Perception Flashcards
Where is the retina located?
- We have the cornea and the pupil in the front
- And in the back we have the Retina, and in the retina we have 2 types of receptors
What are the two receptors in the retina?
Rods
Cones
What are the properties of Rods?
- Sensitive to light and movement
- 125 million in the retina
- Magnocellular Pathway = sensitive to motion, most input from rods
What are the properties of cones?
- colour vision, sharpness of vision
- 6 million in the outer regions of the retina
- Parvocellular Pathway = sensitive to fine detail, most input comes from cones
What is the pathway from eye to brain step by step?
- Retina
- Optic nerve
- Optic chiasm
- Lateral Geniculate Nucleus
- Cortical area V1
What are the 3 properties of visual neurons?
Receptive fields
Retinopy
Lateral inhibition
What are receptive fields?
every neuron is responsible for a certain region of space
- And it will fire more when when something happens in that space and won’t fire when something happens in another space
What retinopy?
The neurons that are near to each other in space are processed in cells that are physically near to each other
What is Lateral inhibition?
one neuron can inhibit a neighbouring neuron (useful for enhancing contrast at edges of objects)
What is the first stop in the brain before going to the cortex?
Lateral Geniculate nucleus
- Part of the thalamus
- Cells have a centre- surround receptive field
- Maintains a retinotopic map
What is the stop after the lateral geniculate nucleus?
Primary visual cortex (V1)
- Extracts basic information from visual scene
- Sends this info for later stages of processing.
- Maintains retinotopy
What does functional specialisation theory propose?
Different parts of the visual cortex are specialised for different visual functions
What is the function of V1 and V2 according to functional specialisation theory?
Early stage of visual perception
What is the function of V3 and V3a according to functional specialisation theory?
Responsive to form
What is the function of V4 according to functional specialisation theory?
responsive to colour
What is the function of V5/MT according to functional specialisation theory?
responsive to visual motion
What does damage to V1 cause?
- leads to clinical diagnosis of cortical blindness
- The patient cannot consciously report objects presented in this region of space
- However they can still make some visual destinations in the “blind” area e.g. orientation of the movement of the object
What does damage to V4 cause?
Patients with cortical Achromatopsia
- cant see colours due to damage to V4 but also often due to damage to V2 and V3
What does damage to V5/MT cause?
- leads to Akinetopsia
Motion perception becomes deficient
What are the two pathways beyond the visual cortex?
- Parietal/ dorsal processing pathway
- Temporal/ ventral processing pathway
What is the parietal/ dorsal processing pathway?
the where pathway
Concerned with movement processing
What is temporal/ ventral processing pathway?
the what pathway)
Concerned with colour and form processing
What is gestalts law of organisation
explain how humans perceive stimuli and create shortcuts in our brains to make sense of incomplete pictures.
- Proximity
- Similarity
- continuation
- closure
State the 4 step model of object recognition
- Early visual processing
- Perceptual segregation (grouping visual elements)
- matching between grouped visual description with a representation of a object stored in the brain
- Attach meaning to the object (such a chair = what you sit on)
What is known to be the cause of an object recognition deficit
Agnosia = Impairment in object recognition is caused by damage to this pathway
What are the two types of Agnosia?
Apperceptive agnosia
Associative agnosia
What is apperceptive agnosia?
- Impairment in the process which constructs perceptual representation from vision
- Results in seeing parts but not the whole
What is associative agnosia
- Impairment in the process which attaches meaning to the object
- Seeing the whole but not its meaning
