sensation and perception Flashcards
sensation
describes the registration and initial encoding of sensory information
perception
refers to how the brain organizes sensory information into meaningful representations
retina
several layers of cells at the back of the eye
begin initial representation of visual work
extension of the brain
retinal tissue is derived from the neural tissue during embryological development
cones
colour
large size
conical shape
bright light
central location
opsins are red, green and blue
rods
black/white
small size
narrow shape
dim light
periphal location
opsin is rhodopsin
parallel processing
begins with the photoreceptor cells in the retina
rods and cones are an input response
pigments in the rods and cones
absorb light energy and transform it into electrochemical energy used in the nervous system
how many rods and cones do we have
120 million rods
6 million cones
what causes the release of NT’s in the photoreceptors
the cascade of chemical changes inside the rod/cone which changes membrane depolarization
this signals to the next layer of cells within the eye
what are the 3 types of ways rods and cones differ
types of pigments
distribution across the retina
interaction with ganglion cells
pigment in rods
rhodopsin: saturated in broad daylight therefore rod system will not function
sensitive to very small amounts of light
not sensitive to fine detail because so many feed into one ganglion cell
pigments in cones
each contain a different pigment sensitive to a different wavelength in the visible light spectrum
blue (short wavelength), green (medium wavelength) and red (long wavelength)
- pattern of activity in these receptors enables the variation in colour
cones retinal distribution
densely in the fovea
rods retinal distribution
located in the periphery
fovea
main area of focus for vision
rods interaction with ganglion cells
many rods feed into a ganglion cell
feature makes it respond to low levels of light
cones interaction with ganglion cells
few cones feed into ganglion cell
allows for more fine detail - cannot function under low light conditions
blind spot
where optic nerve leaves the eye
ganglion cells
cell bodies located in the retina, axons stretch out from retina
output response from eye to brain
two main types of cells M cells and P cells which both form functional pathways
send their input to different destinations in the brain
M cells
magnocellular = large
responsive to coarse pattern and detect rapid motion
P cells
parvocellular = small
preserve colour information
small bistratified
has unique projection to the thalamus
receptive fields
the specific region of visual space a cell responds to
when the eye is stationary, light from a particular location in space only falls on a specific part of the retinal surface - this stimulates specific subgroups of rods or cones which send messages to specific ganglion cells
light must be absorbed by a specific rod or cone for that photoreceptor to respond
the brain knows where light has struck by knowing which ganglion cells are excited
centre-surround structure
what the receptive fields of retinal ganglion cells have
light in a particular spot in visual space will excited a ganglion cell, but light in the donut shape area encirculating it will enhibit it - can also work in the opposite manner
this enhances contrast (edges and borders of objects)
tectopulvinar pathway
allows us to oriente important visual info quickly
fast-acting
sensitive to motion and apperances of novel objects in visual periphery
recieves most its input from M ganglion cell
sends visual info from retina directly to th superior colliculus
superior colliculus
pathway that extends to the pulvinar nucleus in the thalamus and to cortical areas that processes info about visual motion
sends projections to motor regions that control eye and head movements
info leaving optic nerve can terminate here
fast-acting
not sensitive to fine detail
site for integration of auditory and visual senses together
allows for orientations of eyes to periphery to be brought to central vision and then go to geniculostriate pathway
tectum
in midbrain
includes inferior colliculus (auditory)
superior colliculus (visual)
the geniculostriate pathway
extends to lateral geniculate and then to striate cortex
90 percent of optic nerve fibers project to this pathway
enables our consious experience to seeing
axons terminate in the lateral geniculate nucleus of the thalamus
lateral geniculate nucleus
continues info to the primary visual (striate) cortex
enables perception of colour
info from the right side of both retina is sent to the LGN on the right side of the brain and vice versa
has six main layers stacked on top of one another and then folded into a knee like shape
each layer recieves input from only one eye, but all layers recieve info from the contralateral visual field
optic tract
ones the nerve fibers cross at the optic chiasm they are reffered to as this
koniocellular layers
small cell layers in-between the main LGN layer
receive input from the small bistratified ganglion cells and the superior colliculus
relevance to blindsight
magnocellular layer
obtains input from M cells
detects motion
parvocellular layers
obtain input from p cells
detect colour and detail
retinotopic map
each main layer in the LGn contains this of half the visual field, laid put by the retina itself
ensures that info does not get jumbled up when it reaches the LGN
fMRI studies show this
where does visual info go once it passes through the LGN
Primary visual cortex (striate cortex)
Primary visual cortex (striate cortex)
projections from the LGN to here maintain their spatial location
not much info from the periphery reaches here, mostly dedicated to the center
cortical magnification factor
describes the mm’s of cortical surface that are devoted to one degree of angle of the visual world
higher for the fovea compared to the periphery
