Vision (Chapter 7)

DF

Slide 7: Patient Profiles Patient ________- bilateral damage to her ventral prestriate cortex- responds accurately to visual stimuli that she does not consciously see (cant visually engage and tie them to her memory, but is able to understand objects in space) Patient AT- lesion on the occipitoparietal region- could easily recognize objects and demonstrate their size with her fingers (can recognize familiar objects, but can not integrate with motion to grab the object) Slide 8: Location in the Visual World Visual Field o Region of the visual world that is seen by the eyes o Divided into left and right halves o Info in left visual field goes to the right hemisphere o Info in right visual field goes to the left hemisphere Slide 9: Diseases /Conditions Scotoma- blind in a specific area of the receptive field o Perimetry- mapping the extent of a patients scotoma Visual Agnosia- visual lack of knowledge, patient can not recognize objects unless they are touching them o Usually damage occurs in the temporal cortex Prosopagnosia- inability to recognize faces and complex objects with curved surfaces o Fusiform Face Area (FFA) lesion Akinetopsia- loss of motion perception, unable to judge direction and speed of moving objects o Large bilateral lesions involving the temporoparietal cortices area o Patient MP- saw the world as a series of snapshots rather than as a moving image Motion Blindness- the inability to determine the direction, speed, and whether objects are moving o Likely caused by damage in area MT o Some people are blind except for the ability to detect which direction something is moving ▪ Area MT probably gets some visual input despite significant damage to area V1 Slide 10: Color Vision Color determined by wavelength or mixture of wavelengths o Subtractive color mixing: mixture occurs within stimulus itself o Additive color mixing: mixing of different wavelengths of light Perception of different colors determined by the ratio of activity among the 3 cone receptors Brightness, lightness, saturation Slide 11: Photoreceptors 3 types of cone pigments- absorb light over a range of frequencies, but their maximal absorptions are: o 419 nm " (blue "or short wavelength) o 531 nm ("green "or middle wavelength) o 559 nm ("red "or long wavelength) There are approximately equal numbers of red and green cones, but fewer blue cones.

Heminasal

________- anything happening on the nose side of the eyeball; Hemitempal- anything happening on the other side of the eyeball Myopia- nearsightedness, in most cases the eyeball is slightly too long and causes the focal point of light falls short of the retina (Lasik surgery slices thin layers off to make it shorter) Hyperopia- farsightedness, in most cases the eyeball is slightly too short and causes the focal point of light falls too long of the retina (much more rare than myopia) Presbyopia- age- related farsightedness, nothing to do with the length of the eyeball, has to do with the lens (see explanation above) Slide 3: The Retina An outgrowth of central nervous tissue Specialized neurons that detect light o Rods- play a key role in night vision and peripheral vision ▪ More numerous than cones ▪ Sensitive to low levels of light (dim light) ▪ One type of pigment only o Cones- play a key role in daylight vision and color vision ▪ Highly responsive to bright light ▪ Located in the fovea only ▪ 3 types of pigment Photopigments- light sensitive chemicals in rods and cones that initiate transduction of light waves into electrical neural impulses (rhodopsin) Blind Spot- point where optic nerve exits eye, no rods or cones present (literally blind in this area)

rods and cones

receptors in the retina

iris

connected to muscles and contracts/releases and allows more/less pupil to be seen - changes the amount of light that comes in

ciliary muscles

pull the lens tighter (helps to look far away and releases to look close up)

lens

behind the pupil, becomes more rigid as we get older, inverts info - brain flips it back when we receive it

sclera and choroid

white part of the eye, rigid protein membrane, helps form the shape of the eye

retina

all neurons in eyeball

fovea

central focus region and color vision region

optic nerve

ganglion cells leave the eyeball in a tight bundle, blood flows in and out of same space

heminasal

anything that happens on nose side

hemitemporal

anything on the temple side

myopia

nearsightedness; eyeball slightly too long and focal point of light falls short of the retina

hyperopia

farsightedness; eyeball slightly too short and focal point of light falls too long of the retina

presbyopia

age-related farsightedness due to lens rigidity

rods

key role in night vision and peripheral vision; more numerous than cones; sensitive to low light, one type of pigment only

cones

key role in daylight vision and color vision; responsive to bright light, located in fovea only, 3 types of pigment

photopigment

light sensitive chemicals in rods and cones that initiate transduction of light waves into electrical neural impulses (rhodospin)

blind spot

point where optic nerve exits, no rods/cones present

horizontal cells

interconnects adjacent photoreceptors and outer processes of bipolar cells

amarcine cells

connects adjacent ganglion cells and inner processes of bipolar cells

ganglion cells

axons in the optic nerve and also the reason for the blind spot

optic chiasm

junction of the optic nerve from each eye; axons from the nasal halves cross over to the opposite sides of brain

LGN (lateral geniculate nucleus)

only stop off point for neurons in the thalamus

geniculostriate system

primary visual cortex in the occipital

dorsal stream

visual spatial perception

ventral stream

visual pattern recognition

scotoma

blind in a specific area of the receptive field

perimetry

mapping the extent of a patient's scotoma

visual agnosia

patient can't recognize objects unless touching them (damage in temporal cortex)

prosopagnosia

inability to recognize faces and complex objects with curved surfaces (FFA lesion)

akinetopsia

loss of motion perception, unable to judge direction/speed of moving objects (large bilateral lesions)

motion blindness

likely caused by damage in area MT

subtractive color mixing

mixing occurs w/in stimulus itself

additive color mixing

mixing different light wavelengths

short wavelength

blue

middle wavelength

green

long wavelength

red