Lecture 9 and 10: Visual Pathways

Question 1

What is the path that a visual stimulus follows?

Answer 1

Eyes → thalamus → Occipital striate cortex (V1)

Question 2

What is the orientation of the image when if passes the eye lens?

Answer 2

Upside down

Question 3

What is the optic chiasm?

Answer 3

Visual information is processed contralaterally

Question 4

What is the Primary Optic Pathway?

Answer 4

Retina (optic disc) → Optic Nerve → Chiasm → Optic tract → Thalamus → Optic Radiations → V1

Question 5

What are the optic radiations?

Answer 5

• From Thalamus to the Visual Cortex (V1)
• inverted images
  
  • retinotopic map
• Meyer’s loop

Question 6

What is Meyer’s Loop?

Answer 6

• Axons coming from the upper quadrant of the visual field make a loop such that the information reaches the lower part of V1
• In other words, it inverses the image again

Question 7

How is the Occipital cortex structured?

Answer 7

• Primary visual areas: striate cortex
  
  • V1
• Secondary visual areas: extrastriate areas
  
  • V2, V3, V3A

Question 8

True or False

Visual information requires several steps from V1 to temporal lobe in order to be fully processed.

Answer 8

True

Question 9

How are images mapped to our brain?

Answer 9

• Visual map
  
  • Retinotopic organization
    
    • Every neuron has a specific receptive field
    • So every aspect of the image gets mapped into the visual map according to the receptive field that each neuron is responsible for

Question 10

True or False

Neurons in the visual cortex, can be activated by any visual stimulation.

Answer 10

False, neurons or groups of neurons are activated by specific stimulations.

Question 11

How does the integration of the information coming from all the neurons (or group of neurons) happen?

Answer 11

• The information travels from V1→ V2 → V3 which respond to more and more complex stimulation, so the integration of what is being seen takes place.
• The information also the CC in order complete the integration of the stimulus

Question 12

Which are the visual pathways?

Answer 12

• Dorsal Pathway (‘where?’)
• Ventral Pathway (‘what?’)

Question 13

Dorsal Pathway

Answer 13

• Where pathway
• Occipital to Parietal lobe
• Function:
  
  • Location of objects
  • movement direction, velocity of objects
  • Spatial orientation
  • Allows us to guide our actions directed to objects
  • Integration of the body-environment spatial relationship
• Note: all this is not necessarily conscious

Question 14

Which part of the Visual cortex takes care of detecting moving objects?

Answer 14

V5 (also known as MT)

Moving objects and direction

Question 15

MT Area

Answer 15

• Medial Temporal
• V5
• Perception of movement and direction

Question 16

Ventral Pathway

Answer 16

• What Pathway
• Occipital to Inferior Temporal
  
  • V1 → V2 → V3 → V4 → TEO → TE
  • There is also subsequent connection to the temporal and frontal limbic structures
    
    • Have to do with cognitive associations (memory, emotions, …)
      
      • ex) red circle → memory access → apple

Question 17

Fusiform Face Area

Answer 17

• FFA
• Function:
  
  • Perception and recognition of faces
  • I could be an area for visual expertise
    
    • Some studies have reported that experts show activation in this area when presented with cars or birds
• Location:
  
  • Inferior temporal cortex

Question 18

Give some example of a study looking at the activation of FFA given a visual expertise.

Answer 18

• Participants:
  
  • Pokemon experts
  • Control group
• Results
  
  • Greater activation of FFA when the characters were shown to experts

Question 19

Visual Word Form Area

Answer 19

• Region specialized for letter strings
• It also becomes specialised for specific visual categories with the development of expertise

Question 20

What happens if you damage your Occipito-temporal area?

Answer 20

• Problems with memory
• Problems with Vision

Question 21

How did we discover that some neurons got activated by some specific stimulus?

Answer 21

• We know:
  
  • neurons in V1 look at a very small and specific group of receptive fields
• Procedure:
  
  • Electrode in the temporal cortex
    
    • To read if a neuron would respond to a specific stimuli
• Results:
  
  • Respond to orientation, shape or colour
  • Texture cells
  • Elaborate cells
  • Anterior IT neurons

Question 22

Texture Cells

Answer 22

• Texture cells:
  
  • scattered throughout the IT
  • Respond to specific patterns

Question 23

Elaborate cells

Answer 23

• Located:
  
  • Anterior Inferior Temporal cortex
• Function:
  
  • respond to the shape of the contour
  • shape + texture
  • shape + colour
  • texture + colour

Question 24

Anterior IT neurons

Answer 24

• Anterior TE neurons
• Located:
  
  • Anterior IT
• Function:
  
  • larger receptive fields than Posterior IT (TEO) neurons

Question 25

What is a Grandmother cell?

Answer 25

• The term refers to a neuron that would respond only to a specific, complex and meaningful stimulus
• But it was noticed that it is not a SINGLE neuron that responds but rather a population of cells that are sparsed.
• Steps:
  
  • Ventral pathway
    
    • activity distributed across populations of neurons
      
      • each responds to some discrete visual feature
        
        • Neurons become more more selective for combinations of features
          
          • So less neurons get activated and they are sparse
• Grandmother cells are the theoretical limit of sparsness where the representation of an object is reduced to single neuron.

Question 26

Why would sparseness be advantageous?

Answer 26

• Compact coding maximizes total storage capacity

Question 27

Describe the Quiroga Paper?

Answer 27

• Patients:
  
  • epilepsy patients
• Procedure:
  
  • recorded the neural activation of medial temporal lobe
    
    • areas associated with late-stage visual processing and long-term memory
• Results
  
  • Noticed that there was a unit that selectively responded to Jennifer Aniston (name and different images of her)
• Conclusion:
  
  • The neuron probably had more to do with memory than visual

Question 28

Invariance

How do we recognize an object given different images (positions, shadows, etc.)

Answer 28

• The neurons (grandmother or Jennifer Aniston’s) respond to abstract representations of the individual or objects shown
• Invariance is learned based on associations, and NOT geometric transformations of the visual structure
  
  • Encode concepts rather than visual appearance

Question 29

So how do we retrieve the information given a visual input?

Answer 29

• Anatomical connections between the ventral visual pathway and the medial temporal lobe
• When shown faces, objects and places, there is an activation in the medial temporal lobe
• To consciously remember the perception of a visual stimuli, the hippocampal system is needed.

Question 30

Explain Mishkin’s Experiments with monkeys

Answer 30

• Mishkin trained the monkeys to discriminate between stimulus and select the correct stimulus by giving them some reward.
• Two experiments:
  
  • Lesions in L and R Inferior temporal areas
    
    • Couldn’t learn to visually discriminate
    • Discrimination was possible via tactile stimulus or auditory stimulus
    • Also, positional discrimination
  • Parietal lesions:
    
    • Couldn’t do position discrimination
    • Able to discriminate based on visual input
• Conclusion:
  
  • Learned more about the ventral and dorsal pathways