Interaural level difference processing as a function of frequency

Abstract

To localize in the azimuthal plane, humans utilize interaural time differences and interaural level differences (ILDs). For sounds presented in the free field at different azimuthal locations, ILDs generated by the head are complex functions that are frequency dependent and non-monotonic, and are thought to contribute towards sound localization primarily at frequencies above 1500 Hz. However, previous studies have shown that ILD sensitivity is relatively frequency independent for tones presented over headphones, even at frequencies below 1500 Hz. The purpose of this study was to carefully re-investigate the frequency dependency of ILD sensitivity in normal-hearing listeners. Ten normal-hearing listeners were presented ILDs using insert earphones at 31 frequencies between 100 and 11,000 Hz. A 20-dB range of level roving was used to limit listeners’ ability to use monaural level cues to perform the task. On average, ILD sensitivity had several high and low sensitivity frequency regions, was best at 7000 Hz (1.5 dB) and worst at 1000 Hz (2.5 dB). Individuals also showed some unique frequency dependent patterns. These results suggest that ILD sensitivity is frequency dependent and neural models of ILD processing need to accommodate this dependency.