lecture 8: hearing Flashcards
how are loudness and pitch related
loudness and pitch are related to amplitude and
frequency, but not identical
Whereas loudness depends on the energy of the wave. In general, the pitch is the reason behind the difference in voice quality of different individuals. The pitch of a sound depends on the frequency while loudness of a sound depends on the amplitude of sound waves.
pure vs complex tones
a pure tone consists of only a single frequency. It’s wave form is a pure sine wave. A complex tone is not a pure sine wave but it is periodic–it has an underlying pattern that repeats
Timbre
Two non-identical
sounds can have the
same loudness and
pitch.
Timbre depends on the
frequency spectrum, the
sound pressure and the
temporal characteristics
of the sound
Shepard Tone
The Shepard tone is colloquially referred to as an auditory illusion. The effect is an endless ascension of pitch, seemingly rising to some sort of resolution but never getting there
illusion from manipulating loudness and pitch: barberpole of sound, seems to rise but doesnt and is great in building suspense for movies
bones in the middle ear
malleus, incus, stapes
cochlea
The cochlea is a fluid-filled, spiral-shaped cavity found in the inner ear that plays a vital role in the sense of hearing and participates in the process of auditory transduction. Sound waves are transduced into electrical impulses that the brain can interpret as individual sound frequencies
eardrum
The eardrum vibrates from incoming sound waves and sends these vibrations to three tiny bones in the middle ear
how many types of visual receptors do we have
two- rods and cones
how many types of auditory receptors so we have
one- hair cells
hair cells
The function of the cochlear hair cell is to convert mechanical vibration induced by sound waves into electrical signals that are transmitted to the brain via the auditory portion of the VIII cranial nerve.
The cochlear hair cells in humans consist of one row of inner hair cells and three rows of outer hair cells. The inner hair cells are the actual sensory receptors, and 95% of the fibers of the auditory nerve that project to the brain arise from this subpopulation.
ipsilateral
same side
contralateral
opposite sides
what are the 3 parts of the auditory pathway
Neurons in secondary auditory cortex represents a greater range of frequencies, loudness, location, and combinations of features (somewhat analogous to simple
and complex cells in striate and extrastriate visual cortex)
is the auditory system cross wired
not completely unlike visual system
Overlap of what/where in vision and audition
Sound Localization:
where
Inter-aural time difference (loudness & timing)
Distortions of sound by head & pinnae
“what” specialization in
audition: voice selective regions
Beyond Auditory Cortex, two pathways. The
ventral stream is for what and a dorsal stream
for where/how
- Basic acoustic features represented in auditory
cortex pitch, spectrotemporal properties,
intensity - A few categories appear to have selective
processing regions (or neurons), but evidence
is more sparse than in vision - Voice recognition, music, speech
McGurk Effect
an auditory-visual illusion that illustrates how perceivers merge information for speech sounds across the senses. For example, when we hear the sound “ba” while seeing the face of a person articulate “ga,” many adults perceive the sound “da,” a third sound which is a blend of the two
visual vs auditory systems
Music Processing
(Peretz & Coltheart, 2003)
Congenital Amusia (tone deaf) individuals show
differences in grey matter density in right auditory
cortex and right inferior frontal gyrus
Reward regions respond to pleasurable music
and ‘chills’: Nucleus accumbens, dorsal striatum
Music and Pleasure
Pitch processing occurs in
the auditory cortex, but
melodies are comprised
of combinations and
sequences of pitches, as
well as temporal
information engaging
both the ventral and
dorsal routes.
Frequency
how many times a a wave cycles every second (pitch)
Amplitude
how high the wave becomes (loudness)
How are frequency and amplitude related to what we hear
every day?
Frequency: Pitch
* Amplitude: Loudness
Pinna
focus sound into
the ear canal
Ear canal:
carry the
sound further into the
ear to tympanic
membrane
- Tympanic membrane:
When sound waves reach the tympanic membrane they cause it to vibrate. The vibrations are then transferred to the tiny bones in the middle ear
3 bones carry information to cochlea:
(stapes,
maleus, incus)
tonotopic map
- The cochlea is organized in a ‘tonotopy’
- cells at one end of the cochlea respond to the highest frequencies and
cells at the other end respond to the lowest frequencies of sound waves,
with a gradient in between
hair cells
Cochlea is covered in hair cells
* The movement of the fluid in the cochlea moves the hair cells
* Movement of hair cells physically pulls open ion channels to
start transduction of signal
pro and con of cochlear implant
The ability to hear sounds around them for safety and better quality of life
The sound experienced with a cochlear implant is different than normal hearing, and the brain needs time to learn how to use the new input.
Partial ‘Cross-wiring’ in Auditory Pathway
Like visual information, auditory information crosses the axis of the body.
Unlike visual information, only some of it crosses over.
Auditory input leaving the cochlea is
processed by a series of structure sin the
brain stem, midbrain, and thalamus
This auditory pathway gives input to
primary auditory cortex (A1)
A1 in each hemisphere receives input from
both the left and right ears
Tonotopy in primary auditory cortex
Like the cochlear membrane, there is a topographic organization of frequency in the brain.
Region names
* Primary auditory cortex (A1), also known as the “core” area
* Belt area (A2) surrounding A1
* Parabelt area (A3) adjacent to lateral side of belt
Neurons in belt and parabelt can be
tuned to more varied patterns of input
experiment to Discovering category selectivity in the
auditory cortex
Present every type of sound you can think of. Test whether
different parts of the brain care about any specific category.
- Some parts of auditory cortex (in both humans, left, and
monkeys, right) respond to the identity of the person who is
making vocalizations rather than the exact utterance
McGurk effect
The McGurk effect is a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound.
