lecture 13: pattern perception

Question 1

two theories of pattern perception

Answer 1

1. bottom up theories
2. top down theories

Question 2

bottom up theories

Answer 2

• it is the way the visual system is constructed, starting with analysing low level features (eg: dots, lines) and then building on that until a complex image emerges (eg: face)
• relies on sensory info
• evidence for bottom up processing: errors and confusion
  eg: we are more likely to confuse E and F than E and A

Question 3

top down theories

Answer 3

• hypothesis testing
• relies on knowledge and experience
• speed of recognition and speed of reading are so fast it seems unlikely that we are engaging bottom up processing mechanisms
• also we are faster to recognise an object against a background than one by itself despite the fact that in the former there is more info to process

Question 4

how can we apply both bottom up and top down processing

Answer 4

ambiguous and reversible figures

Question 5

different types of depth perception

Answer 5

1. binocular cues
2. monocular cues

Question 6

binocular cues

Answer 6

–> retinal disparity
- two images (a and b) at different depths will result in different image distances on the retina
- your brain interprets that difference as depth
–> convergence and divergence
- objects nearby (a) cause the eyes to converge and objects at a distance (b) causes eyes to diverge
- your brain interprets those differing signals as depth

Question 7

monocular cues

Answer 7

• interposition, relative size, linear perspective, height in plane, texture gradient, and light and shadow are all monocular cues to depth perception
  –> if these cues arent used or used poorly it impacts all of these aspects

Question 8

colour perception theories

Answer 8

1. young helmholtz trichromatic theory
2. opponent process theory

Question 9

young helmholtz trichromatic theory

Answer 9

• postulated the existence of three cones in the retina each maximally sensitive to a certain colour
• triggering any number of these cones might allow us to see the colours that we see
  short wavelength = “blue” cones
  medium wavelength = “green cones”
  long wavelengths = “red” cones

Question 10

limitations to the young helmholtz trichromatic theory

Answer 10

1. why colour blindness occurs in pairs
2. why you get colour after effects

Question 11

opponent process theory

Answer 11

• bipolar and RGCs are opponent process cells
  –> for example, a RGC can be blue-ON/green-OFF OR blue-OFF/green-ON

Question 12

RGC

Answer 12

= retinal ganglion cells
- play a key role in visual processing