Examinations Students must complete all assignments with a satisfactory record. All assignments must be typed and completed within one week. Grading will occur within one week. Students will take a written, final exam with open, closed book questions.
P1: Psychology of Hearing Rob van der Willigen http://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppt
Audition (Hearing) “Detecting and recognizing a sound are the result of a complex interaction of physics, physiology, sensation, perception and cognition.” John G. Neuhoff (Ecological Psychoacoustics 2004; p. 1)
Psychoacoustics Auditory Perception or Psychoacoustics is a branch of Psychophysics. Psychophysics studies relationships between perception and physical properties of stimuli.
Physical vs. Perceptual Dimensions Physical Dimensions: Fundamental measures of a physical stimulus that can be detected with an instrument (e.g., a light meter, a sound level meter, a spectrum analyzer, a fundamental frequency meter, etc.). Perceptual Dimensions: These are the mental experiences that occur inside the mind of the observer. These experiences are actively created by the sensory system and brain based on an analysis of the physical properties of the stimulus. Perceptual dimensions can be measured, but not with a meter. Measuring perceptual dimensions requires an observer.
Psychoacoustics Psychoacoustics is the study of subjective human perception of sounds. Psychoacoustics can be described as the study of the psychological correlates of the physical parameters of acoustics. Acoustics is a branch of physics and is the study of sound.
A Sensor Called Ear Sensory Coding and Transduction
Peripheral Auditory System Outer Ear: - Extents up to Eardrum - Visible part is called Pinna or Auricle - Movable in non-human primates - Sound Collection - Sound Transformation Gives clues for sound localization Sensory Coding and Transduction
Peripheral Auditory System Sensory Coding and Transduction Elevation (deg) -40 -20 0 +20 +40 +60 The Pinna creates Sound source position dependent spectral clues. Frequency “EAR PRINT”
Middle Ear: (Conductive hearing loss) - Mechanical transduction (Acoustic Coupling) - Perfect design for impedance matching Fluid in inner ear is much harder to vibrate than air - Stapedius muscle: damps loud sounds Three bones (Ossicles) A small pressure on a large area (ear drum) produces a large pressure on a small area (oval window) Peripheral Auditory System Sensory Coding and Transduction
Inner Ear: The Cochlea is the auditory portion of the ear Cochlea is derived from the Greek word kokhlias "snail or screw" in reference to its spiraled shape, 2 ¾ turns, ~ 3.2 cm length Peripheral Auditory System Sensory Coding and Transduction
The cochlea’s core component is the Organ of Corti, the sensory organ of hearing Peripheral Auditory System Sensory Coding and Transduction Cochlear deficits cause Sensorineural hearing loss
The Organ of Corti mediates mechanotransduction: Peripheral Auditory System Sensory Coding and Transduction The cochlea is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear via the oval window. As the fluid moves, thousands of hair cells are set in motion, and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells.
Peripheral Auditory System Sensory Coding and Transduction
Peripheral Auditory System Sensory Coding and Transduction The organ of corti is the hearing sense organ and lies on the BM (basilar membrane) The tectorial membrane lies above the stereocilia, shearing motion between BM and tectorial membrane causes stereocilia to be displaced It consists of supporting cells and hair cells 2 groups of hair cells: inner and outer hair cells Protruding from each hair cell are hairs called stereocilia
Peripheral Auditory System Sensory Coding and Transduction The auditory nerve consists of vestibular and cochlear nerve Cochlear nerve: the axon fibres of neurons whose cell bodies are in the spiral ganglion of the cochlea. The cochlear nerve transmits hearing information from cochlea to central nervous system. Dendrites of these neurons synapse with the hair cells. Important findings from recording impulses in single auditory nerve fibres are: Spontaneous firing, frequency selectivity of fibres, phase locking.
Six basic steps: Peripheral Auditory System Sensory Coding and Transduction
The Problem of Hearing Now we know the sensor of the process called hearing. It leaves open, however, the question of how sound is actually encoded at the sensory level.
The Problem of Hearing “Only by being aware of how sound is created and shaped in the world can we know how to use it to derive the properties of the sound-producing events around us.” Albert S. Bregman (Auditory scene analysis, 1999; p. 1) Albert S. Bregman (Auditory scene analysis, 1999; p. 1)
Sound is a longitudinal pressure wave: a disturbance travelling through a medium (air/water) The Adequate Stimulus to Hearing http://www.kettering.edu/~drussell/demos.html
The Adequate Stimulus to Hearing http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2a.html Particles do NOT travel, only the disturbance Particles oscillate back and forth about their equilibrium positions Compression Decompression or rarefaction Compression Distance from source Duration
The Adequate Stimulus to Hearing http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/ Transverse waves Longitudinal waves Type of waves
Physical Dimensions of Sound http://www.physpharm.med.uwo.ca/courses/sensesweb/ Time or Distance from the source Pressure High Low LOUD sound Large change in amplitude SOFT sound Small change in amplitude In air the disturbances travels with the 343 m/s, the speed of sound Amplitude is a measure of pressure Amplitude Amplitude (A)
Physical Dimensions of Sound Time or Distance from source Pressure High Low LOW pitched sound Low frequency Long wavelength Pressure changes are slow T is the Period (duration of one cycle) λ is wavelength (length of one cycle) f is frequency (speed [m/s] / λ [m]) or (1/T[s]) HIGH pitched sound High frequency Short wavelength Pressure changes are fast Frequency (f) ; Period (T) ; Wavelength (λ) One cycle
The Mathematics of Waves The Pure Tone has infinite duration, but only one frequency is periodic and has a phase is known as the “harmonic function” = 2 f, is the angular frequency [rad/s] = is phase, t is time
The Mathematics of Waves Phase ) Phase is a relative shift in time or space
The Mathematics of Waves Superposition Waves can occupy the same part of a medium at the same time without interacting. Waves don’t collide like particles. Two waves (with the same amplitude, frequency, and wavelength) are traveling in opposite directions. The summed wave is no longer a traveling wave because the position and time dependence have been separated.
