Lecture 8 - Human Colour Vision Flashcards
What is colour coding information
Coding, grouping and segmentation of packets of information by means of colour
When is colour coding information used
In occupational environments and transmitting information
Examples of colour coding information
- Traffic light - information is signalled very fast, transmit information
- Air traffic control - enhances visual performance - use of colour - for traffic conflicts and weather warnings
- Plane landing - show lights for landing in colour, pattern of where to land
Why should you colour code in different colour
See more clearly
Why is the use of colour vision in occupational environments important
It enables efficient coding of signals and information - enhances visual performance
What are the uses of colour signals
- Enhancement of object visibility
- Pop out and parallel processing of objects defined by colour
- coding of known information by means of colour
- Segmentation ( break down ) of complex scenes into groups of areas of interest by means of colour
How many visual channels are there
3
How do we perceive colour
Light focused onto retina by cornea and lens - triggles signals into 3 cones - red,green and blue - travel to brain
The cone photoreceptors in the retina contain 3 different pigments ( opsins ) that absorb in different parts of visible spectrum
What are the 3 colours ( cones ) involved in these signals/chromatic channels
Red, green and blue
How do you get normal colour vision
If all 3 cone photopigments ( R,G,B ) are present in visual system
How do you get colour vision deficiency
Genetic mutations or expression in L and/or M cone genes = shift in peak sensitivity = differences in colour vision - affect specific sites on amino acid chain
What are the two types of anomalies
Congenital
Acquired
Congenital Anomalies
- Present from birth
- Stable throughout life in terms of classification and severity
- Affects both eyes equally
- Affects males more than females
- Red/green deficiencies are most common
- Deficiency can vary in severity from minimal to severe
- Available clinical tests are designed to detect only red/green deficiencies
- Normal visual function
- Differences in luminosity discrimination amongst colour deficients
Acquired Anomalies
- Frequently associated with other visual function loss (i.e. acuity, visual fields,…)
- Onset after birth (colour vision previously normal)
- Type and severity changes with time
- Monocular differences in severity frequently occur
- Monocular testing required
- Equal prevalence in males and females
- Affects both red/green and yellow/blue colour channels
- Clinical tests are not designed to detect or monitor acquired deficiencies
What are the 3 cones
S = blue M = green L = red
What happens during a normal trichromat
3 cones/colours - normal colour vision
What happens during anomalous trichromatism
Peak sensitivity of that cone shifted away from normal position, all 3 cones present but not in normal wavelength postion
Tritanomalous
S cone shifted
Deuteranomalous
M cone shifted
Protanomalous
L cone shifted
What happens during dichromatism
2 colours present only, 1 cone missing completely
Tritanope
S cone missing
Deutranope
M cone missing
Protanope
L cone missing
Cone Monochromat
Colour blind - one cone only - grey
Rod Monochromat
Colour blind - only rods - grey
Absent cones
Protanope
Deutranope
Protanope
Different cones
Protanomalous
Deuteranomalous
Tritanomalous
Prevalence of congential deficiencies
’ Red/green’ are the most common, affecting 8% of men and 0.4% of women, ‘yellow/blue’ deficiency are rare
Why is prevalence of congential deficiencies higher in men compared to women
Due to X - chromosome inheritance
Autosomal inheritance
Affects men and women equally
