Fish Auditory Psychophysics

The ears, auditory system, and sense of hearing of present day fishes provide important clues to the structures and functions of the first vertebrate auditory systems that evolved hundreds of millions of years ago. The auditory systems of the early fishes formed the basis for subsequent developments of hearing among vertebrate animals, including human beings. In the fish psychophysics laboratory, we use classical, or Pavlovian, conditioning combined with modern psychophysical methods to quantitatively investigate the capacities of fishes to detect, discriminate, and perceive simple and complex sounds. In these experiments, fish are conditioned to briefly reduce their gilling movements when a sound is presented, or when a ackground sound changes in intensity, frequency content, or temporal pattern. Measuring the gilling movements is a way to know that the fish has detected the sound or the change in sound presented. Past and ongoing experiments have determined that goldfish
  1. can be as sensitive to sound as all other vertebrates studied,
  2. hear primarily in a low-frequency range, from below 40 Hz to about 2500 Hz,
  3. are able to discriminate differences in sound intensity and frequency as well as many other vertebrate animals,
  4. have mechanisms for enhancing the processing of simple sound signals when listening in noisy nvironments,
  5. can perceptually segregate and recognize signals even when they are heard in a complex mixture of other signals,
and are able to classify complex sounds with respect to pitch, timbre, and temporal pattern. This latter ability is analogous to a person's ability to recognize the notes and rhythms played by a musical instrument, and to recognize the individual musical instruments playing the same note and rhythm.
These experiments have shown that the sense of hearing in the simplest class of vertebrates is essentially similar to that of all other vertebrate animals tested. This suggests that many fundamental aspects of the human sense of hearing were developed among early fishes and have been passed on throughout vertebrate evolution. Present and planned experiments focus on some of the more complex aspects of sound source perception so that we can begin to identify what, if any, aspects of human hearing were derived or developed more recently.