Lecture 9 and 10: Visual Pathways Flashcards
What is the path that a visual stimulus follows?
Eyes → thalamus → Occipital striate cortex (V1)
What is the orientation of the image when if passes the eye lens?
Upside down
What is the optic chiasm?
Visual information is processed contralaterally
What is the Primary Optic Pathway?
Retina (optic disc) → Optic Nerve → Chiasm → Optic tract → Thalamus → Optic Radiations → V1
What are the optic radiations?
- From Thalamus to the Visual Cortex (V1)
- inverted images
- retinotopic map
- Meyer’s loop
What is Meyer’s Loop?
- 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
How is the Occipital cortex structured?
- Primary visual areas: striate cortex
- V1
- Secondary visual areas: extrastriate areas
- V2, V3, V3A
True or False
Visual information requires several steps from V1 to temporal lobe in order to be fully processed.
True
How are images mapped to our brain?
-
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
- Retinotopic organization
True or False
Neurons in the visual cortex, can be activated by any visual stimulation.
False, neurons or groups of neurons are activated by specific stimulations.
How does the integration of the information coming from all the neurons (or group of neurons) happen?
- 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
Which are the visual pathways?
- Dorsal Pathway (‘where?’)
- Ventral Pathway (‘what?’)
Dorsal Pathway
- 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
Which part of the Visual cortex takes care of detecting moving objects?
V5 (also known as MT)
Moving objects and direction
MT Area
- Medial Temporal
- V5
- Perception of movement and direction
Ventral Pathway
- 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
- Have to do with cognitive associations (memory, emotions, …)
Fusiform Face Area
- 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
Give some example of a study looking at the activation of FFA given a visual expertise.
- Participants:
- Pokemon experts
- Control group
- Results
- Greater activation of FFA when the characters were shown to experts
Visual Word Form Area
- Region specialized for letter strings
- It also becomes specialised for specific visual categories with the development of expertise
What happens if you damage your Occipito-temporal area?
- Problems with memory
- Problems with Vision
How did we discover that some neurons got activated by some specific stimulus?
- 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
- Electrode in the temporal cortex
- Results:
- Respond to orientation, shape or colour
- Texture cells
- Elaborate cells
- Anterior IT neurons
Texture Cells
-
Texture cells:
- scattered throughout the IT
- Respond to specific patterns
Elaborate cells
- Located:
- Anterior Inferior Temporal cortex
- Function:
- respond to the shape of the contour
- shape + texture
- shape + colour
- texture + colour
Anterior IT neurons
- Anterior TE neurons
- Located:
- Anterior IT
- Function:
- larger receptive fields than Posterior IT (TEO) neurons
What is a Grandmother cell?
- 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
- Neurons become more more selective for combinations of features
- each responds to some discrete visual feature
- activity distributed across populations of neurons
- Ventral pathway
- Grandmother cells are the theoretical limit of sparsness where the representation of an object is reduced to single neuron.
Why would sparseness be advantageous?
- Compact coding maximizes total storage capacity
Describe the Quiroga Paper?
- Patients:
- epilepsy patients
- Procedure:
- recorded the neural activation of medial temporal lobe
- areas associated with late-stage visual processing and long-term memory
- recorded the neural activation of medial temporal lobe
- 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
Invariance
How do we recognize an object given different images (positions, shadows, etc.)
- 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
So how do we retrieve the information given a visual input?
- 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.
Explain Mishkin’s Experiments with monkeys
- 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
- Lesions in L and R Inferior temporal areas
- Conclusion:
- Learned more about the ventral and dorsal pathways
