Illusions as key to reality, space and time

Question 1

What are contemporary illusion factories

Answer 1

• Use of illusions in adverts, games and movies
• VR, links sensory systems
  From illusions we can learn about perception and cognition, how our brain works

Question 2

Properties of an image (example)

Answer 2

‘Primrose’s field’
- Two dimensional
- Static Image
- Basic properties; brightness, colour and patterns
- We ‘see’ more as we see the image constantly flickering

Question 3

Black and White and Colour

Answer 3

• Black and white is a result of the amount of light
• Grey Scale; 5,000 shades of grey
• A computer has no more than 256 grey levels
• Colour, it’s hard to say how many colours there are
• Some people have different constructions of the retina meaning they become confused between red and green
• 3Million different colours
• The computer can give you 16Million different colours as they have more colours than you can actually perceive

Question 4

The most important measure is the Contrast

Answer 4

• In a darker background, the same grey can look lighter than on the lighter background

Why does this happen?
- Filters subtract lightness from the outside region from lightness in the central region
- This means that the balance between the centre section and the outside section is seen as perceived brightness to the centre
- Relative stimulus intensity, in comparison to it’s surroundings

Question 5

Brightness and Contrast illusion

‘Herman Grid’

Answer 5

• Grey dots in the cross section of the grids - it’s an illusion there aren’t actually grey spot’s

Why does this happen?
- We subtract what is in the surrounding from what is in the centre.
- The grey spots are as a result of opponency filtering (contrast enhancement)
- The black squares, no overall excitation&raquo_space;Dark
- The White bars, excitation dominates inhibition&raquo_space;Light
- Intersection, Small overall excitation&raquo_space; grey

Question 6

Brightness and Contrast illusion

‘Scintillating Grid’

Answer 6

• Can see black spots jumping around, when you chase the grey spots they go.

Question 7

A zoo of brightness contrast illusions

Answer 7

• Simultaneous contrast
• Mach-Bands
• Induced Grating
• Koffka - Ring
• Craik-Cornsweet

Question 8

Simultaneous Colour Contrast

Answer 8

• Contrast illusion, enhancement of colour differences when presented next to each other.
  Example, strawberries look most tempting next to green leaves.

Question 9

Can we see true colours?

Answer 9

Munker White Illusion
- Colour assimilation
- The two red squares which are the same colour, look different shades a result of one having yellow stripes across and the other having blue stripes across
- Higher level colour interaction - not in the retina, it’s in the brain

Colour illumination impacts the shades of colours also i.e. the colour varies outside and inside

Question 10

Successive colour contrast

Answer 10

• Colour contrast before and after images i.e. fixation on black dot, then when look at a blank screen you see the reverse of the colours around the dot.

Question 11

The third dimension is depth

Answer 11

• Reconstructed from flat images
  Multiple Cues can be used:
• Size, perspective, occlusion
• Texture, contrast, shading
• Using two eyes
• Motion parallax

Question 12

Depth Cues 1: Pictorial Cues

Answer 12

• A variety of information regarding the depth can be gathered from a static monocular image.
• Perspective cues
• Texture (clear when close and can’t see when further away)
• Size (further away is smaller)
• Contrast, closer is higher contrast, further is lower contrast

Question 13

Depth Cues 2: Binocular

Answer 13

• Refers to us having two eyes
• When you close one eye and not the other, the world seems flatter
• Why do we have two eyes, extends the visual field. Creates binocular images which are created as depth images
• Use the two eyes for Stereopsis

Question 14

How does stereopsis work

Answer 14

• When you look to the horizon, the eyes are parallels
• Distant objects are presented to the left and right side of the left and right eye, the angle is called delta
• Close objects are the same, delta left and right. The angle is smaller so called delta prime.
• The difference between delta and delta prime, can be used to estimate the difference of the object
• This is a stereoptic system and our eyes constantly do this (measure the distance of an object)
• red green anaglyphs - 3D movies

Question 15

Single Image Stereopsis: Magic Eye

Answer 15

• 2D images look 3D

Question 16

Depth Cues 3: Relative Size

Answer 16

• Train lines, the slats get smaller and smaller with distance
• Ponzo illusion, the line looks longer than another one but because of the distance change (of the train tracks) they are actually the same size

Question 17

Ames Room

Answer 17

• Objects seem distorted in size
• Two objects are the exact same size
• But the room is constructed in a diagonal shape so it looks like a rectangle but it’s actually squeezed
• Because one object is further away in the room it looks smaller than the other

Question 18

Space and Time

Answer 18

Space- See’s stars in the sky, the separation between the stars is space (Temporal)

Time- Star going away and coming back (Spatial)

Motion- Space and time together a moving star

Question 19

Motion Correspondence Problem

Answer 19

• Ambiguous motion, up down or right left
• Vertical proximity, up down
• Horizontal proximity, right left
  = The distance of movement is smaller horizontally than it is vertically
  Gestalt = law of proximity

Question 20

Motion Illusion After affect

Answer 20

• Focus on red dot in the middle of the spiral
• Then look at the coin, you should see it shrinking
• Disapears when you blink, reset
• Successive motion contrast
  Brexit in action ;)

Another example, is the red white and blue barbers pole, it looks like it is moving
- The shape of the barbers pole, makes it seem as though it is moving up
- The movement is horizontal but looks like it is moving up