244
frequencies (≤200 Hz) in addition to those tuned to higher frequencies (Lu and Fay
1993 ; Fay and Ream 1986 ; Suzuki et al. 2002 ). This suggests that the maintenance
of low frequency encoding may be a general characteristic found in all fi sh auditory
systems. This low frequency hearing may be driven by environmental constraints of
the underwater environment that favor the detection of low frequency sounds that
propagate farther distances than high frequency sounds, as well as facilitate the
localization of sound sources using directional particle motion cues (Zeddies
et al. 2012 ).
4.2 Comparison of Different Auditory Physiology Recording
Techniques
Our comparison of different electrophysiological recording techniques illustrates
the limitation of comparing data sets among studies that use different methods, and
the value of using multiple techniques to examine auditory encoding in a single species. In the Hawaiian sergeant fi sh, different recording techniques revealed a similar
detectable range of frequencies, but the thresholds or sensitivity measures varied
considerably among methods. For example, auditory thresholds varied by as much
as 10–25 dB among techniques, with the greatest differences occurring at low frequencies (75–400 Hz). Since the spectral content of the sounds produced by the
Hawaiian sergeant fi sh is also at these same low frequencies to which their auditory
system is most sensitive, the threshold differences have important biological implications. This generalization of comparable frequency range but varying thresholds
appears to hold true for other species such as batracoidids, but not for goldfi sh,
which shows more overlap in thresholds obtained by different recording techniques
(Fig. 6 ). The oyster toadfi sh, for example, also shows differences in thresholds
between AEP and primary afferent recordings from the saccular nerve, with a 40 dB
difference between the techniques at 100 Hz. In the Lusitanian toadfi sh, differences
of 10–25 dB are also evident between AEP and saccular potential recordings across
the low frequency range tested. These observed differences in auditory sensitivity
among recordings in the same species could be due to methodology differences
(e.g., electrode placement, threshold criteria, tank acoustics), or inherent biological
characteristics of each recording location (e.g., summation, convergence, relative
inputs from inner ear and lateral line) that are important for the animals perception
of its auditory world.
While our study attempted to keep as many experimental conditions constant
across recording methods as possible, there were several unavoidable variations that
cannot be ruled out as contributors to the observed threshold differences. For example, the experimental tank, as well as the position of the entire fi sh and saccule
beneath the water surface in AEP experiments differed from that of the other three
techniques in which the saccule was closer to the water surface due to the surgical
intervention required for electrode placement. Since the acoustics in small tanks and
near the air–water interface can be complex (Parvulescu 1967 ; Akamatsu et al. 2002 ),
K.P. Maruska and J.A. Sisneros
frequencies (≤200 Hz) in addition to those tuned to higher frequencies (Lu and Fay
1993 ; Fay and Ream 1986 ; Suzuki et al. 2002 ). This suggests that the maintenance
of low frequency encoding may be a general characteristic found in all fi sh auditory
systems. This low frequency hearing may be driven by environmental constraints of
the underwater environment that favor the detection of low frequency sounds that
propagate farther distances than high frequency sounds, as well as facilitate the
localization of sound sources using directional particle motion cues (Zeddies
et al. 2012 ).
4.2 Comparison of Different Auditory Physiology Recording
Techniques
Our comparison of different electrophysiological recording techniques illustrates
the limitation of comparing data sets among studies that use different methods, and
the value of using multiple techniques to examine auditory encoding in a single species. In the Hawaiian sergeant fi sh, different recording techniques revealed a similar
detectable range of frequencies, but the thresholds or sensitivity measures varied
considerably among methods. For example, auditory thresholds varied by as much
as 10–25 dB among techniques, with the greatest differences occurring at low frequencies (75–400 Hz). Since the spectral content of the sounds produced by the
Hawaiian sergeant fi sh is also at these same low frequencies to which their auditory
system is most sensitive, the threshold differences have important biological implications. This generalization of comparable frequency range but varying thresholds
appears to hold true for other species such as batracoidids, but not for goldfi sh,
which shows more overlap in thresholds obtained by different recording techniques
(Fig. 6 ). The oyster toadfi sh, for example, also shows differences in thresholds
between AEP and primary afferent recordings from the saccular nerve, with a 40 dB
difference between the techniques at 100 Hz. In the Lusitanian toadfi sh, differences
of 10–25 dB are also evident between AEP and saccular potential recordings across
the low frequency range tested. These observed differences in auditory sensitivity
among recordings in the same species could be due to methodology differences
(e.g., electrode placement, threshold criteria, tank acoustics), or inherent biological
characteristics of each recording location (e.g., summation, convergence, relative
inputs from inner ear and lateral line) that are important for the animals perception
of its auditory world.
While our study attempted to keep as many experimental conditions constant
across recording methods as possible, there were several unavoidable variations that
cannot be ruled out as contributors to the observed threshold differences. For example, the experimental tank, as well as the position of the entire fi sh and saccule
beneath the water surface in AEP experiments differed from that of the other three
techniques in which the saccule was closer to the water surface due to the surgical
intervention required for electrode placement. Since the acoustics in small tanks and
near the air–water interface can be complex (Parvulescu 1967 ; Akamatsu et al. 2002 ),
K.P. Maruska and J.A. Sisneros