Mammal preference for unpredictability could help deaf

9 February 2007

Deafness Research UK scientists have discovered that the mammalian brain is designed to respond more strongly to randomness and chance. This discovery gives researchers a better understanding of the way the brain processes sound, and could lead to improvements in cochlear implants for the deaf.

A new study published today by Dr Jan Schnupp and Jose Garcia-Lazaro from the Oxford University Auditory Neuroscience group, has found that the human brain is hard-wired to respond better to random, abrupt changes in the environment – in this case in sound.

Dr Schnupp said: “We believe this work is fundamentally very interesting, and is likely to result in insights that will help facilitate the development and improvement of future generations of cochlear implants and hearing aid technologies”.

The world we inhabit is constantly subjected to countless random influences which may occasionally conspire to bring about large and abrupt changes in our environment, but which more often will cancel each other out, and thus provoke only little or no change. Imagine a boy playing a game where, on every round, he tosses twenty coins, and for every head he will take a step to the left, while for every tail he will take a step to the right. In most rounds, the number of heads will be very similar to that of the tails, and the boy’s net position will change only a little, but occasionally it might be almost all heads or all tails and the boy will make a sudden large leap to the left or right.

Many things in nature are pushed around by a combination of random influences much like the boy in this game, from dust grains in a drop of water pushed about by the collision with water molecules to flocks of animals roaming across a pasture. Scientists would say that their movement is “approximately 1/f distributed”, which means simply that there is an inverse relationship between the size and the likelihood of a change. Small changes occur often (at a large frequency) while large, abrupt changes occur with a proportionately smaller frequency.

In the 1970s, the American scientists Voss and Clarke noticed that even music, speech and natural soundscapes appear to behave according to the 1/f rule. Large, abrupt changes in loudness or in musical pitch are proportionally less frequent than small, gradual ones, and when human volunteers are asked to rate computer generated random melodies they instinctively prefer those melodies that obey the 1/f rule to those that do not. Melodies that change more abruptly than the 1/f rule would predict sound unpleasantly erratic. In contrast, melodies that change more slowly sound boring.

Now, in a new study, a team of scientists led by Dr Jan Schnupp at the Oxford University Auditory Neuroscience group has discovered that this preference for 1/f distributed soundscapes appears to be hard-wired into the mammalian brain. Individual neurons in the auditory cortex were found to respond more strongly and more reproducibly to stimuli with random pitch and loudness fluctuations which conformed to the 1/f rule than to other stimuli which did not. This results in a more accurate representation of the 1/f distributed sounds within the brain. 1/f behaviour has a strong random element, but is nevertheless not entirely unpredictable, and it appears that our sensory systems have evolved to expect this partial predictability as “natural”, and to exploit it to become particularly efficient at processing sensory inputs which exhibit “just the right amount of randomness”.

- - ends - -

Further information

If using this story in print or online please include the Deafness Research UK Information Service Number 020 7679 8970 and a link to the website www.deafnessresearch.org.uk

Please note: Jan Schnupps and Jose Garcia-Lazaro are both at a conference this week in Baltimore. Interviews can be arranged after 2pm GMT – please call. Other experts available.

For further information or interviews contact:

Georgina Vincent
phone 020 7679 8973
email

Notes to editors

• Reference for this paper: Garcia-Lazaro et al.: "Tuning to Natural Stimulus Dynamics in Primary Auditory Cortex." Current Biology 16, 264-271, February 7, 2006. DOI 10.1016/j.cub.2005.12.013 www.current-biology.com
• The researchers include J.A. Garcia-Lazaro, Bashir Ahmed, and J.W.H. Schnupp of the University Laboratory of Physiology in Oxford, United Kingdom. This work was supported by Biotechnology and Biological Sciences Research Council (UK) grant 43/S1959 to J.W.H.S. and studentships from Consejo Nacional de Ciencia y Tecnologia (National Council for Science and Technology, Mexico) and Deafness Research UK to J.A.G.-L. Michigan probes were kindly provided by the Center for Neural Communication Technology, Michigan, with funding from the National Institutes of Health/National Center for Research Resources (grant code P41 RR09754).
• Deafness Research UK is the only national charity dedicated to supporting medical research into deafness and other hearing problems. It changed its name from Defeating Deafness on 12th September 2005.