3. Hearing Flashcards
what is sound caused by?
changes in air pressure
how are these air pressure waves characterised?
These pressure waves are characterised by amplitude, frequency,
and phase.
what is amplitude?
loudness
Decibels: dB
what is frequency?
Pitch
Hertz; Hz
What is phase?
position within a cycle
what is a pure tone?
A sine wave, which is the simplest sound wave
what is the loudness of a space shuttle launce (from 45m)
180
What is the loudness of the Loudest Rock band?
160dB
What is the loudness pain threshold?
140 dB
What is the loudness of loud thunder?
120 dB
what is the loudness of the loudest record shout?
111 dB
What is the loudness of the heavy traffic noise?
100 dB
What is the loudnes of a vacuum cleaner?
80 dB
What is the loudness of a normal conversation?
60 dB
What is the loudness of a quiet office?
20 dB
What is the human hearing range?
20-20 000 Hz
What do most of our auditory experiences involve?
Most of our auditory experience involves only a small fraction of
this range
• e.g., typical vocal range: 80–1100 Hz
how are complex sounds built?
Complex sounds can be built up from series of sine waves of varying amplitude, frequency, and phase.
How can we decompose complex sounds?
We can decompose complex sounds into their sine wave components by a process called Fourier analysis.
What is the fundamental?
The lowest frequency component of a complex sound
What are many complex sounds made up of?
harmonics—integer
multiples of the fundamental
If the fundamental frequency is 440 Hz, then the 2nd harmonic will be
880 Hz, the 3rd harmonic will be 1320 Hz, and so on
What are the 4 main components of the ear?
Outer ear
Middle ear
Inner ear
Cochlear
What parts of the ear are in the outer ear?
Pinna, External auditory canal, eardrum
What does the Pinna do?
» increases the sound amplitude
» helps determine the direction from which a sound is coming
What does the external auditory canal do?
» provides protection
» increases the sound amplitude
What does the eardrum do and what is its scientific term?
(tympanic membrane)
» vibrates in response to sound waves
» moves bones in the middle ear
What is in the middle ear?
Ossicles
What are the types of Ossicles?
Malleus
Incus
Stapes
What are the smallest bones in the human body?
Ossicles
What do Ossicles do?
The ossicles transmit the vibration of the eardrum (with some
amplification) into the choclea through lever actions
They also provide protection against high amplitude sounds
Muscles attached to the ossicles restrict the bones’ movements
What does the inner ear consist of?
Semicircular canals and the cochlear
What do the cochlear contain?
sensory receptors and an oval window
What is the oval window?
- Membrane covering an opening in the cochlea
- The stapes is attached directly to the oval window (i.e., this is
where vibrations get into the cochlea) - The oval window is much smaller than the eardrum—this size
difference further helps amplify sound waves
What does the cochlear do?
The cochlea is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear
What are the three canals in the cochlear?
» Vestibular canal
» Tympanic canal
» Cochlear duct
How are the three canals in the cochlear separated?
These canals are separated by:
• Reissner’s membrane
• Basilar membrane
Which vibrate in response to vibrations of the oval window
What is located o the Basilar membrane?
auditory receptor cells
hair cells) (in the cochlear duct
What happens when the basilar membrane vibrates?
When the basilar membrane vibrates, hair cells are also set in motion. This converts the vibrations into neural signals
What is the process of receiving auditory signals to the brain?
Nerve fibres vibrate in each cochlear synapse in a number of sites on the way to the primary auditory cortex. The signal arriving at the cochlear nucleus splits and goes to each of the superior olivary nuclei • Beyond this point, input from both ears is present in both hemispheres
What are the sites in the cochlear synapse?
» The cochlear nucleus
» The superior olivary nucleus
» The inferior colliculus
» The medial geniculate nucleus
What auditory tasks can be performed without the auditory cortex according to animal studies?
» The onset of sound
» Changes in sound intensity
» Changes in sound frequency
What auditory tasks cannot be performed without the auditory cortex according to animal studies?
» Discriminating the pattern of several tones
» Discriminating the duration of sounds
» Localising sounds in space
According to animal studies that show that some auditory tasks can and cannot be performed without the cortex, what does the cortex deal with?
it seems that the cortex deals with more complex auditory tasks while the lower structures deal with simple aspects of
sounds
What does speech perception require?
Speech perception requires structures beyond the primacy auditory cortex
What are sounds made up of?
Sounds are made up of a mixture of sine wave components
What does the auditory do to identify the frequencies of sound components?
The auditory system isolates and identifies the frequencies of these components (as though it carries out Fourier analysis).
How long and stiff is the basilar membrane?
The basilar membrane is about 30 mm long and varies in stiffness
and width along its length.
What moves along the basilar membrane?
Travelling waves
What do travelling waves do?
Travelling waves move along the basilar membrane and peak at different point depending on the frequency of the sound.
What identifies the frequency of sound?
The location of the basilar membrane’s peak
what happens when people have damage to a specific part of the cochlea?
When people have damage to a specific part of the cochlea, they tend to suffer from frequency-specific hearing loss
what does stimulating auditory nerves at different cochlear locations lead to?
Stimulating auditory nerves at different cochlear locations leads to
perception of sounds in different pitch
• Actually, this is one way in which a cochlear implant works
how do cochlear implants work?
