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Chapter 12

Chapter 12. 聽覺定位與聲景分析. 聽覺定位. 前方最準確，後方及兩側最不準確. 位置訊息 視覺 — 直接收錄 聽覺 — 須經計算. Fig. 12-3, p. 267. 位置線索有哪些？. 雙耳線索（ binaural cues ）  雙耳時間差 (interaural time difference, ITD) 正前方或後方 =0 側面可達 600 mircroseconds. 雙耳位準差（ interaural level difference, ILD ） 頭構成對聲音的屏障，使高頻音無法抵達異側耳 ILD 受音源位置影響.

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Chapter 12

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  1. Chapter 12 聽覺定位與聲景分析

  2. 聽覺定位 • 前方最準確，後方及兩側最不準確

  3. 位置訊息 • 視覺—直接收錄 • 聽覺—須經計算 Fig. 12-3, p. 267

  4. 位置線索有哪些？ • 雙耳線索（binaural cues） • 雙耳時間差 (interaural time difference, ITD) • 正前方或後方=0 • 側面可達600 mircroseconds

  5. 雙耳位準差（interaural level difference, ILD） • 頭構成對聲音的屏障，使高頻音無法抵達異側耳 • ILD 受音源位置影響

  6. The ILD is greater for location at higher frequencies.

  7. Fig. 12-6, p. 269

  8. ILD = ITD ? Cone of Confusion • Places with similar ambiguous information (see Fig. 12.7) • Ex. Both point A and B have the same left-ear distance and right-ear distance • Binaural cues vs. Monaural cues

  9. 單耳線索（monaural cue） • 雙耳時間或位準差無法用以瞭解音源之高度 • Head related transfer function (HRTF) • 是一種spectral cue • 耳朵所接收的聲波與音源不完全相同—經過了頭與耳殼的多次折射，與音源位置有關 • 如果戴耳機，消除了這些線索，會產生聲音來自頭部之內（internalization）的感受

  10. ITD, ILD & HRTF之比較 當聲音中有低頻成分時 ITD是低頻音音源判斷的主要線索 ILD對於高頻音音源判斷重要 ITD固定，ILD&HRTF變動 三者皆變動 （對於Azimuth location的判斷重要） Fig. 12-8, p. 270

  11. 落於elevation軸的音源判斷 • ITD, ILD不適用 • eg., A, B, C 的 ITD, ILD皆為0 D, E 的 ITD, ILD相等 • HRTF

  12. Fig. 12-9, p. 271

  13. 3-D 音響科技在軍事上的應用 • 美國AFRL (air force research lab)在軍機上裝設3-D ADG (audio display generator) • Benefits of 3-D audio technology to fighter pilots include improving situational awareness, workload management, and dynamic tactical operations.

  14. Specifically, these improvements would be realized by spatially separating radio communications, integrating radar warning receivers with 3-D audio to better perform friend-or-foe identification tasks, and using off-boresight targeting. • AFRL engineers demonstrated off-boresight targeting with an HMD in the Joint Air Strike Technology (JAST) aircraft.9 They integrated the 3-D ADG with an HMD by way of the mission computer. Then they presented potential target locations spatially with headphones. Pilots guided their visual line of sight using the 3-D audio sounds while flying at an angle to the potential target. • As a result of the successful JAST flights, the F-35 Joint Strike Fighter System Program Office currently lists 3-D audio as a planned technology upgrade.

  15. Auditory Localization: Narrowly Tuned ITD Neurons • Specific coding: Neurons narrowly tuned to a specific ITD • Inferior colliculus & superior olivary nuclei

  16. Jeffress Model for narrowly tuned ITD neurons • Coincidence detectors fire when signals from both ears arrive at the neuron simultaneously. • Other neurons fire to locations corresponding to other ITDs. Neuron 5: ITD = 0 Neuron 3 detects ITDs when the sound comes from a specific location on the right

  17. Auditory Localization: Broadly Tuned ITD Neurons • Broadly-tuned ITD neurons • Neurons in the left hemisphere respond best to sound from the right, and vice versa. • Location of sound indicated by the ratio of responding for two types of broadly tuned neurons. • Distributed coding Stimuli from: Left Front Right

  18. 生理基礎 • 雙耳時間差偵測器（神經元） • A1 neurons that fires when there is a specific time difference, each most responsive to a particular difference

  19. Topographic map (Barn owl) • Mesencephalicus lateralus dorsalis (MLD) • (inferior colliculus in mammals) • 對於音源位置（空間範圍）具選擇性反應的神經元 • A, B, C三個神經元的空間位置鄰近性與其接受域的空間鄰近性是平行的→topographic

