Lecture 7 - colour

Question 1

Why do people see the dress in different colours?

Answer 1

• Image is over-exposed
• Different viewing conditions
• People apply different names to the same colour
• Colour blind
• Individual differences in colour processing
• Individual differences in experience
• Failure of colour constancy

Question 2

Image is over-exposed

Answer 2

• It leads to colours in image being different from real dress
• However people varied in how they saw colour so over-exposure not only cause

Question 3

Different angle/viewing conditions

Answer 3

• Viewing conditions matter as researchers found variations in perceived colour with chance in size and viewing angle
• However even under lab conditions where external light source, size of picture and viewing angle controlled = 54% saw blue-black and 40% saw white-gold = cant just be viewing conditions

Question 4

People apply different names to same colour

Answer 4

• Given a forced choice = leading question
• Study:
• -> 2 groups
• -> 1 given free choice to name colour and other given force choice
• -> People still came up with blue-black or white-gold even when freely asked
• -> Even when given colour swatches people still gave same answer

Question 5

Colour blind explanation

Answer 5

• Retina tuned to see small portion of EM
• Circadian rhythms = population of ganglion cells with light detection properties = causes brain to respond in certain ways at different times

Photoreceptor types:

• 3 types
• Blue = S type
• Green = M type
• Red = L type
• Each detects light at different frequency
• With only one cone type can see wide range of colours but cant discriminate
• One type of rode = for non-colour, luminous info at night

Question 6

Colour vision and the visible spectrum

Answer 6

• Most mammals = 2 cone types
• Humans, apes, monkeys = 3 cone types
• Snakes = infrared
• Birds and snakes = ultra-violet

Question 7

Colour blindness

Answer 7

• Some have mis-tuned cone types so cant discriminate certain colours well
• Fewer have missing cone types = dichromats
• Most common form = mistuned green cone
• Red-green cone colour gene on X chromosome = more common in men
• Some women have 4 cone types
• Small number of people have no cones = rod monochromats = truly blind
• Monochromatic = one cone type
• Protanopia = no red cone
• Protanomaly = miss-tuned red
• Deuteranopia = no green
• Deuteranomaly = miss-tuned green
• Tritanopia = no blue = most rare

Question 8

Cerebral achromatopsia

Answer 8

• Following stroke or injury patient may not be able to see colour
• Photoreceptors, retina, LGN and V1 all intact
• Stroke affects V8
• Cannot perform tasks based on colour but luminous info still intact
• Number of people colour blind in population low so this is unlikely to be reason

Question 9

Individual differences in colour processing

Answer 9

• Colour processed in antagonistic fashion
• Way in which colour detected in retina and LGN based upon properties of retinal ganglion cells and how they respond to colour

Individual differences:

• Blue and brown dots measured colours from dress and image = found most variation on blue-yellow system
• Red dots show people setting for neutral grey and white tones = showing what people see as neutral varies between the colours in dress image
• Individual variations in blue-yellow system explains peoples perception of dress

Question 10

Individual differences in experience

Answer 10

• Have small contribution to peoples ability to perceive colour
• Experience of colour can change over space and time due to brain inhibiting that colour
• If you look at colour relative to background colour it starts to change
• When stare at picture for long time may experience small after effect
• Simultaneous colour contrast and filling in may explain effects due to surrounding colours
• Surrounding and ambient colours change throughout the day but not enough to explain data collected under lab conditions

Question 11

Failure of colour constancy

Answer 11

• Colour of light reflected from objects depends on colour and colour of light shining on it
• This is done in sub-section of V4 (V8)
• Idea we need to discount/ignore light source and ability to do this takes place in V8
• Colour constance = ability to perceive light to be the same regardless of light shined on it
• People who saw dress as white-gold assumed it was lit by daylight so brain ignores blue day light
• People who saw blue-black assumed assumed warm artificial light shined on it = brain ignores red wave lengths
• Individual difference in yellow-blue system may promote one perception over the other and after effects may produce biases over time = causing someone to change perception
• Most likely answer