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