Slides Week 3 Flashcards
Two definitions of sound
- Physical Definition
- Perceptual Definition
Physical Definition of Sound
Sound is pressure changes in the air or other medium
Perceptual Definition of Sound
• Sound is the experience we have when we hear
What is sound?
- Sound is created when objects vibrate
- When an object vibrates it causes molecules around it to vibrate creating pressure change
- Atmospheric pressure holds a pattern of fluctuation of sound
Amplitude
- The magnitude of displacement of a sound pressure wave
- Perceived as loudness and measured in Decibels (dB)
Frequency
- The number of times per second that a pattern of pressure change repeats
- Perceived as pitch and measured in Hertz (Hz)
Hearing frequencies in Humans
- Humans have a limited range of frequencies and sound pressure levels
- Range from about 20-20,000 Hz across a very wide range of intensities or sound pressure levels
Describe sounds
- The simplest sounds are pure tone, but they are uncommon
- Most sounds are complex
- All sound waves can be described as a combination of sine waves
- Complex sounds are best described as a spectrum that displays how much energy is present in each of the frequencies
Sound - Loudness
• The psychological aspect of sound related to perceived intensity or amplitude
Sound – Pitch
• The psychological aspect of sound related to mainly the sound frequency
Sound - Timbre
• The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar
How is sound recognised by the auditory system?
- Sense of hearing has evolved over millions of years
- Many animals have different hearing capabilities
Outer Ear
- Sounds are first collected from the environment by the Pinnae
- Soundwaves are funnelled by the pinnae into the ear canal
Ear Canal
- Collects sound waves and funnel the to the tympanic membrane
- Length and shape of ear canal enhances certain sound frequencies
- Insulates and protect the tympanic membrane
Tympanic Membrane
- Also called eardrum
- Thin layer of tissue in the human ear that receives sound vibrations from the outer air
- Transmits to the auditory ossicles, which are tiny bones in the tympanic (middle-ear) cavity.
- Vibrates in response to sound
Middle Ear
- Pinnae and ear canal make up the outer ear
- Tympanic membrane is border between outer ear and middle ear
- Middle ear consists of three tiny bones called ossicles
- Malleus
- Incus
- Staples
- Ossicles amplify and transmit sound to the inner ear
Name the Ossicles
- Malleus
- Incus
- Stapes
- These are the smallest bones in the body
- Provide essential amplification to assist us to hear faint sounds
Malleus
- Receives vibrations fromthe tympanic membrae and is attached to the incus
- Also known as the Hammer
Incus
- Also commonly known as the Anvil
- Receives vibrations from the malleus, to which it is connected laterally
- Transmits these to the stapes medially
Stapes
- Connected to the Incus on one end and the oval windo of the cochlea on the other
- Also commonly know as the Stirrup
- Situated between the incus and the inner ear
- Transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear.
Muscles in Ossicle System
- Tympani Muscle
- Stapedius Muscle
- Located in the Middle Ear
- Decrease vibrations when tensed
- They muffle sounds and protect the inner ear
Inner Ear
Where fine changes in sound pressure are transduced into neural signals
Cochlear
Spiral Structure of the inner ear containing the organ of Corti
Cochlea Parallel Canals
- Vestibular Canal
- Tympanic Canal
- Middle Canal
Vibrations transmit through ltympanic membranes and middle ear bones cause stapes to push and pull the flexible oval window which moves the Cochlear fluid.
Organ of Corti
- a structure on basilar membrane of the cochlea
- composed of hair cells and dendrites of auditory nerve fibres
- Movments of the cochlear partition are translated into nueral signals by structures in the organ of Corti
- Cochlear partition extends the entire length of the cochlea
- a specialized sensory epithelium that allows for the transduction of sound vibrations into neural signals
Tectorial Membrane
- Gelatinous structure tht exteds to the middle canal of the ear
- Floats above the inner hair cells
- Touches outer hair cells
- Vibrations cause displacement of Tectorial Membrane
- Stereocilia attach to hair cells and cause release of neurotransmitters
Basilar Membrane
- Different parts of the cochlea are sensitive to different frequencies
- Membrane is thick and narrow towards the base cochlea and thin and wide at the apex
Top Down Influences - Auditory System
- Inner hair cells convey almost information about sound waves to brain
- Outer hair cells receive inforation from the brain
- Outer hair cells can make parts of the cochlear partition stiffer
- Makes inner hair cells more sensitive and more sharply attuned to specific frequencies
Cochlear Nucleus
- The first brain stem nucleus at which afferent auditory nerve fibres synapse
Superior Olive
- An early brain stem region in the auditory pathway
- Where inputs from both ears converge
Inferiour Colliculus
A midbrain nucleus in the auditory pathway
Medial Geniculate Nuclues
- Part of the Thalamus
- Relays auditory signals to the temporal cortex
- Receives input from auditory cortex
- Information from each ear is processed in both sides of the cortex
Primary Auditory Cortex - (A1)
The first area within the temporal lobes of the brain responsible for processing acoustic organisation
Belt Area
- A region directly adjacent to (A1)
- Receives input from A1
- Where neurons respond to more complex characteristics of sounds
Parabelt Area
- a region of auditory cortex
- lateral and adjacent to the Belt Area
- where neurons respond to more complex characteristics of sounds as well as to input from other senses.
