Perception 2- brightness & colour

Question 1

Stimulus for vision overview

Answer 1

Light
Different wavelengths are associated with different colour perceptions
Light is small packets of energy called photons

Question 2

What type of properties are brightness and colour?

Answer 2

Perceptual properties

Question 3

Ways that light interacts with objects and surfaces

Answer 3

Absorption as photons collide with particles of matter
Reflection as light strikes opaque surfaces
Transmission as light passes through transparent matter

Question 4

Human eye overview

Answer 4

Single-chambered- convex cornea projects image onto retina
Enables directional sensitivity- represents spatial structure rather than total of light
Photoreceptors trance light into an electric potential
Signals go through neurone to retinal ganglion cells then out via optic nerve

Question 5

Two types of photoereceptors

Answer 5

Rods and cones

Question 6

Rods

Answer 6

Located primarily in peripheral retina
operate in low light levels

Question 7

Cones

Answer 7

Concentrated in centre of retina
Require higher light levels
3 different photopigments sensitive to different wavelengths

Question 8

Main visual pathway (eye to brain)

Answer 8

Retina, optic nerve, optic chasm, LGN, Primary visual cortex

Question 9

Brightness perception- bottom-up

Answer 9

The retina doesn’t record light intensities
Responses shaped by process in the retina

Question 10

Brightness perception- top-down

Answer 10

Brain uses knowledge about how light interacts with objects
Can result in errors

Question 11

Brightness perception- light/dark adaptation

Answer 11

Perceived in the same way due to brightness constancy
sensitivity of the retina is constantly adjusted to compensate for changes in mean luminance
Sensitivity: reduced when the mean intensity is high and increased when it’s low

Question 12

Brightness perception- negative afterimages

Answer 12

Brought on by prolonged viewing of stimulus
Vital for function in different light conditions
Can produce illusions

Question 13

Brightness perception- lateral inhibition

Answer 13

makes visual system sensitive to changes in luminance
Early for of information processing in retina
Retinal ganglion cells receive excitatory and inhibitory input from photoreceptors
Arranged in centre- surrounded configuration

Question 14

Colour perception in low light

Answer 14

Only rod photoreceptors operate
Only contain single type of photopigment
Different wavelengths can elicit same response
Impossible to accurately signal different wavelengths

Question 15

Colour perception- trichromacy

Answer 15

Cone photoreceptors contain one of three different photopigments
Relative output of different cones allows unambiguous signalling of wavelength

Question 16

S-cones

Answer 16

Sensitive to short wavelengths
(blue cones)

Question 17

M-cones

Answer 17

Sensitive to middle wavelengths
(green cones)

Question 18

L-cones

Answer 18

Sensitive to long wavelengths
(red cones)

Question 19

Monochromacy

Answer 19

Individuals have 0 or 1 functioning cone type

Question 20

Dichromacy

Answer 20

Only 2 function cone types
Protanopia- missing L-cones
Deutreranopia- missing M-cones
Tritanopia- missing S-cones

Question 21

Anomalous trichromacy

Answer 21

Defect in one of the cone types
Most common form of colour perception deficiency
Protanomaly- L-cone defect
Deuteranololy- M-cone defect
Tritanomoly- S-cone defect

Question 22

Types of colour perception

Answer 22

Opponency- shaped by bottom-up processing
Negative afterimages- reduction in sensitivity of cone type, creates in imbalance in the inputs to opponent ganglion cells

Question 23

Herman grid illusion

Answer 23

Grey spots appear in white areas between black squares
Because retinal ganglion cells responding to this location are inhibited more than cells responding at other positions along the line