Checking for a heartbeat: Patricia Barber in peformance at Au Bar.

When Patricia Barber sits down at the piano and begins to play, she bends her ear to the keyboard like a doctor listening attentively for a heartbeat. Satisfied that all is well, she relaxes into a voluptuous surrender. Her mouth falls open, and she gasps in amazement as her thoughts are expressed and developed in dialogues that challenge the resources of the other three musicians in her excellent quartet.

But even after the juices start to flow, the musical conversations begun by Ms. Barber, a singer and songwriter as well as a first-rate jazz pianist, revel in the tension between her ivory-tower intellectual rigor and musical sensuality. Ms. Barber's verbose original songs can throw in references from Greek mythology and French philosophy, and use thorny words like "syllogistically" rarely heard in popular songs. The lyrics are sung in a cool, clipped conversational voice that sometimes lowers to a near-murmur.

This songwriting voice, which suggests a literary critic, philosophy student and needling social commentator (her song "Touch of Trash") rolled into one, is the springboard for jazz, whose mood, if not its structure, seeks its antithesis of academic detachment. And the substitution of the vibraphonist and electronic wizard Joe Locke, for Ms. Barber's regular guitarist, Neal Alger, on Thursday evening at Au Bar, pushed her further than usual in that direction.

Mr. Locke, who continues through May 15 after which Mr. Alger returns (through May 15), brought a discreet showmanship to the set. He and Ms. Barber tussled in a playful (and fruitful) power struggle, engaging in games of copycat that reached a peak of contagious euphoria in Dizzy Gillespie's "Groovin' High," a number kicked up an extra notch by Eric Montzka's drums and Michael Arnopol's bass.

Each arrangement distilled a singular mood. Ms. Barber's "Dansons la Gigue" wallowed in a dreamy, glowing impressionism with a melancholy undertone. The Beatles' "Norwegian Wood" evoked a surreal night of lovemaking in front of an open fire. Fats Waller's "Jitterbug Waltz" suggest a rapidly rotating musical color wheel, spinning out sparks. By the time of the encore, a sultry "Light My Fire," the heat index was summery.