  20. 聽皮質 • 聽皮質受損的病人也喪失聽覺定位能力 • 但對特定空間區域調適的（topographic）神經元在猴子卻找不到？ • panoramic neurons • 對所有方位都有反應，但程度反應組型）不同 Fig. 12-11, p. 273

  21. 音源辨認 • 聲景分析（Auditory scene analysis） • 如何辨認聲音中的不同來源者？ Fig. 12-10, p. 272

  22. 聽覺組織（auditory grouping）原則 • 是否也（如同視覺系統）是一些經驗法則（heuristics）的運用？---例如，來自同一來源的聲音通常也是源於某一個空間位置 • 位置（location） • 來自同一來源的聲音通常也是來自某一個空間位置或者一個逐漸改變的空間位置（如駛過的汽車） • 相似性（similarity of timbre and pitch） • The Wessel effect • 二種不同音色，節奏慢時呈現二種樂器輪流吹奏，節奏快時呈現二個 Fig. 12-13, p. 274

  23. Examples of auditory stream segregation • http://www.psych.mcgill.ca/labs/auditory/01.wav Fig. 12-14, p. 275

  24. Fig. 12-15, p. 276

  25. auditory stream segregation by pitch CD demo • http://www.psych.mcgill.ca/labs/auditory/01.wav Fig. 12-16, p. 276

  26. Captor tones • Distracter tones出現時，無法明確判斷X與Y的順序（b） • 但當與distracter tones 同音高的captor tones (C’s) 加入時，因為形成了一個stream，所以可以和X, Y分開，順序判斷因而恢復正確 Fig. 12-17, p. 277

  27. Grouping by frequency similarity

  28. 高低音錯覺（scale illusion） • Left ear – lo-hi-loright ear – hi-lo-hi as in (a) • The perceiver groups by similarity in pitch and perceive (b)--- the use of similarity heuristic that is correct most of the time Fig. 12-18, p. 277

  29. Grouping by pitch similarity

  30. 時間鄰近性（proximity in time） • 時間鄰近的聲音來自同一來源 • Good continuation • 維持恆定或平順改變的聲音應該來自同一來源

  31. Fig. 12-20, p. 278

  32. 經驗 • Three blind mice + jumping octave • The use of melody schema • 聽正常版本或被告知後就可認得出交織的旋律 Jumping octave version Normal version

  33. Hearing inside rooms • Direct vs. indirect sound

  34. Precedence effect • Fusion – lead and lag speaker 同時，聲源正中 • Lead領先1-5 ms，聲源落在接近lead speaker處 • 時間差> 5ms，兩個聲源 • Echo threshold • 室內聽覺經驗受影響 • 知覺聲音來自音源，而非反射處 Fig. 12-22, p. 279

  35. Fig. 12-23, p. 279

  36. Architectural Acoustics • Sounds reflected in rooms • Factors that affect perception in concert halls. • Reverberation time - the time is takes sound to decrease by 1/1000th of its original pressure • If it is too long, sounds are “muddled.” • If it is too short, sounds are “dead.” • Ideal times are around two seconds.

  37. Factors that Affect Perception in Concert Halls • Intimacy time - time between when sound leaves its source and when the first reflection arrives • Best time is around 20 ms. • Bass ratio - ratio of low to middle frequencies reflected from surfaces • High bass ratios are best. • Spaciousness factor - fraction of all the sound received by listener that is indirect • High spaciousness factors are best.

  38. Acoustics in Classrooms • Ideal reverberation time in classrooms is • .4 to .6 second for small classrooms. • 1.0 to 1.5 seconds for auditoriums. • These maximize ability to hear voices. • Most classrooms have times of one second or more. • Background noise is also problematic. • Signal to noise ratio should be +10 to +15 dB or more.

  39. Fig. 12-24, p. 281

  40. 視覺與聽覺的交互作用 • Visual capture • Sekuler et al. (1997) • Hearing influenced vision

  41. Fig. 12-25, p. 282

  42. 視覺影響聽覺 • 從小視覺剝奪的貓，在其anteriro ectosylvian sulcus (AES)發現視覺，聽覺，體感覺區的相對大小改變 • 盲人聽覺能力變佳 • The ERP response to light stimulation in parietal lobe is larger in deaf subjects than in hearing subjects.

  43. Information for distance • 手臂長度範圍內的判斷仰賴雙耳位準差（距離愈近，相差愈多） • 超過手臂長度的距離判斷表現不佳，可能與下列有關 • 聲壓水準低，距離遠 • 聲音低沈不清，距離遠 • Movement parallax • 在運動的時候，近的聲音改變位置較快 • 反射 • 間接的反射音多，距離遠

  44. 聽皮質不可或缺 • 右腦nonprimary auditory cortex有對於聲音運動方向具選擇性的神經元（cp w/ vision) • 猴子 • 病人 • 正常人fMRI

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