Richard R. Fay - rfay@luc.edu
Director, Parmly Hearing Institute and
Interdisciplinary Neuroscience Minor
Professor of Psychology
Loyola University Chicago
6525 N. Sheridan Rd.
Chicago, IL 60626
Popular version of paper 4aAB7
Presented Thursday Morning, November 13, 2003
146th ASA Meeting, Austin, TX
Behavioral experiments using Pavlovian conditioning focused on revealing subtle aspects of the sense of hearing in goldfish. Human listeners judge the pitch of a complex harmonic sound (essentially like that of a musical instrument playing a given note or pitch) to be equal to the fundamental frequency of the harmonic complex (the lowest frequency component in a harmonic series).
For humans, this pitch estimate is very secure, and remains the same even when the fundamental frequency component of the complex sound is removed. Thus, it is said that human listeners don't miss the fundamental in the sense that the pitch of a given complex sound is the same whether the fundamental frequency component is present or not.
These experiments on goldfish asked whether they do or do not miss the fundamental in a complex harmonic sound. Animals were conditioned to respond to a complex sound, and then tested for responses to novel sounds that were slightly different acoustically. In general, animals conditioned to a harmonic sound with the fundamental present generalized robustly to similar sounds in which the fundamental was absent. Other groups of animals were conditioned to a sound with the fundamental missing, and then tested for response to sounds with the fundamental present.
The pattern of response for both groups was similar, indicating that an important perceptual feature of these harmonic sounds remained the same whether the fundamental frequency component was present or not. In this sense, goldfish do not miss the fundamental. We hypothesize that this perceptual feature is analogous to pitch as perceived by human listeners. We also hypothesize that this is also true for other fish species. However, small differences in the pattern of response to the two types of sounds indicate that goldfish are aware of the acoustic differences (as human listeners are), but that the pitch value is not affected by the presence or absence of the fundamental frequency component. Further experiments indicate that the pitch-like perceptions shown by goldfish are based on the temporal periodicity in these sounds, and arise in the brain through an analysis of the temporal response patterns that are transmitted over the auditory nerve from the ears.
This similarity between goldfish and human auditory perception suggests that all vertebrate animals may hear such sounds similarly. This may be an example of parallel or convergent evolutionary developments in response to some of the fundamental features of acoustical physics that must have been confronted by all vertebrate species in their development of a sense of hearing.