Columns & Pathways Flashcards
(25 cards)
The LGN is part of which structure?
Thalamus
How many layers does the LGN have?
6
- > 2,3,5: Ipsilateral Eye
- > 1,4,6: Contralateral Eye
Neurons in layers 1 & 2 in the LGN…
… are the largest
… receive input from M ganglion cells
… respond to large, fast moving objects
Neurons in layers 3 - 6 in the LGN…
… are smaller
… receive input from P ganglion cells
… respond to stationary objects
Retinotopy
- > Neighboring points on the retina correspond to neighboring points in the LGN -> Receptive fields are represented
- > Each layer has it’s own map perfectly on top of each other
Other words for V1
- Primary Visual Area
- Striate Cortex
Organization of receptive fields in V1
side-by-side rather than center-surround
Simple Cells
- respond best to bar-like stimuli
- Orientation tuning curve: Each cell responds best to a certain angle
Cells in V1
- Simple cells
- Complex cells
- End-stopped cells
- > Are called “feature-detectors”
Complex Cells
- responds best to moving, bar-like stimuli
- has preferred angles as well
End-Stopped Cells
- fire when detecting (moving) corners, angles, or lines of specific lengths
Retinotopy in the Striate Cortex
- V1 also has a retinotopic map
- Cortical Magnification: fovea: 0.01% of space on the retina, but 8 - 10% in V1
Types of columns in V1
- Location Columns
- Orientation Columns
- Ocular Dominance Columns
- Hypercolumns
Location Columns
Receptive fields in the same column in V1 are located close to another on the retina
Orientation Columns
Neurons in one column all have the same orientation tuning. Adjacent columns have slightly different tuning.
Ocular dominance Columns
Neurons in one column preferably respond to one specific eye. (Organized in L-R-L-R fashion)
Hypercolumns
All 3 Types of columns are united in one complex column.
Selective Adaptation
After firing for a while, neurons get fatigued and stop firing. This process is selective, since neurons only respond to a specific feature.
Ventral Pathway
- > “What”-Pathway
- > From V1 to Temporal Lobe
- > Identifying Objects
Dorsal Pathway
- > “Where”/ “How” - Pathway
- > Where is the object located and how can I interact with it?
- > Movement planning + localization
Feedback
When a signal does not only travel one way along a pathway -> Bottom-up process gets “feedback” from the brain -> Top-down
Visual Agnosia
- > Can’t recognize, but can grab object
- > Damage in ventral (what) pathway
Optic Ataxia
- > Inability of reaching for an object effectively
- > Damage in dorsal (where/how) pathway
Prosopagnosia
- > Face blindness
- > Can’t recognize faces
- > Special form of Visual Agnosia
