Chapter 11 聲音，聽覺系統與音調知覺

聽覺可以感知視覺系統某些不及之處

聽覺之功能 訊號（signaling） 溝通（communication） 樂趣（pleasure） 過街時的導盲鈴、身後的腳步聲 speech Blindness isolates you from things, but deafness isolates you from people. Helen Keller 樂趣（pleasure） 音樂

什麼是聲音？--物理或知覺屬性 森林中一棵大樹倒下，但沒有人聽到，這樣算有聲音嗎？

Yes, 聲音來自空氣或其他介質中的壓力變動 No, 聲音是來自於「聽」的經驗 聲波

聲音的物理與知覺屬性 聲波 速率340m/sec (light 1,500m/sec) 振幅（Amplitude）

振幅愈大，響度愈大 Figure 11.3: Increases of the physical property of amplitude from small to large (blue arrow) are associated with increases in the perceptual experience of loudness (red arrow). Fig. 11-3, p. 236

振幅測量 反映最大與最小的差距，但壓縮較大值端，以模擬心理響度 分貝（dB）- after A. G. Bell 20 log (p/p0) p0 - 比較基準（1000Hz純音恰可被聽到的閾值水準，約為20 micropascals） eg., p=20 20 log (20/20)=20 x 0=0 dBSPL p=2000（100倍） 20 log (2000/20) = 20 x 2=40 dB SPL 100倍 +40 dB 10倍 →+20 dB 100倍→ +40 dB 1000倍→ +60 dB

響度隨強度（dB）呈線性增加

頻率（Frequency）與音調（pitch）有關 Hertz-cycles/sec 500 Hz 1000 Hz 4000 Hz Figure 11.5: Increases of the physical property of frequency from low to high (blue arrow) are associated with increases in the perceptual experience of pitch (red arrow). Fig. 11-5, p. 237

Complex Tones The repetition rate of a complex tone : Fundamental Frequency = First Harmonic Ex. 200 Hz First harmonic Second harmonic Third harmonic Fourth harmonic

Removal of the first harmonic results in a sound with the same perceived pitch, but affect perception of the tone. The repetition rate is still 200 Hz.

八度（octave） A0=27.5, A1=2xA0, A2=4xA0,………..

20~20000 Hz為人類可聽範圍(range of hearing) 可聽曲線（audiblity curve） 最敏感2000-4000 Hz—與speech有關 聽覺反應區（auditory response area）

Threshold for feeling OSHA 不可大於90 dB (8hr/day) 其他動物 更低頻：大象，鴿子 更高頻：海豚，狗

等響曲線（equal loudness curve） 響度由聲壓水準及頻率共同決定 eg., 40dB, 100Hz -- B 40dB, 1000Hz --C B與C並未落在同一條等響曲線上—響度不同（C>B） 等響曲線（equal loudness curve）

音強時，各種頻率的感受性相近；但音弱時，最高或最低頻音都不易聽見 eg., 與40dB1000Hz相等響度的音構成“40” 曲線 音強時，各種頻率的感受性相近；但音弱時，最高或最低頻音都不易聽見 「LOUDNESS」鍵

Perceiving sound: pitch, loudness, and timpre. 音色（Timbre） 純音vs.複合音 單一vs. 多種頻率組成 White noise Complex sound 樂器的差異 樂音多由若干頻率純音組合而成，但其他日常生活中常見的聲音則更為複雜

組合方式界定每種樂音的獨特性 相加合成（additive synthesis） 純音440Hz 2nd harmonic 880Hz 3rd harmonic 1320Hz 相加合成（additive synthesis） 由fundamental frequency加上harmonics（是fundamental frequency 的倍數） 組合方式界定每種樂音的獨特性 Figure 11.8: Additive synthesis. (a) Pressure changes for a pure tone with frequency = 440 Hz. (b) The second harmonic of this tone, with a frequency of 880 Hz. (c) The third harmonic, with a frequency of 1,320 Hz. (d) The sum of the three harmonics creates the waveform for a complex tone. Fig. 11-8, p. 240

Frequency spectrum

Figure 11.10: Frequency spectra for a guitar, a bassoon, and an alto saxophone playing a tone with a fundamental frequency of 196 Hz. The position of the lines on the horizontal axis indicates the frequencies of the harmonics and their height indicates their intensities. Fig. 11-10, p. 240

聽覺系統的結構與功能 聽覺系統需要達成三項功能 將聲波傳達至受器 將聲波所傳達的氣壓變動轉換為電訊號 設法使電訊號傳遞如音調，響度，音色，定位等聲音的屬性

聲音如何抵達受器？ 外耳（outer ear） Pinna Auditory canal 約3cm，保護耳膜，中耳 對2000-5000 Hz有放大效果（resonant frequency of the canal）

Figure 11.11: The ear, showing its three subdivisions—outer, middle, and inner. Fig. 11-11, p. 242

中耳（middle ear） 耳膜（tympanic membrane） 聽小骨（ossicles） Tympanic membrane  malleus（槌骨）  incus（砧骨）  stapes（鐙骨）  oval window

