Sensation

eyelid - cornea/schlera-aqueous humor-iris-pupil-lens-vitreous humore-retina-fovea-choroid

• Necessary to focus light
• Function of the lens

process of using muscles to change the shape of the lens so that objects come into focus

thin

fat

• Emmetropia
• Presbyobia
• Hyperopia
• Myopia
• Astigmatism

• No refractive error
• Can see right on point
• Refracts light perfectly

• (old eyes)
• the lens harden
• near point increases, ass you age, that point get further and further away
• Doesnt get to one precise point in th eretina

• farsightedness
• Problems seeing neer objects clearly
• Focus light on retina by using a convex lens

• nearsightedness
• problems seeing distant objects
• focus light on retina by using a concave lens
• (could be because lens is too long; retina is normal)

• we watch things too closely
• raising child with nightlight when sleeping

if the cornea isnt spherical, then light isnt refracted properly

Fondus

the black dot test. Blind spot

not usually in both eyes. Photo receptors just dies for some reason

• Contains several layers of cells
• Photyoreceptors change light energy into a neural energy (tansduction)

• Rods
• Cones

Everywhere else outside the fovea

in fovea

motion

• color; because you only have cones in the fovea. Everything in your peripheral is black and white
• (if you see color in your peripheral then it is your brain tricking you)

photoreceptors speak directly to the bipolar cell. No information gets lost

• A whole bunch of rods share a bipolar cell.
• Perception is that there is one black dot out there - lose some information
• Lost information(lack of detail

Ability to see small detail

• Ability to see very dim things
• Example: going to the bathroom in the middle of the night

• there is very little convergence; there is very little spatial summation (averaging)
• Detail is preserved=the less everaging, the more detail you will have

• Cones cant detect low levels of light
• But you do have detail (looking at stars)

• lots of convergence, therefore there is alot of spatial summation (all kinds of information is lost)
• Detail is not preserved

Rods can detect/see dim light

• P cells
• M cells

• part of the parvocellular pathway (cones)
• small receptor field

• part of the magnocellular pathway (rods)
• large receptor field

the egzagerated darker line when looking at shadows is the mach band

• a process that enhances our ability to detect borders.
• Increases contrast; results in a sharpening od vision (happens in horizontal cells)

mach bands

inhibit a neighboring cell

intensity of the stimulus (assume 10%)

See gray spots at intersection because there is more inhibition there

see different things

the region in which stimuli will activate a neuron

the further you go from the fovea, the receptor field gets bigger and bigger

smaller in finger - the smaller the field the more detail.

• Surrounds receptive field in ganglion cells
• 3rd layer of processing(ganglion cells)

• arousal
• alcohol/drugs
• lying

• uses cones (fovea)
• works best in daylight
• high acuity, poor sensitivity

• uses rods (peripheral vision)
• Works best in nighttime, levels of lumination
• Poor acuity, high sensitivity

Process of adjusting to more dimly lit rooms

• Coming out of movie theater in afternoon
• Waking up to bright light
• takes 20 minutes for eyes to adapt fully to the dark

• Cones start to fade out
• Visual field becomes less and less clear
• Comes with age and fatness

Example: looking at someones face, blurry

• Lose retina, half of the visual field is gone
• Can see some in the middle, black frame around it (keeps moving in-tunnel vision)

People born deaf, and then they lose their vision in middle ages. Genetic

Difference between dark and light bars

Shows how our sensitivity changes due to high/low contrast objects

cant see

very low and very high spatial frequencies

less contrast

• medium size objects-faces
• larger objects are harder to see, will see person before car

• The psychologists electrode
• Our visual system contains neurons selective for spatial frequency

What we can see. Determines the smallest thing that we can see

maximum excitation + maximum inhibition

Produces a small response

• Minimum excitation + minimum inhibition
• Produces small response

Maximum excitation + moderate inhibition

Produces strongest response

• Unthoff's symptom
• Night blindness
• Glare sensitivity
• Side effect of Lasik surgery

• Excercise or emotional strain impairs vision for several minutes
• Retain acuity, but world appears washed out
• Sensitivity to contrast decreases

Causes: cataracts, retinitus pigmentosa, vit A deficiency, drugs...

associated with degenerative retinal disease

• A change in sensitivity to contrast
• Things inside are darkened, not enough light/but sunlight is way too bright.

• tests from contrast sensitivity problems
• letters fade out gradually

Foced choice preferential -looking paradigm (babies under 6m can tell difference in limas) lose this skill as the age

high spatial frequency

eyes are not properly alligned

reduced visual acuity in one eye, will cause problems with depth perception

orient you/ alert you

• cortical magnification
• topographical mapping

more cells processing information coming from fovea than other areas of vidual fields

• Orderly
• Information is split in optic chiasm-left visual fiels is blue, right visual field is red

• Ipsilateral
• temporal stuff

when information crosses hemispheres

• cells respond best to bars of light, not spots of light
• gets information from all of the 4 cirlces

• Neurons respond more to bars of certain orientations and less to others (V1)
• Tuning curves

• very specific
• respond to straight lines, edges
• location specific
• Orientation specific(angle of edge has to be just right)

• more relaxed than simple cells
• straight lines
• orientation specific

Some cells prefer bars of light of a certain length

Weisal thought that these were called hyper-complex, this is where they went wrong

• Each cell in V1 has preffered eye
• But they respond to input from both eyes

Within each column, all neurons have the same orientation tuning

Orientation column + ocular dominance column