why is the primary visual cortex considered striate
because the distinct layers make it appear to be striped
cells of the striate cortex
not tuned to light, responds to bards of light oriented in different ways
simple cells
complex cells
hyper-complex cells
simple cells
respond to bard of different orientations
excitatory centre, inhibatory surround - only fire is bar is oriented in a certain way
complex cells
respond best to certain line orientations
less picky about where exactly the line is located - do not have an on and off region
show preference for direction of movement
hyper-complex cells
or end stop cells
prefer lines of certain lengths
columns in the striate cortex
cells that prefer a given line orientation are grouped together forming orientation columns
ocular dominance columns
are made of cells segregated according to which eye sends them input
hypercolumn
contains cells that are all tuned to respond to stimulation at a particular spatial location
have blobs within - involved in coding colour info
each responds to a different retinal location
across all, all orientations in space are represented
referred to as ice cude tray model
importance of having two eyes
helps with depth perception as it is computed by the brain
info from both eyes is integrated
binocular disparity
the image that falls on each retina is different as the eyes are positioned in different locations
- more different when eyes are clos, then when they are far
the brain uses this info to determine depth
some cells in the striate cortex are especially tuned to certain amounts of binocular disparity
- different cells code for different amounts
response relies of context - can modulate
cerebral achromatopsia
posterior ventral cortex damage and altered colour perception
report the world in shades of gray
V4 area
colour
cells demonstrate colour constancy
responsive to other properties like line orientation, depth and motion
humans show an association between ventral extrastriate subregions and colour processing, but the exact association is still subject to debate
cortical blindness
blindness due to a cortical issue rather than a problem in the eye or optic nerve
demonstrates that the primary visual cortex is necessary for conscious awareness of the world
blindsight
condition where people have no conscious experience of seeing, because of extensive damage to striate cortex, but can make rudimentary visual discriminations
likely due to intact tectopulvinar pathway when geniculostriate pathway is damaged
feel like smt is there so you respond to it but do not know why
explanations?:
involves retention of some visual capabilities without the conscious experience of seeing
a small number of LGN pathways bypass striate cortex and go to extrastriate regions instead
maybe a combo of both
two main routes that leave the striate cortex
ventral - what pathway, identifying objects
dorsal - where pathway, representing their spatial locations
audition
the perception of sounds
a crucial sensory function essential for unique human capacities such as language
different sensory features such as the pitch, loudness, timing of sounds must be processed in order to: recognize specific auditory events, separate specific sounds from background noises, locate sounds in space
auditory pathway
pinna
tympanic membrane
ossicles
oval window
cochlea
pinna
where sound enters
ossicles
transmit fluid into the cochlea
push in and out on oval window
the cochlea
an organ in the inner ear that contains hair cells
hair cells
translate sound vibrations into neural impulses
different sound frequencies stimulate different subsets of hair cells within the cochlea (creates tonotopic map) by knowing which har cells were stimulated, the brain determines which frequencies are present in the sound
stimulated when the membranes more back and forth
movement of cilia in response causes cells ot emit graded potentials
synapses onto spiral ganglion cells - axons make up the auditory nerve
have receptors where ions will flow inside - send signals to ganglion cells
organ of corti
contains hair cells
in middle of cochlea
fluid filled canal that contains lymph surround the organ of corti
basilar membrane
tonotopically organized
apex: wide and floppy, low frequency
base: narrow and stiff, high frequency
where does auditory info go before reaching the auditory cortex
medulla: cochlear nucleus (auditory nerve synapses onto), superior olivary nucleus
midbrain: inferior colliculus
thalamus: medial geniculate nucleus
then info gets sent to primary auditory cortex
interaural time difference
will reach right ear before it reaches your left
interaural intensity difference
will be louder when it reaches your right ear
head will block some of the sound
where are sounds from above and below computed
shaped differently by the structures of the outer ear
cues are analyzed by the auditory system to determine location in the vertical dimension
computation of spatial location
appears to take place in the brainstem
done in part by using delay lines and cells call coincidence detectors tht take into account the different arrival times of a sound at the left nd right ears
core
receives input from the medial geniculate nucleus
belt
receives most of its input from the core
parabelt
receives input from the belt
what is the auditory cortex divided into
core, belt, and parabelt
tonotopic maps
map of sound frequencies
cells that respond best to lower frequencies located rostrally, cells that responds best to higher frequencies located caudally
individual cells have preferred sound frequencies within a particular range will excite the cell
sharply tuned curves
only fires for very specific Hz
broadly tuned curves
will fire for a range of Hz
planum temporale
important for speech perception
auditory pattern recognition
posterior regions of auditory cortex
information about spatial locations
where
anterior regions of auditory cortex
information about nonspatial features
what
