Perception Flashcards
why is it important to see colours?
colours facilitate object detection by increasing figure segmentation and aids object recognition
What is electromagnetic radiation?
a form of energy. any source that radiates generates electromagnetic radiation.
what are wavelengths measured in?
units called nanometres (nm)
What is the range of the visible light spectrum?
400-700 nanometres
Where are the only receptors in humans that can detect the light?
the retina in the eye
What are the two receptors in the eye and how many classes of each kind ?
-Rods (night vision)
-Cones (day vision) of which there are three classes
-There is a fifth photoreceptor that is not used in image forming.
What does white light break down into?
-components all the way from blue to reds
-eg. Newton’s experiment
Surfaces scatter light explain this:
-surfaces always scatter light, they don’t produce it
-every surface scatters a part of the spectrum
-if a surface attracts all the electric magnetic radiation and doesn’t emit any of it the surface will look black
-white paper reflects all aspects of the spectrum
-a blue pigment only scatters over a short wavelength blue part of the Spectrum
-red surfaces such as tomatoes look so red because the tomato skin absorbs a band of electromagnetic radiation from 400 to approx. 600nm. the only thing it doesn’t absorb is the colour red
what wavelength are we most sensitive to in the daylight and the night vision?
-555nm in the daylight which matches the brightness of the sun which appears yellowish in colour
-507-510 nm in the moonlight hence moonlight being blue ish
-we evolve to match our surroundings
What are opsin molecules?
-basic fundamental aspects of our senses in our retina as part of our photopigment
-a photopigment contains lots of opsin molecules which change shape as a response to light, and then reverses shape again
how do opsin molecules send a pulse to your brain?
the change of shape in the opsin molecules lead to a series of chemical reactions that end with a pulse going into the brain
Why do all animals experience different colour vision and light sensitivity?
A tiny adjustments on opsin molecules change the colours that the molecules are most sensitive to e.g. greens or reds or blues or oranges, which differ in all animals
Summarise the Univariance principle:
a photoreceptor’s response is summarised by one variable that specifies the amount of light absorbed
What would happen to an eye with only one type of photo pigment ?
It cannot see colours
What are three features of rods:
-they are highly sensitive and hence can navigate the dark
-they are highly saturated and when the lights turn on they cease operating very quickly
-if you only saw the world in rods it would appear very blurry
What photoreceptors are more useful in central vision?
Rods are more dense in the peripheral vision. Cones drop in the peripheral vision and populate central vision which is best for looking straight ahead. This is why it is better to look at stars from an angle
Why would a two-pigment system confuse colours?
any one wavelength can be matched by a pair of wavelengths
What does it mean that the human eye is ‘trichromatic’?
the human eye has three photopigments sensitive under photopic conditions. any wavelength will produce three responses
Does the retina have an equal amount of S M and L cones?
the retina has less S cones than M and L cones, central parts have no S cones.
what is the overlying yellow pigment in the retina called?
the macular pigment
if you stare at green image for a minute and then look at a grey patch, a red aftereffect of the image will be seen for a few moments. What is this called?
colour opponency
is human vision trichromatic or trivariant?
human vision is trichromatic meaning we have three colour processes- red, green, and blue
what are the opponent colour channels?
red/green, yellow/blue
define hue, value and chroma
hue= quality that distinguishes colours
value aka brightness related to intensity of light
chroma aka saturation distinguishes pale from vivid
which is present from birth: congenital or acquired?
congenital. acquired is when those with normal colour vision develop partial or total loss of colour vision
describe the nature of anomalous trichromacy, dichromatic colour deficiency, and rod or cone monochromacy?
anomalous trichromacy: all three cone types are present, however one has an abnormal absorption curve.
dichromatic colour deficiency: two cones are present and one is completely absent. this leads to protanopia, deuteranopia, or tritanopia, depending on which cone is missing (L, M, S)
rod or cone monochromacy: only one cone type present, this results in no colour perception (black and white)
Two potential acquired abnormalities of colour vision:
cerebral achromatopsia/dyschromatopsia: selective loss or deterioration of colour vision due to damages to temporal and occipital areas of ventral pathway.
aging and disease of the eye: illness, ageing, trauma causing CV anomalies and defects.
typically what losses are resulted from retinal vascular system and ageing disorders?
yellow-blue
what damages are likely to result from optic nerve lesions?
red-green
What are you tasked with in the Farnsworth-Munsell 100-hue test?
you are instructed to arrange a sequence of coloured slides correctly
What does depth perception register?
the distance between the object and the observes using depth cues
What is the difference between monocular and binocular vision?
monocular depth cues can be provided by both eyes or one eye alone. Binocular cues rely on input from each eye.
