Vision Flashcards
what is meant by retinotopic
the spatial layout of the retina is preserved in the brain. nearby cells in retina connect nearby cells in visual cortex - forming a map
what is the primary function of V1 (primary visual cortex)
basic feature detection (orientation, motion, edges)
is v1 retinotopic
yes
what did hubel and Wiesel find about v1
cells in v1 respond to specific orientations and directions of stimuli
what is a hyper-column in v1
a group of columns that represents all orientations for a particular area of the retina, approx 1mm of cortex
where is the v1
occipital lobe
how are orientation-sensitive cells organised in v1
arranged in columns , each column contains cells that prefer a specific orientation
what are ocular dominance columns
columns of cells in v1 that prefer input from one eye over the other
what are blobs in v1
groups of cells involved in colour processing
what is cortical magnification
more cortical space is dedicated to processing input from the fovea, leading to higher visual acuity
what does the visual cortex hierarchy look like
v1 (basic features) -> v2 (more complex patterns) -> v3/v4 (form and colour) -> v5/mt (motion)
what does v2 do
processes simple and moderately complex patterns (contours, illusory edges)
what does v4 do
involved in processing colour and form; it shows strong attentional modulation
what does v5/mt do
processes motion
what does damage to v5/mt do
causes motion blindness (akinetopsia)
what did patient lm suffer from
akintopsia due to a stroke damaging v5/mt
what were the implications of lm illness
couldn’t pour coffee, or cross the street, or walk in crowds
what is akinetopsia
see the world in a series of still images
difference between dorsal and ventral streams
dorsal = where
ventral = what
what is dorsal (where) stream responsible for
motion and spatial info
what is ventral (what) stream responsible for
object identity and detail
what happens if ventral stream is damaged
difficulty in object recognition
what happens if the dorsal stream is damaged
difficulty in spatial awareness
what is blindsight
the ability to respond to visual stimuli without conscious perception due to v1 damage. visual info can still reach other brain regions like parietal via the superior colicus
what is balint-holmes syndrome caused by
caused by parietal lobe damage
symptoms of balint-holmes syndrome
they can describe objects but have trouble interacting with them
example of ballint-holmes syndrome
able to identify a slit but have trouble posting a letter through it
what is the binding problem
challenge of how the brain integrates features processed in different areas (colour, motion, shape) into a single coherent perception
what is the grandmother cell theory
the idea that a single neuron could respond to a complex object (e.g. grandmother)
what is opponent coding
the brain compares signals from cones in ratios to perceive colour
what are the three types of cones
L-cones (long wavelength)
M-cones (medium wavelength)
S-cones (short wavelength)
what do L cones respond to
red
what do M cones respond to
green
what do S cones respond to
blue
what is meant by red + green = luminance
L cones(red) and M cones(green) are both sensitive to brightness, so adding their signals together gives a measure of overall luminance (brightness) of the scene
what is happening in red/green (red vs green)
the brain compares how much the red cones are firing vs how much the green cones are firing
what happens if red > green
the object looks reddish
what happens if green > red
the object looks greenish
what happens if red = green
the colour is neutral (grey or yellowish)
what is meant by red + green/blue = yellow-blue detection
red + green = yellow
so this ratio is asking how much yellow vs blue is there
what happens if red+green > blue
you see yellow
what happens if blue > red+green
you see blue
what happens if red+green = blue
you see a neutral white or greyish colour
why does the brain use ratios for colour recognition
so brain can keep recognising colours even under different light conditions - colour constancy
do cones fire more as brightness increases
yes
what is colour constancy
the ability to perceive colours consistently despite changes in lighting
where does colour constancy occur
V4
how does visual information travel from the eye to the brain
retina -> optic nerve -> optic chiasm -> optic tract -> LGN (thalamus) -> V1
where is the LGN
the thalamus
why do we detect changes in light rather than overall light levels
ganglion cells respond to contrast and edges, making visual processing more efficient and reducing unnecessary information
what is a receptive field
the area of the retina that influences the firing of a particular ganglion cell
why is more cortical space given to the fovea
because it provides detailed vision and has the highest visual acuity, a larger portion of the cortex processes its input (cortical magnification)
what is the fovea
central part of the retina where your vision is the sharpest
why does the cortex magnify inout from the fovea
the brain prioritises detailed vision. you need high-res processing for tasks such as reading and recognising faces
An OFF-centre ganglion cell responds best to:
a spot of light shone only on its surround
The “where” visual route is also known as:
dorsal pathway
The primary visual cortex is also known as ___.
V1
Which of the following statements best describes rods?
A.
Functional in dimly lit environments
B.
Wavelength sensitive
C.
More numerous at the center of the retina
D.
High visual acuity
A
Which thalamic nucleus receives visual information from the retina?
lateral geniculate
