Core Vision Flashcards
Where is the retina located?
At the back of the eye
Name the two visual receptor cells in the retina
rod cells and cone cells (Retinal ganglion cells receive input from a
few cones or hundreds of rods) 120 mil photoreceptors containing the nucleus
Describe the function of cone cells
involved in colour and detail perception mainly located in the fovea (which is the centre of field of vision) which is usually in the middle of the retina
Describe the function of rod cells
involved in the vision in dim light located in the periphery
How do photosensitive pigments play a role in the eye?
it changes shape when a photo of light touches it generating an electrical impulse.
Explain the process of projection from the eye/retinal to the visual cortex
1.physical energy absorbed which is the detection of photons (reception)
2.this energy is then converted into an electrochemical pattern in the neurons (transduction)
3.One-to-one correspondence between aspects of the physical stimulus and aspects of the resultant nervous system activity (coding)
What is a photon?
a tiny (energy) particle or bundle of electromagnetic radiation which can travel at the speed of light.
define transduction
the transportation/transformation of something from one place to another (in this case, info from the physical world is transformed into neural patterns)
What are the two main aspects of the Retina-geniculate-striate system?
1.the parvocellular pathway
2.the magnocellular pathway
what is the parvocellular pathway?
-it’s sensitive to colour and fine detail
-most input comes from cone cells
what is the magnocellular pathway?
-it’s most sensitive to motion
-most input comes from rod cells
True or False:the left/right visual fields are contralateral to the hemispheres
True
what does LGN stand for?
lateral geniculate nucleus
what does V1 stand for?
primary visual cortex (takes 60ms for info to arrive here)
Which type of cells leaves the eye and synapse in the lateral geniculate nucleus?
Retinal Ganglia Cells
Which of the following best describes the ascending visual hierarchy?
Eye > Geniculate Nucleus > Striate Cortex > Extrastriate Cortex
Functional specialisation theory (Zeki, 1993, 2016):what’s the functions of V1/V2?
basic visual processing
V1=primary visual cortex (or striate cortex)
V2=the area surrounding the primary visual cortex
Functional specialisation theory (Zeki, 1993, 2016):what’s the functions of V3 and V3A?
involved in form perception (especially of moving stimuli)
V3=visual areas/extrastriate cortex
V3A=a cortical area(located in the cerebral cortex)
Functional specialisation theory (Zeki, 1993, 2016):what’s the functions of V4?
involved in colour and shape perception
V4=visual area 4 which is the third cortical area in the ventral stream,
Functional specialisation theory (Zeki, 1993, 2016):what’s the function of V5/MT in humans?
involved in motion perception
Functional specialisation theory (Zeki, 1993, 2016):what’s the function of LOC, OFA and FFA?
LOC – Object Perception
OFA – Face perception
FFA – Face perception
What are the advantages of Zeki’s functional specialisation theory?
it’s an ambitious and an extremely influential theoretical approach
What are the main three disadvantages of Zeki’s functional specialisation theory?
1.visual brain areas are less specialised than theoretically assumed
2.visual brain more complex than assumed (V1 associated with 50 other brain areas)
3.the binding problem remains unsolved
Given functional specialisation, how is visual information combined and integrated?
binding visual features together
Explain the Binding-by-synchrony hypothesis
– Neurons that code difference dimensions start to oscillate in synchrony/connect together. (unclear how and why the synchrony might occur.)
– Precise synchrony is implausible
How do neurons synchronise?
they switch between low and high excitability to synchronise allowing better communication.
What are the main features of the Perception-action model (Milner & Goodale, 1977)
the dorsal and ventral stream (they’re not really early visual systems)
What is the ventral stream?
■ “What” pathway
■ Vision-for-perception
■ Allocentric (object-centred) coding
■ Sustained representation (lasts roughly a second)
■ Usually conscious awareness
■ Input from the fovea
What is the dorsal stream?
■ “Where” pathway
■ Vision-for-action e.g., returning a tennis ball (fast reaction) using visual info to control action
■ Egocentric (body-centred) coding
■ Short-lived representations
■ Usually unconscious
What’s the key difference between the dorsal and ventral streams?
Ventral is consciousness representation whereas dorsal is rapid action and as they’re both specialised any damage in the brain will have a different effect
What is the Müller–Lyer illusion?
Both vertical lines are the same length.
What were the findings of Bruno et al., 2008?
- When pointing (using vision-for-action system), illusion size was 5.5%
- When verbalising a response (using vision-for-perception system), the illusion size was 22.4%
Explain the link between illusions and both streams
illusions are mediated by the ventral stream and action the dorsal so pointing doesn’t have as much as an effect
Explain the Ebbinghaus illusion
Both centre circles are same size but the one in the top figure looks larger than the one in the bottom figure
* Illusion greater with vision-for-perception system than vision-for-action system
* Only perceptual judgements influenced by distance between the centre circle and contextual circles (Knol et al., 2017)
What are the complexities of grasping movements in relation to the streams?
Grasping objects requires both the ventral stream (vision-for perception) and dorsal stream (vision-for-action)
when:
1. Information from memory required to control grasping movements
2. Conceptual knowledge needed to make most appropriate grasping movement (e.g., grasping a toothbrush by its handle rather than bristles)
What’s the advantage of the perception action model?
