Upon hearing the blare of a siren, you would quickly home in on the source and direction of the sound and take the necessary action, or precaution, such as pulling your car over or foregoing crossing the street until the ambulance has cleared. Mammals rely on sound localization skills to communicate, escape threats, and forage, among many other tasks. All through development the adult brain retains the capacity to rewire the networks that underlie these skills but its not clear which tasks benefit from plasticity or how the brain engenders this flexibility. In a study published in the open access journal PLoS Biology, Oliver Kacelnik, Andrew King, and colleagues showed by manipulating the hearing of adult ferrets that ferrets with obstructed hearing can quickly adapt to altered auditory cues when trained to do so in order to perform a necessary task. Their findings reveal that the frequency of the training was crucial in boosting the rate and extent of their improvement.
Measuring the accuracy with which ferrets can localize sound. (Photo: King et al.)
The brain processes spatial cues in the sound waves that enter each ear to localize sound and interprets sound on the horizontal plane by using disparities in how the sound reaches each ear, called interaural time differences and interaural level differences. Changes in level at different frequencies can reveal the sources elevation.
To study adaptive hearing in an adult mammal, the authors blocked the left ears of ferrets with specially outfitted earplugs and measured their ability to localize sounds in the horizontal plane. They trained ferrets to approach a sound source to receive the reward. When the ferrets licked a waterspout, they triggered a burst of noise from one of twelve speakers. They were presented with sound bursts lasting either 1,000 or 40 milliseconds. Without earplugs, ferrets had no trouble localizing the sounds. They were slightly less adept at localizing the brief bursts. With earplugs, performance dropped considerably for both bursts. Ferrets had the most trouble with sounds coming for their left (obstructed) side, but errors increased significantly for all 12 sound sources. The authors retested one group of earplugged animals every six days to see if they could use the altered cues to recover their localization skills. By three weeks, the animals localized sound coming from the right side about as well as they had before the ear was plugged. The speed and accuracy with which the ferrets recovered their localization abilities depended on training, with more complete recovery when the animals received more frequent training.
Paul Ocampo | EurekAlert!
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