Abstract
A sound source with non-zero azimuth leads to interaural time level differences (ITD and ILD). Studies on hearing system imply that these cues are encoded in different parts of the brain, but combined to produce a single lateralization percept as evidenced by experiments indicating trading between them. According to the duplex theory of sound lateralization, ITD and ILD play a more significant role in low-frequency and high-frequency stimulations, respectively. In this study, ITD and ILD, which were extracted from a generic head-related transfer functions, were imposed on a complex sound consisting of two low- and seven high-frequency tones. Two-alternative forced-choice behavioral tests were employed to assess the accuracy in identifying a change in lateralization. Based on a diversity combination model and using the error rate data obtained from the tests, the weights of the ITD and ILD cues in their integration were determined by incorporating a bias observed for inward shifts. The weights of the two cues were found to change with the azimuth of the sound source. While the ILD appears to be the optimal cue for the azimuths near the midline, the ITD and ILD weights turn to be balanced for the azimuths far from the midline.
Highlights
The localization of sound sources plays a crucial role in animal behavior, and it is a very important function for humans
Detecting sound source direction in horizontal plane is based on the disparities in time and the intensity of the sound reaching both ears, namely interaural time difference (ITD) and level differences (ILD) which are assumed to be responsible for sound lateralization in low and high frequencies, respectively [1]
Studies conducted on the hearing system suggest that ITD and ILD cues to sound lateralization are processed in the medial superior olive (MSO) and the lateral superior olive (LSO) sub-nulei of the superior olivary complex (SOC) located in the brainstem, respectively
Summary
The localization of sound sources plays a crucial role in animal behavior, and it is a very important function for humans. Detecting sound source direction in horizontal plane is based on the disparities in time and the intensity of the sound reaching both ears, namely interaural time difference (ITD) and level differences (ILD) which are assumed to be responsible for sound lateralization in low and high frequencies, respectively [1]. This frequency-based behavioral dichotomy, which is known as the duplex theory of sound lateralization, has a physio-anatomical counterpart in the brain as is briefly explained below. These impulses provide excitatory input to the neurons of ipsilateral
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