PSYC 320 Lecture Notes - Lecture 5: Visual Cortex, Neural Coding, Graded Vector Space

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2.6.17
Vision in the Brain: Part 2
From LGN to Primary Visual Cortex (V1)
o Your visual cortex in V1 is only getting input from the LGN which can give
rise to the blind spot
o Visual cortex represents a slightly more macroscopic view
o Optic Radiations are a track of white matter- this is where the grey matter of
the cell bodies project on to the next stage of visual processing
o V1 is in the back of the occipital lobe
Orientation in V1: Simple Cells
o Integrating units from dots to line segments
o Many V1 cells respond best to oriented bars, representing the contours of
objects
o Reflects further spatial summation of visual signals
o The preferred orientation will give you the strongest response
The neurons are pulling from other neurons that have different
receptive fields
Taking individual points of light and looking at the union to get the
optimal response
Discovery of V1 Cell Properties
o Learned about how cells responded by accident
o Cats were the original species that the studies were done in to study the
visual cortex to see what drives the neuron in the back of the cats brain
Orientation Tuning of Simple V1 Cells
o 1 neuron corresponds to 1 state/property of an object- this is not how it
happens
It does not fire above baseline when you see anything else
o A lot of cases happens as a gradient representation- a neuron responds the
strongest to a particular object but will continue to respond to other things
as well
o A major driver of the magnitude or rate of the cell is the strength of the input
o You have 2 issues your brain has to put together- responses are intensity
dependent and orientation dependent
o You can represent a rich array of visual information from a gradient of
neurons instead of just looking at each individual neuron
o The idea is that a neuron has a gradient response because the cell is pulling
responses from the LGN from a variety of cells
o V1 likes straight orientations
o V1 is concerned with edges but the principal as a whole is not confined to
straight lines
Stimulus Intensity, Response Output, and Population Coding
o You will not know from the cell if the response is a preferred orientation with
a weak response or a nonpreferred orientation with a strong response
Simple vs. Complex Cells
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