Lateralization based on interaural differences in the second-order amplitude modulator

Mathias Dietz, Stephan D. Ewert, and Volker Hohmann,
J. Acoust. Soc. Am.  131(1), 398-408 (2012)

Humans have the ability to blindly localize sound sources. A sound wave impinging on the head from the right side will reach the right ear earlier than the left ear (interaural time difference) and have a higher intensity at the right ear than at the left (interaural intensity difference). The human auditory system is highly sensitive to determine these interaural differences by comparing neural responses from the left and the right ear. Research into binaural hearing deals with how the brain exploits these interaural differences.

In controlled laboratory experiments binaural stimuli are often presented via headphones and an interaural time difference is introduced between the signal presented to the left and right ear. The interaural time difference usually results in a lateralization of the percept toward the side of the head that receives the temporally leading signal.

In this psychoacoustic study with normal hearing listeners, the interaural time difference was applied only to the function that temporally alters the amplitude modulation depth, not to the entire amplitude modulation or to the entire signal. The main result is that the stimuli were not always lateralized.

The obtained data helped refining models of binaural hearing which in turn are important to improve digital hearing aids. In particular the data supports recent neurophysiologic findings that a chain of delay compensating elements does not exist in mammals including humans.

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