Vision

Question 1

What does the optical nerve do?

Answer 1

Carries information to the thalmus, in the very centre of the brain.

Question 2

Where in the cortex is the visual cortex?

Answer 2

At the back of the cortex

Question 3

How is information processed in the visual cortex?

Answer 3

The information fans out and is integrated with other signals, from memory and other sensory modalities and other aspects of our cognition.

Question 4

What side of the brain do signals from the left sides off the retina in both eyes go to?

Answer 4

Right side of the brain

Question 5

Where is the layer that detects the light in the eye?

Answer 5

At the back of the eye.

Question 6

What detects light in the eye?

Answer 6

Photoreceptors, these don’t spike, but they convert light into electrical activity

Question 7

What are the two types of photoreceptors?

Answer 7

Rods: These are important for vision in low light
Cones: Which are responsible for colour vision and important for vision in normal lighting

Question 8

What do ganglion cells do?

Answer 8

Aggregate activity from a number of photoreceptors, along with the activity from some inhibitory cells in the intermediate layer and their axons from the optic nerve, carrying information to the thalmus.

Question 9

What are receptive fields?

Answer 9

The receptive field of an individual sensory neuron is the particular region of the sensory space (e.g., the body surface, or the visual field) in which a stimulus will trigger the firing of that neuron.

Question 10

What is V1?

Answer 10

Primary visual cortex

Question 11

What cells make up V1?

Answer 11

Simple cell that have edge like receptive fields.

Complex cells

Question 12

rbar=r0+sum(wij*Iij)

What are the variables?

Answer 12

rbar is the firing rate
r0 is the background firing
wij is the receptive field
Iij is the illumination point in the visual field.

Question 13

We need to choose __ to minimise the average squared error.

Answer 13

wij the receptive field.

Question 14

Feature selection firing rate equation?

Answer 14

a_s=sum(w_ij^s*Iij)
Where a_s is the firing rate,
w_ij is the receptive field
Iij is the illumination point

Question 15

What does the following equation estimate:

Iij=sum(a_sW_ij^s)

Answer 15

Estimates the image using the firing rates.

Reconstructed image may not be equal to the original image and will just be an approximation to it.

Question 16

Roughy, the _ neurons needed to reconstruct an image, the more of the image each neuron is coding for

Answer 16

Lower. For this to work without having a vast number of neurons covering every possible combination of pixels, the neurons must code for features.

Question 17

Let I be a image and Ibar be an approximation to the image formed from features.
Ibar is an approximation because the a_s are not just chosen to give an accurate reconstruction, but to do so in a sparse way; theyaare chosen to minimize what equation?

Answer 17

E=sum(I_ij-Ibar_ij)^2+ßsumf(a_s)
First term being squared error between I and Ibar, the second is the intended measure of sparseness.
ß determines the trade off between accuracy and sparseness. If ß is small, the squared error dominates if ß is large the sparseness dominates.

Question 18

What is the update rule for the features W_ij^S

Answer 18

Wij^s->Wij^S-eta(dE/dWij^s) where eta is the learning rate and E is the average error.