Market researcher Naomi Henderson tells focus group participants they are being watched. Otherwise she would have been embarrassed when a participant leaned against the mirror dividing the rooms and fell through. Or when a client fell asleep behind the mirror and snored loud enough to drown out her voice.

No matter what happens, moderators such as Henderson, president of Riva Market Research, must maintain "unconditional positive regard."

"How interesting" is her favorite noncommittal phrase. "Even when a participant tells me something that is erroneous or off the wall, I say, 'Oh, how interesting.' I do not correct them. Anything anybody says related to the topic is fine. You don't pass judgment on it."

It doesn't always work, however, admits Henderson, recalling the time she tested an after-dinner liqueur which she "personally thought was horrible."

"I passed out the little glasses and said, 'Please tell me the first thing that comes to your mind. How do you feel about it and what would you call this product?' Most people said little polite things, but one woman said, 'This tastes like antifreeze smells.' I said, 'I know what you mean.' " The liqueur never made it to the market.

The moderator's job, says Henderson, is like "a sheep dog herding sheep. They just keep barking and move them over to the corner. The sheep don't know where they're going and then off they go. I move people down the line, tactfully, and make it safe to talk and we're done in 90 minutes."

Henderson, who's done over 600 groups in the past eight years, never tires of the play of perceptions.

"I cannot believe such variations on the human mind. People come up with things, and you go, where did that come from? I don't agree with them, I don't even get half of them. But I'm interested in the process by which people choose one thing over another. I have formed this about human nature: Mankind is incredibly diverse. Incredibly."

For more information on Naomi Henderson's moderator training courses, call (202) 363-1241 or (202) 362-4417 or write Riva Market Research, 4417 Brandywine St. NW., Washington, D.C. 20016. Three-day training session on Jan. 9-11: $595.