Week 6 Flashcards
What are the layers of the V1
6 layers
layer 4 subdivided into 4a 4b 4c
4c into 4c (alpha) 4c (better)
Input and output in the 4c layer of the V1
Most of input arrives in layer 4c
magnocellular pathway terminates in 4cA
parvocellular pathway terminates in 4cB
K cells terminate in layers 2, 3
What occurs within the V1
- Cortical Magnification
- Processing attributes and RF properties
Orientation processing
Binocular vision
Motion direction processing
Enhanced colour processing - Receptive Field Classification
- Columnar organisation
what is orientation selevtivity
striking characteristics of cortical cells
any particular cell will respond only only if orientation of edge or line falls somewhere within rather narrow range – about 15 deg to either side of optimal
Cells in layer 4, less orientation selective than those in other layers
oblique effect definition
consistent superiority in performance when visual stimuli are horizontal or vertical, as opposed to oblique
what is binocularity in the LGN
Once leave layer 4, ocular segregation gives way to binocular integration.
With few exceptions, all cells outside layer 4 are binocularly driven.
How do cortical cells work in their receptive fields
- Large subset of cortical cells respond best to moving contours
- Typically respond to one direction of motion only
- RFs vary in size and for any given region of visual field there are multiple sizes represented
- Some cortical cells register information about colour
- Double-opponent processing
single cells in V1 receptive fields
Elongated RFs with elongates excitatory and inhibitory regions
Respond best to a bar or an edge of correct orientation and size in correct position on retina
Thus selective for orientation, size and position
Display little or no spontaneous discharge
comples cells in V1 receptive structures
Have larger RFs which are not so easily described in terms of discrete On- and Off- regions
Because their responses are not simply given by linear summation of sensitivities of subregions, they are described as non-linear
Respond best to rapidly flickering or moving stimuli, have a preferred orientation and size like simple cells, but are not so specific for stimulus position
What are endstopping cells
Some cell responses depend not only on contour orientation but contour length as well – also know as end-stopped cells
Extending the bar length beyond this optimal value dramatically reduces cells response
End-stopping found amongst both simple and complex cells
properties of V1
columar organisation of a preferred eye
comulnar organisation of preferred stimulus orientation
all cells in each column have similar preferred orientation
what are hypercolumns
This combining of adjacent columns to cover a complete range of stimulus orientations and ocular dominance
Each hypercolumn contains neural machinery for analyzing visual
visual information within a local region of the retina
what are colour blobs in V1
Cortical slices stained for enzyme Cytochrome Oxidase reveal “blobs” of cells at the centre of ocular dominance columns
Blob cells are specialised for colour (R/G; B/Y)
Cortical colour processing is more complex
It is called “double opponent” processing
what is colour selectivity
responded to some colours but not to others
what are preliminary areas in the V1 used for
information about all visual sub-modalities (luminance, colour, movement, stereopsis
