Body size and assessment of auditory function: A comparative conundrum

Abstract

One goal of the bioacoustics community is to compare auditory function among species representing the entire animal kingdom, including terrestrial mammals. As an alternative to behavioral measures, it is frequently necessary, and/or desirable, to assess auditory function using electrophysiological approaches. Body size is an important factor that can effect the distribution and amplitude of evoked brain potentials (EP) measured from the surface of the head and the ranges of body mass and size within Mammalia are extensive. Consequently, the development of comparison protocols must include consideration of factors affected by size differences, e.g., the distance between EP generators and recording electrodes and the thickness of the skull. Ultimately, these factors, along with the acoustical character of the recording environment itself, affect acquired signal-to-noise ratios (SNR). In this context it is notable that the SNR associated with large animals are reduced relative to those observed in smaller animals, making the comparison of results from one species to another complex. This procedural challenge is further complicated by the requirement to acquire data efficiently and rapidly in recording environments that are non-optimal from an acoustic perspective. These issues will be addressed by considering auditory brainstem responses in tigers, bobcats, manuls, sandcats and rodents.