Week 2 VISUAL PROCESSING (HIGHER CENTRES)

Question 1

How does processing in the Lateral geniculate nucleus (LGN) occur?

Answer 1

• first brain area the visual info meets on pathway to processing
• from LGN it goes to the primary visual receiving area occipital lobe (the striate cortex)
• then through two pathways to the temporal lobe and the parietal lobe
  – Finally arriving at the frontal lobe

Question 2

What occurs at the optic chiasm?

Answer 2

X-shaped structure formed by the crossing of the optic nerves in the brain. The optic nerve connects the brain to the eye. Here, visual stimuli is swapped between the two hemispheres of the brain.

Question 3

True or False: visual information from the left hemisphere travels to the right hemisphere and vice versa.

Answer 3

FALSE. everything in left visual FIELD travels to right hemisphere and vise versa.

Question 4

What is the major function of the LGN?

Answer 4

To regulate neural information from the retina to the visual cortex. e.g. visual “librarian”
Gets feedback from brain (cortex, brain stem, thalamus)

Question 5

What is an example of bottom-up processing and top-down processing in relation to visual processing in the LGN?

Answer 5

bottom-up: info coming from the retina to the LGN

top-down: information/ feedback coming from the cortex to the LGN

Question 6

Which layers of the LGN receive signals from the ipsilateral eye (eye in the SAME hemisphere as the observed LGN)?

Answer 6

Layers 2, 3 and 5

remember this: 2 + 3 = 5.
There are 6 layers all together of the LGN.

Question 7

Which layers of the LGN receive signals from the contralateral eye (eye in the OPPOSITE hemisphere as the observed LGN)?

Answer 7

Layers 1, 4 and 6.

note: each eye sends signals to both LGNs and the information for each eye is kept separated.

Question 8

What is a retinotopic map?

Answer 8

a map where locations in the physical world correspond to an area in the LGN. Each place on the retina corresponds to a place on the LGN.

Question 9

How to determine retinotopic map?

Answer 9

• record from neurons with an electrode that penetrates the LGN obliquely

– Stimulating receptive fields on the retina shows the location of the corresponding neuron in the LGN

Question 10

Differentiate between simple cortical cells, complex cortical cells, and end- stopped cortical cells.

Answer 10

Differences:

• Complex cortical cells are different from simple cells because they have a preference for MOVING bars of a particular orientation
• End-stopped cells do not respond to stimuli that are too long
• End-stopped cells respond to stimuli of a specific length
• End-stopped cells respond to moving corners or angles

Similarities:

• complex and simple cells are similar because they both respond to bars of light of a particular orientation.
• End-stopped cells are similar complex cells in that they respond to moving stimuli

Question 11

What are simple cortical cells?

Answer 11

Cells which respond to bars of light of a particular orientation - light which is oriented along the length of the receptive field

They are depicted by tuning curves which show the response of simple cortical cells for orientations of stimuli.

Question 12

What are complex cortical cells?

Answer 12

cells which respond to bars of light of a particular orientation (like simple cells), however, complex cortical cells respond to movement of bars of light in a specific direction.

Question 13

What are end-stopped cells?

Answer 13

• Moving lines of specific length
• Moving corners or angles
• Does not respond to stimuli that is too long

Question 14

Why are the specialized cortical cells sometimes called “feature detectors.”?

Answer 14

• Neurons which fire to specific features of a stimulus
• cortical cells are called feature detects because they respond to particular orientations, lengths and movement of specific stimuli.

Question 15

What is adaptation in relation to selective adaptation?

what does selective adaptation mean?

Answer 15

Adaptation is when neurons become fatigued and this results in:

• the firing of that neuron decreasing as it is exposed to the stimuli for prolonged periods of time
• our perception of that stimuli becomes distorted/ less accurate

selective adaptation: only neurons that respond to specific stimuli will experience fatigue

Question 16

Describe the method used for selective adaptation to orientation

Answer 16

• measuring the sensitivity range for stimulus
• experience fatigue/adaptation by prolonged exposure to stimuli
• remeasure sensitivity rate to see how adaptation has altered the perception of that stimuli
• grating is used

Question 17

What are gratings?

Answer 17

• altering light and dark bars
• changing orientation of bars (vertical/ horizontal) allows for the sensitivity to orientation to be tested
• sensitivity to contrast is tested by differences in intensity of that line

Question 18

Define contrast threshold

Answer 18

minimum contrast that can be resolved by the patient. The contrast sensitivity is equal to 1/contrast-threshold.

Question 19

What is the logic behind lesion/ ablations studies?

Answer 19

The results reveal which portions of the brain are responsible for specific behaviours.

Question 20

Discuss why the dorsal stream has been labeled the “how” stream by describing
research on patient D.F., and rod-and-frame task performance in non-brain damaged
people.

Answer 20

how pathway doesn’t just locate objects, it tells you what to do with them when you find them.

Patient DF:
– Damage to ventral pathway due to gas leak
– Not able to match orientation of card with slot
– But was able to match orientation if she was placing card in a slot
– Other patients show opposite effects
– Evidence shows double dissociation between
ventral and dorsal pathways

rod-and-frame task:
– Observers perform two tasks: matching and
grasping
• Matching task involves ventral (what) pathway
• Grasping task involves dorsal (how) pathway
– Results show that the frame orientation affects
the matching task but not the grasping task.

Question 21

What is the difference between single dissociation and double dissociation.

Answer 21

Establishing a single dissociation between two functions provides limited and potentially misleading information, whereas a double dissociation can conclusively demonstrate that the two functions are localized in different areas of the brain.

Question 22

What happens when the fusiform face area (FFA) is damaged?

Answer 22

This part of the brain is responsible for the recognition/response to faces. Damage to this area results in an inability to recognise faces.

It functions is the same as Inferotemporal (IT) cortex in monkeys.

Question 23

What does the Parahippocampal place area (PPA) of the brain respond best to?

Answer 23

spatial layouts/ visual environments.

Question 24

What does the Extrastriate body area (EBA) of the brain respond best to?

Answer 24

full bodies and body parts

Question 25

What does the Lateral occipital complex (LOC) of the brain respond best to?

Answer 25

objects

Question 26

Discuss how natural selection may be responsible for neuron specialization.

Describe the method and results of research that shows that neurons can be shaped by
experience in both monkeys and humans.

nature vs nurture

Answer 26

Evolution: (nature)

• new born monkeys hardwired to respond to direction of movement and depth of objects
• babies prefer looking at pictures of assembled parts of faces

Nurture:
in humans, experience-dependent plasticity
- Brain imaging experiments show areas that
respond best to letters and words.
- fMRI experiments show that training results in areas of the FFA responding best to:
–Cars and birds for experts in these areas
–Greeble stimuli

this evidence shows that humans can be tuned to perceive things we find important to find the visual differences between.