為何需要三塊聽小骨？ 由外耳/中耳低密度的空氣至內耳較高密度的液體時，聲波的震動只能傳遞極少的部分 聽小骨協助放大訊號以解決這個問題 魚就不需要「中耳」的功能

如何放大？ Acoustic reflex 將較大面積的耳膜振動集中於較小面積的鐙骨以增加單位面積接收的壓力 聽小骨的槓桿運作 Middle-ear muscles 與聽小骨連結，在音量極高時收縮來牽制聽小骨的動作 增加22倍

鐙骨振擊卵形窗造成內耳（inner ear）液體振動 內耳結構 耳蝸（cochlea） 充滿液體 scala vestibuli（上半） scala tympani (下半) Cochlea partition

organ of Corti 有hair cell—聽覺受器 Inner hair cell vs organ of Corti 有hair cell—聽覺受器 Inner hair cell vs. outer hair cell 耳蝸內液體振動造成cochlea partition 上下運動，hair cell頂端纖毛彎曲，傳送電訊號 basilar membrane tectorial membrane

stapes oval window liquid in scala vestibuli basilar membrane stapes pulls back, then basilar membrane  Organ of Corti  Tectorial membrane 

Cilia bend in a specific direction  Ion channels opening  Ions flow across the cell membrane Electrical signals The release of neural transmitter from the inner hair cell

Inner hair cell 之纖毛彎曲造成depolarize 或 hyperpolarize （釋放神經傳導物質或停止傳導），傳送電訊號 可以產生電訊號的纖毛彎曲幅度不大—敏感度高

Place theory of hearing 聽覺系統如何代表頻率訊息？

Bekesy’s theory (1961諾貝爾生理與醫學獎得主） traveling wave motion of the basilar membrane

Basilar membrane的基部（base）較窄，較緊

Envelope of the traveling wave可以顯示不同部位hair cell受到最大影響的幅度 P點附近的hair cell送出最強的神經訊號 P點的位置受聲音頻率的影響

P點的位置受聲音頻率的影響 低頻-apex 高頻-base

位置編碼的生理證據 tonotopic map 低頻.-apex 高頻.-base

測量恰可引發神經元反應的dB SPL，可得頻率調適曲線（tuning curves） 該神經元最為敏感的頻率稱為characteristic frequency

貓聽神經的 frequency tuning curve

心理物理證據 auditory masking pp. 275

Envelope的重疊程度解釋何以有不對稱的遮蔽效應

tuning curve 為何很窄？ Outer hair cells產生的運動影響basilar membrane的運動 依頻率使特定範圍的basilar membrane 活動受強化 高頻音—base 低頻音--apex

Basilar membrane上的頻率分析 Cochlea包含多組濾波器（filters），每組處理特定的頻率範圍

Figure 11.30: The procedure for measuring a psychophysical tuning curve. (a) A 10-dB SPL test tone (blue arrow) is presented; (b) then a series of masking tones (red arrows) are presented at each frequency. The psychophysical tuning curve is determined by measuring the sound pressure of each masking tone that reduces the perception of the test tone to threshold. Fig. 11-30, p. 251

一系列的tuning curve，低點連起來恰符合audibility curve 的型態 顯式有一系列的頻率分析器，各自負責很窄的範圍，而產生整體的可聽曲線 也符合聽覺神經元的tuning curve

Basilar membrane對複合音的反應 --在進行Fourier analysis ? 複合音的不同組成造成對不同頻率反應的f濾波器產生反應

Updating Békésy’s Place Theory 心理物理實驗發現一般人區辨頻率的能力很強 但是鄰近頻率的vibration pattern卻有很大的重疊 Fig11.24 The action of the outer hair cells: cochlear amplifier

New research Using “live membranes” shows that there is less overlap in vibration patterns between nearby frequencies. Outer hair cell elongation and contraction as the cilia bend in different directions - increase the motion of the basilar membrane and sharpen its response to specific frequencies.

The slide can be used to talk about the importance of the function of the outer hair cells and what happens if they are damaged. Figure 11.32 Effect of OHC damage on frequency tuning curve. The solid curve is the frequency tuning curve of a neuron with a characteristic frequency of about 8,000 Hz. The dashed curve is the tuning curve for the same neuron after the outer hair cells were destroyed by injection of a chemical (Adapted from Fettipalce & Hackney, 2006).

