161
behavior is either enhanced (through reinforcement) or suppressed (through punishment), before and/or after a cued stimulus. This form of conditioning can either
enhance or suppress voluntary behaviors; continued behavioral reinforcement
eventually leads to an association of the behavior and a consequence for that
behavior. A similar apparatus to Parker ( 1903 ) was used to show that minnows
( Pimepheles notatus ; McDonald 1922 ), mudminnows ( Umbia limi ; Westerfi eld
1922 ), and wrasses ( Crenilabrus melops ; Bull 1928 ) could be conditioned using an
auditory stimulus, and therefore demonstrated that these fi shes could detect auditory stimuli and thus possessed a sense of hearing. Operant conditioning methods
were later used by von Frisch ( 1936 ) in an attempt to train minnows to localize
sound for a food reward and thereby establish whether fi sh could localize sound
sources. Von Frisch tried to modify the “feeding refl ex” of European minnows
using an operant conditioning paradigm wherein minnows were trained to approach
one of multiple available feeding stations when they heard a loud sound (the conditioned stimulus) that was produced by an underwater horn positioned under one
of the feeding stations. Von Frisch was unsuccessful in his training of the fi sh and
eventually he (incorrectly) concluded that fi sh could not localize sound sources,
but the use of operant conditioning methods persisted and were later successfully
used in subsequent fi sh hearing studies. For example, Schuijf ( 1975 ) used a forced
choice conditioning method to successfully show that acoustic directional sensitivity in fi sh was mediated by the inner ear and not the lateral line. For a more complete review of the behavioral experiments used to investigate directional hearing
and sound source localization in fi shes see Hawkins ( 1981 ) and Sisneros et al. (in
this volume).
Operant conditioning methods using feeding (positive) reinforcement have been
successfully used in the studies of vision in fi sh (Yager and Thorpe 1970 ; Allen and
Fernald 1985 ), but these methods have not been extensively used in the study of fi sh
hearing. One excellent use of an operant conditioning paradigm was that used by
Yan and Popper ( 1991 ), who developed an automated positive reinforcement system in which fi sh could be trained to respond to a piezo-pressure paddle via a feeding refl ex when it heard a particular sound (Fig. 2 ). Goldfi sh ( C. auratus ) were
trained to strike an observation paddle to initiate the trial after which they would
strike a second “report” paddle if they heard a sound. Correct responses were
rewarded with food, whereas false positive responses resulted in a punishment with
the lights being turned off removing any possibility of successful prey capture.
During the testing phase, sounds of varying frequencies and intensities were played,
and responses were recorded, but not rewarded/punished. This paradigm was used
to measure audiograms in goldfi sh, and was later used for intensity discrimination
(Yan and Popper 1993 ), and in measuring audiograms in the cichlid Oscar
( Astronotus ocellatus ; Yan and Popper 1992 ).
There are three primary reasons why operant conditioning methods are rarely
used in fi sh hearing studies. First, operant condition methods require the fi sh to be
unrestricted and free-swimming. Most studies use a speaker to deliver acoustic
stimuli, and a freely moving fi sh would likely encounter different aspects of the
sound fi eld at different points within the testing arena or apparatus, which makes it
Revisiting Psychoacoustic Methods for the Assessment of Fish Hearing
behavior is either enhanced (through reinforcement) or suppressed (through punishment), before and/or after a cued stimulus. This form of conditioning can either
enhance or suppress voluntary behaviors; continued behavioral reinforcement
eventually leads to an association of the behavior and a consequence for that
behavior. A similar apparatus to Parker ( 1903 ) was used to show that minnows
( Pimepheles notatus ; McDonald 1922 ), mudminnows ( Umbia limi ; Westerfi eld
1922 ), and wrasses ( Crenilabrus melops ; Bull 1928 ) could be conditioned using an
auditory stimulus, and therefore demonstrated that these fi shes could detect auditory stimuli and thus possessed a sense of hearing. Operant conditioning methods
were later used by von Frisch ( 1936 ) in an attempt to train minnows to localize
sound for a food reward and thereby establish whether fi sh could localize sound
sources. Von Frisch tried to modify the “feeding refl ex” of European minnows
using an operant conditioning paradigm wherein minnows were trained to approach
one of multiple available feeding stations when they heard a loud sound (the conditioned stimulus) that was produced by an underwater horn positioned under one
of the feeding stations. Von Frisch was unsuccessful in his training of the fi sh and
eventually he (incorrectly) concluded that fi sh could not localize sound sources,
but the use of operant conditioning methods persisted and were later successfully
used in subsequent fi sh hearing studies. For example, Schuijf ( 1975 ) used a forced
choice conditioning method to successfully show that acoustic directional sensitivity in fi sh was mediated by the inner ear and not the lateral line. For a more complete review of the behavioral experiments used to investigate directional hearing
and sound source localization in fi shes see Hawkins ( 1981 ) and Sisneros et al. (in
this volume).
Operant conditioning methods using feeding (positive) reinforcement have been
successfully used in the studies of vision in fi sh (Yager and Thorpe 1970 ; Allen and
Fernald 1985 ), but these methods have not been extensively used in the study of fi sh
hearing. One excellent use of an operant conditioning paradigm was that used by
Yan and Popper ( 1991 ), who developed an automated positive reinforcement system in which fi sh could be trained to respond to a piezo-pressure paddle via a feeding refl ex when it heard a particular sound (Fig. 2 ). Goldfi sh ( C. auratus ) were
trained to strike an observation paddle to initiate the trial after which they would
strike a second “report” paddle if they heard a sound. Correct responses were
rewarded with food, whereas false positive responses resulted in a punishment with
the lights being turned off removing any possibility of successful prey capture.
During the testing phase, sounds of varying frequencies and intensities were played,
and responses were recorded, but not rewarded/punished. This paradigm was used
to measure audiograms in goldfi sh, and was later used for intensity discrimination
(Yan and Popper 1993 ), and in measuring audiograms in the cichlid Oscar
( Astronotus ocellatus ; Yan and Popper 1992 ).
There are three primary reasons why operant conditioning methods are rarely
used in fi sh hearing studies. First, operant condition methods require the fi sh to be
unrestricted and free-swimming. Most studies use a speaker to deliver acoustic
stimuli, and a freely moving fi sh would likely encounter different aspects of the
sound fi eld at different points within the testing arena or apparatus, which makes it
Revisiting Psychoacoustic Methods for the Assessment of Fish Hearing