Vision Flashcards
What are the 2 visual receptor cells in the retina?
cone cells
rod cells
Where is the retina?
at the back of the eye
Where do impulses from the retina leave the eye via?
the optic nerve
What are cone cells?
sensitive to colour and detail perception
Where are cone cells located?
in the fovea (central part of retina)
What are rod cells?
used for dim light
sensitive to light levels
Where are rod cells located?
in the periphery (edges of visual field and retina)
What cell receives input from cones and rods?
retinal ganglion cells
Is central retina cone dominated or rod dominated?
cone dominated
Is peripheral retina cone dominated or rod dominated?
rod dominated
What is the process of reception?
the absorption of physical energy (light) when it hits the retina
What is the process of transduction?
the absorption of light which is then converted into electrochemical patterns in neurons (electrical signals) that reach the brain
Which hemisphere does information from the left visual field go to?
right hemisphere
Which hemisphere does information from the right visual field go to?
left hemisphere
What is the retina-geniculate-striate system?
where information goes from the retina to the lateral geniculate nuclear (LGN) to then the striate cortex
What is the primary visual cortex?
striate cortex
What are the 2 parallel paths from retina to visual cortex?
parvocellular
magnocellular
What is the parvocellular path?
sensitive to colour and fine detail
most input comes from cones
What is the magnocellular path?
sensitive to motion
most input comes from rods
Mather (2009): Visual cortical areas
box sizes reflect sizes of each brain region
arrows show proportion of fibres in each pathway
vertical positions of boxes indicate response latencies of cells
What does Zeki’s functional specialisation theory discuss (1993, 2016)?
areas of the visual cortex in brain
assumed colour, motion, form are processed in anatomically separate areas
Zeki: areas of visual cortex
V1 and V2
V3 and V3A
V4
V5 (MT in humans)
LOC
OFA
FFA
What is V1 and V2?
basic / early stage of visual processing
What is V3 and V3A?
respond to form perception (especially of moving stimuli)
What is V4?
colour and shape perception
What is V5?
motion perception
referred to as MT in humans
What is LOC?
object perception
What is OFA and FFA?
face perception
What is a strength and weakness of Zeki’s theory?
ambitious and influential
more complex than assumed as V1 is connected to at least 50 other areas
binding problem still remains unsolved
What is Milner and Goodale’s perception-action model (1977)?
believe there is 2 visual pathways
ventral stream and dorsal stream
What is the ventral stream?
the “what” system
vision for perception (controls perception)
What is the dorsal stream?
the “where” pathway
Vision for action
(controls action)
What are 4 differences between ventral and dorsal system?
ventral = allocentric, conscious, extension of parvocellular pathway, temporal lobes
dorsal = egocentric, unconscious, extension of magnocellular pathway, parietal lobes
What does allocentric mean?
object centred
What does egocentric mean?
body centred
Visual illusions: Muller-Iyer Illusion
vertical lines actually being the same length
Muller-Iyer illusion findings (Bruno et al, 2008)
when pointing as a response to which line is longer (use vision for action) illusion size was 5.5%
when verbalising a response (vision for perception) illusion size was 22.4%
illusion requires ventral over dorsal
Ebbinghaus illusion
where both centre circles are same size but on on top looks larger than on at bottom due to circles surrounding it being smaller
illusion greater with ventral (vision for perception) system
What stream is needed for grasping objects?
both the ventral stream (vision for perception) as well as dorsal stream (vision for action)
What are the strengths and limitations of Milner and Goodale’s theory?
influential approach
findings with visual illusions are variable
But there are 2 dorsal systems (dorso-dorsal and ventro-dorsal)
What does hue mean?
the colour itself
What does saturation mean?
influenced by amount of white present
determine if it’s vivid or pale
What is the dual process theory? (Mather, 2009)
states there are 3 cone classes:
red = long wavelength light
green = medium
blue = short
provide input to 3 channels:
- red-green
- blue-yellow
- light-dark
What does colour constancy mean?
perceived colour remains the same despite changes in wavelength in light source
objects have intrinsic colour
What does chromatic adaptation mean?
refers to when sensitivity to illuminant (light source) of any given colour decreases over time
What is retinex theory? (Land, 1986)
observers compare light reflected from a surface against that reflected from opposite surfaces
What are some evaluation software colour constancy?
large individual differences are still poorly understood
research focuses on artificial visual environments
What cues are used in depth perception?
monocular cues (using only one eye)
What are 3 examples of monocular cues?
texture gradient
interposition
motion parallax
What is interposition?
where nearer objects hide part of a more distant one
What is motion parallax?
movement in one part of retinal image
objects that are closer appear to move faster than objecters further away
What enhances depth perception?
stereopsis
allows us to see the environment 3-dimensionally
very powerful at short distances only
What is amblyopia?
“lazy eye”
have impaired stereoscopic depth perception
How is information from different cues combined?
- additivity (info from all cues combined)
- selection (info from single cue is used others ignored)
- weighting of cues (on more reliable ones)
What does size constancy mean?
object is still perceived as having the same size when presented at different viewpoints
What is the size distance invariance hypothesis?
perceived size is proportional (equivalent) to retinal size and perceived distance
infer distance from depth cues
What is blindsight?
ability to respond to visual stimuli without conscious visual experience or awareness
What is type 1 blindsight?
no conscious experience
What is type 2 blindsight?
some residual awareness
