| 摘要: | 音高知覺是語音理解、音樂欣賞以及聽覺場域分析中的關鍵因素。音高的產生大致來自兩個主要的機制理論：時間理論，源自神經元相位鎖定的放電模式以追蹤聲波的週期性；以及位置理論，源自耳蝸音頻拓樸(tonotopy)上的分佈。雖然兩種機制皆獲得支持，但它們的交互作用仍未被完全釐清，尤其在高頻音，調幅(AM)扮演更重要的角色。音訊中的調幅或包絡如何影響音高知覺，以及載波特性如何影響時間性音高 (time pitch)，仍是未解之謎。 本研究使用轉置音(transposed tones)，將位置(載波)與時間(包絡)線索分離，以探討音頻拓樸對時間性音高的影響。
實驗一，包絡被轉置到 1至10 kHz 的高頻載波以及噪音載波上。透過音高辨別、音程辨別與旋律識別任務，我們確認高頻聲音中的時間包絡能引發強而明顯的音高知覺，其表現隨著載波頻率增加而提升，且在純音載波上優於噪音載波。這些結果顯示，時間包絡對音高知覺的重要性，及其所受音頻拓樸的影響。
實驗二進一步檢驗多載波的轉置音。雖然諧波會產生基音的音高知覺，但此現象在轉置後並不存在。我們發現，轉置音的音高知覺乃是由最低頻載波的包絡週期性所決定的。此外，我們更發現，包絡頻率比載波更能決定轉置音的音高知覺。
為了分析這些結果，我們採用全域希爾伯特頻譜分析（Holo-Hilbert Spectral Analysis, HHSA），這是一種非線性方法，特別適合分析非線性與非穩態訊號，能提供載波頻率與調幅頻率的二維呈現。結果顯示，HHSA 呈現出的主要調幅頻率與轉置音的音高知覺完全相符。
總結而言，本研究證明了時間性的資訊(包絡)能夠在高頻聲音中提供強而明顯的音高知覺。同時，HHSA 提供一個良好的聽覺訊號分析，可以分析出與音高知覺相符的調幅頻率。這些基於轉置音實驗與 HHSA 的研究，不僅深化了在音高知覺中，音頻拓樸與時間訊息交互作用的理解，也為聽覺輔具的發展提出了新的方向。
;Pitch perception is essential to speech understanding, music appreciation, and auditory scene analysis. It arises from two complementary mechanisms: the time theory, derived from phase-locked neural firing patterns tracking waveform periodicity, and the place theory, derived from excitation along the cochlear tonotopic map. While both mechanisms are supported, their interaction remains unresolved, particularly in high-frequency hearing where amplitude modulation (AM) cues dominate. Although AM is preserved throughout the auditory system, how it contributes to pitch perception and how carrier properties shape temporal pitch remain open questions.
This dissertation uses transposed tones, which dissociate spectral (carrier/place) and temporal (envelope/time) cues, to probe tonotopic influences on temporal-based pitch. In Experiment 1, AM envelopes were transposed onto carriers from 1 to 10 kHz and onto noise carriers. Pitch discrimination, interval discrimination, and melody identification tasks confirmed that temporal envelope fluctuations in high-frequency sounds evoke a robust pitch percept. Performance improved with increasing carrier frequency and was stronger for tonal than noise carriers. These findings indicate that pitch information provided by temporal envelope is more pronounced than previously assumed and shaped by tonotopic position.
Experiment 2 extended this by examining transposed tones on multiple carriers. Though harmonic complexes normally produce a fundamental pitch, this phenomenon failed to preserved after transposition. We found the envelope periodicity on the lowest-frequency tonotopy dominates the pitch of transposed tones. Furthermore, we found pitch perception is driven more by envelope frequency than carrier spectrum in transposed tones.
To analyze these results, we employed Holo-Hilbert Spectral Analysis (HHSA), a nonlinear method providing a two-dimensional representation of instantaneous frequency and AM. Unlike Fourier or wavelet analyses, HHSA is adaptive and suitable for nonlinear and non-stationary signals such as speech or music. HHSA consistently revealed the dominant AM frequency that matched perceived pitch.
In summary, this work demonstrates that temporal envelope cues can support robust pitch perception at high frequencies. HHSA further provides a powerful analytic framework to reveal the AM dynamics underlying these percepts. These findings from transposed-tone experiments and HHSA advance understanding of the interplay between spectral and temporal coding in pitch perception and suggest new directions for auditory prosthetics. |
