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Topic 3: Signals and Perception - Coggle Diagram
Topic 3: Signals and Perception
LO 3.1
Signals and perception
sensory signals must be received by specific receptors + converted into electrical signals to travel through the nervous system
data driven signals direct from sense transmitted to brain
concept driven
used to create percept that can feed into our understanding of situation
used to determine appropriate behavioural response
LO 3.1
Difference between sensation and perception
sensation
sensory signals
perception
how we interpret sensory signals
LO 3.2
General principles of sensory processing
sensory receptor cells have receptive field + threshold
transduction
sensory receptor cells translate physical stimuli into currency of nervous system (i.e. membrane potential)
sensory receptor cells produce change in membrane potential
LO 3.2
The process of hearing
sensory signals must be received by specific receptors + converted into nerve impulses to travel through nervous system
signals in the brain are:
combined with previous experience + attention
used to create percept that can feed into our understanding of a situation
used to determine appropriate behavioural responses
sensory signals
sensory receptors
the brain
experience + attention
percept
perceptual understanding
behavioural response
LO 3.2
Auditory signals
longitudinal wave in air created by vibration of objects
sound waves have amplitude
greater amplitude generally associated with louder sound
sounds waves have a frequency
time over which cycle repeats indicates frequency
higher frequency typically associated with greater pitch
humans can hear sounds from 0-14 dB + 20 Hz-20KHz
LO 3.2
Structure of the ear
outer ear
part we can easily see + touch
pinna, auricle + external auditory canal
funnels sound inwards
amplifies sound by acting as tube for it to echo in
protection = water resistant wax which is anti-fungal + antibacterial, acidic environment + hairs which prevent entry
tympanic membrane
separates outer ear from air filled middle ear cavity which contains three tiny bones (malleus, incus + stapes)
acoustic impendence matching means pressure created by sound created by soundwave amplified to prevent loss of signal as it enters fluid filled cochlea
stapes
contacts entrance to cochlea where auditory hair cells are + so soundwaves must get all the way into inner ear before they can be sensed
cochlea made up of 3 distinct structures: scala tympani, scala media + scala vestibuli with each separated from another by specific membrane
the organ of corti is found within the scala media + sits on top of the basilar membrane + extends upwards towards the tectorial membrane
within here are inner hair cells which are responsible for transducing sound waves into electrical signals
the ear can be divided into outer, middle + inner ear
LO 3.2
Inner hair cells
consist of spikey hair-like structures that stick out the top of cell known as stereocilia
each stereocilia has mechanically gated K+ channels on the end + are connected to neighbouring one via tiny fibres called tip links
main part of cell contains usual organelles as well as voltage gated Ca2+ channels + vesicles of glutamate
hair cells synapse with postsynaptic neuron, forming parts of auditory nerve that contains AMPA receptors for glutamate
when stereocilia bend towards the kinocilium, this forces mechanical opening of K+ channels
when stereocilia anything other than vertical, this is an indication they're transducing sound signals
influx of K+ creates receptor potential which triggers depolarisation induced opening of Ca2+ channels
due to concentration of K+ being very high outside the cell, when K+ channels open, K+ floods into the cell down its concentration gradient as well as down electrostatic gradient because inside of hair cell negatively charged
Ca2+ floods in, causing release of glutamate which then binds to AMPA receptors on neurons of auditory nerve causing action potential to be produced
LO 3.2
How is information transported from the cochlea to the primary auditory cortex?
leave cochlea + sends signal to cochlea nuclei complex + superior olivary complex (both in brainstem)
proceeds to midbrain in inferior colliculus before reaching thalamus in which it travels to specific nucleus called medial geniculate nucleus within thalamus
after this, signal travels to primary auditory cortex
LO 3.2
Visual signals
light is a transverse wave but it also considered a particle
wave particle duality
visible spectrum is very small part of electromagnet system
relationship between wavelength + frequency
speed = frequency x wavelength
violet has shortest wavelength (around 380nm) whilst red has longest wavelength (around 700nm)
LO 3.2
The structure of the eye
actual transduction occurs in the retina but sensation wouldn't be possible if dioptric apparatus didn't work properly
consists of cornea + lens
cornea is transparent + tough + allows light to pass through without being diffracted
the lens can be diffracted in shape to give different amounts of refraction
light focussed by the cornea + retina should reach focal point on retina
refractive errors caused by light signals being incorrectly focussed
incorrect focus can arise from power of dioptric apparatus being incorrect or from length of eyeball being different to typical
if light is bent too much or they eyeball is too long then focal point will fall short of the retina
if light is not bent enough or length of eyeball is too short then focal point will fall too long for retina
the retina
the photo receptors where transduction occurs are at the very back of the retina so light passes through several transparent retinal layers first
once light has been transduced by the rods + cones it's passed back towards front of retina
first rods + cones connect to bipolar cells
cones have 1-2-1 mapping whilst rods converge so sensitivity gained but acuity lost for rods
these bipolar cells carry signal to ganglion cells
axons of RGCs form optic nerve + carry signal to the brain
LO 3.2
Rods and cones
Rods
outer segment contains series of tiny discs within cellular membrane which contain rhodopsin
inner segment contains some of typical organelles of animal cells
there is a region of synaptic contact (synaptic terminal is where rods synapse with bipolar cells)
Cones
outer segment that contains opsin
LO 3.2
Transduction of the visual signal
visual transduction is a complex process involving G-proteins
ion channels react to sensory stimulus arriving (ion channel is cation channel)
channel closes when light falls on eye, preventing normal incoming positive/depolarising current
cell becomes hyperpolarised, preventing release of neurotransmitter + bipolar cell not activated
means there's communication in the dark (dark-current)
LO 3.3
How does information travel from the retina to the brain?