Microphone worn over the ear. The speech processor that codes sounds electronically. The codes go through wires. The implant receiver that translates radio waves into electrical impulses. The electrode implanted in cochlea that stimulate the auditory nerve
what are hair cells tined to?
Hair cells are tuned to different ranges of frequency according to the location along the basilar membrane
how are auditory neurons arranged?
The auditory neurons are arranged in an orderly manner. This organization is seen repeatedly in the auditory pathways. That is, tonotopic maps are present in the auditory system
how are auditory neurons arranged?
The auditory neurons are arranged in an orderly manner. This organization is seen repeatedly in the auditory pathways. That is, tonotopic maps are present in the auditory system
In pitch perception, what is the perception of a missing fundamental?
When higher-order harmonics are present in the
absence of the fundamental (first harmonic), the
missing fundamental is “filled in”
What happens if some harmonics are heard through only one ear?
A missing fundamental is perceived even when
harmonics are presented to different ears
in binaural pitch encoding, what do structures beyond the cochlear nucleus do?
Structures beyond the
cochlear nucleus should be
contributing to pitch
perception
What is the human auditory range in terms of loudness?
approx. 0–120 dB
– 0 dB = absolute hearing threshold
– 120 dB = loud thunder
What is the range of loudness intensity in humans?
1000000000000 to 1
what are the two basic mechanisms of loudness perception?
– Overall firing rates
– Range of firing
When do more neurons fire?
when a sound is more intense (loudness wise)
what are factors that affect loudness perception?
– Sound duration (longer = louder)
– Frequency
Generally what are high frequency sounds perceived to be with regard to loudness?
Generally, high-frequency sounds are perceived to be louder (up to about 5000 Hz) – Around 3000–5000 Hz, sounds are perceived to be loudest
What is the effect of amplitude on frequency?
As the amplitude goes
up, the effect of
frequency becomes
smaller
What do we try to determine in auditory space perception?
a sound’s:
– horizontal direction (azimuth) not bad
– vertical direction OK, with head movement
– distance
what does vision provide with regard to locations?
Overall, vision provides more precise information
about an object’s location
What makes it questionable as to why we can auditorily localise sounds?
Nothing on the basilar membrane directly indicates
sound locations
what sort of process is auditory space perception?
Auditory space perception is a binaural process
What is involved in auditory space perception?
– Interaural time difference
– Interaural intensity difference
what is involved in interaural time difference?
- Onset difference
* Phase difference
what is onset difference in interaural time difference?
Unless a sound is directly in front of or behind you, it reaches two ears at different times (onset difference)
how is the onset difference detected in interaural time difference?
The onset difference can be detected by a simple “delay line” mechanism in the brain
what is phase difference in interaural time difference?
The same sound will most likely be in different
phases when it reaches each of the two ears
(phase difference)
– But the phase difference is less useful for localizing
high-frequency sounds
what is interaural intensity difference?
The same sound should be a bit more intense at
an ear that is closer to the sound source
– The energy of a sound
decreases as it travels
farther
what is the role of the head in interaural intensity difference?
The head works as a barrier that reduces the intensity of the sounds (sound shadow) • This effect is more pronounced for high-frequency sounds
what type of frequency is interaural time difference (phase difference) useful for localising?
Interaural time difference (phase difference) is
useful for localizing low-frequency sounds
what type of frequency is interaural intensity difference useful for localising?
Interaural intensity difference is useful for
localizing high-frequency sounds
which interaural cue works best for sounds in the middle range?
Interestingly, neither cue works particularly well for
pure tones around 1000–3000 Hz
what is the role of head movements in sound localisation?
• Head movements are generally helpful for
auditory localization
• By changing the positions of the ears, you can
experience changes in interaural time/intensity
differences
What perception direction do humans perceive better?
Humans perceive horizontal directions better than vertical directions through auditory cues
What is the pinnae more effective in distinguishing with regard to auditory localisation?
Pinnae are more effective in distinguishing front/back
than above/below
What is the role of ear positions in auditory localisation?
Ear positions can be varied more freely along the
horizontal dimension
• Two ears are located on the same horizontal plane
• A greater range of head movement is possible along the
horizontal dimension than the vertical dimension
What are most auditory localisaiton cues dependent on?
Most of the auditory localization cues are
dependent on the distance between a sound
source and ears
• As a result, it is difficult to
distinguish locations of sounds
that are equidistant to an ear
– Cone of confusion
What are the two cues for auditory distance perception?
– Loudness
– The energy ratio of direct and reverberant
sound (not available in open space)
The utility of these cues is usually limited
what can loudness tell us?
Loudness cues can tell us only about relative distance
How do reverberation cues vary?
Reverberation cues vary depending on various
properties of the reflection surface
What are the weaknesses of human auditory distance perception?
• When we have auditory cues only, we
underestimate the distance to a sound source
• Our perception of auditory distance tends to be
variable (imprecise) too
what tends to overwrite auditory localisation?
When we can visually perceive where a sound
“should be” coming from, it tends to overwrite
our auditory localization
what strongly affects how we hear sound stimulus?
When we have some visual information about
how a stimulus “should” sound, it strongly affects
how we actually hear the stimulus
– e.g., The McGurk effect
What do information do we give more weight to?
We give more weight to information that (we
think) is more informative
What is vision a good source of?
spatial infromation
what is audition a good source of?
temporal information
how does auditory information influence our visual perception?
Auditory information can influence our visual
perception by providing conflicting temporal
information
– e.g., Sound-induced flash illusion
