Nature 450, 1240-1244 (20 December 2007)
Performance variability enables adaptive plasticity of 'crystallized'
adult birdsong
Evren C. Tumer & Michael S. Brainard
Significant trial-by-trial variation persists even in the most
practiced skills. One prevalent view is that such variation is simply
'noise' that the nervous system is unable to control or that remains
below threshold for behavioural relevance1. An alternative hypothesis
is that such variation enables trial-and-error learning, in which the
motor system generates variation and differentially retains behaviours
that give rise to better outcomes. Here we test the latter possibility
for adult bengalese finch song. Adult birdsong is a complex, learned
motor skill that is produced in a highly stereotyped fashion from one
rendition to the next. Nevertheless, there is subtle trial-by-trial
variation even in stable, 'crystallized' adult song. We used a
computerized system to monitor small natural variations in the pitch
of targeted song elements and deliver real-time auditory disruption to
a subset of those variations. Birds rapidly shifted the pitch of their
vocalizations in an adaptive fashion to avoid disruption. These vocal
changes were precisely restricted to the targeted features of song.
Hence, birds were able to learn effectively by associating small
variations in their vocal behaviour with differential outcomes. Such a
process could help to maintain stable, learned song despite changes to
the vocal control system arising from ageing or injury. More
generally, our results suggest that residual variability in well
learned skills is not entirely noise but rather reflects meaningful
motor exploration that can support continuous learning and
optimization of performance.
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Jean-Francois Julien
Centre de Genetique Moleculaire
C.N.R.S.
1, avenue de la Terrasse
F-91190 Gif sur Yvette
phone: 33 1 69823226
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