Perception is dependent on what?

detection of electromagnetic spectrum

Visible spectrum for humans ranges from 400-700 nanometers (blue on 400 side (short side), red on 700 side (long side)

What is the process of perception relative to the eye? What happens if  light is unfocussed?

Light enters the eye through the pupil and is focused by the cornea and lens to a sharp image on the retina

Rods and cones are visual receptors in the retina that contain visual pigment that responds to light

The optic nerve carries information from retina to the brain

The cornea (which is fixed) accounts for about 80% of focusing

The lens automatically adjusts shape for object distance to maintain focus and accounts for the other 20% of focusing

Light must be focused or objects will be blurry

What is accommodation and why does it occur?

Automatic adjustment of the lens to maintain focus

Accommodation results when ciliary muscles are tightened which causes the lens to thicken

ability of accommodation is lost with age.

Occurs when the lens can no longer adjust for close objects loses flexibility

Lens begins to harden and ciliary muscles weaken

What is an effect of loss of accommodation, and what is a solution?

presbyopia “old` eye” the increasing of near point along with age

Near point is the closest distance to you at which the image can be sharpened on the back of the eye

Corrective lenses needed for close sight activities such as reading

What two defects are associated with bad vision?

Myopia and hyperopia

Myopia or nearsightedness is the inability to see distance objects clearly

Image is focused in front of retina

Caused by refractive myopia or axial myopia

In refractive myopia the cornea or lens bends too much light

In axial myopia the eyeball is too long

Solutions for myopia

Move stimulus until it lies within the far point

LASIK surgery

Distance when light becomes focused is called the far point

Hyperopia or farsightedness is the inability to see nearby objects clearly

Focus is behind the retina

Usually caused by an eyeball that is too short

Constant accommodation for nearby objects can lead to eyestrain and headaches

corrected with lenses

what is isomerization and how does it fit into transduction?

isomerization is when the  Retinal changes shape a due to light absorption

transduction occurs when the retinal absorbs one photon of light

Receptors have outer segments which contain visual pigment molecules that have two components

Opsin and Retinal

How are rods and cones distributed in the eye and how does this effect vision (blind spots)?

Rods are large and cylindrical approximately  120 million rods

Cones are small and tapered approximately 6 million cones

Fovea consists solely of cones

Peripheral retina has both rods and cones (majority rods)

Blind spot is located at edge of visual field and the brain “fills in” the blind spot

blind spot exists where the optic nerve leaves the eye We don’t see the blind spot as one eye covers the blind spot of the other

name the 2 diseases that effect  vision

Macular degeneration and Retinitis pigmentosa

Macular degeneration

affects cones only

Creates a blind spot on the retina

Most common in older people

Retinitis pigmentosa

Genetic disease

Rods are destroyed first, destroying peripheral vision

Severe cases result in complete blindness

What is an effect of isomerization and what methods does it emoloy?

dark adaptation is caused by isomerization

Dark adaptation occurs following extended exposure to the dark

Three different types of experiments have been used: cone adaptation experiment,  rod adaptation experiment and cone and rod adaptation experiment

To assess both rods and cones

[image]Observer looks at a fixation point but pays attention to a test light to the side

Results show a dark adaptation curve (rapid drop, slight curve/leveling followed by rapid fall again)

rod-cone break is the point in the adaptation curve where there is a gradual improvement in sensitivity (the leveling of the curve)

Dark adapted sensitivity is about 100,000 times greater than light adapted sensitivity

Experiment for cone adaptation

Place light at fovea so test light only stimulates cones

Results show that sensitivity increases for three to four minutes then levels off

Experiment for rod adaptation

Must use a rod monochromatic (people born without cones)

Results show that sensitivity increases for about 25 minutes and then levels off

Define spectral sensitivity

Spectral Sensitivity is the sensitivity of rods and cones to different parts of the visual spectrum

monochromatic light used  to determine threshold at different wavelengths

Thresholds for light is lowest in the middle of the spectrum

How is rod and cone sensitivity determined?

To determine separate sensitivity of rod and cones to light wavelengths similar methods to dark adapation are used

For cone sensitivity stimuli is presented solely to the fovea Most sensitive at 560 nm

For rod sensitivity the observers dark adapt for 30 minutes an wavelength sensitivity is then tested (as only rods would be utilized at this point)more sensitive to short-wavelength light at 500nm

What is the absorption length for rods and cones?

rod pigments absorbs best at 500nm

cone pigments absorb best at 419nm (short) 531nm  (medium) and 558nm (long)

what has occurred when things blue in color are more visible than things that are red in color?

Purkinje shift-enhanced

sensitivity to short wavelengths during dark adaptation when the shift from cone to rod vision occurs

due to cones being more sensitive to longer wavelengths than rods

what is the structure and function of neurons?

three key components of neurons

cell body

dendrites

axons or nerve fiber

function is transmission of electrical signals

Describe how neurons transmit data

through action potential and synapses

action potentials

have a  propagated response (travels without decreasing in size) and a refractory period of 1ms and firing rate up to 800 impulses per second

spontaneous activity can occur without stimulation which permits inhibitory effect

the resting the  potential negative charge of the neuron relative to its surrounding

the action potential is the peak from the jump of an electrical impulse

Synapses is the small space between neurons and the jump of information between neurons is achieved using neuro transmitters

Neurotransmitters are                                   

Released by the pre-synaptic neuron from the vesicles

Received by the  postsynaptic neuron on the receptor sites

Specific receptor sites have a “key/lock” match

How many types of Neurotransmitters are there? what are they?

two types of transmitters: Excitatory and inhibitory transmitters

Excitatory transmitters cause depolarization in post-synaptic neuron

Neuron becomes more positive

Increases the likelihood of an action potential

Inhibitory transmitters cause a hyper-polarization

Neuron becomes more negative

Decreases the likelihood of an action potential

What is the structure of the retinal and how does it proccess light?

Retinal composition consists of (in ascending order)

Ganglion cells               

Amacaine cells

Bipolar cells

Horizontal Cells

Rod and cone receptors

Light rays must pass through all receptors and is then sent back along the same

done this way to reduce light scatter and image degradation

Rods and cones send signals vertically through

Bipolar cells

Ganglion cells and axons

Signals are sent hotizontally

Between receptors by horizontal cells

Between bipolar and ganglion cells by amacrine cells

Explain convergence

126 million rodes and cones converge to one million ganglion cells

Higher convergence of rods then cones

Average 120 rods to one ganglion

Six cones to one ganglion

Cones in the fovea have a one to one relation to ganglion cell

Rods have greater convergence increasing likelihood of response

Rods cannot distinguish details very well

foveal vision results in high visual acuity

One to one wiring leads to ability to discriminate small details

More convergence = better sensitivity to light but a loss of resolution/discrimination

What is a sinusoid?

Sinusoid is the shape of electromagnetic light waves

The distance between the peaks of sinusoids is what we call wavelength