Lecture 13 - Pattern perception

Question 1

Two opposing theories of pattern perception

Answer 1

Two opposing theories - bottom up theory and top down theory

Question 2

Bottom-up theories

Answer 2

It is the way the visual system is constructed
You recognise an object by breaking it down into its component elements and then building it back up again

Errors and confusion (the fact that we get errors supports this theory)

To get from the eyes to the far reaches of the ventral system where your visual system puts together the best representation it can - it takes 100 milliseconds (1/10 of a second) - but you can recognise things faster so because of this and many other reasons we also have the top down theory of pattern perception

Question 3

Top-down theories

Answer 3

Can still read a nonsense sentence which means that we are clearly not breaking everything down that we see into its constituent elements and then build everything back up again to recognise it

Hypothesis testing (think you have enough information out there)

Speed of recognition

Speed of reading

Duck and rabbit image is an example of the ambiguous and reversible figures that supports this theory

Subjective contours e.g. square floating image, there is enough information to say that there is a cube there

Interactive theories of pattern perception

Question 4

Binocular cues

Answer 4

Retinal disparity

Convergence and divergence

Question 5

Monocular cues

Answer 5

Interposition 
Relative size 
Linear perspective
Height in plane 
Texture gradient 
Light and shadow

Question 6

Retinal disparity

Answer 6

Binocular

2 objects at different depths, each cast an image on to the retina but the distance between the left and the right is different

Retinal disparity results from your eyes being separated in space, producing stimulation from slightly different angles. The stimulation from objects which are far away is much more similar for both eyes than the stimulation from close objects.

Question 7

Convergence and divergence

Answer 7

Binocular

Look at things close then your eyes converge in
You are looking at things in the distance then your eyes diverge - eyes are attached to muscles and send signals to the brain and you are getting the perception of depth through this process of convergence and divergence

Question 8

Interposition

Answer 8

the shapes of near objects overlap or mask those of more distant ones

Question 9

Relative size

Answer 9

if seperate objects are expected to be of the same size, the larger ones are seen as closer

Question 10

Linear perspective

Answer 10

Parallel lines that run away from the viewer seem to get closer together

Question 11

Height in plane

Answer 11

near objects are low in the visual field, more distant ones are higher up

Question 12

Texture gradient

Answer 12

the texture is coarser for near areas and fine for more distant ones

Question 13

Light and shadow

Answer 13

Patterns of light and dark suggest shadows that can create an impression of three dimensional forms

Question 14

Colour perception - in the eye there are …

Answer 14

3 cones that are each maximally sensitive to certain wave lengths of light

Question 15

Young-Helmholtz Trichromatic theory

Answer 15

Young-Helmholtz trichromatic theory states that within your eye are tiny cells that can receive waves of light and translate them into one of three colors: blue, green, and red. These three colors can then be combined to create the entire visible spectrum of light as we see it.

Question 16

Problems with Young-Helmholtz Trichromatic theory

Answer 16

Theory says we see all colours because of differential activation of the three cone systems and this is true but it is not complete as it does not explain the following questions
Why does colour blindness occur in pairs?
Why do you get colour after effects?

Question 17

Opponent process theory

Answer 17

Occurs at the same time as the other theory that is going on
Retinal ganglion cells are opponent process cells - because of the way you have you cones they project in certain combinations

opponent process theory suggests that the way humans perceive colours is controlled by three opposing systems.

According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa.

Question 18

Colour blindness is rare to be … and likely to be …

Answer 18

Colour blindness is rare to be V4 damage but it is highly likely that you are missing one or some of these cones