Transcript Dynamic neural field model links neural and computational

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.