chapter 2-the first steps in vision Flashcards
light
narrow band of electromagnetic radiation that can be conceptualized as a wave or a stream of photons
waves
property of light; color and reflection (and refraction)
photons
packets of energy/ligh
low light situations and absorbing
ray
light travels in particular direction
energy varies with
wavelength
visible light between ___ and ___ nm
400 (violet, more energy), 700 (red, less energy)
absorbed
energy that is taken up, not transmitted at all, necessary for detection
scattered
energy that is dispersed in an irregular fashion; less focused, atmosphere
reflected
energy that is redirected when it strikes a surface, needed to see nonlight sources
transmitted
energy that is passed on through a surface, without much alteration of direction
refracted
energy that is altered as it passes into another medium, focusing, good thing-lenses
cornea
front of eye, transparent cells (no blood vessels), refraction, transmitted
pupil
hole that light goes though, center of iris
iris
muscle that controls the width of pupil and the amount of light, absorbs light (not useful), reflect (eye color)
lens
transparent cells, refraction, control shape to focus
retina/fovea
sensation, absorb, transduction, location of photoreceptors
presbyopia
old age relatedd vision loss, stiffening of the lens
refraction is necessary to focus light rays onto the ___ and this is accomplished by the ____
retina, lens
accommodation
process in which lens changes its shape, altering its refractive power, focus image on retina, most useful for up close objects, moves image point forward
emmetropia
happy condition of no refractive error
way the lens refracts light causes point of focus of the image to be in front of or behind the retina
problems of refraction
myopia
nearshightedness, when light entering the eye is focused in front of the retina, and distant objects cannot be seen sharply
eyeball too long for given refractive power, too much power
hyperopia
when light entering the eye is focused behind the retina, farsightedness
eyeball is too short given refractive power, not enough power
accommodation cans what refraction problem
hyperopia
resolution
the ability of the eye to resolve fine spatial detail in the image
sensitivity
ability of the eye to respond at very low levels of retinal illumination
____ requires distinguishing between responses of nearby receptors; subtractive differentiation
resolution
___ is improved by summing responses across nearby photoreceptors; grouping things
sensitivity
photoreceptors
cells in the retina that initially transduce light energy into neural energy
rods
photoreceptors that are specialized for night vision; respond well in low luminance conditions, not process color
cones
photoreceptors that are specialized for daylight vision, fine visual acuity and color, best in high luminance conditions
center of the retina, packed full of cones
fovea
age related macular degeneration
central part of vision deteriorates
dry macular degeneration
less individual photoreceptors,
wet macular degeneration
wide loss of photoreceptors because of fluid release
bipolar cells
exist between photoreceptors and ganglion cell, transmits information; vertical movement
amacrine cells
makes synaptic contacts with bipolar cells and ganglion cells; spread horizontally; enhancement and temporal sensitivity
horizontal cells
lateral inhibition, influence overall light response
___ and ___ form lateral path in the retina
amacrine and horizontal cells
rod bipolars are all ___ cells, connect rods to ___ cells, and then connect to ON or OFF cone bipolars
ON, amacrine
ON bipolar cells
activated by the presence of light
OFF bipolar cells
activated by offset/absence of light
diffuse bipolar cell
spread out to receive input from multiple cones
midget bipolar cell
small, central in retina and receives input from 1 cone
property: photoreceptor type
fovea:
periphery
mostly cones
mostly rods
property: bipolar cell type
fovea
periphery
midget
diffuse
property: convergence
fovea
periphery
low (p ganglion cells)
high (m ganglion cells)
property: receptive field size
fovea
periphery
small
large
property: acuity (detail)
fovea
periphery
high
low
property: light sensitivity
fovea
periphery
low
high
convergence
idea of many into few, lots of rods into less ganglion cells
divergence
less onto many, cones
vertical pathway of retina
photoreceptors, bipolar cells, and ganglion cells
P ganglion cells
connect to the parvocellular pathway
parvocellular pathway
visual acuity, color and shape processing
temporal resolution
measurement with respect to time
finer resolution _____ in size with retinal eccentricity
increases
retinal eccentricity
the difference between the retinal image and the fovea
M ganglion cells
connect to the magnocellular pathway
magnocellular pathway
involved in motion processing
poor temporal resolution but good spatial resolution
P ganglion cells
good temporal resolution but poor spatial resolution
M ganglion cells
spatial resolution
pixels
receptive field
region of the retina in which stimuli influence a neurons firing rate, all the photoreceptors that will activate retinal ganglion cell
receptive fields are sensitive to
different intensity of light in the center and in the surround
light on receptive field
strong response
light off receptive field
weak response
center-surround receptive fields because luminance variations tend to be smooth within objects and sharp between objects, emphasize
object boundaries
retinal ___cells act like a filter for information coming into the brain
ganglion
center surround receptive fields most sensitive to ___ in the intensity of light
differences
looking at different from center and surround
resolution
sums across the center
sensitivity
