Vision 1 & 2

sensation

transformation of physical chars of the world —> elec signals in the NS

transduction

transmission of visual signals down the optic nerve

perception

becoming aware of smth thru the senses

y can perception be inaccurate

brain can misinterpret stim (illusions

2 visual illusions that demonstrate misinterpretation

1. muller-lyer

2. necker cube

3 properties of light

1. wavelength

2. amplitude

3. purity

what does wavelength deter

colour (visible spectrum)

what wavelengths correspond to red & violet light

red = 750nm = longer

violet = 360nm = shorter

what does amplitude effect

perceived brightness

what does purity effect

saturation (richness of colour)

how many cone types do humans have

3

why did colour vision evolve in primates

to distinguish food

enhance contrast btwn objects & bg

colour blindness

partial or complete loss of func of 1(+) cone types

monochromacy

black & white vision

protanopia

loss/dysfunction of long wavelength(red) cones

deuteranopia

loss/dysfunction of medium-wavelength(green) cones

tritanopia

loss/dysfunction of short-wavelength(blue) cones

trichromat

normal-sighted person w all 3 cones types

dichromat

person w only 2 functioning cone types

cornea

begins focusing light

~80% of focusing

sclera

tough white outer covering of eye

iris

muscle band controls pupil size

when do pupils dilate (larger opening)

low light i.e. not enough light reaches retina

when do pupils constrict (tiny opening)

bright light i.e. too much light reaches retina

lens

final focusing of light onto retina

~20% of focusing

curvature flips & reverses image

accommodation

lens shape change to focus objects at diff distances

how does lens change to focus objects at near/close distances

gets rounder to produce clear image

how does lens change to focus objects at far distances

gets elongated to focus image on back of eye

hyperopia/farsightedness

see things far, objects close blurry

shorter eye length

less curved lens

imaged focused behind retina

myopia/nearsightedness

see thing close, object far blurry

longer eye length

more curved lens

image focused in front of retina

vitreous humour

clear jelly filling main chamber of eye

diagram eye

retina

neural paper thin tissue that lines back of the eye

y is the retina ‘inside-out’

photoreceptors receive nutrients from the retinal pigment epithelium (RPE)

what are the 3 layers of the retina

1. photoreceptor

2. bipolar cells

3. ganglion cells

retina: photoreceptor layer

cells that translate physical stimulus of light —> neural signal that’s relayed to the brain

retina: photoreceptor layer: rods

night vision

low light

no colour

poor visual acuity

concentrated in periphery

retina: photoreceptor layer: rods: what pigment do they contain

rhodosphin

make highly sensitive to light

retina: photoreceptor layer: cones

day vision

colour

good visual acuity

concentrated in fovea

retina: photoreceptor layer: cones: what pigment do they contain

iodopsin

makes less sensitive to light

retina: bipolar cells

relay signals from photoreceptors to ganglion cells

retina: bipolar cells: horizontal & amacrine cells

combine & process info w/in retina

retina: ganglion cells

send visual signals to the brain via the optic nerve

retina: ganglion cells: what causes the blind spot

optic disc has no photoreceptors

receptive field

area of retina where stimulation affects a ganglion cell’s firing

receptive field: centre-surround organization

center stimulation = incs firing rate

surround stimulation = no change firing rate

y is visual acuity highest in the fovea

1 cone often connects to 1 ganglion cell

y is peripheral vision less precise

many photoreceptors converge onto 1 ganglion cell

what happens in the 1st few mins of darkness

cones rapidly inc sensitivity

rod-cone break

after 5-10min in darkness, rods become more sensitive than cones

which hemisphere processes the left visual field

right hemisphere

optic chiasm

where optic nerve axons cross

lateral geniculate nucleus (LGN)

end of optic tract

axons synapse here

in thalamus: relay to cortex

P-cells

small retinal ganglion cells

detailed info of colour, pattern, form, texture, depth

layers 3-6 of LGN receive input

M-cells

large retinal ganglion cells

convey info abt movement

layers 1-2 of LGN receive input

primary visual/straite cortex diagram (V1)

3 cells of V1

1. simple cells

2. complex cells

3. hypercomplex cells

3 cells of V1: simple cells

sensitive to orientation of bars of light

3 cells of V1: complex cells

sensitive to orientation of bars of light & direction of its movement

3 cells of V1: hyper complex cells

sensitive to orientation of bars of light, direction of its movement, & length of it

ocular dominance columns

neurons that respond preferentially to input from either L or R eye

orientation columns

neurons that respond preferentially to stimuli of specific angles

extrastraite cortex

V2-5 & IT

colour

motion

object recognition

dorsal stream

‘where’ pathway - where objects are

depth & motion

extrastriate cortex —> parietal lobe

V2, V4, IT

ventral stream

‘what’ pathway - what object is

colour & form

extrastriate cortex —> temporal lobe

V3, V5

monocular depth cues

only need to captured by 1 eye

monocular depth cues: 2 motion based

1. motion parallax

2. optic flow

monocular depth cues: 2 motion based: motion parallax

based on relative speeds of near & far objects while in motion

monocular depth cues: 2 motion based: optic flow

perceived motion of visual field that results from ones own movement thru the enviro

monocular depth cue: 4 pictorial based

1. interposition

2. linear perspective

3. aerial perspective

4. shading

monocular depth cue: 4 pictorial based: interposition

1 object overlaps & tf occludes another object

monocular depth cue: 4 pictorial based: linear perspective

parallel lines observer appear to converge on a single vanishing pt on the horizon

monocular depth cue: 4 pictorial based: aerial perspective

visual effect of light when passing thru the atmosphere that causes distant objects to appear hazy/blurry

monocular depth cue: 4 pictorial based: shading

helps us infer direction of light

binocular depth cue

need to be captured by both eyes

binocular depth cue: stereopsis

perception of depth via binocular disparity

binocular depth cue: convergence

as object moves closer to face the gazes of our eyes converge

adjustable lens

humans

allows accommodation

cumulative selection

evolutionary process where new adaptations are layered onto older adaptations

factors affects eye architecture across species

light avail

food position (above or below)

movement, shape, colour of prey

simple eyes

vertebrates

single lens

compound eyes

arthropods

made of many ommatidia: tiny light-capturing ind arrangements of tubule units

good 4 detecting movement at close dis

2 funcs of eye

1. resolution (acuity/discern fine detail)

2. sensitivity (ability to detect light, faint or vivid)

effect of eye size on vision

larger = better resolution & sensitivity = useful for hunting & foraging

small = species that spend time underground

trade-off btwn acuity & night vision

can’t max both due to high metabolic cost

round lens adv

good close-up focus

circular pupil adv

better for night vision

slit-shaped pupil adv’s

enhances visual acuity

reduces chromatic aberration: tendency for wavelength light to enter at periphery = blur retinal image

horizontal pupil adv’s

grazing animals

enhances panoramic vision

laterally-directed eyes

wide total field view

2 sep visual fields

poor depth perception

prey animals

front-facing eyes

narrow total field of view

single overlapping field

excellent depth perception

predatory animals

preferential looking paradigm

method used to deter infant visual acuity

visual acuity at birth

least developed sensory sys at birth

when does visual development begin

prenatally

2nd prenatal month

eyes r formed

6th prenatal month

fetus reacts to light

retinal cells fire randomly

visual development relies on

heavy visual input from enviro

newborn visual limitations

weak lens muscle

inconsistent pupil rxns

vision @ 3 mons

almost adult-like focusing

retinal ganglion cell development

conts until early childhood