PSYCH 1XX3 - Vision

longer wavelengths are...?

red (750nm)

shorter wavelengths are...?

violet (360nm)

what is the visible spectrum?

light we can see (10^3nm or 10^-6m)

what animal can see smaller wavelengths than us?

bees, differentiate different colours of flowers that we can't

what animal can see longer wavelengths than us?

snakes, allows them to see body heat given off their prey

what animals can't see in colour?

mammals other than primates

how many types of cones do primates have?

3

what do wavelengths/frequency pertain to?

colour or hue

what does amplitude pertain to?

brightness

what does purity pertain to?

saturation

cornea

transparent window at the front of the eye, 80% of the eye's focusing power

sclera

white part of the eye, tough membrane, connected to the cornea

pupil

where information passes from the cornea to

iris

coloured part of the eye, band of muscles controlled by the brain that controls the size of the pupil

when does the pupil dialate?

if there isn't enough light

when does the pupil constrict?

when there is too much light

lens

curved and flexible structure of the eye, 20% of the eye's focusing power

why does the image appear reversed and backwards after passing through the lens?

the lens is curved

accomodation

the process by which the lens is adjusted by contracting or relaxing the muscles around the lens

retina

back of the eye, final place light is passed

vitreous humour

clear jelly like substance that is the main chamber of the eyeball, light passed from the lens through here to the retina

what is a rounder lens good for?

close focus

what is an elongated lens good for?

far focus

how is the retina arranged?

three layers of neurons in an inside-out fashion

light photoreceptor cells

layer one of retina

two types of cells (rods and cones)

why are the layers of the retina organized inside-out?

photoreceptor cells get nutrients from back of the retina from retinal pigment epithelium (RPE)

how many rods and cones are there in human eyes?

125 million rods and 6 million cones

cones

good for high light intensity

day vision

colour vision

good visual acuity

concentrated towards the fovea

fovea

tiny spot in the middle of retina where most cones are concentrated (why we line something up in the middle of our eyes to see it in detail)

rods

good for low light intensity

night vision

no colour

poor visual acuity

increasing concentration in region peripheral to fovea

ganglion cells

third layer of the retina

receives input from rods and cones and relays information to the brain

horizontal, amacrine and bipolar cells

second layer of the retina

information passes from rods and cones to bipolar cells, then moves to ganglion cells

optic disc

our blind spot, an exit for axons where there are no photoreceptors

how does each hemisphere receive information from both eyes?

the axons from the inner nasal region of the retina cross over

optic chiasm

point where inner optic nerve crosses over to the other side

where do most axons synapse

lateral geniculate nucleus (LGN)

area V1

primary visual cortex

extrastriate cortex

everything outside frontal visual cortex

dorsal stream

"where pathway"

depth and motion

information goes to parietal lobe

ventral stream

"what pathway"

colour and form of object

information goes to temporal lobe

what creatures were the first to have light sensitive pathways

algae

light sensitive patches

how eyes could have started

similar to what leaches have

light sensitive patches with a curve

second step in possible eye evolution

allows direction of light to be sensed

aperture developed (pinhole)

third step in possible eye evolution

pinhole to help focus light

crude lens

fourth step in eye evolution

increased focus (with lens, cornea and spherical shape)

solid and can't change shape much

seen in fish and scallops

adjustable lens

fifth step in eye evolution

allows accommodation

seen in vertebrae's like humans

what factors affect eye variance across species?

do they live in an area with light or not?

does the food come from above or below?

movement, shape and colour of their prey

what are the two categories of eye?

simple eyes

compound eyes

simple eyes

vertebraes and mollusks (octopus and squid)

eyeball, lens and retina (including crude and adjustable lens)

environment factors play a role in where feature are located

compound eyes

anthropods (insects and crabs)

arrangement of individual tubular units (ommatidium) - each in a different direction to gather light directly in front, light gathered forms a single image

good for detecting movement at close distances

two functions of eye

resolution and sensitivity

larger eyes have...?

better resolution and sensitivity

larger pupil size is good for...?

sensitivity

more rods is better for...?

sensitivity

species like humans and hawks have good _____ but bad ______

acuity, low light vision

species like cats, horses and owls have good ______ but bad ______

low light vision, acuity

deep sea creatures have good ______

acuity and low light vision

eye placement at either side of the head

laterally directed

large total view but bad depth perception

prey animals

eye placement in front of head

direct view

better depth perception for less total view

predator animals

when do eyes form?

2 months after conception

6 months after conception

eyes can react to light

random firing of retinal cells determines what cells are connected, creates neural pathways

why are eyes the least developed at birth?

visual system requires stimulus

newborns have...?

weak lens muscles

inconsistent pupil reactions

low cell density in retina - retina cells are immature, especially in fovea

at 3 months babies have...?

almost adult-like focusing

at 11 years old...?

visual brain development completes

at 20 feet newborns can see...?

what adults see at 600 feet

at 20 feet 6 month olds can see...?

what adults see at 100 feet

Müller-Lyer illusion

where two identical lines are made to look like they are different lengths by the placement of the arrows

Necker cube

a line drawing of a transparent cube that has an ambiguous perception in regards to its 3D shape

sensation

transformation of the physical characteristics of our world into electrical signals in our nervous system

transduction

transmission of electrical signals down the optic nerve

perception

ability to become aware of something through our senses

how many primary colours do pigeons have?

5

they're able to perceive infrared light

what estimated amount of the cortex is involved in visual processing?

50%

hyperopia

farsightedness, intact ability to see things far away but objects up close appear blurry

myopia

nearsightedness, intact ability to see things up close away but objects far away appear blurry

what eye length do nearsighted people tend to have?

slightly longer eye length

what eye length do farsighted people tend to have?

slightly shorter eye length

less curved lenses

rhodopsin

light-sensitive pigment found in the retina

iodopsin

iodopsin photopigments are less sensitive to light and thus are found in cones which are better for day vision

convergence

refers to some number of neurons receiving input and relaying the signal onto fewer neurons

on average, how many rods converge on one ganglion cell?

120

on average, how many cones converge on one ganglion cell?

5

dark adaptation

cones adapt quickly to the dark by lowering their threshold for activation

rods then catch up and account for a majority of activation, becoming more important than cones

receptive field

area where a stimulus elicits a response

nasal field

area of the retina closest to the nose

temporal field

area of the retina closest to the temples

localize

identify the direction and distance of a sound source

lateral geniculate nucleus

located at the end of the optic tract for both sides of the brain; acts as the primary relay station for visual information

how many layers does the LGN have?

6

what are the two types of retinal ganglion cells?

M-cells (magnocellular cells) for layers 1 and 2 of the LGN

P-cells (parvocellular cells) for layers 3,4,5,6 of the LGN

how many layers of cells does V1 have?

6

line of Gennari

stripe in the cortex, why V1 is also called the striate cortex

simple cells

cells located in the visual cortex that are sensitive to the orientation of bars of light

complex cells

cells located in the visual cortex that are sensitive to the orientation of bars of light as well as the direction of movement

hypercomplex cells

cells located in the visual cortex that are sensitive to the orientation of bars of light as well as the direction of movement and the length of a bar of light

ocular dominance columns

columns of neurons in the visual cortex that respond preferentially to input from either the right or left eye

orientation columns

columns of neurons in the visual cortex that respond preferentially to stimuli of specific angles

what areas does the primary extrastriate cortex include?

V2, V3, V4, V5 (also known as MT) and IT

areas V2, V4 and IT are regarded as the ______ pathway

"what"