Central Visual Processing I Flashcards
In the visual system as you go from the retina to V1 to V2 to V4 and the temporal cortex….what happens to the receptive fields?
The receptive fields get larger because higher order visual processing requires integration and analysis over greater and greater regions of space
What is the most important target of the retinal ganglion cells for visual perception?
The retino-geniculo-striate pathway
Where does the reticulo-geniculo striate pathway end?
The primary visual cortex (area 17, striate cortex, or V1)
What is the reticulo-geniculo striate pathway responsible for?
Form, color, and depth vision, visual motion perception, visual object recognition and localization
What is a second important target of the retina?
superior colliculus
What is the pathway from the retina to the superior colliculis responsible for?
Eye movements and head/ attentional orientation
What is retinotopy?
A faithful spatial representation of visual space/ position
How is intensity/ luminance visual information transduced, processed, and represented?
Photons absorbed/ transduced by photo-pigments, rods vs cones
How is differential spectral absorption transduced, processed and represented?
3 cone types (color opponency
How is spatial contrast transduced, processed and represented?
Center-surround receptive fields (edge detection)
Due to the optics of the eye, what happens to visual field mapping onto the retina?
Visual field mapping onto the retina is inverted and flipped
Ex: The superior nasal visual field maps to inferior (central) temporal retina
How do retinal ganglion cell axons leave the eye?
Optice nerve
Do nasal or temporalhemiretinal axons cross the optic chiasm?
Nasal! Temporal do not cross.
At which levels are the visual field representations crossed?
At the level of the optic tract, LGN and cortex
How is the LGN organized?
It is organized into 6 layers that presevers eye of origin
Going from layer 1 to layer 6….what is the contra/ ipsa order of the layers?
Contral, ipsa, ipsa, contra, ipsa, contra
How does the LGN provide input to V1?
The LGN creates the optic radiation to V1
What is the primary layer in the striate cortex (V1) that the LGN projects to?
Layer 4
Is the input to V1 segregated in an eye-specific and retinotopic manner?
Yes it is!
What is the basis for the occular dominance columns of V1?
The segregation of eye specific input into V1
When does eye specific information being to combine?
It beings to combine and interact within the circuitry of V1
How are retinal receptive fields constrcucted?
They are constructed by retinal circuitry and are center-surround of two signs, sometimes with differing cone types in center vs surround (the creates a color opponent cell)
What are the two Center-surround receptive fields in the retina?
On-center and OFF- center
What are the receptor systems that vision is divided into in the retina?
Rods and 3 classes of cones (R-long, G- medium, B- short)
What are the signaling pathways that vision is divided into in the retina?
Parvo pathwya, Magno pathway, Konio pathway
Where is the origin of the M, P ad K pathways?
The retina
What is the Magno system specialized for?
High temporal resolution (speed) and higher contrast gain, and possibly motion perception
What is the Parvo pathway specialized for?
Emphasizes higher visual acuity and color
What is the Konion system specialized for?
Color perception
How many M layers are in the LGN? How many P layers?
M layers= 2
P layers= 4
How are K layers presented in the LGN?
They are in between (intercalated) the 6 layers if the LGN
Which visual field, Ipsilateral or contralateral, does the LGN recieve visual input from?
Contralateral
What layer of V1 does the LGN receive feedback from?
Layer 6 of V1
Describe the cells of the LGN?
Center-surround receptive fields
What happens to the M, P, and K pathways when they get to the visual cortex?
They intermix substantially….excpet the M pathway is partially segregated in the outputs of V1 and in higher visual cortex
In V1, what is the most cortex devoted to?
More cortex is devoted to central vision
Describe the anatomical structure of V1:
It is 2 mm thick sheet of cells, it has 6 layers
Where does output from V1 come from?
Output from V1 comes from layers 2 and 3 (and then goes to extrastriate cortex (V2)
What does layer 5 of the V1 do?
It does to the superior colliculus
What is ocular dominance in regards to V1 neurons?
Eye preference— the cells of V1 receive input primarily from one eye
What is a binocular V1 neuron?
A neuron that receives input from both eyes
How can the ocular dominance property of a single neuron be predicted?
It can be predicted if you know where the cell is located relative to the pattern of the ocular dominance columns
Do V1 neurons have center-surround receptive fields?
No they USUALLY do not have center-surround…rather they have oriented receptive fields and are orientation tuned.
Some are center-surrond receptive fields and are color-selective (color opponent)
What does orientation tuning refer to?
It refers to the preference of a cell to be stimulated by an edge of light presented at a particular angle (horizontal, vertical or inbetween)
Why does V1 want to created oriented cells?
Orientation tuning is the early stage of form vision analysis. The visual system needs to determine within a visual scene what objects and what is background. The borders can be thought of as edges of differing orientation
What are the two color opponent signals that are created in the retina and propagated into V1?
Red vs Green and Blue vs Yellow
Functionally, how is V1 organized?
It is columnar in organization. Each column has similar receptive field properties
How do ocular dominance columns alternate in V1?
They alternate between left eye and right eye
What are blobs in V1?
CO (cytochrome oxidase) blobs are centered on the OD columns and contain monocular, unoriented color cells
What is a hypercolumn?
A hypercolumn is a collection of functional cortical columns that cover the entire range of possible values of one stimulus parameter for a given point in visual space
Where are hypercolumns found?
They are found in V1
What are the two major visual processing streams after V2?
The dorsal pathway and the ventral pathway
Where does the dorsal pathway go and what does it do?
The parietal visual cortex—- it is most concerned with motion perception and the localization of visual objects
Where pathway
Where does the ventral pathway go and what does it do?
The temporal visual cortex and is concerned with object and pattern recognition
What pathway
Is V2 retinotopically organized?
Yes, it is and it has larger receptive fields than V2
What do V2 stripes suggest?
They suggest a separation of the visual processing for form, color, motion and depth