info leaves the retina via the optic nerve
reaches optic chiasm, at which point info can cross over the midline so all left visual field info now on right side of brain + vice versa
pathway continues to right LGN in thalamus
LGN has six main layers as well as sublayers with each receiving specific info from specific cell types + only from one eye
info then sent to primary visual cortex for further processing
LO 3.3
Frequency coding
place theory/place code
specific hair cells in the cochlea response to specific frequencies
hair cells then excite specific auditory neurons + this specific mapping is found all the way up the pathway
tonotopic relationships
two hair cells next to each other will activate two auditory neurons next to each other
if the brain knows where the signal has come from, it can deduce the frequency
poor method for low frequencies but can be used for frequencies above 1000 Hz + is the only method of coding for frequencies over 3000 Hz
temporal/rate code
hair cells oscillate at frequency of incoming sound wave which means neurotransmitter released at same frequency
means auditory neuron action potentials are at same frequency so frequency of firing matches frequency of sound
can hear higher frequencies than our neurons can fire
thought that neurons work together to phase lock (volley principle)
this method is most helpful for lower frequencies when place code won't work
LO 3.3
What is intensity coding?
begins in the cochlea
first way brain can deduce intensity is from frequency of firing in auditory neurons
louder sounds mean greater amplitude of sound wave creating greater movement in the cochlea, bending the stereocilia more
creates greater influx of K+ and subsequently greater influx of Ca2+ glutamate release
more glutamate release increases chances of binding to receptors + causing EPSPs
second way brain can deduce intensity is from number of neurons firing
higher intensities cause more movement in cochlea so hair cell with appropriate CF is depolarised but so are some of its neighbours to a lesser extent
neighbouring cells also release some glutamate + activate their auditory neuron, so more cells overall are activated
LO 3.3
What is location coding?
vertical location coding in humans is from the way sounds bounce of the ridges of outer ear
horizontal coding works in several ways + is carried out by the superior olivary complex as it requires info from both ears + looks at the differences between them
LO 3.4
Types of hearing loss
conductive
any hearing loss before sound reaches cochlea arising from damage to upper/outer ear
glue ear
type of conductive hearing loss
arises when eustachian tube fails to function as it should
results in build up of fluid in the middle ear
means that much of the sound arriving at the middle ear is reflected back because the fluid creates too much resistance to movement
conductive hearing loss because signal lost before it's conducted to receptors
typically occurs in one ear + results in problems with hearing threshold rather than discrimination
effects
hearing loss
balance problems
delayed speech development
ear pain
social isolation
behavioural problems
treatment approaches
watch + wait (4-6 weeks)
treatment of concurrent infection
grommets
hearing loss can be classified based upon where damage occurs/where signal fails to be transmitted
cochlear
any hearing loss resulting directly from damage to the cochlea
retrocochlear
any damage in the auditory pathway from the cochlea nerve onwards
LO 3.2
Other than in the cochlea and the brain stem, where else can sound processing occur?
posterior dorsal stream travels upwards initially to posterior parietal cortex then heads forwards towards prefrontal cortex
thought to help brain process where info located
anterior ventral stream travels down through superior temporal region then heads forward in the brain
thought to help encode info
LO 3.4
Cochlea hearing loss - noise-induced hearing loss (NIHL)
NIHL is the most common form of sensorineural hearing loss
caused by exposure to high intensity noises + normally comes on over a period of time so gets greater with age, during which hair cells are damaged or die
normally bilateral + symmetrical hearing loss + can impact threshold discrimination
LO 3.4
Classification levels of hearing loss
Mild = 20-39db HL >>> following speech difficult, especially in a noisy environment
Moderate =40-69db HL >>> difficulty following speech without using hearing aid
Severe = 70-89db HL >>> usually need to lipread or use sign language, even with use of hearing aid
Profound = 90-120db HL >>> usually need to lip read or use sign language, hearing aid ineffective
LO 3.4
Colour blindness
decreased ability to see colours
can take on range of forms but most common is inherited form which affects males more than females
no cure
at cellular level, there could be missing cones or shift in spectral sensitivity of cones
LO 3.2/3.3
Colour opponency
connection between different types of cones to create colour coding in RGC cells
red cones excite RGC + green cones inhibit, resulting in red-green RGC
red cones excite + green cones excite, giving luminance channels
blue excites + luminance inhibits to give blue-yellow RGC