from photons to phenomena (week 3)

Question 1

what are rods and how many do we have?

Answer 1

rods are photoreceptors for vision in dim light, we have 125 million and they are mostly located in our peripheral/outer regions of the retina

Question 2

what are cones and how many do we have?

Answer 2

cones are photoreceptors for colour and sharpness of vision, we have 6 million and they are mostly located in the fovea

Question 3

what are the steps in the eye to cortex process?

Answer 3

reception (absorption of physical energy) > transduction (physical energy converted into an electro chemical pattern in the neurons) > coding (one-to-one correspondence between aspects of the physical stimulus and aspects of the resultant nervous system activity

Question 4

which light are our eyes most sensitive to?

Answer 4

light in the green range

Question 5

what is trichromatic theory?

Answer 5

confirmed Hermann Von Helmholtz’ theory - there are three types of cones that prefer different wavelengths: short (blue), medium (yellow green), and long (red)

Question 6

what is the opponent-process theory? (Hering, 1878)

Answer 6

this theory works at the level of the neurons - before red, green, and blue signals are processed in your brain, they are reprocessed and redescribed in an opponent-process manner: a scale from red to green, a scale from blue to yellow, and a scale from light to dark

Question 7

what is colour constancy?

Answer 7

the tendency to perceive something as the same colour, regardless of what colour light is illuminating it - what cones know are different from what a person percieves

Question 8

there are two pathways after the retina, the parvocellular (P) pathway, and the magnocellular (M) pathway, what is the difference?

Answer 8

the parvocellular (P) pathway receives most input from cones (sensitive to colour and fine detail), whereas the magnocellular (M) pathway receives most input from rods (most sensitive to motion)

Question 9

what are receptive fields (properties of visual neurons)?

Answer 9

the region of sensory space (i.e., retina) within which light will cause a neuron to fire

Question 10

what is retinotopy (properties of visual neurons)?

Answer 10

things that happen close to one another, are processed by neurons that are close together

Question 11

what is lateral inhibition (properties of visual neurons)?

Answer 11

neurons that are next to each other can inhibit each other; this is useful for enhancing contrast at edges of objects

Question 12

what is the information’s direction of travel after the retina?

Answer 12

retina > optic nerve > optic chiasm > lateral geniculate nucleus (LGN) > cortical area V1

Question 13

what is the lateral geniculate nucleus (LGN)?

Answer 13

part of the thalamus and a subcortical relay for most of the brains sensory input and motor output - the LGN maintains a retinotopic map

Question 14

what is the primary visual cortex (V1)?

Answer 14

extracts basic information form the visual scene and sends this information for later stages of processing of shape and movement etc. - maintains retinotopy

Question 15

what does damage to V1 cause?

Answer 15

leads to clinical diagnosis of cortical blindness - the patient can’t consciously report the object presented in this region of space - however, the patient can still make judgments about things in this “blind” area of visual field, suggesting their are other routes from the eye to brain

Question 16

what is the functional specialisation theory (Zeki, 1992;1993)?

Answer 16

argues different parts of the visual cortex are specialised for different visual functions

Question 17

what are V1 and V2 specialised for? (functional specialisation theory)

Answer 17

early stage of visual perception e.g., shapes

Question 18

what are V3 and V3a specialised for? (functional specialisation theory)

Answer 18

responsive to form (especially moving objects)

Question 19

what is V4 specialised for? (functional specialisation theory)

Answer 19

responsive to colour - Zeki et al. (1991) found V4 more active for colour than greyscale images

Question 20

what is V5/MT specialised for? (functional specialisation theory)

Answer 20

responsive to visual motion - Zeki et al. (1991) found V5 more active for moving dots compared to static - brain damage to V5/MT leads to akinetopsia

Question 21

what is cortical achromatopsia?

Answer 21

patients with this cannot see colour due to damage to V4, but also often due to V2 and V3

Question 22

what is the binding problem?

Answer 22

sighted people don’t perceive the colour of something separately to its shape, but our brain processes this separately - where in the brain is something perceived?

Question 23

what is the ‘where’ pathway?

Answer 23

the where pathway: the parietal (or dorsal) processing pathway - concerned with movement processing - “vision for action”

Question 24

what is the ‘what’ pathway?

Answer 24

the what pathway: the temporal (or ventral) processing pathway - concerned with colour and form processing - “vision for perception”

Question 25

what are the four steps in the model of object recognition?

Answer 25

1. early visual processing: colour, motion, edges etc. 2. perceptual segregation grouping of visual elements (gestalt principles, figure-ground segmentation) 3. matching grouped visual description onto a representation of the object stored in the brain (called visual descriptions) 4. attaching meaning to the object (based on prior semantic knowledge)

Question 26

what are the gestalt laws of perceptual organisation?

Answer 26

the law of proximity, similarity, good continuation, and closure

Question 27

what is figure ground segregation?

Answer 27

ambiguous drawings for example, face-goblet illusion - whichever you perceive to be in front of the other, it is assumed that more attention is paid to the figure than the ground

Question 28

what are some problems with gestalt psychology?

Answer 28

1. segmentation processes aren't always bottom-up and following the laws of perceptual organisation - perceptual segregation processing is faster with prior experience with the objects in question 2. most evidence descriptive not explanatory 3. relies heavily on introspection and evidence from 2D drawings 4. some segmentation clearly occurs via top-down prior knowledge

Question 29

what is agnosia?

Answer 29

the impairment in object recognition

Question 30

what are the two types of agnosia and what are their differences?

Answer 30

apperceptive agnosia and associative agnosia

Question 31

what is apperceptive agnosia?

Answer 31

impairment in processes that construct perceptual representation from vision - seeing the parts but not the whole - this is associated with lateral occipital lobe damage

Question 32

what is associative agnosia?

Answer 32

impairment in the process which maps a perceptual representation onto knowledge of the object's function and association - seeing the whole but not its meaning - this is associated with occipito-temporal damage

Question 33

are faces "special" in terms of recognition?

Answer 33

we don't know, but probably 1. there is evidence faces are processed more holistically than other objects 2. there is evidence for face-specific brain regions, thought this could be a visual expertise region too 3. after brain injury, some patients appear to have impairment in face but not object recognition, suggesting that faces are special