聲音於空間中的定位是大腦聽覺系統的基本功能。與其它感覺器官不同，聽覺器官對聲源空間位置的判斷，主要依賴於雙耳資訊的差異比較；雖然在某些情況下，利用頭部轉動或是單耳資訊亦可判斷出聲源的位置。 自然界的大部分聲音皆經過振幅調變(AM)或頻率調變(FM)而成，其中頻率調變掃描訊號(FM sweeps)即為 FM 訊號中一種重要的類型。本研究之主要目的，乃是以線性頻率掃描訊號(Linear FM sweeps)為工具，探討於虛擬環境中，大腦聽覺系統對於一個複合音所產生的雙耳差異資訊，其偵測機制為何；並進一步討論訊號的調變速率對聲音定位能力所產生的影響。 目前初步結果顯示，對於相同掃描幅度的 FM sweeps，訊號長度越長，聽覺系統越容易產生訊號移動的感覺，使得聲音定位效果減弱；而對於相同時間長度的 SFM(Sinusoidal Frequency Modulated)訊號，較快的調變速率，聽覺系統則產生較好的定位效果；而這些相關複合音的空間定位之研究，則將在本文中被討論。 The basic ability of human auditory system is spatial sound localization.Different from other sensory organs, for determining sound sources in space, the auditory organ depends mainly on the differential comparison of binaural cues; although it could be also ascertained by turning heads or using monaural cues under some conditions. The aim of this research firstly is to investigate the ability of human observers to process interaural time difference produced by complex tone. We use directional FM sweeps, one of an important class of FM sounds, commonly discovered in natural communication signals such as speech. Secondly, it examines the effect of modulation rate to sound localization. The preliminary results suggest that for the same sweep range of FM signals, as the signal length extends, the ability of sound localization decreases, due to the fact that it is easier for the auditory system to percept signal motion. As for the SFM of the same temporal length, the higher the modulation rate, the better the sound localization determined by the auditory system. Implications of these findings for the localization of complex sounds are discussed.
