7. Electrophysiological Techniques
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frequency pairs simultaneously presented during two 30-min sessions. The
similarity in shape between the behaviorally obtained audiogram-and
EFR-is encouraging. An average difference of 16dB was found between
the two audiograms. Thus, this technique provides a potentially very rapid
estimation of an individual's audiogram.
4. Summary
The auditory capabilities of the cetaceans are truly remarkable in both their
frequency as well as temporal capabilities. These animals rely heavily on
audition as their primary means of acquiring sensory information; this
investment in audition is manifested in the significant hypertrophy of auditory structures exhibited by these animals. Because of their reliance on
acoustics for both echolocation and communication tasks, the auditory
system of these animals is of special interest to researchers in the field of
auditory processing.
The cetaceans appear to be highly specialized for the preservation of
temporal information in acoustic signals. Rapid conduction of auditory
information through the auditory system, a prerequisite for high-fidelity
extraction of temporal information, is insured by large fiber diameters and
hypertrophy of auditory nuclei, particularly those nuclei that have in other
mammals been implicated in the processing of temporal information.
The use of noninvasive electrophysiological techniques, in particular
auditory evoked potentials, is proving to be a highly effective and efficient
approach to the investigation of auditory processing by the cetacea. The
most widely used technique involves the measurement of the auditory brain
stem response to transient stimuli. However, more recently the use of long
duration, amplitude-modulated tones and measurement of the envelop following response has greatly widened the applicability of AEPs in the characterization and assessment of the auditory capabilities and processing of
these animals.
The short response latencies obtained from transient- or tone burstevoked ABRs, as well as the group delays obtained with amplitudemodulated stimuli, indicate an extremely rapid conduction of information
through the auditory pathway. These short latencies are in keeping with
what would be predicted based on the very large diameter neurons within
the auditory pathway and overall hypertrophy of auditory structures found
in the cetacea. Collectively, these results describe an auditory system that
is highly specialized for the extremely rapid conduction of auditory information from the periphery to more central structures for higher-order
processing and interpretation. Such adaptations would clearly be of tremendous benefit in echolocation tasks.
Moreover, the latency of the transient-elicited ABR, reflecting the
sequential excitation of neuronal populations, demonstrates a remarkable
323
frequency pairs simultaneously presented during two 30-min sessions. The
similarity in shape between the behaviorally obtained audiogram-and
EFR-is encouraging. An average difference of 16dB was found between
the two audiograms. Thus, this technique provides a potentially very rapid
estimation of an individual's audiogram.
4. Summary
The auditory capabilities of the cetaceans are truly remarkable in both their
frequency as well as temporal capabilities. These animals rely heavily on
audition as their primary means of acquiring sensory information; this
investment in audition is manifested in the significant hypertrophy of auditory structures exhibited by these animals. Because of their reliance on
acoustics for both echolocation and communication tasks, the auditory
system of these animals is of special interest to researchers in the field of
auditory processing.
The cetaceans appear to be highly specialized for the preservation of
temporal information in acoustic signals. Rapid conduction of auditory
information through the auditory system, a prerequisite for high-fidelity
extraction of temporal information, is insured by large fiber diameters and
hypertrophy of auditory nuclei, particularly those nuclei that have in other
mammals been implicated in the processing of temporal information.
The use of noninvasive electrophysiological techniques, in particular
auditory evoked potentials, is proving to be a highly effective and efficient
approach to the investigation of auditory processing by the cetacea. The
most widely used technique involves the measurement of the auditory brain
stem response to transient stimuli. However, more recently the use of long
duration, amplitude-modulated tones and measurement of the envelop following response has greatly widened the applicability of AEPs in the characterization and assessment of the auditory capabilities and processing of
these animals.
The short response latencies obtained from transient- or tone burstevoked ABRs, as well as the group delays obtained with amplitudemodulated stimuli, indicate an extremely rapid conduction of information
through the auditory pathway. These short latencies are in keeping with
what would be predicted based on the very large diameter neurons within
the auditory pathway and overall hypertrophy of auditory structures found
in the cetacea. Collectively, these results describe an auditory system that
is highly specialized for the extremely rapid conduction of auditory information from the periphery to more central structures for higher-order
processing and interpretation. Such adaptations would clearly be of tremendous benefit in echolocation tasks.
Moreover, the latency of the transient-elicited ABR, reflecting the
sequential excitation of neuronal populations, demonstrates a remarkable