sensation and perception exam 1 review

why is the eye so important

larry hester lost his vision from a rare genetic disorder, lead to poor night vision, loss of peripheral vision, and loss of central vision (completely blind). his experience shows the importance of the eye and the retina

what is light

spectrum of electromagnetic energy that ranges from short wavelength gamma rays to long wavelength radiowaves

what is a wavelength

the distance between peaks in the electromagnetic wave

what is the most perceived light

reflected light

what is the visible spectrum for humans

400-700 nanometers

what are the basic components of the eye

pupil, cornea, lens, retina, photoreceptors

what is the pupil

the hole in the center of the eye, an opening where light reflected from objects enters the eye

what is the cornea

transparent focusing “element”, the first structure that light passes through as it enters the eye

what is the lens

transparent focusing “element” where light enters AFTER passing through the cornea

what is the retina

network of cells that covers the back of the eye

what are photoreceptors, and what are the types

receptors of vision, rods and cones

can the lens change shape, and why

yes, it changes shape to focus (accomodation)

what are rods

cylinder shaped photoreceptors that are responsible for dim light (ex: night vision)

what are cones

cone shaped photoreceptors responsible for high illumination vision (daytime), colors, and detailed vision

what is in the inner segment of rods and cones

cell body/soma

what is in the outer segment of rods and cones

contain visual pigments, which are light sensitive chemicals that react to light and trigger electric signals

what is the circuitry of the retina

rods and cones, bipolar cells, and retinal ganglion cells

what are bipolar cells

connections between photoreceptors and retinal ganglion cells

what are retinal ganglion cells

they gather info from multiple bipolar cells and output them to the brain via the optic nerve (optic nerve is RGC axons)

what is the fovea and foveal vision

fovea is a small area of the eye with only cones, foveal vision is for very detailed and colored vision

what is the peripheral retina/vision

peripheral retina is the area outside the fovea and contains both rods and cones. there are more rods than cones, so peripheral vision is for less detailed vision that lacks color

what is the basic function of vision

acuity, the smallest amount of detail you’re able to perceive and tell apart

what happens if the fovea and surrounding areas degenerate

macular degeneration, most common blindness in old people, creates blind region in central vision

what happens if the peripheral retina degenerates

retinitis pigmentosa, degeneration of rod receptors in periphery, cause poor peripheral vision. foveal cones are attacked too, which can result in complete blindness

what is the one area in the retina with no photoreceptors

the optic nerve (RGC axons), this results in a blind spot

how is light focused onto the retina

a two element system, the cornea and the lens

how much does the cornea impact the eye focusing

accounts for 80% of the eye’s focusing power

how much does the lens account for the eyes focusing power

20%, changes shape depending on distance of object using ciliary muscles

what is accomodation

changing of the lens shape to bring objects at different distances into focus

what are refractive errors

errors that happen from the inability of the cornea or lens to properly focus

what is presbyopia

“old eye” age related changes, can’t accommodate for near objects, from lens hardening (weakening of ciliary muscles)

what is myopia

nearsightedness, can’t see distance objects. could be from refractive myopia (cornea/lens bends light too much) or axial myopia (eyeballs too long)

what is hyperopia

farsightedness, can’t see close objects, usually due to short eyeballs

what are the two parts that the light sensitive visual pigments in rods and cones contain

opsin: a long protein, retinal: light sensitive molecule

what happens when visual pigment asborbs light

it isomerizes/changes shape

what happens when visual pigment isomerizes

it creates a chain reaction within the photoreceptor, causing it to go from depolarized (resting state in the dark) to hyperpolarized (from closure of ion channels) called phototransduction

what is the basic function of a sensory system

adaptation, to accommodate for changes luminance levels

what is sensory adaptation

resetting of sensitivity according to the surrounding conditions, this is a dual system of rods and cones that adjusts to RGC outputs depending on levels of surrounding luminance (ex: pirate eyepatches)

what is scotopic vision

vision under dark (night) conditions, not very good color vision, poor acuity, rods are active but cones are not

what is mesopic vision

vision under low light conditions (dawn/dusk), both rods and cones are active

what is photopic vision

vision under high light conditions (daytime) ,good color and acuity, cones are active, rods are not

what does the dark adaptation curve show

when a participant becomes more sensitive to light

what is the difference between light and dark adapted sensitivity

light adapted is your eye adapting to light so it doesn’t blind you while dark adapted is your eye becoming more sensitive to light after spending time in a dim room

