7
Electrophysiological Measures of
Auditory Processing in Odontocetes
WILLIAM FORD DOLPHIN
1. Introduction
The cetaceans, most notably the small odontocetes, possess extraordinary
auditory faculties, remarkable in both their frequency as well as temporal
capabilities. As has been abundantly documented in this volume and elsewhere, cetaceans make extensive use of sound in echolocation as well as
communication behaviors. The cetaceans exhibit extremely broadband frequency sensitivity with hearing extending from below 100Hz (possibly
less than 10Hz in the great whales) to greater than 150kHz. Moreover,
the smaller toothed whales in particular appear to combine high temporal
resolution with very sharp frequency tuning.
The majority of information we have concerning the auditory capabilities of cetaceans and other marine mammals has been obtained from behavioral and psychophysical studies; much of this information has been
reviewed in other chapters of this volume. This chapter presents results of
studies characterizing the auditory system of cetaceans using electrophysiological measures. Due to ethical and legal considerations, invasive, singleunit studies, such as have been widely conducted in bats and other animals,
are not possible with any cetacean. However, the use of auditory evoked
potentials (AEPs) are highly appropriate for use with cetaceans and other
marine mammals. AEPs are far-field electrophysiological recordings of
minute voltages generated by neural activity within the brain in response
to acoustic stimuli. AEPs are easily recorded from the scalp surface in many
species and so can be obtained in a totally noninvasive manner. Evoked
response audiometry using AEP techniques has been broadly applied with
great success with human patients unable or unwilling to cooperate in
more traditional behavioral tests. The application of such AEP techniques
to studies of cetacean auditory processing offers an attractive alternative to
behavioral studies under certain conditions for the same reasons that they
have been so widely employed with humans, namely, (1) they require no
or only minimal cooperation from the subject, (2) responses are rapidly
obtained and highly robust, (3) response detection can be fully automated
294
Electrophysiological Measures of
Auditory Processing in Odontocetes
WILLIAM FORD DOLPHIN
1. Introduction
The cetaceans, most notably the small odontocetes, possess extraordinary
auditory faculties, remarkable in both their frequency as well as temporal
capabilities. As has been abundantly documented in this volume and elsewhere, cetaceans make extensive use of sound in echolocation as well as
communication behaviors. The cetaceans exhibit extremely broadband frequency sensitivity with hearing extending from below 100Hz (possibly
less than 10Hz in the great whales) to greater than 150kHz. Moreover,
the smaller toothed whales in particular appear to combine high temporal
resolution with very sharp frequency tuning.
The majority of information we have concerning the auditory capabilities of cetaceans and other marine mammals has been obtained from behavioral and psychophysical studies; much of this information has been
reviewed in other chapters of this volume. This chapter presents results of
studies characterizing the auditory system of cetaceans using electrophysiological measures. Due to ethical and legal considerations, invasive, singleunit studies, such as have been widely conducted in bats and other animals,
are not possible with any cetacean. However, the use of auditory evoked
potentials (AEPs) are highly appropriate for use with cetaceans and other
marine mammals. AEPs are far-field electrophysiological recordings of
minute voltages generated by neural activity within the brain in response
to acoustic stimuli. AEPs are easily recorded from the scalp surface in many
species and so can be obtained in a totally noninvasive manner. Evoked
response audiometry using AEP techniques has been broadly applied with
great success with human patients unable or unwilling to cooperate in
more traditional behavioral tests. The application of such AEP techniques
to studies of cetacean auditory processing offers an attractive alternative to
behavioral studies under certain conditions for the same reasons that they
have been so widely employed with humans, namely, (1) they require no
or only minimal cooperation from the subject, (2) responses are rapidly
obtained and highly robust, (3) response detection can be fully automated
294