7. Electrophysiological Techniques
325
demonstrated extremely sharp frequency tuning as well. The sharpness of
tuning, measured in terms of the 010, is the highest that has been obtained
from any animal. Sharp frequency tuning allows for the discrimination and
isolation of energy in discrete frequency regions. Sharp frequency resolution makes possible the extraction of information from the fine spectral
structure of a signal, for instance, spectral notches that contain information
concerning the material composition and fine details concerning the shape
of a target object.
Given limited resources (i.e., time and "neural ware") as well as computational power, there is a trade off between time and frequency resolution
in the processing of acoustic information. Maximization of resolution in one
domain is at the expense of resolution in the other domain. Possession of
the capability for both very high temporal resolution and extremely sharp
frequency resolution makes possible the optimization by the animal of the
combination and balance between time and frequency resolution in the
neural representation of the animal's auditory world. The "optimal" balance
may be highly task specific, that is, during a particular echolocation task the
relative weighting of time and frequency information in a spectrotemporal representation may be under the control of the animal and may
depend on such factors as target characteristics, environmental conditions
(including ambient noise and clutter), and the nature of the task being
performed.
This chapter has summarized information obtained on the auditory processing capabilities of cetaceans using electrophysiological techniques.
Such techniques appear to offer an attractive alternative to behavioral/psychophysical paradigms for certain tasks and under certain conditions. Two
major advantages of AEP techniques as discussed here are the rapidity of
response acquisition and the need for only minimal cooperation on the part
of the subject. An increasing number of investigators are applying techniques as described in this chapter to the examination of cetacean auditory
processing. Auditory evoked potentials can be used in a wide range of questions, which may include further characterization of auditory filter shapes,
clarification of cognitive processing during discrimination and classification
tasks, identification of features used during echolocation tasks, temporary
threshold shifts resulting from sound exposure, and masking effects of
human-made noise. Many such studies have been proposed or are currently
underway.
Regardless of the technique used to examine the hearing capabilities of
these animals, our understanding of mammalian auditory functioning in
general will benefit greatly from an increased understanding of the auditory processing carried out by cetaceans.
Acknowledgments. I wish to acknowledge and thank Dr. Sam Ridgway
and Dr. Don Carder (Naval Ocean Systems Center, San Diego), Dr.
325
demonstrated extremely sharp frequency tuning as well. The sharpness of
tuning, measured in terms of the 010, is the highest that has been obtained
from any animal. Sharp frequency tuning allows for the discrimination and
isolation of energy in discrete frequency regions. Sharp frequency resolution makes possible the extraction of information from the fine spectral
structure of a signal, for instance, spectral notches that contain information
concerning the material composition and fine details concerning the shape
of a target object.
Given limited resources (i.e., time and "neural ware") as well as computational power, there is a trade off between time and frequency resolution
in the processing of acoustic information. Maximization of resolution in one
domain is at the expense of resolution in the other domain. Possession of
the capability for both very high temporal resolution and extremely sharp
frequency resolution makes possible the optimization by the animal of the
combination and balance between time and frequency resolution in the
neural representation of the animal's auditory world. The "optimal" balance
may be highly task specific, that is, during a particular echolocation task the
relative weighting of time and frequency information in a spectrotemporal representation may be under the control of the animal and may
depend on such factors as target characteristics, environmental conditions
(including ambient noise and clutter), and the nature of the task being
performed.
This chapter has summarized information obtained on the auditory processing capabilities of cetaceans using electrophysiological techniques.
Such techniques appear to offer an attractive alternative to behavioral/psychophysical paradigms for certain tasks and under certain conditions. Two
major advantages of AEP techniques as discussed here are the rapidity of
response acquisition and the need for only minimal cooperation on the part
of the subject. An increasing number of investigators are applying techniques as described in this chapter to the examination of cetacean auditory
processing. Auditory evoked potentials can be used in a wide range of questions, which may include further characterization of auditory filter shapes,
clarification of cognitive processing during discrimination and classification
tasks, identification of features used during echolocation tasks, temporary
threshold shifts resulting from sound exposure, and masking effects of
human-made noise. Many such studies have been proposed or are currently
underway.
Regardless of the technique used to examine the hearing capabilities of
these animals, our understanding of mammalian auditory functioning in
general will benefit greatly from an increased understanding of the auditory processing carried out by cetaceans.
Acknowledgments. I wish to acknowledge and thank Dr. Sam Ridgway
and Dr. Don Carder (Naval Ocean Systems Center, San Diego), Dr.