From my faithful correspondent Joseph Zitt (and originally posted as a comment on my book site):
One useful buzzphrase: when I took a performance workshop led by Deborah Hay in Austin, one thing that she insisted on for all performers was that they “Invite being seen.” Performers have to be conscious that they don’t become invisible once they stop sounding, and that, unless they are playing in the dark or physically obscured from the audience, they will been, and what the audience sees as their state affects how things are heard.
A while back, I saw a performance by a good Bay Area rock band, invited by one player of the moment (who has since moved on to another town). When she asked for my reaction, I said that she played the music well, but was a problem when not playing — she would twiddle noiselessly with her instrument, stare off into space, or look blankly in a random direction. I suggested that she use that time to visually channel the audience’s attention toward the other members of the band as appropriate: either the lead singer, or another performer who either was taking a solo or playing a significant other part. (This was especially true since she was strikingly attractive, and a lot of the audience was watching her anyway, thus increasing her resposibility to channel their attention.) This appeared to work, and a later performance seemed my tighter, even though the sound of it was identical, through her attention to the audience’s attention.