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The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This pathlength difference results in a time difference between the sound's arrivals at the ears, which is detected and aids the process of identifying the direction of sound source. When a signal is produced in the horizontal plane, its angle in relation to the head is referred to as its azimuth, with 0 degrees (0°) azimuth being directly in front of the listener, 90° to the right, and 180° being directly behind. ==Different methods for measuring ITDs== *For an abrupt stimulus such as a click, onset ITDs are measured. An onset ITD is the time difference between the onset of the signal reaching two ears. *A transient ITD can be measured when using a random noise stimulus and is calculated as the time difference between a set peak of the noise stimulus reaching the ears. *If the stimulus used is not abrupt but periodic then ongoing ITDs are measured. This is where the waveforms reaching both ears can be shifted in time until they perfectly match up and the size of this shift is recorded as the ITD. This shift is known as the interaural phase difference (IPD) and can be used for measuring the ITDs of periodic inputs such as pure tones and amplitude modulated stimuli. An amplitude modulated stimulus IPD can be assessed by looking at either the waveform envelope or the waveform fine structure. 15315113 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Interaural time difference」の詳細全文を読む スポンサード リンク
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