248
complex and unknown particle displacement fi elds (Parvulescu 1964 , 1967 ;
Akamatsu et al. 2002 ), it is important to recognize the relative contribution of
otolithic endorgan versus lateral line system input to “hearing thresholds” across
species. While in most cases it may not matter to the fi sh whether a biologically
relevant stimulus is detected by the inner ear, lateral line, or both, it does become
important when characterizing the response dynamics of individual sensory systems [see Braun and Sand 2014 for discussion of overlap between lateral line and
auditory systems in fi shes, and also Higgs and Radford, in this volume].
5 Conclusions and Future Directions
Our study comparing auditory threshold tuning curves measured by different electrophysiological methods in a single species highlights the great variability in
thresholds within an animal’s spectral range of best sensitivity among the different
techniques, suggesting that single curves generated for a particular species should
be interpreted with caution. Despite our current knowledge, there are still many
remaining questions and important areas of future work, several of which are briefl y
mentioned below.
1. More studies should be performed using multiple recording methods within a
single species, as well as in representatives of diverse species with different anatomical specializations. These studies should help clarify the methodological
and biological reasons for the different thresholds measured across multiple levels of the auditory pathway from peripheral endorgan hair cells to central processing levels in the brain. Ideally these studies should be conducted in the same
lab with identical experimental setups using similar stimulus delivery (i.e.,
speaker or shaker system) and threshold criteria, as well as characterization of
the stimulus in terms of both sound pressure and particle motion.
2. To truly understand the auditory capabilities of a particular species, multiple
electrophysiological recording techniques should also be combined and compared with behavioral audiograms within a single species. These data could then
be used in combination with an assessment of the ambient noise and sound
propagation properties of the fi sh’s natural habitat to gain a better understanding
of the ecology and evolution of a species’ auditory system. Electrophysiology
recordings using playbacks of natural sounds in addition to tonal stimuli will
also be informative. The enormous diversity of fi sh auditory sensitivities, inner
ear morphologies, and accessory hearing structures should provide fruitful future
comparisons for the selective pressures that have shaped the evolution of the
auditory system.
3. More electrophysiological recordings are also needed from the other putative
auditory endorgans, the utricle and lagena. In comparison with the numerous
studies on the saccule, there are few physiological recordings from these other
endorgans in fi shes (Fay and Olsho 1979 ; Lu et al. 2003 , 2004 ; Maruska and
K.P. Maruska and J.A. Sisneros
complex and unknown particle displacement fi elds (Parvulescu 1964 , 1967 ;
Akamatsu et al. 2002 ), it is important to recognize the relative contribution of
otolithic endorgan versus lateral line system input to “hearing thresholds” across
species. While in most cases it may not matter to the fi sh whether a biologically
relevant stimulus is detected by the inner ear, lateral line, or both, it does become
important when characterizing the response dynamics of individual sensory systems [see Braun and Sand 2014 for discussion of overlap between lateral line and
auditory systems in fi shes, and also Higgs and Radford, in this volume].
5 Conclusions and Future Directions
Our study comparing auditory threshold tuning curves measured by different electrophysiological methods in a single species highlights the great variability in
thresholds within an animal’s spectral range of best sensitivity among the different
techniques, suggesting that single curves generated for a particular species should
be interpreted with caution. Despite our current knowledge, there are still many
remaining questions and important areas of future work, several of which are briefl y
mentioned below.
1. More studies should be performed using multiple recording methods within a
single species, as well as in representatives of diverse species with different anatomical specializations. These studies should help clarify the methodological
and biological reasons for the different thresholds measured across multiple levels of the auditory pathway from peripheral endorgan hair cells to central processing levels in the brain. Ideally these studies should be conducted in the same
lab with identical experimental setups using similar stimulus delivery (i.e.,
speaker or shaker system) and threshold criteria, as well as characterization of
the stimulus in terms of both sound pressure and particle motion.
2. To truly understand the auditory capabilities of a particular species, multiple
electrophysiological recording techniques should also be combined and compared with behavioral audiograms within a single species. These data could then
be used in combination with an assessment of the ambient noise and sound
propagation properties of the fi sh’s natural habitat to gain a better understanding
of the ecology and evolution of a species’ auditory system. Electrophysiology
recordings using playbacks of natural sounds in addition to tonal stimuli will
also be informative. The enormous diversity of fi sh auditory sensitivities, inner
ear morphologies, and accessory hearing structures should provide fruitful future
comparisons for the selective pressures that have shaped the evolution of the
auditory system.
3. More electrophysiological recordings are also needed from the other putative
auditory endorgans, the utricle and lagena. In comparison with the numerous
studies on the saccule, there are few physiological recordings from these other
endorgans in fi shes (Fay and Olsho 1979 ; Lu et al. 2003 , 2004 ; Maruska and
K.P. Maruska and J.A. Sisneros