Week 3

Question 1

Give 4 reasons why people see different colours?

Answer 1

The image is over exposed, They are looking from different angles, People see the same colour but call them different names, Some people are colour blind

Question 2

What 3 colour classes allow us to differentiate between colours in the electromagnetic spectrum?

Answer 2

Blue, Green, Red

Question 3

What is the function of the visual system for colour?

Answer 3

To differentiate between pairs of colours

Question 4

How do cones play a role in identifying colours?

Answer 4

They are excited by a particular frequency of light (tells us about a particular colour)
A cone will fire the strongest when it is about a particular colour

Question 5

What are the two types of colour blindness

Answer 5

1. Protanopia: fail to have a particular cone (no red)
2. Protanomaly: cones not firing maximally at a certain wave length (miss-tuned red)

Question 6

Why does the visual system compare colours in pairs?

Answer 6

Due to how receptive fields are organised

Question 7

What does damage to the V8 cause?

Answer 7

Can detect brightness, but not colour

Question 8

What is colour opponency?

Answer 8

Visual system is comparing how much of one colour to the amount of another colour; also comparing amount of luminous

Question 9

What provides the mechanisms for colour opponency?

Answer 9

Centre-surround properties of retina ganglion cells

Question 10

What is the function of the retina ganglion cells in colour opponency?

Answer 10

They calculate the ratio of colours and provide edge detection mechanism

Question 11

Can there be individual differences in colour opponency?

Answer 11

Yes

Question 12

What effect does inhibition over time have?

Answer 12

“colour after effects”

Question 13

What does the colour after effect include? Why?

Answer 13

Seeing the complementary colour to the initial colour; Due to how the brain processes colour

Question 14

How does the “water colour illusion” work?

Answer 14

Colour centre-surround cells (in retina) transmit only colour edges; the cortex then reconstructs the body colour of the object; they pass through retina > cortex = automatically fills in the gaps with a sense of colour

Question 15

What is colour constancy?

Answer 15

Where the colour of light reflected form an object, depends n their colour and the colour of light that shines on them

Question 16

Where does colour constancy occur?

Answer 16

V8

Question 17

What are the functions of cortical areas V1, V2, V4 and V8

Answer 17

V1 and V2 colour sensitive cells cluster into regions of the cortex
Colour signals are passed to a sub-section of V4 (called V8)
V8 = responsible for conscious perception of colour

Question 18

How did the classical view of V1 come about?

Answer 18

Hubel and Weisel (1950’s) classified the sensitivity of cells, by looking at animals brain reactions to changes in line drawings

Question 19

What is the main function of simple cells?

Answer 19

Orientation sensitivity

Question 20

What is the difference between simple cells in V1 and in the retina?

Answer 20

In V1 = fire maximally when stimulus excites the on part of the receptive field
Retina = stimulus always excites same part of receptive field

Question 21

Explain the position sensitivity function of simple cells?

Answer 21

They can detect the position of an object
When shone on inhibitory part = turns cell off
When shone open excitatory part = excites it maximally

Question 22

Explain the size sensitivity function of simple cells?

Answer 22

Wide object = will cancel out both regions
Narrow object = maximally overlap with on-part of receptive field

Question 23

How are simple cells made?

Answer 23

By combining the output of many concentric receptive fields from the LGN

Question 24

What do simple cells in the V1 respond to?

Answer 24

Edges at particular locations and orientations within the visual field

Question 25

What are the main characteristics of complex cells?

Answer 25

High resting output (no stimulus = more activity) Defined receptive fields, but unstructured = they overlap Maintain orientation and spatial frequency sensitive Not sensitive to line position within receptive field Length summation

Question 26

How are complex cells made?

Answer 26

complex cells are connected to many simple cells by OR function - stimuli detected by simple cells will make complex cell fire

Question 27

What are the function of hyper complex cells?

Answer 27

They can detect a particular length of an object; it can turn the cell off when the stimulus gets too long

Question 28

What are hyper complex cells sensitive too?

Answer 28

Line length and orientation

Question 29

How are the receptive fields organised in hyper complex cells?

Answer 29

A receptive field is at the side of 2 inhibitory cells

Question 30

How might inhibition work in hyper complex cells?

Answer 30

Inhibitory input from receptive fields at either end of the excitatory receptive field could signal length As stimulus gets longer = maximally excites the cell, inhibitory end stop mechanism turns off complex cell

Question 31

What is texture?

Answer 31

Spatial detail at a scale which is finer than which the observer currently defines as the object scale

Question 32

What are textures defined by?

Answer 32

Statistical properties [2 textures have same statistical properties = same] [2 textures have same different properties = separable]

Question 33

What does statistical properties allow us to do?

Answer 33

Enables us too see edges of objects

Question 34

What is the basis of Julesz'[s (1984) texton theory?

Answer 34

Texton = simplest defining properties of textures; textures will segment if they differ in density of textons

Question 35

What are 3 characteristics of textons?

Answer 35

Elongated blobs with orientation and length Line endings Line crossings

Question 36

What is an updated version of Julesz's texton theory?

Answer 36

Northdruft (1990/1991) - Texture segmentation based on line crossings and line endings is more affected by certain visual manipulations, than is segmentation by orientation

Question 37

What are the two classes of cells in V1?What are their function?

Answer 37

Single opponent - respond to single orientation and when orientations contrasts with a different orientation Double opponent - respond to 1+ orientation and when vertical and horizontal contrast with orientation of the object and the surrounding periphery

Question 38

What is the difference between simultaneous tilt illusion and the simultaneous contrast illusion?

Answer 38

Tilt is sensitive to orientation, not light

Question 39

Does simultaneous contrast work for size?

Answer 39

Peripheral stimulus = turn off cell less (because peripheral info is smaller) = tricks into thinking the circle is larger than what it actually is