked web of shirt hangers and feeding bowls, from here to ear, was a consensus favorite at P.S. 1. Other aviaries have been installed in the vast Glass Courtyard of the Beaux-Arts de Paris and the CAC in Cincinnati, and the manifestation with electric guitar perches and Marshall amps is in the permanent collection of the new Museum of Old and New Art in Hobart, Tasmania.

Boursier-Mougenot’s first exhibit at Cooper Gallery, untitled, was a wry tableaux of five inflated pools with gentle, motor-driven currents in which teacups and assorted porcelain bowls chimed, tinkled, and jostled—an exquisite, aleatory soundscape that infrequently sounded like a drunk had tipped over the cupboard. In autumn 2001, videodrones juxtaposed a pillow sofa facing five broad video screens with the unintended unease (the “War on Terror” was just underway) of surveillance cameras trained outside the gallery, producing inputs from which the music was processed. Then, in 2006, came harmonichaos, a chorus of thirteen sedate vacuum cleaners contrapuntally puffing harmonicas in a quotidian array of divinely comic chords.

For this latest version of index, a partnership has been established with the prestigious piano manufacturer Pleyel. A long-term exhibition of the piece at the Théâtre Genevilliers in Paris, where theater visitors check email on ten computers, is on hiatus so the piano could be shipped to New York. One of Boursier-Mougenot’s aviaries will be on display this summer in Nantes, on the Loire River, and in autumn he installs a version of videodrones in a fishpond at the Musée Chagall in Nice. The prospect of aquatic life becoming music displays again the environmental relativity in Boursier-Mougenot’s approach.

It also suggests the formal kinship with the musical source of index. An ur-moment in his art came some fifteen years ago, when he was composing a piece for voice. Boursier-Mougenot wanted to place his music behind the sexual nature in Homer’s text about Odysseus listening to the forbidden song of the Sirens. “But how could I compose music that is not a subjective, arbitrary projection?” he recalled. “I composed a melody, or a monody, trying to illuminate the specificity, but the unspecificity came back very soon!” Requesting that the singer only use her soft, natural voice, he found the intervals in the melody were cut into letters and phonemes of the lyric. “This view gave me a kind of atomic consensus of what a text is.”

Such particularity between sound and source plays through both Boursier-Mougenot’s video works and index, an on-the-spot transduction that is key to the pieces. “People don’t realize that before we could reproduce sound like this, mechanically,” he said, “that sound was a question of being in the same time in the same space.” The independent piano becomes instrumental for index, rather than making a virtual installation by simply piping the processed music into the exhibition space. “It’s like being with a creature, something which is alive,” Boursier-Mougenot said. “And sounds are alive. We can consider sound as being.”

index plays the Paula Cooper Gallery, 534 W. 21 St., through April 25.