Vision and optical illusions

Question 1

What is bottom-up vs top-down in vision?

Answer 1

Bottom-up: raw sensory input from eyes to brain. Top-down: brain influences perception through prior knowledge, expectations, and focus. Vision relies heavily on top-down processing.

Question 2

What is the concept of “inverse optics” in vision?

Answer 2

It refers to the brain interpreting light reflected off objects, not the source. This reflection helps us perceive texture, shape, and lightness.

Question 3

What range of the electromagnetic spectrum can humans see?

Answer 3

~380–750 nm. Light outside this range (e.g., infrared, ultraviolet) is invisible to humans.

// 1nm

Question 4

What does the amount of light dictate vs the pattern of light

Answer 4

amount of light = brightness
pattern = shape and texture

Question 5

photon

Answer 5

particle of light - represents one wavelength of electromagnetic radiation

Question 6

fast vs slow vibration impact on wavelength

Answer 6

fast: shorter wavelength = greater energy
slow: longer wavelength, less energy

Question 7

4 ways light interacts with matter

Answer 7

absorption
- absorbed by the matter and converted to energy
reflection
- light bouncing off an obstacle
diffraction
- light bending around an obstacle
refraction
- change in direction of light when passing from one medium to another

Question 8

what 4 structures help focus the light onto the retina

Answer 8

lens (curved, bends light), corona (transparent covering over the eye), pupil (controls amount of light to enter), iris (coloured part of the eye)

Question 9

What things influence pupil dilation and constriction

Answer 9

Light levels, Automatic nervous system, drugs and age

constrict = bright light
dilate = low light

Question 10

lens accomodation

Answer 10

modify focal length of the eye by changing the curvature of the lens
- adjust to seeing near and far objects
- focusing

Question 11

cataracts

Answer 11

lens losing transparency due thickening of the lens
- happen with age, UV exposure

Question 12

hyperopia

Answer 12

far sightedness
- far objects seem clearer than near sighted objects

Question 13

retina

Answer 13

lines the back of the eye
- contains photoreceptors (rods and cones)

Question 14

order of light to brain

Answer 14

light, retina, photoreceptors, bipolar cells, retinal ganglion cells, out axons from optic nerve, some cross at optic chiasm and go to LGN of thalamus, remaining little bit follow optic nerve to optic tract to LGN. from here goes from v1,v 2,v3,v4,v5.

Question 15

% of visual info going to LGN and Superior Colliculus

Answer 15

80% LGN, 20% Superior colliculus

Question 16

Rods

Answer 16

• located in periphery
• peak absorption -500nm
• good for low light conditions (scotopic)
• low acuity

Question 17

cones

Answer 17

• located very central near the fovea
• absorption 440 (blue), 530 (green), 560nm (red)
• used in higher light bright conditions (phototopic vision)
• high acuity

Question 18

photopic vs scotopic

Answer 18

photopic: bright light relying on cones for colour perception
scotopic = low light relying on rods and black and white vision

Question 19

dark adaptation curve

Answer 19

the dark adaptation curve shows how the eyes sensitivity to light increases over time when transitioning from a bright to dark environment

two phases:
- cones dominate first portion of graph showing the decline of cone intensity to about 10mins, can only see some detail in dim light but not a lot
- rod adaptation take over the rod cone break, becomes very sensitive overtime allowing for vision in dim conditions this vision is low acuity (not sharp and no colour)

Question 20

number of rods vs cones

Answer 20

more rods (multiple synapse onto one bipolar cell)
- amplify the signal sent to BP cells
- 95 million rods
- low acuity peripheral vision

less cones:
one cone per ganglion cells
- 4.5million cones
- high acuity central vision

Question 21

fovea

Answer 21

tiny depression in centre of the macula (part of the retina
- responsible for high acuity detailed vision where light is focused when looking at something
- cones located around fovea

Question 22

Rods inhibitory

Answer 22

rods are inhibited by light
- stop releasing glutamate when

no light = rod is depolarised (excited), activated bipolar cell which activates ganglion cell

Question 23

cones excitatory and inhibitory

Answer 23

glutamte will open or close differing ion channels

when light hits cone it can either inhibit or active Off or On bipolar cells

On bipolar cells are HYPERpolarised by glutamate

Off bipolar cells are depolarised by glutamate

Question 24

On/off off/on centre surrounds

Answer 24

receptive field organisation of retinal ganglion cells and bipolar cells

improtant for how we detect contrast, edges and changes in light

Question 25

on centre off surround

Answer 25

excited when light hits centre, inhibited when light hits surround e.g a bright spot on dark background

Question 26

off centre and on surround

Answer 26

inhibited when light hits centre, excited when light hits surround e.g dark spot on bright background

Question 27

lateral inhibition

Answer 27

a fundamental principle in neuroscience where a neuron's firing can inhibit the firing of its neighboring neurons - used to detect contrast, process edges

Question 28

how far is the blind sport from the centre of vision?

Answer 28

13 degrees

Question 29

Visual field nasally and temporally

Answer 29

nasal = toward the nose 60 degrees from vertical meridian temporal = toward periphery 107 degrees from the vertical meridian

Question 30

convergence vs divergence

Answer 30

conv = reducing interocular angle - pointing inward nasally - look at close objects div = increasing interocular angle - toward periphery

Question 31

images mapped upside down...

Answer 31

because eyes lens bends light lens is convex, so when light passes through it refracts and flips the image upside down and left to right brain automatically flips right way

Question 32

binocular stereoscopic vision

Answer 32

both eyes - see something slightly differently - brain merges them together

Question 33

saccade

Answer 33

quick eye movement

Question 34

what happens w visual info at superior colliculus?

Answer 34

responsive to sudden shifts in light - allowing for saccades

Question 35

what do RGC respond to

Answer 35

pattenrs of light surrounded by dark aka contrast on likes white off likes black

Question 36

v1

Answer 36

primary visual cortex repsonds to edges lines and colours

Question 37

v2

Answer 37

involved in more complex features like shapes

Question 38

v3

Answer 38

role in processing spatial info

Question 39

v4

Answer 39

needed for object recognition

Question 40

v5

Answer 40

medial temporal lobe, crucial for perceiving and processing visual motion

Question 41

B/W dress example

Answer 41

if you think image taken in blue light - dress loks white and gold artificial light dress looks blue and black macular pigment optical density - varies in people higher MPOD = more blue light absorption into retina = white and gold dress