- Brain has tonotopic organisation
- neurons that respond to different frequenies are organised anatomically in order of frequency
Tonotopic Orgnisation
When spatial arrangment in brain corresponds to anatomy of the sensory organ in order of frequency of stimulation
Common Causes of hearing loss
- Obstruction of ear canal
- Excessive build up of ear wax
- Conductive hearing loss caused by problems with the bones of the middle ear
- Hearing loss is a natural consequence of aging
Sound Localisation
- How do we locate sound?
- Similar dilemma to determining how far an object is.
- We need two ears: this is critical for determining auditory locations
Left-Right Localisation in sound
- Interaural Time Differences (ITD)
- Interaural Level of Difference (ILD)
- Shape and form of Pinnae
Azimuth
- The angle of a sound source on the horizon relative to a point in the center of the head between the ears
- Signaled by the difference in arrival times between the ears
- The relative amplitude of high-frequency sounds (the shadow effect)
- Asymmetrical spectral reflections from various parts of our bodies, including torso, shoulders, and pinnae.
Interaural Time Differences (ITD)
- The difference in time between a sound arriving at one ear versus the other
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Interaural Time Differences (ITD)
- ITD for different positions around the head
Medial Superior Olive (MSO)
- A relay station in the brain stem
- Where inputs from both ears contribute to detection of ITDs
- ITD detectors form connections from inputs coming from two ears during the first few months of life
Interaural Level Differences (ILD)
- The difference in intensity between a sound arriving at one ear versus the other
- For frequencies above 1000Hz the head blocks some of the energy reaching to opposite ear
- ILD is largest and 90o and -90o
- ILD is nonexistant for 0o and 180o
Physiology of ILDs
- Lateral Superior Olive
- Medial Superior Olive
Lateral Superior Olive
- A relay station in the brain stem where inputs from both ears contribute to the detection of ILDs
- Excitatory connections to LSO come from ipsilateral ear
- Inhibitory connections to LSO come from contralateral
Potential Problems with ITD & ILD for sound localisation
- Cone of Confusion
- A region of positions in space where all sounds produce the same ITDs and ILDs
- Elevation
- Adds another dimension to sound localisation
Turning the head can disambiguate ILD/ITD similarity
Directional Transfer Function (DTF)
- A type of measurement
- Describes how the pinnae, ear canal, head and torso change the intensity of sounds
- different frequencies arrie at each ear from different locations in space.
- Azimuth and Elevation
- Each person has their own DTF based on ther own body
- this helps us to locate sounds
Neuroplasticity in Human Auditory System
- Hoffman et al. (1998)
- fitted participants ears with moulds worn continuously for 6 weeks.
- tested sound localisation before, during and after molds fitted
Hoffman et al 1998 Results
Neuroplasticity in Human Audition
- Localisation performance was accurate before mould
- Introduction of Moulds impaired localisation
- Gradual improvement as auditory systems calibrated
- Performance returned to near baseline immediately after moulds removed
Auditory Distance Perception
- Simplest cue is relative intensity of sound
- Decrease in intensity is equal to the distance squared
- As distance from a sources increases, intensity decreased faster
Speech Production Involves:
- Respiration from the lungs
- Phonation from vocal chords
- Articulation from the vocal tract
Vocal Tract
- The airway above the larynx used for the production of speech
- Includes the oral tract and nasal tract
- flexibility of vocal tract - important in speech production
Respiration and Phonation
- Initiating speech - diaphragm pushes air out of lungs, through trachea, up to larynx
- Phonation: the process through which vocal folds are made to vibrate when air pushes out of the lungs
- At larynx air must pass through two vocal folds
Speech Production: Articulation
- The manner of producing a speech sound using the vocal tract
- Humans can change the shape of their mocal tract by manipulatiing their jaw, lips, toungue and soft palate
Spectrogram
A pattern for sound analysis that provides a three-dimensional display plotting time on the horizontal axis, frequency on the vertical axis, and intensity in color or gray scale
Speech Production: Formant
- A resonance of the vocal tract that creates a peak in the speech spectrum
- Labeled by number from lowest to highest (F1, F2, F3 etc)
- concentrations in energy occur at different frequencies depending on length of vocal tract
Speech Production: Phoneme
- Shortest segments of speech
- if changed they change the meaning of the word
- number of phenomes varies across languages
- 11 phenomes in Hawaiian
- 47 in American English
