Chapter 4: Sensation and Perception 4.4 (Hearing) Flashcards
Sound waves
changes in air pressure unfolding over time
Pure tone
a simple sound wave that consists regularly of alternating regions of higher and lower air pressure, radiating outward in all directions from the source
Frequency (or repetition rate)
depends on how often the peak in air pressure passes the ear or a microphone, measured in cycles per second or hertz (Hz); perceived as the pitch
Pitch
how high or low a sound is, as ordered on a musical scale; low frequency (low-pitched sound) and high frequency (high-pitched sound)
Amplitude
refers to the intensity of sound wave, relative to the threshold for human hearing (set at 0 decibels or dB); perceived as loudness
Loudness
high amplitude (loud sound) and low amplitude (soft sound)
Complexity
mixture of frequencies, influences perception of timbre; simple (pure tone) and complex (mix of frequencies)
Timbre
quality of sound that allows you to distinguish two sources with the same pitch and loudness
3 parts of the human ear
(1) Outer ear- collects sound waves and funnels them towards the middle ear (2) Middle ear- transmits the vibrations into the inner ear, embedded in the skull (3) Inner ear- where sound is transduced into neural impulses
Outer ear
consists of the visible part of the outside of the head (pinna), the auditory canal, and the eardrum
Eardrum
an airtight flap of skin that vibrates in response to sound waves gathered by the pinna and channeled into the canal
Middle ear
a tiny, air-filled chamber beside the eardrum where the ossicles take airborne pressure wave at the eardrum and transfer it into fluid, act as a lever that mechanically transmits and amplifies vibrations, pushing against the oval window, to the cochlea of the inner ear
Ossicles
the three smallest bones in the body named for their appearance as hammer, anvil, and stirrup
Why do the ossicles amplify vibrations?
Fluid requires more energy to vibrate
Inner ear
contains the cochlea, which is divided along its length by the basilar membrane
Cochlea
fluid-filled tube containing cells that transduce sound vibrations into neural impulses
Basilar membrane
structure in the inner ear that moves up and down in time with vibrations relayed from the ossicles, transmitted through the oval window
Movement of sound waves in the basilar membrane
Sound causes basilar membrane to move up and down in a traveling wave: at low frequency, the wide, floppy tip (apex) moves the most and at high frequency, the narrow, stiff end closest to oval window (base) moves the most
Inner hair cells
specialized auditory receptor neurons embedded in the basilar membrane that are stimulated when it moves up and down and the cochlear fluid moves back and forth
Back-and-forth bending of hair cells in the cochlear fluid
generates rhythmic action potentials in the auditory nerve axons that travel to the brain and are timed with the pressure peaks of the original sound wave
Which auditory nerve axons fire the most?
those connected to hair cells in the area of the basilar membrane that moves the most
Neural impulses to the brain
action potentials in the auditory nerve travel to several regions of the brainstem, to the thalamus, then to area A1, the primary auditory cortex in the temporal lobe
2 distinct streams of the auditory cortex
spatial (where) auditory features and features that allow you to identify the sound (what it is)
Spacial auditory features
allows you to locate the source of a sound in space, handled by areas towards the back of the temporal lobe and in regions that may overlap with the visual dorsal stream
Features that allow you to identify sound
handled by areas in the lower (ventral) part of the temporal lobe, may overlap with the ventral visual pathway
Perceiving loudness
signaled by the total amount of activity in the hair cells
Perceiving pitch
(1) placal code, where brain uses information about the relative acitivity of the hair cells across the whole basilar membrane (2) temporal code, where the brain uses timing of the action potentials in the auditory nerve
Perceiving timbre
depends on the relative amounts of different frequency components in a sound, thus the relative activity of hair cells across basilar membrane
Localizing a sound
(1) frequency of sound emphasized by the pinna depends on where it is coming from (2) speed of sound is much slower than speed of light, sounds arrive sooner at the ear nearer to the source for lower-frequency components (3) higher-frequency components are more intense in ear closer to the sound because the head blocks higher frequencies
2 main causes of hearing loss
conductive hearing loss and sensorineural hearing loss
Conductive hearing loss
damage in eardrum or ossicles which stop them from conducting sound waves to the cochlea, a mechanical problem, which can be corrected with medication, surgery, or sound amplification from hearing aid (conduction via surrounding bones)
Sensorineural hearing loss
damage to the cochlea, hair cells, or auditory nerve that happens to almost everyone as we age
2 main effects of Sensorineural hearing loss
sensitivity decreases so sounds have to be more intense (hearing aids can help) and acuity decreases so sounds smear together on the basilar membrane, making them harder to understand
Causes of Sensorineural hearing loss
genetic disorders, premature birth, infections, medications, accumulated damage from sound exposure, aging
Cochlear implant
an electronic device that replaces parts of the function of the hair cells, consist of a microphone and a processor, an external transmitter (on scalp) behind the ear, receiver inside skull and thin wire containing electrodes inserted into cochlea to stimulate auditory nerve
Stereophonic hearing
Sound is louder when the source is closer to the ear and the sound waves arriving sooner at near ear (timing) indicates direction of the source
Top-down processing in hearing
Perceptions e.g. previous exposure, background, knowledge, expectation, or context helps us make sense of what we hear
