Lecture 8: From V1 to the cortex, p3 Flashcards
T.M
How can midget ganglion cells transmit to the ventral (temporal) pathway? And what do they detect?
The midget ganglion cells take the parvo pathway. Via the parvolcellular cells of the LGN, they go through the layers of the visual cortex in V1 till layer III. Then it will arrive in V2 where color and orientation is detected. Then in the V4, color and form complexity will further be processed.
- Color can also be immediatly interpreted from V1 to V4.
How can parasol ganglion cells transmit to the dorsal (parietal) pathway? And what do they detect?
The parasol ganglion cells take the magno pathway. Via the magnocellular cells of the LGN they will enter the cortex layers of V1. From layer 4B, it will it will go to V2 where direction and depth is interpreted. From V2 it will come in the MT –> middle temporal area (V5)
What are the visual primitives?
Orientation, color, contrast, depth, movement
Based on what is a generated unified visual field represented?
By assembling local elements of an image into a unified percept of objects and background.
The way in which a visual is perceived depends on everything that surrounds the feature => visual context
+ taken into account: build in logic and wiring, expectations from experience, previously learned rules
Which cells, located in the V1, are highly selective for the position of a line or edge in space? And which are highly selective for a line/edge within their receptive field?
- Simple cells
- Complex cells
What is the difference between the visual field and the visual receptive field?
The visual field is what you see, how detailed (complex) the visual is. The visual receptive field is what a neuron sees (like pixels)
How does lateral inhibition in the retina contribute to the Hermann grid illusion?
Lateral inhibition causes retinal ganglion cells at grid intersections to receive more inhibition from their bright surroundings, reducing their response and creating the perception of dark spots. Along the grid lines, less inhibition occurs, so these areas appear brighter. The effect dimishes with direct fixation due to smaller receptive field in the fovea.
Which V can detect illusory contours?
V2
NOTE: also more disparity selective cells are found in V2.
On which cues does depth-perception depend?
Monocular and binocular cues
In which V are cells often more selective for higher order shape discription?
V4
When are neurons considered as ‘component direction-selective’?
When they respond to a preferentially to motion in a specific direction of an individual component of moving stimulus, instead of the overall motion of a complex pattern
What do pattern cells do and where are they found?
They signal the global object motion that we perceive by combining the information from the appropriate component cells.
- Found in the MT area
What is akinetopsia?
Motion blindness: Can see objects, perceive color and shape but not perceive their motion.
E.g. patient with bilateral lesion in the occipito-temporal extrastriate cortex including MT
What is achromatopsia?
Full colorblindess –> everything seen in black and white
e.g. focal lesion in medial inferior temporal cortex
What is color constancy?
Ability to perceive color of an object as relatively constant, even under varying light conditions.