Timing theory of frequency coding 時間編碼（temporal coding) phase-locking Neurons fire in synchrony with the phase of a stimulus: Fire only at peaks Larger number of fibers fire in response to high frequency than low frequency Works for frequency up to 4000Hz

Conductive hearing loss Sensorineural hearing loss Two types Conductive hearing loss Blockage of sound from the receptor cells Sensorineural hearing loss Damage to hair cells, the auditory nerve, or brain Most common type: Prebycusis

Hearing Loss Presbycusis Greatest loss is at high frequencies Affects males more severely than females Apparently caused by exposure to damaging noises or drugs because people in preindustrial cultures often do not experience large decreases in high-frequency hearing in old age

Mosquito teen repeller http://www.youtube.com/watch?v=X5gpKArR34A http://www.teenbuzz.org/

Noise-induced hearing loss Loud noise can severely damage the hair cells MP3 players: “Leisure noise” can also cause hearing loss 3-hour Game Safe Level

聽皮質的頻率分析 聽覺通道（auditory pathway ） cochlear auditory nerve fiber  cochlear nucleus  superior olivary nucleus (brain stem)  inferior colliculus (midbrain)  medial geniculate nucleus (thalamus, near LGN)  primary auditory receiving area (A1, in temporal lobe)

階層處理 (in monkey) core (simple sounds) →belt (complex sounds, eg., monkey calls)→parabelt Figure 11.37: The three main auditory areas in the cortex are the core area, which contains the primary auditory receiving area (A1), the belt area, and the parabelt area. Signals, indicated by the arrows, travel from core, to belt, to parabelt. The temporal lobe is pulled back to show areas that would not be visible from the surface. 與視覺消息處理性質相近 Fig. 11-37, p. 254

聽覺的what & where What路徑始於core與belt的前區，至側葉，前額葉 Where路徑始於core與belt後區，至頂葉與前額葉 Figure 11.38: Areas in the monkey cortex that respond to auditory stimuli. The green areas respond to auditory stimuli, the purple areas to both auditory and visual stimuli. The arrows from the temporal lobe to the frontal lobe represent the what and where streams in the auditory system. Fig. 11-38, p. 255

神經生理證據 JG側葉受損，無法從事聲音辨認 ES頂葉，前額葉受損，無法從事聲音定位 Fig. 11-39, p. 255 Figure 11.39: (a) Colored areas indicate brain damage for J.G. (left) and E.S. (right). (b) Performance on recognition test (green bar) and localization test (red bar). The horizontal line indicates normal performance. Fig. 11-39, p. 255

What task – 辨認音調（pitch） where task – 偵測位置 Figure 11.40: Areas associated with what (yellow) and where (blue) auditory functions as determined by brain imaging. Fig. 11-40, p. 255

A1在音調知覺中的角色 A1 located within the core Tonotopic map

聽覺皮質受損的pt Figure 11.43: Performance of patient A, with auditory cortex damage, on 4 tasks. See text for details. Fig. 11-43, p. 257

Bendor and Wang (2005): Pitch neurons in the marmoset auditory cortex These stimuli with different frequencies were perceived as having a pitch corresponding to the 182-Hz fundamental frequency. The corresponding cortical neurons responding only to stimuli associated with the 182-Hz tone Figure 11.43 Records from a pitch neuron recorded from the marmoset auditory cortex. (a) Frequency spectra for tones with fundamental frequency of 182 Hz. Each tone contains three harmonic components of the 182 Hz fundamental frequency; (b) Response of the neuron to each stimulus. (Adapted from Bendor & Wang, 2005).

Experience dependent plasticity human hearing 25% more auditory cortex was activated by piano tones in musician vs. nonmusician (and the electrical activity was twice as strong in musician)

訓練增加owl monkey A1對於相關頻率的反應區域面積 Experience dependent plasticity Figure 11.42: (a) Tonotopic map of the owl monkey’s primary auditory receiving area (A1), showing areas that contain neurons with the characteristic frequencies indicated. The blue area contains neurons with CF = 2,500 Hz. (b) Tonotopic map of an owl monkey that was trained to discriminate between frequencies near 2,500 Hz. The blue areas indicate that after training more of the cortex responds best to 2,500 Hz. Fig. 11-42, p. 256

Task related plasticity Neuron in a ferret’s auditory cortex Training complex sound → lick water pure tone (of a particular freq) → stop licking After a few trials, the neuron’s response profile has changed The auditory sys tem shapes its neurons to behaviorally important stimuli

Green – average level of firing Blue – decreased firing Red/yellow –increased firing

Figure 4. 24 (a) Greeble stimuli used by Gauthier Figure 4.24 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Brain responses to Greebles and faces before and after Greeble training. (a: From Figure 1a, p. 569, from Gauthier, I., Tarr, M. J., Anderson, A. W., Skudlarski, P. L., & Gore, J. C. (1999). Activation of the middle fusiform “face area” increases with experience in recognizing novel objects. Nature Neuroscience, 2, 568-573.)

a microphone worn behind the ear, a sound processor, Cochlear Implants Electrodes are inserted into the cochlea to electrically stimulate auditory nerve fibers. The device is made up of: a microphone worn behind the ear, a sound processor, a transmitter mounted on the mastoid bone, and a receiver surgically mounted on the mastoid bone.

Figure 11.46 Cochlear implant device. See text for details.

Cochlear Implants Implants stimulate the cochlea at different places on the tonotopic map according to specific frequencies in the stimulus. These devices help deaf people to hear some sounds and to understand language. They work best for people who receive them early in life or for those who have lost their hearing, although they have caused some controversy in the deaf community.

Shepard tone (scale)