The Chick Corea New Trio, the Chucho Valdés Quartet and Sphere are scheduled to play at La Jolla's Neurosciences Institute in a spring series of piano concerts organized by the Athenaeum Music & Arts Library.

The series begins on Sunday April 8 with Chucho Valdés. Reputed to be Cuba's greatest jazz pianist, Valdés has been described elsewhere as the most complete pianist in the world.

In fact, all three of these bands defy definition. "If you want to use terms like bebop or avant garde or straight ahead to describe these three bands I think you'll be totally off," said Buster Williams, the distinguished bass player of Sphere.

Likewise piano stylist Chick Corea, who will play two concerts on Tuesday May 15, is not inclined to place his music in any category. "Styles of music can be total red herrings when it comes to understanding what elements make up any music one comes across."

"If you want to describe Sphere as an avant-garde band you'd be totally wrong," Williams said. Sphere may play four tunes in a set and one of them may be described as avant garde, another can be described as bebop and yet another may be mainstream. "But in the course of one performance, you may hear all of that," he said.

Williams corrected the rumor that Sphere's drummer Ben Riley had a stroke and would not be appearing with the band on Monday, May 7. "It wasn't a stroke at all," he said. "He had problems with his lungs."

Riley's breathing difficulties hospitalized him for a while and, according to Williams, the exact cause remains something of a mystery. "Ben Riley is coming along just fine, Williams said. "I went to see him just the other day. He's up and about, breathing normally and getting his exercise. I definitely think he's going to be able to play."

Williams was also quick to dispel the idea that Sphere is dedicated entirely to playing the music of Thelonious Monk. "That was what the writers locked into, especially when the first album came out right after Monk passed away." He said the intention all along was to play material by Monk as well as "a real array of different composers" such as Sphere's Grammy-nominated pianist Kenny Barron, drummer Ben Riley and by the band's tenor sax player, Gary Bartz's predecessor, the late Charlie Rouse.

"We play some of Monk's music because we love Monk," he said. "I can't get away with a night of playing two or three sets without playing a Monk composition. Monk is one of our venerable American composers."

He said Sphere's first album, Four in One, comprised Monk compositions for two reasons. Firstly so that Monk's publishing company would get the royalties, and secondly because the whole band loved Monk's music and they hoped it would be an inspiration to the ailing composer who, at that time, had not played publicly in ten years. "So that's what we did," said Williams. "And while we were in the studio, he passed away."

After the studio date, the band was still searching for a name when Barron suggested Sphere. "And it happened to be Monk's middle name," Williams said. "But his reason for suggesting Sphere was as a descriptive statement of what we wanted to do musically, which was to be well rounded."

According to Williams, Sphere disbanded after Rouse's death in 1988. "We didn't get back together again until '98." The group functions as a cooperative, and each member leads his own band during the months when Sphere is not touring. "Kenny Barron and I love playing together," he said. "So we try to do a few tours each year."

"We call it good music," he said. "Those who feel they have to call it whatever they call it, call it something else."

Tickets to the three-concert series are $63 ($54 to Athenaeum members), tickets to individual are $23 (members $20) and may be reserved by calling the Athenaeum, 454-5872. All concerts start at 8 p.m. except for the two Chick Corea shows which will start at 6 p.m. and 8:30 p.m. on Tuesday, May 15.

The Neurosciences Institute, 10640 John Jay Hopkins Drive, is easily accessible from Interstate-5 via Genessee Avenue. There is ample free parking.