lecture 6 - auditory/sensory Flashcards
sensory system characterized by (3 things
hierarchical organization
functional segregation
parallel processing
describe hierarchical organization of sensory system
damage to each area?
top down or bottom up flow of info?
- low level processing at primary, move up levels = more complex.
ranked: receptor -> primary -> secondary -> association
organized by functional complexity: simple,general -> complex, specific
damage to low level = loss of function. damage to higher level = specific sensory deficit
sensory info goes bottom up, but can use top-down to hone in on what youre looking for and inhibit detection of things youre not looking for.
sensation vs perception
detecting stimuli = sensation
interpreting stimuli = perception
agnosia
cant ID object but can interact. perceptual problem
functional segregation of sensory systems
different processes/functions processed in different areas.
parallel processing of sensory systems
various systems have overlapping pathways and cross talk between them
- influence behaviour without conscious awareness
- influence behaviour by engaging conscious awareness.
the binding problem
how do we perceive anything as a whole?
all perceptions must be combined somewhere. => claustrum. thin layer of neurons under neocortex. very top of sensory hierarchy.
how do we hear sound?
vibration of air molecules transduced into auditory information
3 important aspects of waves
amplitude = loudness frequency = pitch complexity = timbre
pure tones
one sine wave. not naturally made
cant localize, uncomfortable to listen to
complex sound waves
complex addition of waves.
what is fourier analysis
mathematical breakdown of complex waves in to component sine waves
- theory that auditory system does fourier analysis
perceiving pitch = fundamental frequency or missing fundamental frequency
fundamanteal frequency = the highest frequency of the bunch is the one detected.
missing : beat frequencies present in all sounds. when fundamental is not there, the beat frequency is still present so fundamental fequency can be perceived.
outer ear - transmission of sound waves into ear.
sound waves travel down auditory canal tympanic membrane (eardrum) vibrates. vibration transferred to ossicles - malleus, incus, stapes. stapes knocks oval window (inner ear) - pushes liquid inside cochlea, causing movement in organ of corti inside cochlea.
inner ear
transfers vibrations to perilymph of cochlea (long, coiled tube with internal membrane)
internal organ of corti - holds hair cells = transducers. filled with fluid = endolymph.
organ of corti
2 membranes
basilar membrane: hair cells mounted on this one.
tectorial membrane - rests on hair cells.
round window
dissipates vibrations and the end of the cochlea.
organ of corti - where frequencies fall on organ.
white noise
tonotopic map
higher frequency = hair cells by oval window
lower frequency = by tip of basilar membrane
white noise = all component frequencies at equal amplitude.
tonotopic map - carried by auditory nerve. to temporal. each level of auditory system organized by frequency.
how hair cells respond to sound
on tip of hair cell = cilia. connected to adjacent cilia via tip link which is attached to cation channel.
the cilia increase in length along axis. only tallest touches tectorial membrane. when sound comes thru, tectorial membrane moves ( perilymph above) and shears hair cell. mechanical movement of cilia causes conformation change in tip link opening K influx. K+ influx induced VG-Ca2+ channel to open which releases NT on auditory nerve.
outer hair cells
- attach to tectorial membrane. help mediate auditory attention.
make membrane looser is you dont want to hear frequency. make membrane tighter if you do want to hear frequency.
== top- down control on organ of corti by brain.
essential for normal hearing
endolymph
fluid in organ of corti. rich in K+. energy storage.
ear to A1 pathway
organ of corti -> auditory nerve -> cochlear nucleus (ipsilateral) -> superior olives (combined input), inferior colliculus -> medial geniculate nucelus (thalamus) -> A1
- Lots of auditory processing in brainstem region.
sound localization - lateral and medial superior olives - their functions.
lateral superior olives = notices differences in loudness between info from both ears
medial = responds to difference in time of arrival when comparing info from both ears.
use these two areas to localize sound.
superior olives project to colliculi in the midbrain - inferior & superior
inferior colliculi: high level auditory processing, ID sounds
superior colliculi: coordinates eye movements to orient selves in response to sound.
superior colliculi is retinotopically organized map of auditory space. *info from olives tells where you are, colliculi mediates movement of eyes toward that sound.
A1 and A2
A1 = organized into functional columns. vertical neurons respons to same frequency.
tonotopic map. - fourier analysis probabbly done at this point already
A2 - adjacent to A1. organized by frequency. used to understand speech.
auditory association cortices
PFC
PPC
PFC - anterior auditory pathway. “what” ID sounds.
PPC - posterior auditory path. “where” locate sounds, help prep for action.
auditory and visual interaction - in assoc cortex
PPC - 2-ary for V and A. mutli-modal area. integral in sensory processing
damage to auditory system
auditory cortex damage is rare if it does occur. its hidden in a fissure so its harder to damage.
there are less severe permanent deficits if damaged alone because subcortical circuits are doing a lot of complex things.
deafness = conductive, nerve
damage to inner or middle ear.
conductive deafness = damage to ossicles, eardrum
nerve deafness = originates from nerve damage. ex: loss of hair cell receptors.
cochlear implants
help with deafness = bypass hair cell damage. converts sound to electrical signal and carries directly to auditory nerve.
tinnitus
damage to auditory system . constant, whirr, buzz. not debilitating usually.
continues despite auditory nerve cuts = suggest product of central processing.
somatosensations - define
sensation from body