Magazine article Natural History

Active Perception

Magazine article Natural History

Active Perception

Article excerpt

To enhance sensory perception, many animals, including humans, engage in "active sensing," the enlistment of the body's motor systems in the processing of sensory information. In the case of hearing, dynamic movement can help to isolate important sounds-such as those made by prey species-from background noise. Echolocating bats are prime subjects in which to study this behavior, as they must coordinate their movements with feedback from the sonar vocalizations they use to locate prey.

Recently, neuroethologist Melville Wohlgemuth and his colleagues at Johns Hopkins University and the University of Maryland studied the mechanics of head and ear motion in big brown bats (Eptesicus fuscus). To overcome the difficulty of measuring these movements in flight, the team trained the bats to wait on a platform for their food-tethered mealworms-and used specialized motion-capture video to record the bats while they tracked prey.

The researchers found that as echolocating bats received auditory feedback, they made very quick adjustments, on a millisecond timescale, to their head and ear positions. When the target was far away, the bats held their ears upright. This positioning helps to accentuate sounds returning down the midline, explains Wohlgemuth. As the target became closer, the bats tilted their ears down, increasing the sensitivity of their auditory system to more peripheral locations. …

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