Task 3 - On columns and pathways Flashcards
What is the optic chiasm?
An X-shaped bundle of fibers where some optic nerve fibers cross to the opposite hemisphere.
Where do most optic nerve fibers go after the optic chiasm?
90% go to the lateral geniculate nucleus (LGN) in the thalamus.
How is the LGN structured?
It has 6 layers:
Layers 1, 4, 6: Receive input from the contralateral eye. Layers 2, 3, 5: Receive input from the ipsilateral eye.
What are the two major divisions of the LGN?
Magnocellular layers (bottom 2 layers): Receive input from M ganglion cells (motion detection).
Parvocellular layers (top 4 layers): Receive input from P ganglion cells (fine details & color).
What is the function of the superior colliculus?
Controls eye movements and receives 10% of visual signal input.
Where does the LGN send visual information?
To V1 (primary visual cortex) in the occipital lobe.
What is a retinotopic map?
A spatially organized map of the retina on the visual cortex.
What is cortical magnification?
The fovea occupies only 0.01% of the retina but takes up 8-10% of the visual cortex.
What are simple cortical cells?
Neurons in V1 that respond to edges, bars, and lines of specific orientations.
What is the orientation tuning curve?
A graph showing how a neuron responds to different line orientations.
What are complex cells?
Neurons in V1 that respond to moving bars of light with specific orientations.
What are end-stopped cells?
Neurons in V1 that respond to moving lines of specific lengths or angles.
What are location columns?
Vertical columns where all neurons respond to the same retinal location.
What are orientation columns?
Vertical columns where neurons respond best to slightly different angles of orientation.
What are ocular dominance columns?
Groups of neurons in V1 that prefer input from one eye over the other.
What is a hypercolumn?
A 1mm-wide structure that contains all orientation columns for one location in the visual field.
What are the two major visual pathways from V1?
Ventral (“what”) pathway – to the temporal lobe (object recognition).
Dorsal (“how”) pathway – to the parietal lobe (motion and action)
How do the magnocellular and parvocellular systems relate to these pathways?
Magnocellular (M cells) → Dorsal (How) Pathway → Fast, motion detection.
Parvocellular (P cells) → Ventral (What) Pathway → Slow, object recognition.
Which pathway is faster but colorblind?
The dorsal pathway.
Do the ventral and dorsal pathways work independently?
No, they are interconnected and share information.
What are extrastriate areas?
Brain regions outside V1, such as V2, V3, V4, and V5 (MT), that process different visual features.
How does receptive field size change in higher visual areas?
It increases, allowing neurons to process larger parts of the visual field.
What area in the inferotemporal (IT) cortex responds to faces?
The fusiform face area (FFA).
