[From Bruce Gregory (990608.1030 EDT)]
"A young zebra finch learns through auditory feedback, listening to its
own sounds and comparing them to a song in its head until it gets it
right.
Little has been known about how a mature finch, a "closed learner"
(compared to a canary, for example, which learns new tunes all the time)
maintains its song. But earlier studies with deafened adult finches have
suggested that they use feedback as well.
The new research, by Anthony Leonardo, a graduate student at the
California Institute of Technology, further explores the role of
feedback, not by deafening birds but by confusing them. Leonardo
developed a computer-controlled system for recording a finch as it sings
and then playing back certain notes in time-lagged fashion. So a bird
hears a jumble of notes: its own song out of its beak, plus the playback
from a loudspeaker.
"After a couple of weeks to months, you get very dramatic changes in the
songs," Leonardo said. Some notes were discarded, new ones created and
others distorted. Most of all, the birds started to stutter, repeating
the same note over and over. "To a human, it sounds kind of like a
broken record," said Leonardo, who described his results in the journal
Nature. Once the confusing feedback was removed, the birds' songs
returned to normal over a period of months.
What might be happening, Leonardo said, is that adult birds are using
feedback in much the same way that young birds do, comparing it to what
they intended to sing. "But we're putting an error signal into the song,
and they go about correcting things, and it just gets worse and worse,"
he said.
Another possibility is that the birds are not doing any error correction
at all, but rather using the feedback of one note to prepare the next.
In this case, hearing a faulty note would produce another faulty one:
garbage in, garbage out."
NYT 6/8/99