![]() It proves that when two ears receive a sound stimulus, the resultant loudness sensation is greater than that occurring with just one ear. It is common experience that if one is made to block one ear with an ear plug, the loudness of sound coming from a television in front immediately goes down which is restored as the ear is unplugged. It is, thus, another measurable dimension associated with binaural hearing. This is called binaural loudness summation. ![]() The number doubles when the two ears are used instead of one ear for a sound coming from the front of the listener. Each ear contributes substantially to the action potentials that reach the brainstem. Ii) Binaural summation of loudness: Loudness of a sound depends on the number of action potentials triggered by it. The dual brainstem pathways provide anatomical and physiological correlates of the Duplex theory. ITDs are extracted by MSO neurons in which ITD sensitivity results from the coincident arrival of excitatory inputs from the two ears ILDs are extracted by LSO neurons via a subtraction-like process resulting from inhibitory inputs from the contralateral and excitatory inputs from the ipsilateral ear. Anatomical and physiological studies have revealed two parallel brainstem pathways that appear to encode ITDs and ILDs separately. ITD is a major factor in localizing lower frequency sounds of 5KHz). A trained ear can detect a time difference as slight as 30 microsec. The maximum time lag for sound generated at one side of the head is around 0.6 millisec. These changes are analyzed by lower and higher auditory processing system. This change could be (a) Inter-aural Time Difference (ITD), (b) Inter-aural Loudness Difference (ILD), (c) Inter-aural Frequency Difference (IFD) and (d) Head Related Transfer Function (HRTF). If there is slightest change in any of these characteristics, the hearing mechanism detects it and reacts to this change on a new bit of information to be analyzed in binaural hearing. Similarly, sounds with equal frequency, intensity and time, originating directly at the back of an individual with normal hearing, may also be literally indistinguishable from one another. Thus, two sounds with equal frequency and intensity, originating directly in front of an individual with normal hearing, which arrive at the ears at the same time may be literally indistinguishable from one another. PhysiologyĪ sound stimulus is distinguished from another by its characteristics of frequency, intensity and time. This article aims to help in understanding how the auditory spatial cues arising from individual outer and inner ears are computed and processed at specialized subcortical centres and lead to binaural hearing. Spatial hearing provides cues as to the relative number and location of sound sources and objects in the environment, helps in determining the dimension and characteristics of rooms and enclosed spaces, and contributes to the “cocktail party effect”, whereby the listeners are able to hear out against other interfering voices in crowded listening environments. One of the key factors that empowers him with his communication skill is spatial hearing. Among the mammals, human is considered to be the one gifted with most developed communication skill. ![]() It allows us to (a) ‘map’ the sound in space, (b) pick out soft sounds, (c) pick out distant sound or speech and (d) separate a single voice from surrounding background noise. Binaural hearing is literally opposite of monaural hearing. ![]() Just as we use two eyes to see in three dimensions, we use two ears for “dimensional hearing”. Use of both the ears to perceive the world of sound around us is defined as Binaural hearing. The main difference between the two ears is that they are not in the same place.
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