AUTHOR=HARTMANN WILLIAM M., Macaulay Eric J.

TITLE=Anatomical limits on interaural time differences: an ecological perspective

JOURNAL=Frontiers in Neuroscience

VOLUME=Volume 8 - 2014

YEAR=2014

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2014.00034

DOI=10.3389/fnins.2014.00034

ISSN=1662-453X

ABSTRACT=Human listeners, and other animals too, use interaural time differences (ITD)<br/>to localize sounds. If the sounds are pure tones, a simple frequency factor<br/>relates the ITD to the interaural phase difference (IPD), for which there are<br/>known iso-IPD boundaries, 90$^\circ$, 180$^\circ$~\ldots defining regions of<br/>spatial perception. In this article, iso-IPD boundaries for humans are<br/>translated into azimuths using a spherical head model, and the calculations<br/>are checked by free-field measurements. The translated boundaries provide<br/>quantitative tests of an ecological interpretation for the dramatic onset of<br/>ITD insensitivity at high frequencies. According to this interpretation, the<br/>insensitivity serves as a defense against misinformation and can be attributed<br/>to limits on binaural processing in the brainstem. Calculations show that the<br/>ecological explanation passes the tests only if the binaural brainstem<br/>properties evolved or developed consistent with heads that are 50\% smaller<br/>than current adult heads. Measurements on more realistic head shapes relax<br/>that requirement only slightly. The problem posed by the discrepancy between<br/>the current head size and a smaller, ideal head size was apparently solved by<br/>the evolution or development of central processes that discount large IPDs in<br/>favor of interaural level differences. The latter become more important with<br/>increasing head size.