spatial vision

Question 1

Hypercolumn

Answer 1

Collection of neurons that all have receptive fields that cover same part of visual space but within that they respond to different visual orientations

Question 1

Organisational principles of V1

Answer 1

Neurons stacked on top of each other in V1 have the same optimal orientation
As you move from column to column orientation tilts around 10 degrees
All orientations covered within about 0.5mm
V1 neurons have a preference for eyes, despite binocularity

Question 2

Sinewave/Sinusoidal Gratings

Answer 2

Way to see how hypercolumns work
Can adjust many aspects of them (orientation, spatial frequency, contrast, phase)

Question 3

Visual angle

Answer 3

If you want to specify the size of an input referring to the size of the object, you would need to specify two different numbers
Size of the object
Distance of observer from the object
To simplify this we use the visual angle, which tells us the size of the retinal image

Question 4

Why sinewave gratings?

Answer 4

Every image can be broken down into sinewave components, it is the smallest unit in order to build up any image that can exist in the world
The visual system conducts the equivalent of a local Fourier analysis and puts the inputs into different sinewave components

Question 5

Fourier Analysis

Answer 5

Hundreds and hundreds of components that include orientation, spatial frequency and phase, all can make images

Question 6

Early vision as local Fourier Analysis

Answer 6

Hypercolumns contain neurons tuned to different orientations and spatial frequencies
All of these neurons analyse the same patch of visual space and together they extract spatial frequencies and orientations contained in their local patch

Question 7

Adaptation

Answer 7

Both a method and a process in the visual system

Question 8

Adaptation (method definition)

Answer 8

Stare at the stimulus for a long time

Question 9

Adaptation (process definition)

Answer 9

As a consequence of long exposure, those neurons that are tuned to the stimulus property decrease their sensitivity

Question 10

Tilt aftereffect

Answer 10

Staring at tilted image can perceive vertical lines as one that is straight

Question 11

Population Code Model of tilt aftereffect

Answer 11

All the neurons and their specialised orientation codes create an activation profile across your visual cortex
When staring at the stimulus, as a consequence, our visual system adapts
The neurons that are tuned to this will become less sensitive
Extent to which they become less sensitive depends on how close the stimulus is to that neuron

Question 12

Contrast sensitivity and spatial scale

Answer 12

Tells us how sensitive we are to inputs depending on the size of the inputs
We peak at between 3 to 10 degrees

Question 13

What produces the contrast sensitivity function

Answer 13

Different populations of neurons that have different sensitivities
The different sizes of receptive fields help shape what we are sensitive to

Question 14

Independence of spatial frequency channels - Marilyn and Albert

Answer 14

Marylin’s picture mainly contains low spatial frequencies
Albert’s picture mainly contains high spatial frequencies
When you sit further away, the further away you are from the image and the less you can receive the high spatial frequencies - the only thing that remains is the high spatial frequencies
When you sit closer, you are able to see the high spatial frequencies, and that will dominate the perception