Tones of 500 and 2000hz are heard with alternating interaural phases of +/- 45 degrees
Next the inter aural arrivaltime of a click is varied. The apparent location of the click appears to move
Finally the inter aural intensity difference of a 250Hz and a 4000Hz tone are varied
The most important benefit we derive from binaural hearing is the sense of loc tion of the sound source. Although some degree of localization is possible in monaural listening, binaural listening greatly enhances our ability to sense the direction of a sound source.
Although localization also includes up-down and front-back discrimination, attention is focussed on side-to-side discrimination or lateralization. When we lister headphones, we lose front-back information, so that lateralization becomes exaggerated; the image of the source appears to switch from one side of the head to the other moving "through the head" , or the sound source appears to be "in the head."
Lord Rayleigh (1907) was one of the first to recognize the importance of time and intensity cues at low frequency and high frequency, respectively. Low-frequency sounds are lateralized mainly on the basis of interaural time difference, whereas high-freqency sounds are localized mainly on the basis of interaural intensity differences.
In the first example, tones of 500 Hz and then 2000 Hz are heard with alternating interaural phases of plus and minus 45 degrees. At 500 Hz, the image switches side to side as the phase changes. At 2000 Hz, on the other hand, no such movement perceived. (The interaural time difference varies from delta t =delta theta/2PI f = 250 to -250 microseconds in the first case, but only 62.5 to -62.5 microseconds at 2000 Hz).
In the second example, a 100 microsecond pulse (heard as a "click") is presented with an interaural time difference that cycles from 5 ms to -5 ms, so that the source of the appears to move between left and right.
The third example uses tones of 250 and 4000 Hz to illustrate the effects of interaural intensity difference at low and high frequency. The interaural intensity changes (in 1.25 s) from 32 dB to -32 dB. In both cases, the image moves from side to side. Although the auditory system processes interaural intensity cues at both low and high frequencies the head does not cast much of an acoustic shadow at low frequency (due to dlffraction) and hence there is little intensity difference even when the source is located to one side of the head.