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Lecture 9 Experiments in Psychoacoustics Martin Giese What you should remember 1. Perceptual threshold, JND, PSE 2. Psychometric function (PMF) / psychophysical function 3. Classical methods of psychophysics 4. 2AFC 5. Signal Detection Theory 6. Scaling methods What you should learn today 1. Components of the auditory system 2. Basics on the psychophysics of hearing 3. Some tips for giving good presentations Hearing • Important sense for humans: Deafness more impairing than blindness • High relevance for communication (speech) • Contrary to vision: – covers whole environment (warning !) – cannot be deactivated by attention Sound Sound = mechanical pressure waves wave length • Frequency: 10 Hz … > 109 Hz Hz (Hertz) = oscillations / sec • Speed: 343 m/s in air; 1484 m/s in water • Wave length: 34 cm (1kHz); 3.4 cm (10 kHz) Sound Frequency: low Amplitude: high low high Sound Pure tone: only one frequency Complex sound: multiple frequencies White noise: all frequencies with equal amplitude Sound Frequency regimes: Infrasound: < 10 Hz Normal sound: 10 – 18 kHz (perceived) Ultrasound: > 18 kHz (From Sekuler & Blake, 1994) Sound Amplitude: (logarithmic measure) Sound pressure level (SPL) SPL [dB] = 20 log(p/p0) p0: reference pressure (20 m pa, 1 pa = 1 N / m2) p: amplitude Sound dB value -- p / p0 3 dB – 1.414:1 Compression by 6 dB – 2:1 logarithmic scale ! 20 dB – 10:1 40 dB – 100:1 120 dB – 1,000,000 :1 Hearing in the regime 0…160 dB = 1…108 !!! The Auditory System Ear: Overview Pinna (From Kandel & Schwartz & Jessel, 2000) Ear: Overview (From Sekuler & Blake, 1994) Outer Ear • • • • Auditory canal 2.5 cm long, 7 mm wide “directional microphone” Resonant frequency ~ 3000 Hz Displacement of tympanic membrane: 10-3 … 10-8 mm diameter of H-atom: 10-8 mm Middle Ear Mechanical “impedance converter”: Ear drum: small force large area Stirrup: large force small area ( 9 mm) 20 times smaller Adjacent medium: Air Liquid Force outer ear / force inner ear 1:90 (Sekuler & Blake, 1994) Middle Ear Acoustic reflex: Small muscles (stapedius and tensor tympani) contract in presence of loud sounds Function: • Adaptation for loud stimuli • Sensitivity reduction during speaking and chewing Inner Ear: Cochlea Cochlea = “snail” • • • • • • 2 ½ coils Length (extended): 34 mm, Ø <9 mm 3 channels (scala vestibuli scala media/ scala tympani) Filled with liquid (perilymph, endolymph) no vessels ! Basilar membrane contains receptors (hair cells) Oval and round window (Scala media) (From Sekuler & Blake, 1994) Organ of Corti • • • • Basilar membrane (BM) with hair cells Tectorial membrane – arches over hair cells – Makes contact with cilia – Fixed only at one side During movements of BM ciliae are sheared Otoacoustical emissions (From Kandel & Schwartz & Jessel, 2000) Hair cells Inner hair cells: Outer hair cells: 3500 12,000 / ear Surrounding tissue 95 % Transduction Embedded in fluid 5 % AN fibers connect Amplification (?) (From Sekuler & Blake, 1994) Theories about Cochlea Function Frequency Theory: (E. Rutherford 1886): • Basilar membrane moves as whole (“telephone hypothesis”) • Neurons fire with same frequency as acoustic stimulus Place theory: (H. von Helmholtz 1877): • Sites of the BM resonate for different frequencies, like strings of a piano Theories about Cochlea Function Traveling wave theory: (Bekesy 1928): • • • Movements of stapes induce traveling waves on the inhomogeneous basilar membrane Site with maximum amplitude depends on frequency Tonotopic organization (approx. with log of f) Georg von Bekesy Nobel price, 1961 Theories about Cochlea Function Traveling waves: (From Sekuler & Blake, 1994) Tonotopic organization: Theories about Cochlea Function Conclusion: “Ohm’s Law of Acoustics” The ear decomposes complex sounds in tones. It acts like a Fourier analyzer. Georg Simon Ohm (1787-1854) Auditory Pathway • Different pathways to analyze: – Structure of sound – Localization of sound • Important structures: – – – – – Auditory nerve (50,000 fibres) Cochlear nuclei (monaural) Relay nuclei (olive) in the brain stem (localization) Medial geniculate nucleus Auditory cortex (tonotopy !) (From Sekuler & Blake, 1994) Auditory Nerve Dependence on SPL: Different neurons responsible for different SPL regimes Frequency tuning: (From Sekuler & Blake, 1994) Hearing Audibility Function (AF) • Threshold SPL depends on frequency • 0 dBSPL defined as smallest threshold for 2500 Hz • Limited frequency range (From Sekuler & Blake, 1994) Audibility Function Audible frequency ranges for different species (From Sekuler & Blake, 1994) Loudness Perception Loudness: subjective perceptual experience SPL: physical stimulus strength • Measurement: – Magnitude estimation – Loudness matching Equal loudness contours • Power law: L ~ SPL0.67 • Unit: Phone 1 phone = 1dBSPL for f = 1000 Hz (From Sekuler & Blake, 1994) Loudness Perception Hearing regime: Threshold to limit of pain Equal Loudness Contours (Isophones) Speech area: 200 Hz – 5kHz, 5080 Phone Equalizer: (From Sekuler & Blake, 1994) Masking • Loudness perception and sound detection reduced in presence of background sounds • Types of noise: broad band E narrow band fc: center frequency E B: band width f • Noise reduces sensitivity only within limited frequency range Measure for tuning width of auditory neurons f (From Sekuler & Blake, 1994) Masking • Band pass noise as masking stimulus • Measured: change of threshold SPLs • Results: – – – Maximum effect near center frequency effect over broad frequency range Asymmetry ! reflects asymmetry of traveling wave on BM Egan & Hake (1950) (From Goldstein, 1996) Masking Psychophysical tuning function (Zwicker, 1974) • Test tone with fixed frequency • Vary mid frequency of masking stimulus (narrow band) • Increase amplitude of mask until perception of test tone ceases (From Goldstein, 1996) Clinical Relevance Hearing loss • >20 million Americans • Reasons: – Conduction loss – Sensory / neural loss • Test: bone conduction • Presbycusis (loss of high frequency sensitivity • Damage by (chronic) exposure to noise • Drugs (aspirin) (From Sekuler & Blake, 1994) Clinical Relevance • “loudness recruitment”: rapid increase of loudness with intensity (From Goldstein, 1996) Clinical Relevance Presbycusis ( presbys = “old”) Difficulties dependent on degree of hearing loss (From Goldstein, 1996) Things that We did not Treat • • • • Pitch perception Perception of timbre (sound characteristics) Sound localization (binaural hearing) Speech perception Giving Good Presentations Important Things • • Prepare audio-visual equipment before Clear logical structure, e.g. – – – – • • Intro (Motivation / conditions) Description of experiment Results Conclusion Focus on a few important points Tell a story Recommended + + + + + + Use colors, illustrations attract attention (i.p. begin and end, humor, …) Face the audience, eye contact open stance, clear natural gestures Practice (“test talks”, get feed-back from friends) Have a back-up plan Things to Avoid – – – – – – – Speaking not loud enough Getting nervous (Others don’t notice most errors !) Reading from script Too many details on a sheet (7 items ideal) Abstract general expressions Long sentences Bad timing Literature Suggested readings: Sekuler, R., Blake, R. (1994). Perception. McGraw-Hill, New York. Chapters 9 + 10. Elmes, D.G., Kantowitz, B.H., Roediger III, H.L. (1999). Research Methods in Psychology. Brooks/Cole Publishing, Pacific Grove. Chapter 14. Additional Literature: Goldstein, E.B. (1996). Sensation and Perception. Brooks/Cole Publishing Company, Pacific Grove. Chapters 8 + 9 + 13. Kandel, E.C., Schwartz, J.H., Jessell, T.M. (2000). Principles of Neural Science. Mc Graw-Hill, New York. Chapter 30.