primary and visual pathway

Question 1

How does visual information come into the brain?

Answer 1

• main pathway
• photoreceptors from retina in back of eye
• information carried from retina to lateral geniculate nucleus via optic nerve
• this is the visual relay station for sensory thalamus
• information sent to occipital cortex, primary visual cortex of occipital lobe
• located in occipital lobe (back of brain)

Question 2

what makes up total field of view?

Answer 2

• left visual field
• right visual field
• central field of view (where visual fields overlap)

Question 3

when visual fields of both eyes overlap, which portion of the eye is hit?

Answer 3

Fovea

• central vision is what we use to see something in focus, something sharp, near vision for reading
• all of this involved the fovea

Question 4

what is the lateral geniculate nucleus?

Answer 4

• relay station of sensory thalamus

Question 5

how is sensory information relayed?

Answer 5

• via a specific nucleus of the thalamus
• to primary sensory cortex found in most modalities

Question 6

where does information from right visual field end up in the brain?

Answer 6

the left side

Question 7

where does information from left visual field end up in the brain?

Answer 7

the right side

Question 8

identify a key principle of information processing

Answer 8

information processing is hierarchical

Question 9

outline the stages of information-processing stages in primary visual pathway

Answer 9

RETINA
- photoreceptors
- bipolar cells
- retinal ganglion cells

-optic nerve-

LATERAL GENICULATE BODY

VISUAL CORTEX

Question 10

describe an experimental set up to record visual responses of neurones along the visual pathway

Answer 10

• present visual information
• visual information can be controlled
• present visual information in field of view
• using micro electrodes, electrophysiological recordings of neural activity at these different stages

Question 11

identify other ways of recording visual responses of neurones along the visual pathway

Answer 11

• fMRI
• EEG
• MEG

Question 12

identify the two main types of photoreceptors contributing to vision

Answer 12

• rods
• cones

Question 13

describe Rods

Answer 13

• cannot discriminate wave lengths (therefore cannot discriminate colour)
• 120 million in human retina (more abundant than cones)
• sensitive in low light
• higher density in periphery
• tracks high-rate changes

Question 14

describe Cones

Answer 14

• 6 million in human retina
• can discriminate 3 types of wavelengths (small, medium, large)
• less sensitive in low light
• higher concentration in fovea
• cannot track high-rate changes

Question 15

what are the photoreceptors detection of light translated into?

Answer 15

• excitation or inhibition of retinal ganglion cells
• via bipolar cells

Question 16

what do bipolar cells do?

Answer 16

links photoreceptors to retina ganglion cells

Question 17

what do photoreceptors and bipolar cells vary as they are stimulated?

Answer 17

voltage

(analogue signal)

Question 18

what is the receptive field?

Answer 18

• refers to portion of retina/visual field
• this is where visual stimulation will evoke a change in firing rate
• the size of the receptive fields gets bigger as more information is combined from several photoreceptors
• very small receptive field at photoreceptor stage

Question 19

what does a ‘substructure of a receptive field’ refer to?

Answer 19

• refers to the specific way visual stimuli/information is presented in the receptive field of a visual neurone
• this is so a firing-rate change can be evoked

Question 20

outline the steps that take place from when retinal ganglion neurones receive visual input

Answer 20

• neurones receive input from multiple photoreceptors
• receive input via bipolar cells
• bipolar cell receptive fields become several times the size of photoreceptor field as more information comes in
• bipolar cell receptive fields have ‘on’ and ‘off’ and ‘centre’ surround structure

Question 21

what are bipolar cells?

Answer 21

• one of the main retinal interneurons and provide the main pathways from photoreceptors to ganglion cells,
• i.e. the shortest and most direct pathways between the input and output of visual signals in the retina

Question 22

what structures does bipolar cell receptive fields have?

Answer 22

• on structure
• off structure
• centre surround structure

Question 23

what happens when light is presented in ‘on’ regions of bipolar cell receptive field?

