Physical def of sound
pressure changes in the air or other medium
Perceptual definition of sound
the experience we have when we hear
when diaphragm of speaker moves out pushing air molecules together
when diaphragm of speaker moves in pushing air molecules apart
condensation / rarefaction cycle creates high and low pressure regions that travel through air
created by sine wave
size of pressure change
What is the perception of amplitude?
number of times per second that pressure changes repeat
what is the perception of frequency?
how is amplitude measured?
how is frequency measured?
hertz (Hz); 1 Hz is 1 cycle/sec
the repetition rate
the first harmonic
pure tones that make up periodic complex tones
process of adding harmonics to create complex sounds
display of harmonics of a complex sound
the quality of sound, ranging from low to high; closely associated with frequency of a tone
increasing pitch that accompanies increases in a tone's fundamental frequency
how are the same notes on musical scales related?
have same fundamental frequencies that are multiples of each other
perception as similar tones; ie. music notes on different octaves
constancy of pitch, even when the fundamental or other harmonics are removed
what happens when fundamental frequency is removed?
it does not change the tone's pitch
human hearing range
20 - 20,000 Hz
shows threshold of hearing in relation to frequency
Humans are most sensitive to what frequency range?
2,000 - 4,000 Hz
How are equal loudness curves determined?
-using a standard 1,000 Hz tone
-two dB levels used - 40 and 80
-participants matched perceived loudness of all other tones to the standard
-dB as a function of frequency
how are different tones of different loudnesses perceived at 80 dB?
almost all perceived as equal loudness
how are different tones of different loudnesses perceived at 40 dB?
Softer for high and low frequencies than the rest of the tones in the range
quality that distinguishes between two tones that have the same loudness, pitch and duration but still sound different
Timbre depends on
tone's attack- buildup of sound at the beginning of the tone
tone's decay- the decrease in sound at the end of a tone
pinna and auditory canal
function of pinna
what is auditory canal?
tube-like 3cm long structure
auditory canal amplifies frequencies at what level range?
1,000 - 5,000 Hz
Function of auditory canal
protects tympanic membrane (eardrum) at the end of the canal
What is the middle ear?
two cubic centimeter cavity separating inner from outer ear
middle ear is made up of what?
3 ossicles: malleus, incus, stapes
function of malleus
aka hammer- moves due to vibration of eardrum
function of incus
aka anvil- transmits vibrations of malleus
function of stapes
aka stirrup- transmits vibrations of incus to the inner ear via the oval window of the cochlea
function of ossicles overall
outer and middle ear are filled with air, inner ear is filled with fluid, pressure changes in air transmit poorly into the denser fluid; ossicles act to amplify the vibration for better transmission to the fluid
how do middle ear muscles aid in ossicles's function?
dampen their vibrations to protect the inner ear from potentially damaging stimuli
main structure of middle ear
what is cochlea?
fluid-filled snail-like structure (35mm long) set into vibration by stapes
What is organ of corti?
structure in the cochlea that contain inner and outer hair cell receptors for hearing
transduction takes place by:
-cilia bend in response to movement of organ of corti and the tectorial membrane
-movement in one direction opens ion channels
-movement in other directions closes channels
Bekesys's Place Theory
Frequency of sound is indicated by the place on the organ of corti that has the highest firing rate
-observation in cadavers and model shows the vibrating motion of the membrane is a traveling wave
apex responds best to what frequencies?
base responds best to what frequencies?
cochlea shoes an orderly map of frequencies along its length
How does basilar membrane respond to complex tones?
There are peaks in the membrane's vibration that correspond to each harmonic in a complex tone
conductive hearing loss
blockage of sound from receptor cells
sensorineural hearing loss
damage to hair cells, auditory nerve, or brain
most common type of sensorineural hearing loss
-greatest loss is high frequencies
-males more severely than females
-appears to be caused by exposure to damaging noises or drugs
pathway from cochlea to cortex
-superior olivary nucleus (in brain stem)
-inferior colliculus (in midbrain)
-medial geniculate nucleus (in thalamus)
-auditory receiving area (A1 in temporal lobe)
Pathway of hearing in cortex
-from core, then belt, then parabelt
-simple sounds activate core
-complex sounds activate belt and parabelt
electrodes are inserted into the cochlea to electrically stimulate auditory nerve fibers
surrounds an observer and exists wherever there is sound
position left to right
position up and down
position from observer
why must location for sounds be calculated?
