Lecture 12-Hearing Flashcards
What are sound waves:
-When an object vibrates, its movement causes the molecules of air surrounding it to alternately condense and rarely pull apart.
-These fluctuations in air pressure travel away from the source as a sound wave at approximately 700 miles per hour.
Explain audition (hearing)
-the human ear can transude fluctuations in air pressure if the length of the soundwave is between 1.7 centimeters and 17 meters.
-corresponds to sound waves that oscillate at frequencies between 20 and 20,000 times per second
What are the 3 dimensions of sound?
Loudness: amplitude or intensity of the molecular vibrations
Pitch: frequency of molecular vibration, measured in Hertz (Hz)
Timbre: complexity of the sounds. To help identify the sources of the soundwave.
3 anatomical components of the ear:
- Pinna: where sound is funneled through
- Tympanic membrane: vibrates when sounds come through the ear canal, transferred to the middle ear.
- Middle ear; 3 ossicles (small bones): malleus, incus, stapes,
Cochlea is divided into 3:
scala vestibuli,
scala media,
scala tympani
Organ of Corti, receptive organ contains:
-Basilar membrane:
-Tectorial membrane:
-Hair cells:
-Basilar membrane: bottom
-Tectorial membrane: top
-Hair cells: in the middle
Cilia:
hair-like extensions that transduce sound
-cilia of hair cells are connected by tip links; elastic filaments
-The point of attachment of tip link to cilium is called insertional plaque; single ion channel.
Inner vs outer hair cells:
-3 times more outer hair cells than inner hair cells (only inner transmit auditory info)
-Outer hair cells contract like muscles to adjust the sensitivity of the tectorial membrane to vibrations
-People who do not have working inner hair cells are deaf
-People that do not have functioning outer hair cells can hear but not well.
The effects of loud noise:
-Can easily break the tip links that interconnect cilia, making the hair cells not transmit auditory info
(Tip links can grow back within a few hours, temporary hearing loss)
-This is a protective measure because too much glutamate release into the cochlear nerve causes permanent cell death.
-20% of 20 yr olds have noise induced hearing loss
Place coding vs rate coding (2 perceptions of pitch)
Place: approach encoding sensory info, positions of active hair cells in cochlea indicated frequency of the sound wave
Rate: encoded by very low frequencies
Loudness, Timber and Overtone:
Loudness: corresponds to the total number of hair cells that are active and their overall activity levels.
Timber: is perceived by assessing the precise mixture of hair cells that are active throughout the entire cochlea.
Overtone: sound wave frequency that occurs at integer multiples of the fundamental frequency
Fundamental frequency:
the lowest and most intense frequency of a complex sound. Is what is most often perceived as basic pitch
cochlear implant:
-20-24 electrodes positions along length of cochlea. Speech best when frequency position is 250-6500 Hz are stimulated-
Phase differences and low frequency sounds:
-we detect the source of continuous low pitch sounds by means of phase differences
-Are the ears detecting compressed air at the same time? If so the source must be equidistant from two ears
Loudness and high frequency sounds:
-we detect the source of high pitched sounds by analyzing differences in loudness between the ears.
Different parts of the auditory cortex responds best to different frequencies,
Tonotopic representation:
Organization where different frequencies of sounds are analyzed in different places of the auditory cortex, known as tonotopic representation.
Primary auditory cortex,
Auditory associated cortex,
Posterior auditory pathway:
Primary auditory cortex: is in the upper section of the temporal lobe, mostly hidden in lateral fissure.
Auditory association cortex: belt and parabelt regions
Posterior auditory pathway: involved in sound localization. This pathway meets up with the vision pathway.
Auditory agnosia vs Amusia
Auditory agnosia: brain damage can result in auditory association cortex can cause very specific types of auditory agnosia
Amusia: inability to perceive or produce melodic music, unable to sing or recognize happy birthday songs, they can converse to understand speech and recognize environmental sounds.
Unable to tell consonant and dissonant music (pleasant or unstable)
Vestibular system:
detects gravity and angular acceleration of the head; not necessarily definable conscious sensations, it helps with balance, position, and corrects eye movement.
Cochlea: detects sound
Semicircular canals,
Cupula,
Vestibular sacs:
Semicircular canals: three ring like fluid filled structures that detect changes in head rotation
Cupula: gelatinous mass found in the ampulla of the semicircular canals, moves in response to the flow of fluid in canals.
Vestibular sacs: a set of two receptor organs in each inner ear that detects changes in the tilt of head.
=responds to force of gravity and inform the brain about the heads orientation