Answer 23

• cells become excited
• increase in firing

Question 24

what happens when light is presented in ‘off’ regions of bipolar cell receptive field?

Answer 24

• cells become inhibited
• firing rate decreases

Question 25

explain the rebound effect

Answer 25

- when stimulus is taken back, firing rate shoots in the opposite direction to what light stimulus was - following inhibition, neurone doesn't go straight to baseline rate

Question 26

what happens when the light information is in the centre?

Answer 26

- firing rate increases - when light information taken away, rebound effect occurs

Question 27

what is the response rate of the bipolar cells based on?

Answer 27

sum in ON stimulation - sum of stimulation in OFF region

Question 28

when will neurones only react?

Answer 28

- when there is contrast and boundaries

Question 29

why is it important for there to be contrast and boundaries?

Answer 29

- more efficient world has many things that stay constant therefore we don't need to respond to it all the time more efficient to respond to changes and boundaries - helps preserve appearance of objects regardless of environmental light levels luminance of features = represented relative to their surround can result in illusions

Question 30

how is colour sensitivity perceived by retinal ganglion and lateral geniculate neurones?

Answer 30

- both receive input from cones - you have different types of colour sensitive retinal ganglion and LGN - both have receptive fields - receptive fields have centre-surround organisation - centre = stimulation of certain light property causes excitation - surround = stimulation of certain wavelengths causes inhibition

Question 31

what different types of colour-sensitive retinal ganglion and LGN are there? (colour opponency)

Answer 31

- yellow on, blue off - yellow off, blue on - red on, green off - red off, green on

Question 32

what can colour opponency explain?

Answer 32

visual illusion

Question 33

from the lateral geniculate body in the thalamus, where is information then passed on to?

Answer 33

first visual processing stage primary visual cortex

Question 34

where does the primary visual cortex (in humans) sit around?

Answer 34

Carlcarine fissure (between the hemispheres)

Question 35

identify a key feature of the neurones in the primary visual cortex

Answer 35

they are all orientation selected

Question 36

what is meant by 'orientation-selective' neurones?

Answer 36

- neurones have bigger receptive fields than the neurones at stages before - they respond to light/elongated stimulation presented in a certain orientation - stimuli = elongated

Question 37

what are the type main types of orientation-sensitive primary visual cortex neurones?

Answer 37

- simple cells - complex cells

Question 38

explain what simple cells are

Answer 38

- they have receptive fields with inhibitory and excitatory regions - only become excited if stimulus is presented in the right orientation on this excitatory region - combines inputs from ON and OFF cells in LGN - integrates information from several LGN

Question 39

explain what complex cells are

Answer 39

- a step up in regards to processing compared to simple cells - they combine information/inputs from several simple cells - their fields have no discrete on and off regions - but they respond best to moving stimuli (which reflects response adaptation - the neurone stops firing/reduces firing rate if stimulus doesn’t move)

Question 40

what is the Retino-topic map?

Answer 40

- refers to the orderly mapping of retina/visual field onto visual cortex - different points of the retina interact with specific points in the primary visual cortex - neighbouring areas in the retina excite/interact with neighbouring areas in primary visual cortex

Question 41

what are modules of the primary visual cortex?

Answer 41

- PVC divided into small columnar modules that combine neurones - these are sensitive to different aspects of stimuli presented in small part of visual field - some respond to stimuli of different orientation - some respond to colour

Question 42

what is 'Blindsight'?

Answer 42

- the ability to respond to visual stimuli without consciously perceiving them - a condition which can occur after certain types of brain damage (lesions to primary visual cortex)

Question 43

give examples of blindsight?

Answer 43

- looking (moving eyes) or pointing to visual stimuli - but not being able to 'see' stimuli

Question 44

what does 'blindsight' highlight?

Answer 44

- primary visual pathway = critical for conscious vision - there are also additional visual pathways - brain can perform visual information processing which can guide subjects' behaviour without their conscious awareness