- up to 60 in some African languages
Classifying Speech Sounds
- Place of Articulation - at lips, alveolar ridge etc
- Manner of Articulation - Totally, partially or slightly obstructed airflow
- Whether the vocal chords are vibrating or not is call voicing
Coarticulation
- Where attributes of successive speech speech units overlap in articulatory or acoustic patterns
- Speech production is fast: 10-15 consonants and vowels per second
- Experienced talkers position of the tongue in anticipation of next consonant or vowel
How do humans recognise sounds despite Coarticulation: Categorical Perception
- Researchers can manipulate sound stimuli to vary continuously from ‘da’ to ‘ta’
- People do not perceive the sounds as continuously varying
- Instead they perceive sharp categorical boundaries between stimuli
Motor Theory of Speech Perception
- Motor Processes used to produce speech sounds are used in reverse to understand acoustic speech
- McGurk & MacDonald (1976) showed that what someone sees can affect what they hear
- The McGurk Effect
Using multiple Acoustic Cells
- Perception depends on experience
eg: Dutch listeners use formant information over duration information
But Second language Dutch listeners use duration over formant
Learning to Listen
- Babies learn to listen even before they are born
- Newborns prefer hearing their mother’s voice over other women’s voices
- Four day old french babies prefer hearing French over Russian
- Newborns prefer hearing children’s stories that were read aloud by their mothers
Becoming a Native Listener
- Sound distinctions are specific to various languages
eg R and L are not distinguished in Japanese
- Infants begin filtering out irrelavant acoustics long before they start to say speech sounds
Aphasia
- Paul Broca and Carl Wernicke showed that damage to specific areas of the brain causes language problems
- Broca’s area and Wernicke’s area are both found in the left hemisphere of the temporal lobe
Broca’s Aphasia
- Damage to frontal lobe in the Broca’s Area
- Laboured and stilted speech
- Can only speak in short sentence
- Are capable of comprehending what others are saying.
- Mum Had This.
- Patients with damage to Wenicke’s Area in Temporal Lobe
- Can speak fluently but what is said is extremely disorganised
- Speech is not meaningful
- Great difficulty understand what is said to them.
- Genny Jones had this.
Music
- Music is a way to express thoughts and emotions
- Oldest musical instruments are 30,000 year old flutes carved from animal bones
Music - Melody
- Babies as young as 2 moths can differeniate between familiar vs unfamiliar melody
- Plantinga & Trainor 2009
- Babies show a consistent preference for consonant melodies compared to dissonant melodies from as youn as four months
- Zentner & Kagan 1998
Music - Rhythm
- We automatically divide even regular beats into smaller groups where beats may have different emphasis
Music - Absolute Pitch (AP)
- A rare ability whereby some people are able to very accurately name or produce notes without comparison to other notes
- Highly prized skill among musician
- Debate as to whether AP is due to nature or nurture
- More likely for people who begin musical training at a young age.
Music - Amusia
- An inability to perceive music
- Also known as tone deafness
- Very rare - 4% of the population
- Can be congenita or due to damage anywhere along the auditory system
Why did we develop music perception
- No one really knows why but theories include:
- Sexual attraction
- Group bonding
- Side effect of language evolution
- Lebedeva & Kuhl (2010) found babies recognised changes in syllables better if it was sung compared to if it was spoken
Is Music Perception of Psychological Interest?
Kantrowitz et al., 2014
- In one study, 45% of patients with schizophrenia met the criteria for amusia
- This is compared to 9% of control subjects
- Findings suggest that music therapy may be useful for patients with schizophrenia
Is Music Perception of Psychological Interest?
Guetin et al., 2009
Music therapy used in a number of settings including to improve anxiety and depression in Alzheimer’s
Is Music Perception of Psychological Interest?
Nguyen et al., 2010
- Music improves speech production in Parkinson’s
- Lowers pain and anxiety during lumbar punctures in children with cancer
Is Music Perception of Psychological Interest?
Blood & Zatorre., 2001
Listening to pleasurable music gave people “shivers-down-the-spine” or “chills“, changed heart rate and increased blood flow to reward centres of the brain
Mozart Effect? Rauscher et al. (1993)
- Subjects showed an 8-9 point increase in spatial intelligence after listening to Mozart.
- Failed to replicate in subsequent studies; and any improvements are short-lived.
- Research largely supports the benefit of music training on intelligence, language and memory (Talero Gutierrez & Saade-Lemus, 2018)
