Animal Frequency and Pitch Perception

Pitch is a perception that is evoked by simple tones and many different types of complex sounds, including speech and music. Pitch refers to the subjective experience produced by a sound. The pitch of a sound is closely related to the frequency of a pure tone or to the fundamental frequency of complex sounds, but does not refer to the specific frequency content of the sound. As such, pitch is what results from how the brain analyzes and processes the frequencies present in a sound. This entry describes sensitivity ranges of different animals, the ability to detect frequency differences, and animal perception of naturally occurring sounds.

Animals most likely experience sensations that are similar in many respects to the pitch percepts experienced by human listeners, but scientists cannot directly ask animals about the subjective experience in a way that can be asked of human listeners. To understand animal perceptions, scientists must ask the animal indirectly how it perceives the sound. This is done by training or conditioning the animal to make a behavioral response to a particular feature of a sound that will then be varied. For pitch perception, the frequency content of a sound can be varied. When the animal makes a correct behavioral response, it usually receives some sort of feedback, such as a food reward or avoiding a mild electric shock. Although scientists have no way of knowing exactly what the animal's subjective experience is, from the behavioral responses of the animals, scientists can determine what features of the sounds the animal is analyzing and thus make inferences about what the animal experiences.

It is not surprising that the way in which the brains of animals process the frequency content of sounds is similar, in many respects, to that of the human brain because the general structure of the auditory brain is similar in animals. A major difference among animals is the range of frequencies that animals are able to perceive, and these differences are related to the structures that constitute the outer, middle, and inner ears. The hearing range of frequencies for most fish is fairly low, between 50 and 500 hertz (Hz). However, some fish have accessory auditory structures such as swimbladders and tiny bones that connect the swimbladder to the inner ear. These structures act like the middle ear in land animals and increase the sensitivity to higher frequencies to about 2,000 Hz. Amphibians and reptiles typically have a range of hearing between 100 and 2,000 Hz. Most birds have a relatively narrow hearing range with best sensitivity between 1,000 and 3,000 Hz, but some species of owls have excellent sensitivity as high as 10,000 Hz. Unlike birds, the range of hearing is quite heterogeneous in mammals. For example, the range of hearing for humans is 20 to 20,000 Hz, whereas elephants can hear frequencies below 20 Hz with great sensitivity, and dolphins and bats can hear frequencies above 100,000 Hz with great sensitivity. The range of hearing will determine how the animal perceives the outside world.

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