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Explaining High‐Frequency Hearing
Author(s) -
Heffner Rickye,
Heffner Henry
Publication year - 2010
Publication title -
the anatomical record: advances in integrative anatomy and evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.678
H-Index - 62
eISSN - 1932-8494
pISSN - 1932-8486
DOI - 10.1002/ar.21292
Subject(s) - basilar membrane , acoustics , sound localization , audiology , cochlea , binaural recording , physics , medicine
Kirk and Gosselin-Ildari (2009) have documented a reliable correlation between the volume of the cochlear labyrinth and high-frequency hearing limit among those Primates for which data are available. Specifically, the correlation shows that primates with small cochleas have better high-frequency hearing than those with larger cochleas. In discussing the implications of their finding, they provide a quote from one of our articles (Heffner, 2004) that they claim states that the size of the cochlea and the length of the basilar membrane are not functionally related to high-frequency hearing limit. However, that is a mistaken interpretation. The paragraph from which the quote is taken is making the point that the relationship between functional head size and high-frequency hearing limit is not explained by the size of the middle and inner ear. Functional head size is defined as the maximum time it takes for a sound to travel in air or water from one ear to the other. This measure indicates how high a mammal must hear to use the two high-frequency cues for sound localization—the binaural frequency-intensity spectral cues and pinna cues. The smaller the functional head size, the higher a mammal must hear for its head and pinnae to generate the high-frequency cues needed to locate the source of a sound. Because both functional head size and the dimensions of the ear tend to increase with the size of the animal, it is necessary to perform a partial correlational analysis to determine how much of the variance in high-frequency hearing is accounted for by each factor. Restricting our analysis to those mammals that localize sound, there are 21 species for which we have data on functional interaural distance, basilar membrane length, and high-frequency hearing limit (Table 1). For these species, controlling for the length of the basilar membrane causes the correlation between functional head size and high-frequency hearing, r ¼ 0.870 (P < 0.0001), to fall only slightly to r ¼ 0.814 (P < 0.0001). However, the correlation between highfrequency hearing and the length of the basilar membrane, r ¼ 0.578 (P ¼ 0.006), falls to chance, r ¼ þ0.269 (P ¼ 0.257), when controlling for functional head size. This is why we say that the relationship between functional head size and high-frequency hearing is not explained by the size of the inner ear. Kirk and Gosselin-Ildari have found that among