How Birds Perceive the World

Micheal L. Dent, Ph.D. - dent@physiology.wisc.edu
Department of Physiology
University of Wisconsin-Madison
Madison, WI 53706
phone: 608-262-2429
web: www.physiology.wisc.edu/~dent/

Popular version of paper 2aPP3
Presented Tuesday morning, May 25, 2004
147th ASA Meeting, New York, NY

Birds, just like humans, produce, learn, and use complex acoustic signals for communication. This makes them excellent models to understand how the brain organizes and perceives sounds.

Although different species have different hearing equipment, both birds and humans have developed strategies to overcome many of the environmental effects on acoustic signals. More than humans, birds rely on their auditory systems for basic survival. They use auditory signals to choose potential mates, find prey, avoid predators, and defend their territories.

Recent experiments on the abilities of birds to detect and discriminate complex sounds in quiet or noisy conditions in the laboratory have revealed unusual abilities in discriminating among temporal differences between sounds. Several small species of birds are:

1. Almost three times better than humans at noticing a tiny time difference between two harmonic complex patterns, such as this sound and this sound (Dooling et al., 2002). Those two sounds differ in fine structure, and humans have difficulty discriminating between them.
   
2. Almost an order of magnitude better than humans at detecting timbre changes in sounds (Lohr and Dooling, 1998).
   
3. Much better than humans at spotting unexpected frequency changes in a strain of tones put together like musical notes in a video game [vvorig.wav] (Dent et al., 2000).

The ability to locate sound well has also recently been shown to be unrelated to several other tasks that involve listening with two ears in acoustically complex environments (i.e. in background noise or in rooms with echoes). Small birds, though their heads are only about 10 to 30 cm large, hear like humans and other large animals in these situations. These birds exhibit both the cocktail party effect (Dent et al., 1997), where the separation of a signal from background noise aids in hearing that signal, and the precedence effect (Dent and Dooling, 2003), which suppresses echoes that can interfere with communication in reverberant environments.

Other experiments have focused on the birds' abilities to segregate auditory objects into streams, also known as auditory stream segregation. Hulse and colleagues (Hulse et al., 1997; Wisniewski and Hulse, 1997) have shown that birds maintain their capacity to perceive and classify vocalizations within a number of background distraction conditions (e.g., songs from several other novel singers of the same or different species, played forward or backward, or embedded within a dawn chorus).

Researchers have taken several approaches to studying auditory perception in birds, including laboratory studies on the perceptual abilities to detect and discriminate among very simple sounds, field and laboratory studies on the perception of natural and distorted birdsongs, and laboratory studies on the perception of human speech sounds. As a result, there is probably more known about hearing in birds under both natural and laboratory conditions than in any other non-human organism.

As a whole, the experimental evidence collected to date suggests that overcoming the obstacles embedded in every complex auditory situation plays a role in auditory perception in birds as it does in humans and other animals.

References:
Dent, M.L., Dooling, R.J,. J. Acoust. Soc. Am. 113, 2146-2158 (2003).
Dooling, R.J., Leek, M.R., Gleich, O., Dent, M.L., J. Acoust. Soc. Am. 112, 748-759 (2002).
Dent, M.L., Dooling, R.J., Pierce, A.S., J. Acoust. Soc. Am. 107, 2657-2664 (2000).
Lohr, B., Dooling, R.J., J. Compar. Psychol. 112, 36-47 (1998).
Dent, M.L., Larson, O.N., Dooling, R.J., Behav. Neurosci. 111, 590-598 (1997).
Hulse, S.H., MacDougall-Shackleton, S.A., Wisniewski, A.B,. J. Compar. Psychol. 111, 3-13 (1997).
Wisniewski, A.B., Hulse, S.H., J. Compar. Psychol. 111, 337-350 (1997).