音高知覺為人類溝通(如:語言和音樂等)的重要基石，而包封(envelope)和載波(carrier)是組成音高知覺相關訊號的共通基本元素。先前研究主要皆以改變偵測(change detection)作業間接檢視人的音高聽辨表現，因此無法得知包封和載波構成的複合訊號所促成的直接音高，且包封音高訊息的解析是否受到載波的組成頻區干擾仍具爭議性。此外，對於腦(幹)區神經元的頻率跟隨反應(frequency following response; FFR)如何表徵包封和載波的音高資訊也尚未明瞭。本計畫擬藉由聽覺物理學實驗法和腦區頻率跟隨反應，探討複合訊號中載波的組成成份如何影響聆聽者感知其包封所對應到的音高。實驗一檢視載波組成成份對包封音高區辨表現的影響，使用閾限追蹤法來偵測受試者在聆聽相對音程和兒歌旋律的音高辨識表現，追蹤音高區辨的閾值是否會隨包封移置到不同種類的低頻、高頻載波以及寬頻雜訊上呈現單向增加趨勢。實驗二使用音高系統中第二個八度的音為包封的基頻，並將此包封移到不同種類的低頻、高頻、或寬頻雜訊載波上，再由具有絕對音感能力者可判定訊號中音名(如:"Do Mi So"等)所直接對應到之頻率的特質，以釐清載波組成成份對直接指認包封音高音名準確度之影響。實驗三則以FFR探討神經元記錄複合訊號中包封和載波所促成的音高知覺過程，預期在FFR的頻譜分析上，複合訊號中包封的音高頻率(如:"Do")可在相對應的FFR頻域觀察到峰值，且其振幅大小會和載波組成之頻區範圍有相關。 ;All natural sounds are composed of dynamic temporal modulations of acoustic features (envelope) imposed on carrier signals. The ability to perceive the pitch of these envelope-modulated sounds is crucial in understanding speech, segregating sound sources, and conveying prosodic and melodic information. Current evidence on the pitch percept evoked by the envelope modulation of complex sounds is controversial concerning the role of carrier spectral content. Additionally, pitch change detection or discrimination paradigms primarily used in previous studies have rendered the direct pitch identification performance less examined. The proposed research aims to provide perceptual data from human listeners examining the effect of carrier type on pitch perception of envelope-modulated tone complexes in relation to evidence from neural pitch synchronization via auditory-evoked frequency following response. Experiment 1 investigates whether the pitch percept elicited by carriers composed of different spectral content modulated by the same envelope feature is sufficiently strong to allow the comparison of musical pitch. An adaptive staircase procedure is used to test listener's ability to discriminate musical-pitch interval and identify simple melodies composed of musical-note envelope transposed to different carrier types. Envelope modulation pattern transposed to broadband noise is expected to evoke the strongest melodic pitch percepts compared to high-or low-frequency sinusoidal carriers. Experiment 2 examines whether the "direct”pitch identified from the sound's envelope modulation pattern is contingent on spectral features of the carrier signal. A novel transposed musical-note enveloped complex stimuli is developed to dissociate the tone's spectral carrier and temporal modulation envelope features. Individuals possessing absolute pitch is used to provide a direct pitch assessment of the musical note-name associated with the pitch percept emerged from envelope-modulation feature on different carriers. Performance accuracy of musical pitch identification corresponding to high-frequency transposed tones should significantly diminish if pitch extraction mechanism based on temporal modulation is insufficient for musical-pitch encoding. The last objective of the proposed research is to examine the subcortical synchronization representation of the defining musical pitch percepts evoked by envelope modulation as a function of spectral content of carrier signals. Frequency following responses will be recorded from the same group of absolute pitch listeners in a randomized design with carrier type as separate blocks. We expect to observe a spectral peak in the frequency-following response waveforms at the frequency corresponding to the musical pitch identified based on the musical-note envelope transposed tone-complex. The frequency following response measures coupled with the perceptual data should help to elucidate the mechanisms for integrating envelope and carrier information in coding (musical) pitch percept of complex sounds.