because location cues are not contained in the receptor cells like on the retina in vision
location cues based on the comparison of the signals received by the left and right ears
Interaural time difference
difference between the times sounds reach the two ears; when source is to the side of the observer, the times between each ear will differ
Interaural level difference
difference in sound pressure level reaching the two ears; Reduction in intensity occurs for high frequency sounds for the far ear; no effect for low frequency sounds
cone of confusion
where the interaural time difference and interaural level difference are the same
auditory scene analysis
process by which sound sources in the auditory scene are separated into individual perceptions; this does not happen at the cochlea since simultaneous sounds are together in the pattern of vibration of the basilar membrane
how onset time helps to perceptually organize stimuli
sounds that start at different times are likely to come from different sources
how location helps to perceptually organize stimuli
a single sound source tends to come from one location and to move continuously
how similarity of timbre and pitch helps to perceptually organize stimuli
similar sounds are grouped together
how proximity in time helps to perceptually organize stimuli
sounds that occur in rapid succession usually come from the same source
how auditor continuity helps to perceptually organize stimuli
sounds that stay constant or change smoothly are usually from the same source
sound that reaches the listener's ears straight from the source
sound that is reflected off of environmental surfaces and then to the listener
Factors that affect perception in concert halls
-reverberation time - best is 2 sec
-intimacy time - best is 20 ms
-bass ratio - high are best
-spaciousness factor - high are best
time it takes sound to decrease by 1/1000th of its original pressure
time between when sound leaves its source and when the first reflection arrives
ratio of low to middle frequencies reflected from surfaces
fraction of all the sound received by listener that is indirect
Ideal reverberation time for classrooms
.4 to .6 seconds
Visual capture or the ventriloquist effect
an observer perceives the sound as coming from the visual location rather than the source for the sound
shape of vocal tract is altered by what?
how are vowels produced?
by vibration of the vocal cords and changes in the shape of the vocal tract by moving the articulators
how are consonants produced?
by a constriction of the vocal tract
specific frequencies where peaks of pressure occur due to change in shape of the moving articulators
first formant's frequency
first is lowest, and gets higher as numbers go up
show the changes in frequency and intensity for speech
rapid changes in frequency preceding or following consonants
smallest unit of speech that changes meaning of a word; 47 in english
The variability problem
there is no simple correspondence between the acoustic signal and individual phonemes; Variability comes from a phoneme's context
overlap between articulation of neighboring phonemes also causes variation
Occurs when a wide range of acoustic cues results in the perception of a limited number of sound categories
Voice Onset Time
Time delay between when a sound starts and when vocal cords begins vibrating
Phonemic Restoration Effect
Used to show that speech perception is determined both by the nature of the acoustic signal and by context that produces expectations in the listener
The segmentation problem
there are no physical breaks in the continuous acoustic signal, but breaks between words are still perceived
the chance that one sound will follow another in a language
the process of learning transitional probabilities and other language characteristics; infants as young as 8 months show this
characteristics of the speaker's voice such as age, gender, emotional state, level of seriousness, etc.
Is speech perception a top-down or bottom-up process?
It's both. Knowledge/meaning + acoustic signal leads to speech perception
damage in frontal lobe
Labored and stilted speech, can only speak in short sentences
Capable of comprehending what others are saying
damage in Wernicke's area in temporal lobe
Speak fluently but the content is disorganized and not meaningful
They also have difficulty understanding others and word deafness may occur in extreme cases.
where is voice area in brain?
superior temporal sulcus
dual stream model of speech perception
ventral stream for recognizing speech and a dorsal stream that links the acoustic signal to movements for producing speech
how does damage to parietal lobe impact speech perception?
difficulty discriminating between syllables but can still understand words
Experience Dependent Speech Plasticity
The brain becomes "tuned" to respond best to speech sounds that are in the environment
cutaneous senses, proprioception, kinesthesis
perception of touch and pain from stimulation of the skin
ability to sense position of the body and limbs
ability to sense movement of body and limbs
where are mechanoreceptors located?
in the dermis of the skin
fires continuously while stimulus is present; Responsible for sensing fine details
fires only when a stimulus is first applied and when it is removed; Responsible for controlling hand-grip
fires continuously to stimulation; Associated with perceiving stretching of the skin
fires only when a stimulus is first applied and when it is removed; Associated with sensing rapid vibrations and fine texture
Medial lemniscal pathway consists of
large fibers that carry proprioceptive and touch information
Spinothalamic pathway consists of
smaller fibers that carry temperature and pain information