SATURDAY Discovering Pyschology (PBS, noon to 12:30 p.m.): Premi`ere of a carefully structured series of 30-minute shows that can be used as a college-credit course. It presents everything from archival footage of Pavlov's famous dogs to interviews with leading academics. The aim is to update viewers on this rapidly evolving science and relate it to their daily lives. Echoes of the Big Bands (PBS, 8-10 p.m.): If you feel pop music's all-time best sounds came from the likes of Duke Ellington, Joe Williams, or the Benny Goodman band - then this should prove a feast, with marvelously evocative clips of the greats, including recent ``reminiscent'' gigs at later stages of their careers. It's hosted by that former band singer - turned talk-show host, then entrepreneur - Merv Griffin. MONDAY The Record Breakers of Sports (HBO cable, 8-9 p.m.): It doesn't hurt to be reminded every so often of those liberating moments when top athletes disposed of old barriers - like Roger Bannister breaking the four-minute mile and Joe DiMaggio hitting in 56 straight baseball games. This documentary interviews some of the very people whose historic moments are shown. TUESDAY Politics: The New Black Power (PBS, 9-10 p.m.): A growing leadership role is being taken in America by blacks, and this special tries to put it all together by studying office-holders, scholars, and others - how they achieved their status and what they're doing with it. Please check local listings for all programs, especially on PBS.