PS222 Perception F25 Exam 1

cornea

2/3 of the optical power of the eye

• bends incoming light to focus on the retina (50%)

• astigmatism: not uniformly shaped (cornea)

• clear part front

lens

accommodation, changes thickness to focus on objects (fatter the lens, the more light bends)

• thick for nearby objects

• flattening for distant ones

aqueous humor

cleans the eye and maintains pressure in the eye

pupil

changes sie to let light in (depends on cones and rods)

iris

control size of pupil like muscle

vitreous humor 

maintains shape, removes waste products, protects retina, facilitates light transmission 

why are parts of the eye adaptive for human vision?

allows us to perceive light

• nocturnal more roads

• medium wavelength (visible light)

nocturnal animals have thinner epithelial

3 factors determines focus of an image on the retina

1. optical power of cornea

2. optical power of the lens

3. size & shape of eyeball

presbyopia

unable occomodate nearby objects

• slower to accomodate

• reading glasses

myopic

• near sighted

• cross inside eye

• eye longer, flatter

• helps: decreases optical power

hyperopic

• far sighted

• cross outside eye

• eye taller

• helps: increases optical power

light onto retina

upside down, left-right reversed 

accomodation

ciliary muscles → iris → zonules of zinn

• look far: ciliary muscle relaxed, zonules tight, lens thin

• look close: ciliary muscles contract, zonules slack, lens fat

how does size and shape affect focus? 

focal length/how far the retina is depends on the eye shape 

1. good focus

2. myopic

3. hyperopic 

purpose of ganglion cells

organize infromation from the photo receptor cells

• take electrode in, record how it responds to stimulation in receptive field 

center-surround organization of RGC (receptive ganglion cell)

increase or decrease of activity depends on the inner and outer signs

plus: increase in activity 

minus: decrease in activity 

location on retina matters?

light recevied by photoceptors → translated into neurosignals

light/dark boundaries to identify objects

photoreceptor

• disc: photopigments

• embedded in choroid

• direction of light: synapse → choroid

isomerize

interaction with light causes molecule to change shape → unstable molecule bc changed flow of electrical current in photoreceptor 

degree of reduction indicates level of light

• iso. disrupts/slows down flow. more light → more reduction → lack of glutamate

longer in the dark →

threshhold decreases for visible light

rods

• 5 photons

• peak after 20 min (sensitive)

• more sensitive to super dim light

cones

• several hundred photons to activate (30 min)

• more condensed

diff wavelengths:

1. short - blue

2. medium - green/cyan/yellow

3. long - red

optic disc

• hole 

• no photo receptors 

• blind spot of the eye

• blood vessels enter the eye

macula & fovea

fovea is inside the macula

• 5 mill cones concentrated

REST OF THE RETINA RODS.

periphery

outside fovea

absorbance/reflectance properties

absorb more → lighter

helps us see boundaries/differentiate between light & dark

more light → bigger reaction (proportional)

lateral

• side

• binocular

• prey

frontal 

• front

• monocular

• spatial detail

• predator

rectus eye mucles

• lateral (outside) + medial (middle)

• inferior (bottom) + superior (top)

oblique eye muscles

• superior and oblique

• rotating eye

conjunctive

same direction

disjunctive

diff movements

retina 

transduce light into neurosignals → photoreceptors 

gamma

• reflected off the atmosphere

• highest energy

• shortest length

radio

• around objects

• lowest energy

• long wavelength

light

• fast/parallel prevents displacement

• medium energy/wavelength

threshhold

when stimuliln reaches awareness

absolute thr.

how strong stim has to be to detect that stimulus 

diff threshhold

how much change in a multi intensity for us to tell its diff

psychophysics

measure experience of stimuli 

smaller receptive fields

high resolution (lots of fine detail)

lower sensitivity (less likely to respond to weak stimulus)

larger receptive fields

low res

high sensitivity

physical stimulus energy

1. light

2. virbation

3. chemicals

4. pressure/heat

receptor cells….

detect and transduce (turn into neurosignals)