Post on 01-Jan-2016
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
• 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)
wave length
Sound
Frequency: low high
low
high
Amplitude:
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
Sound
Amplitude: (logarithmic measure)
Sound pressure level (SPL)
SPL [dB] = 20 log(p/p0)
p0: reference pressure (20 pa, 1 pa = 1 N / m2)
p: amplitude
(From Sekuler & Blake, 1994)
Sound
dB value -- p / p0
3 dB – 1.414:1
6 dB – 2:1
20 dB – 10:1
40 dB – 100:1
120 dB – 1,000,000 :1
Hearing in the regime 0…160 dB = 1…108 !!!
Compression by
logarithmic scale !
The Auditory System
Ear: Overview
(From Kandel & Schwartz & Jessel, 2000)
Pinna
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: Stirrup:
small force large force
large area 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 / earSurrounding tissue Embedded in fluid
95 % 5 % AN fibers connect
Transduction 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 inhomo-geneous 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:
Tonotopic organization:
(From Sekuler & Blake, 1994)
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: Frequency tuning:
Different neurons responsible for different SPL regimes
(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
(From Sekuler & Blake, 1994)
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
Loudness Perception
Equal Loudness Contours (Isophones)
(From Sekuler & Blake, 1994)
Hearing regime:
Threshold to limit of pain
Speech area:
200 Hz – 5kHz, 50-80 Phone
Equalizer:
Masking
• Loudness perception and sound detection reduced in presence of background sounds
• Types of noise: broad band narrow band
• Noise reduces sensitivity only within limited frequency range
Measure for tuning width of auditory neurons
E
f
E
f
fc: center frequency
B: band width
(From Sekuler & Blake, 1994)
Masking
Egan & Hake (1950)• 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(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
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.
Literature