242
Hawaiian sergeant fi sh, as shown for several other species (Feng and Schellart
1999 ). Fourth, the dynamic range of threshold values from lowest to highest sensitivity across similar ranges of frequencies is greatest for the midbrain single unit
recordings (37.6 dB), followed by hindbrain units (33.7 dB), AEPs (28.1 dB), and
saccular potentials (12.8 dB). Fifth, there is an approximately 15–20 dB difference
in sensitivity at the best frequency of 100 Hz between the single unit recordings and
the AEP recordings, and a 25 dB difference between the single units and the
saccular potential recordings at this frequency. The reason for these differences in
sensitivity is not known, but may be related to recording locations (e.g., peripheral
vs. central auditory system) and methodology, or properties inherent to different
portions of the auditory processing pathway.
4 Discussion
The goal of this study was to generate auditory threshold tuning curves in the
Hawaiian sergeant fi sh using saccular potentials and AEP recordings, and then compare them to previously determined single neuron recordings from different auditory brain nuclei to determine how threshold measures at different processing levels
compare in a single teleost species. Our results show that the Hawaiian sergeant fi sh
is most sensitive to low frequency tone stimuli (≤300 Hz), regardless of recording
technique, which matches the spectral content of their sound production during agonistic and reproductive behaviors. Relative hearing thresholds, however, differed by
as much as 5–25 dB between the different recording methods, with largest differences occurring at these same low frequencies (≤300 Hz). Our results are interpreted below with the aim of discussing the utility of different electrophysiological
methods in fi sh hearing and bioacoustics research, as well as their biological implications for the study species.
4.1 Saccular Potentials and AEP Recordings in the Hawaiian
Sergeant Damselfi sh
Saccular potential recordings in A. abdominalis revealed best hearing sensitivities at
low frequencies (<125 Hz). Several previous studies used evoked potentials to
determine the sensitivity and response dynamics of saccular inner ear hair cells in
teleost fi shes (Adrian et al. 1938 ; Furukawa et al. 1972 ; Fay 1974 ; Sisneros 2007 ;
Alderks and Sisneros 2011 ), and they are easily identifi ed because they are evoked
at twice the stimulus frequency due to the presence of nonlinearities and oppositely
oriented hair cell populations in the fi sh saccule (Furukawa and Ishii 1967 ; Hama
1969 ; Fay 1974 ; Fay and Popper 1974 ). This frequency doubling effect is also evident in FFT analyses of AEP recordings and is present in the lateral line system
(Flock 1965 ) for similar reasons, but is absent in the cochlea and vestibular system
K.P. Maruska and J.A. Sisneros
Hawaiian sergeant fi sh, as shown for several other species (Feng and Schellart
1999 ). Fourth, the dynamic range of threshold values from lowest to highest sensitivity across similar ranges of frequencies is greatest for the midbrain single unit
recordings (37.6 dB), followed by hindbrain units (33.7 dB), AEPs (28.1 dB), and
saccular potentials (12.8 dB). Fifth, there is an approximately 15–20 dB difference
in sensitivity at the best frequency of 100 Hz between the single unit recordings and
the AEP recordings, and a 25 dB difference between the single units and the
saccular potential recordings at this frequency. The reason for these differences in
sensitivity is not known, but may be related to recording locations (e.g., peripheral
vs. central auditory system) and methodology, or properties inherent to different
portions of the auditory processing pathway.
4 Discussion
The goal of this study was to generate auditory threshold tuning curves in the
Hawaiian sergeant fi sh using saccular potentials and AEP recordings, and then compare them to previously determined single neuron recordings from different auditory brain nuclei to determine how threshold measures at different processing levels
compare in a single teleost species. Our results show that the Hawaiian sergeant fi sh
is most sensitive to low frequency tone stimuli (≤300 Hz), regardless of recording
technique, which matches the spectral content of their sound production during agonistic and reproductive behaviors. Relative hearing thresholds, however, differed by
as much as 5–25 dB between the different recording methods, with largest differences occurring at these same low frequencies (≤300 Hz). Our results are interpreted below with the aim of discussing the utility of different electrophysiological
methods in fi sh hearing and bioacoustics research, as well as their biological implications for the study species.
4.1 Saccular Potentials and AEP Recordings in the Hawaiian
Sergeant Damselfi sh
Saccular potential recordings in A. abdominalis revealed best hearing sensitivities at
low frequencies (<125 Hz). Several previous studies used evoked potentials to
determine the sensitivity and response dynamics of saccular inner ear hair cells in
teleost fi shes (Adrian et al. 1938 ; Furukawa et al. 1972 ; Fay 1974 ; Sisneros 2007 ;
Alderks and Sisneros 2011 ), and they are easily identifi ed because they are evoked
at twice the stimulus frequency due to the presence of nonlinearities and oppositely
oriented hair cell populations in the fi sh saccule (Furukawa and Ishii 1967 ; Hama
1969 ; Fay 1974 ; Fay and Popper 1974 ). This frequency doubling effect is also evident in FFT analyses of AEP recordings and is present in the lateral line system
(Flock 1965 ) for similar reasons, but is absent in the cochlea and vestibular system
K.P. Maruska and J.A. Sisneros