University of Oregon researchers have found that barn owls (Tyto alba) are better able to track changes in the location of a noise, such as that made by a potential meal, when the sound source moves horizontally than when the sound changes direction vertically. The discovery was made using an infrared-monitoring procedure that measures pupil dilation responses that are influenced by changes in sound sources around an owl.
"When we are looking at problems of spatial localization, or how to locate sound in a space, the barn owl provides a great system," said Avinash D.S. Bala, a researcher in the University of Oregon's Institute of Neuroscience and lead author of a new study.
The findings - published in Aug. 1 issue of PLoS ONE, a journal of the non-profit Public Library of Science - confirms and solidifies the results of an earlier study (Nature, Aug. 14, 2003), in which Bala and colleagues first documented the brain mapping of firing neurons to horizontal changes in the source of noises in the owl's brain.
Bala was the lead author on both projects, which were done in collaboration with former UO researcher Matthew W. Spitzer, who now is at Monash University in Australia, and principal investigator Terry T. Takahashi, a UO professor of biology and researcher in the Institute of Neuroscience.
"The barn owl has a portion of the midbrain which serves as a map," Bala said. "Neuron activity can be traced in the map as sound moves. Looking at this map, you can decipher which sounds are being received more actively."
The new study, in which conclusions were based on the recordings of 62 neurons that represent auditory space, also sheds light on how outside information is converted into electrical activity and transformed into behavior.
"The brain, in the case of spatial hearing, judges neuronal activity in a democratic manner," Bala said. "It listens to the responses of neurons, and it goes with an approximate average of responses. This has the advantage of reducing environmental noise that is inducing false positives, which would be more common if the owl was depending on only a few neurons. Overall sensitivity might go down, but the probability of an owl actually hitting its prey becomes much higher."
The monitoring procedure Bala and colleagues have devised, which is in the early stages of human application, has the potential to use the eyes, through changes in the size of the pupil, as a gateway to the human brain. The system would allow for measuring the response to different aspects of sound, such as volume, pitch and location, as well as diagnosing basic sensory deficits and identify areas of damage in the brain.