It’s a very influential theoretical approach
What’s the disadvantages of the perception action model?
-Two systems less independent and more interactive than assumed theoretically (isn’t necessarily a disadvantage just showing it’s getting more precise theory wise)
■ Patients with optic ataxia and visual form agnosia have problems with BOTH vision-for-perception and vision-for-action: no clear double dissociation
■ Findings with visual illusions are variable
There are two dorsal systems:
1. dorso-dorsal systems used to grasp object rapidly;
2. ventro-dorsal system using memorised object knowledge to use objects appropriately
How do both streams differ in connection to the brain?
The ventral stream connects V4, LOC and IT WHEREAS the dorsal stream connects V5 to the posterior parietal lobes.
How do both streams differ in pathways?
The ventral stream is an extension of the parvocellular pathway, stemming from cones in the foveal region WHEREAS the dorsal stream is an extension of the magnocellular pathway.
What is the correct answer?: The ventral stream
1. Supports conscious perception of objects and scenes
2. Generates known visual illusions
3. Controls rapid motor responses like returning a tennis serve
4. A and B but not C
4.
Define Hue
The colour itself distinguishing
red from yellow or blue
Define brightness
The perceived intensity of light
Define saturation
Allows us to determine whether colour is vivid or pale; influenced by the amount of white present
Define colour constancy
A perceived colour will remain the same despite changes in the wavelengths in the illuminant (light source)
Define chromatic adaptation
Sensitivity to illuminant/light source of any given colour decreases over time.
Explain Land’s (1986) Retinex theory
Observers compare light reflected from a surface against that reflected from adjacent surfaces
What is the advantage in colour constancy?
Several factors influencing colour constancy have been identified including object familiarity
which influences early visual processing (Vandenbroucke et al., 2016)
What are the disadvantages in colour constancy?
-Little is known about how factors combine to produce colour constancy
-artificial visual environments used in research simpler than
those in the natural world
-Generally less colour constancy when observers try to make objective judgements about colour (e.g., what colour is it?) rather than subjective ones (e.g., what colour does it look like?
-Large individual differences in colour constancy poorly understood.
What describes the phenomena of colour constancy? i.e. why does colour remain constant?
Objects appear to have an intrinsic(natural/essential) colour, despite variations in lighting and reflection.
Define monocular cues
requiring only one eye
Explain Monocular cues in depth perception
Linear perspective: based on laws of optics (can have crossing lines)
Texture: objects slanting away have a texture gradient
Interposition: a nearer object hides part of a more distant one
Familiar size: the distance of familiar objects is easier to judge than that of unfamiliar ones
Blur: ambiguous (far away or in peripheral vision?)
Motion parallax: movement in one part of retinal image relative to another (speed of motion is proportionate to the depth)
Explain binocular cues and stereopsis
Stereopsis enhances depth perception (and allows us to see the environment in 3D)
■ Stereopsis based on slight difference/disparity between the two retinal mages (binocular disparity) as the retinal image in each eye is different
■ Stereopsis is powerful at short distances only
■ Individuals with amblyopia (“lazy eye”) have impaired stereoscopic depth perception
-binocular disparity can be seen in 3D cinemas
How is information from
different cues combined?
Additivity– Information from all cues is combined or integrated
Selection– Information from a single cue is used, ignoring information from the other cue/s
Weighting of cues– More reliable cues (e.g., those providing consistent information) weighted
more
Explain how information is combined from different cues in
depth perception
■ Small conflicts between cues=adherence to additivity notion and weighting of more reliable cues
■ Large conflicts between cues= heavy reliance on only one
cue: selection
■ Depth perception is often close to optimal
■ In natural environments with rich information available,
observers rely on a global assessment of environmental
structure rather than specific cues
■ This is very different from processing cues independently
followed by integrating
information from them
What are the two main examples of perceptual constancy?
size and colour constancy
explain size constancy
Size perception of objects depends on the memory of their familiar size + perceptual information
■ It is better with familiar objects having invariant size (e.g., bicycles) than variable size (e.g., TV sets)
-size constancy extracts info from the ways things are, not how it appears to be
explain blindsight: perception without awareness
The ability to respond appropriately to visual stimuli lacking conscious visual experience in patients with damaged primary visual cortex (V1) (the brain reorganised itself so information can bypass V1)
Type-1 blindsight: no conscious experience;
Type-2 blindsight: some residual awareness
■ Blindsight patients often show evidence of degraded conscious vision when sensitive measures of conscious awareness are used
■ The reorganisation of brain connectivity in blindsight patients explains many findings
Explain subliminal perception
Subliminal perception involves:
– Subjective measure: the Observer’s failure to report awareness of a stimulus
– Objective measure: the Observer’s ability to make accurate forced-choice decisions about a stimulus
-Numerous studies support subliminal perception but less evidence for subliminal perception with more sensitive measures
of conscious awareness: partial awareness?
– Evidence of weak awareness + response bias (reluctance to report awareness) (Koivisto & Grassini, 2016)
-Subliminal is quick flash might be conscious but perhaps quickly forget what was flashed on the screen
