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. 2014 Oct 1;8:116. doi: 10.3389/fncir.2014.00116

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Copyright © 2014 Grothe and Pecka.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Binaural cues for sound localization depend on sound frequency and head size. Upper left: interaural time differences (ITDs): for frequencies below ∼2 kHz, the difference in the arrival time (Δt) of a sound wave (gray lines) at the two ears is used to localize a sound-source in the horizontal plane. ITDs depend on the angle of the sound-source relative to the head axis and the interaural distance (i.e., head size) of the individual. Upper right: interaural level differences (ILDs): for frequencies higher than ∼2 kHz, the shadowing effect of the head creates differences in the intensity of the sounds at the two ears (ΔI) that are utilized for sound localization in the horizontal plane. ILDs for a particular sound-source position increase with increasing frequencies. Lower: range of ILDs (inner hemicycle) and ITDs (middle hemicycle) are illustrated across the range of azimuthal sound-source positions (outer hemicycle) for a small mammal (the bat Molussus ater). While ITDs are minute even for the most lateralized sound-source positions (±50 μs), sizable ILDs are generated by the relatively small head already at moderately high frequencies (35 kHz for this example). Modified with permission from Harnischfeger et al. (1985).