What Bats are Telling Us About Directional Hearing in Humans

When you're talking with a person in a crowded place, you can focus your attention on the conversation you're having while ignoring the ones happening around you. But how is this possible? Scientists have actually taken a closer look at bats to find out how we manage to focus our attention on one set of sounds like ignoring others.

"With so many stimuli in the world, the brain needs a filter to determine what's important," said Melville J. Wohlgemuth, the lead author of the new study, in a news release. "The bat brain has developed special sensitivities that allow it to pick out sounds from the environment that are pertinent to the animal. We were able to uncover these sensitivities because we used the perfect stimulus-the bats own vocalizations."

In this latest study, the researchers experimented with five brown bats, playing them a variety of sounds while monitoring their midbrain activity. They played recordings of natural chirps, the actual sounds bats made as they hunt. They also played artificial white noise and sounds between the two extremes. All of these sounds were identical in amplitude, duration and bandwidth.

While sensorimotor neurons in the bat midbrain reacted to all of the sounds, the neurons involved in stimulus selection, those that guide orienting behaviors, responded selectively to a subset of the natural chirps. And because all mammals share a basic brain organization, the findings suggest how mammals, including humans, choose which stimuli desert attention.

"Bats produce the sounds that guide their behaviors, and consequently, we know what signals are important to them," said Cynthia Moss, one of the researchers. "By comparing activity patterns of neurons to biologically natural and artificial sounds, we learn general principles of sensory processing that apply to a broad range of species."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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