Question

Describe the two binaural cues used by the auditory system to localize sounds in space. What aspects of the interaction of the sound with the listener lead to the existence of these two cues? What is the duplex theory of sound localization? How does the usefulness of these two cues change as a function of frequency? Is the duplex theory applicable to all types of stimuli? Cite an auditory ability that argues that interaural differences of time can be used when the spectrum of the sound (e.g., the frequencies at which it has energy) is confined to high frequencies. Describe the neurophysiological mechanisms for cells that are selective to different interaural differences of time in the medial superior olive. How does one predict sensitivity of units to interaural differences of time from monaural response properties? How are interaural differences of level extracted in the lateral superior olive?

Answer 1

1. Describe the two binaural cues used by the auditory system to localize sounds in space.

For binaural cues, the information of two ears is needed. They fall into two categories:

a. Interraunal time differences (ITDs):

Interaunal time differences are caused by the different propagation times at the sound wave from the source to both ears. For eg. a source to the left, the sound wave will reach the left ear slightly before it reaches to the right ear.

b. Interaunal level differences (ILDs):

Interaunal level differences are caused by the acoustic shadow of the head. For eg. a source to the left, the sound wave will arrive at the left ear slightly louder than at right ear.

2. What aspects of the interaction of the sound with the listener lead to the existence of these two cues?

The direction or location and distance of the detected sound with the listener lead to the existence of these cues.

Direction: It is also called as azimuth which specifies the locations that vary from left to right relative to the listener and elevation which is the sound location that are up and down relative to the listener.

Distance: The distance of the sound specifies how far the sound source is from the listener.

3. What is the duplex theory of sound localization?

The Duplex theory is proposed by Lord Rayleigh in 1970. This theory provides an explaination for the ability of humans to localise sounds by time differences between the sounds reaching each ear (Interaunal time differences) and differences in sound levels entering the ears (Interaunal level differences).

4. How does the usefulness of these two cues change as a function of frequency?

The first binaural cue i.e. Interaunal time differences provides a cue for sound localization of low frequency whereas the second binaural cue i.e. Interaunal level differences provides a cue for sound localization of high frequency.