The Mathematics of Waves Superposition Waves can occupy the same part of a medium at the same time without interacting. Waves don’t collide like particles. Waves in-phase ( =0) interfere constructively giving twice the amplitude of the individual waves. When the two waves have opposite-phase ( =0.5 cycle), they interfere destructively and cancel each other out.
The Mathematics of Waves Superposition Most sounds are the sum of many waves (pure tones) of different Frequencies, Phases and Amplitudes. Through Fourier analysis we can know the sound’s amplitude spectrum (frequency content). At the point of overlap the net amplitude is the sum of all the separate wave amplitudes. Summing of wave amplitudes leads to interference.
The Mathematics of Waves Fourier’s Theorem Time domain Frequency domain Jean Baptiste Fourier (1768-1830) “Fourier synthesis” “Fourier analysis” Any complex periodic wave can be “synthesized” by adding its harmonics (“pure tones”) together with the proper amplitudes and phases.
The Mathematics of Waves Fourier’s Theorem Linear Superimposition of Sinusoids to build complex waveforms If periodic repeating
The Mathematics of Waves Fourier synthesis “Saw tooth wave”
The Mathematics of Waves Fourier synthesis “Square wave”
The Mathematics of Waves Fourier synthesis “Pulse train wave”
The Mathematics of Waves Transfer from time to frequency domain Time domain Superposition Frequency domain Fourier Analysis
Physical Dimensions of Sound Amplitude - height of a cycle - relates to loudness Wavelength ( λ ) - distance between peaks Phase ( ) - relative position of the peaks Frequency (f ) - cycles per second - relates to pitch Summary
The Problem of Hearing Now we know the sensor of the transduction process called hearing. And we know a little about the physical nature of sound (Acoustics). So it should be possible to understand how sound is encoded at the sensory level.
Organ of Corti Basilar Membrane Auditory nerve Inner Hair cell Outer Hair cells Sensory Coding of Sound
Travelling wave theory von Bekesy: Waves move down basilar membrane stimulation increases, peaks, and quickly tapers Periodic stimulation of the Basilar membrane matches frequency of sound Location of peak depends on frequency of the sound, lower frequencies being further away Sensory Coding of Sound Travelling Wave Theory
Location of the peak depends on frequency of the sound, lower frequencies being further away Location of the peak is determined by the stiffness of the membrane Travelling wave theory von Bekesy: Waves move down basilar membrane Sensory Coding of Sound Place Theory
High f Med f Low f Periodic stimulation of the Basilar membrane matches frequency of sound Sensory Coding of Sound Cochlear Fourier Analysis BASEAPEX Location of the peak depends on frequency of the sound, lower frequencies being further away Position along the basilar membrane
Thick & taut near base Thin & floppy at apex TONOTOPIC PLACE MAP Sensory Coding of Sound Sensory Input is Tonotopic LOGARITHMIC: 20 Hz -> 200 Hz 2kH -> 20 kHz each occupies 1/3 of the basilar membrane
The COCHLEA: Decomposes sounds into its frequency components Sensory Coding of Sound Sensory Input is Non-linear Has direct relation to the sounds spectral content Represents sound TONOTOPICALLY Has NO linear relationship to sound pressure Has NO direct relationship to the sound’s location in the outside world
Perceptual Attributes of Sound The terms pitch, loudness, and timbre refer NOT to the physical characteristics of sound. Pitch (not fundamental frequency) Loudness (not intensity) Timbre (not spectrum envelope or amplitude envelope) They refer to the mental experiences that occur in the brains of listeners.
The Problem of Hearing “Sound has no dimensions of space, distance, shape, or size; and the auditory periphery of all known vertebrates contains peripheral receptors that code for the parameters of the sound pressure wave rather than information about sound sources per se.” William A. Yost (Perceiving sounds in the real world, 2007; p. 3461) William A. Yost (Perceiving sounds in the real world, 2007; p. 3461)
The Problem of Hearing Tonotopie blijft in het auditief systeem tot en met de auditieve hersenschors behouden. “De samenstelling van een geluid uit afzonderlijke tonen is te vergelijken met de manier waarop wit licht in afzonderlijke kleuren uiteenvalt wanneer het door een prisma gaat.” John A.J. van Opstal (Al kijkend hoort men, 2006; p. 8)
The Problem of Audition Problem I: Sound localization can only result from the neural processing of acoustic cues in the tonotopic input of the (two) ear(s)! Problem II: How does the auditory system parse the superposition of distinct sounds into the original acoustic input?
1.This week, we will have the first lab, entitled “Introduction to harmonic waves and Fourier (Spectrum Analysis)” 2.Read the print outs. 3.Importantly, the section MATLAB PRIMER is a complementary material for the very first lab. 4. This week’s reading assignment.Announcements