how long does it take the rods and cones to reach maximum light sensitivity

cones take 4-6 minutes while rods take 20-30 minutes

how do we measure rod adaptation without cones

using rod monochromats, people who were born with no cones at all, and using rod cone break: the place where rods begin to determine the dark adaptation curve

what are the two parts of visual pigments

opsin, a long protein; and retinal; a chemical that reacts to light to start transduction

what happens when light hits the photoreceptors

visual pigments absorb the light. this causes retinal to straighten out (isomerization), and isomerization creates a chain reaction int he photoreceptor

why does visual pigment regeneration happen

because bleached pigments cannot respond to light

how to visual pigments become bleached

eventually, retinal detaches from opsin, causing the opsin to become lighter (bleaching)

how does visual pigment regeneration work

retinal needs to return to opsin to become functional again

what is the difference in bleached and intact pigments in light and dark

in light, eye has some bleached pigments and some intact pigments, but in the dark, bleached pigments regenerate but don’t isomerize so only intact pigments are present

how long does it take cones and rods pigments to regenerate

cone pigments take 6 minutes while rod pigments take 30 minutes

what is spectral sensitivity

how sensitive our visual receptors are to different parts of the visible spectrum

how is spectral sensitivity measured

by determining the spectral sensitivity curve

how do you measure spectral sensitivity

present light at a single wavelength (monochromatic light) and measure a person’s threshold for viewing different monochromatic light

what is threshold curve for spectral sensitivity

how much light is needed to see the wavelength

what do lower thresholds mean

lower threshold means higher sensitivity

what is the cone spectral sensitivity curve

cones are more sensitive to medium and long wavelength light (most sensitive at 560nm), typically done by presenting light to the fovea

what is the rod spectral sensitivity curve

rods are more sensitive to short-wavelength light (most sensitive at 500nm), typically done in the dark with light presented in the periphery

what is the purkinje shift

The way our eyes switch from seeing bright colors to seeing better in the dark by focusing on more blue-green shades

what is an absorption spectra

a chart that shows which colors of light the rods and cones can absorb the best

why are rods and cones sensitive to different colors

because their pigments absorb different wavelengths of light, this is how we see colors and details in various conditions

what do we notice about the absorption spectra and spectral sensitivity curve when it comes to the rods

rod pigment absorption spectra matches the rod spectral sensitivity curve

what do we notice about the absorption spectra and spectral sensitivity curve when it comes to the rods

the average three cone pigment absorption spectra almost matches the cone spectral sensitivity curve, more M and L cones than S cones

what are horizontal cells

transmit info laterally across the retina, synapse with receptors and bipolar cells

what are amacrine cels

transmit information laterally in the retina, synapse with bipolar cells and RGC

what happens when RGCs recieve info from the different kinds of cells

neural convergence, when many neurons/cells synapse into a single cell

why do rods have stronger neural convergence than cones

rods need less light to generate a response compared to cones, so you don’t need as strong stimulation to activate the RGCs

why is there such high acuity in cones in the context of convergence

there is a lack of neural convergence with cones. rods always stimulate the same RGC no matter if lights hit different nearby rods or spaces between them, cones always stimulate a unique RGC, so since cones don’t mix their signals, they help you see things more clearly

what did H. Keffer Hartline discover and how

RGB receptive fields, he isolated a single RGB axon in the opened eyecup of a frog and found that the axon fired if only a small area of the retina was illuminated

what is the receptive field

the area on the retina that influences the firing rate of the neuron

what did stephen kuffler discover

RGC’s have center-surround receptive fields

how does the RGC receptive field work

stimulation in center is either excitatory or inhibitory, stimulation on the edges causes the cell to react in the opposite way, this happens because of lateral inhibition and it helps the cell to focus better and see details more clearly

what is lateral inhibition

when amacrine and horizontal cells in the retina send signals to reduce the activity of nearby nerve cells

how do center-surround receptive fields help us identify certain details

they make it easier for us to see edges

what is the chevreul illusion

helps edges appear sharper

how is visual acuity at birth

poor, acuity develops fast over the first 6 months, and then slowly until year 1

WHY do infants have such poor acuity at birth

widely spaced and poorly developed cones, poorly developed visual cortex