chapter 3: the eye and retina Flashcards
What are the 4 steps of the visual process
- distal stimuli
- proximal stimuli
- receptor transforms light into electric signal
- signals travel through a network of neurons
what are wavelengths
distance between the peaks of the electromagnetic waves
Classify these lights from shortest to longest wavelengths
1. visible light
2. radio waves
3. gamma rays
4. X rays
5. infrared light
2, 5, 1, 4, 3
visible light has wavelengths ranging from ___ to ___ nanometers
400 to 700
Describe what light goes through when it enters the eye
focused by cornea
enters through pupil
focused more by lens
forms images on the retina
What are the two types of photoreceptors responsible for vision
rods and cone cells
what are called the light-sensitive chemicals that react to light and trigger electrical signals and where are they found
visual pigments are found in the outer segments
define the condition called macular degeneration
condition that destroys the cone-rich fovea and a small area that surrounds it which creates a blind region in central vision
which area contains only cones and what is its function
fovea: responsible for sharp central vision
True or false? the peripheral retina contains only rod cells
false, it contains both rod and cone cells but has MANY more rod cells
what is retinitis pigmentosa
degenerative condition that attacks the peripheral rod receptors and results in poor vision in the peripheral visual field
What is the blind spot
area where there is an absence of photoreceptors
how does the cornea and the lens work together to focus light
cornea represents 80% of eye’s focusing power but since it’s fixed, it can’t adjust its focus
lens represent other 20%, since it can change its shape to adjust the eye’s focus
what happens to the lens when an image focuses behind the retina
it becomes bigger
what are refractive errors
errors that can affect the ability of the cornea and/or lens to focus visual input onto the retina
what is presbyopia
age-related loss of ability to accomodate
define accommodation
change in the lens shape that occurs when the ciliary muscles at the front of the eye tighten and increase the curvature of the lens so that it gets thicker
what happens in the eye when someone has myopia
parallel rays of light focus in front of the retina so the image that reaches the retina is blurred
what are the two factors that can result in myopia
- refractive myopia: cornea and/or lens bends the light too much
- axial myopia: eyeball too long
what is hyperopia and how can it be corrected in young people and older people
trouble seeing nearby objects because image focuses behind the retina.
- young people can correct it by accommodation
- older people use corrective lenses
define transduction
transformation of one form of energy into another form of energy
what are the two parts of visual pigments
opsin: long protein
retinal: smaller light-sensitive component
what is isomerization
the change of shape of the retinal from bent to straight when the light hits the retina
dark adaption is…
process by which the eyes become more sensitive to low levels of lights
explain the experiment done to measure the dark adaptation curve
test light shown in peripheral
Ps has to adjust intensity until barely visible
adapting light turned off, Ps in the dark
Ps must decrease light to keep it barely visible
how do researchers measure only cones and only rods in dark adaptation
cones: fovea
rods: in person with no cones
what is the rod-cone break
the place where the rods begin to determine the dark adaptation curve instead of the cones
define the process called visual pigment bleaching
- the retinal separates from the opsin after its change of shape, resulting in the molecule becoming lighter in color
- causes pigments to become unresponsive to light and need time to regenerate
define visual pigment regeneration
retinal returning to its bent shape and reattaching itself to the opsin
explain how visual pigment regeneration increases our sensitivity during dark adaptation
when in the dark, bleached visual pigment continues to regenerate, but there is no more isomerization, so eventually, the concentration of regenerated pigment builds up so your retina contains only intact visual pigment molecules
- increase in visual pigment concentration = increase in sensitivity
what are the two important connections between perception and physiology
- our sensitivity to light depends on the concentration of a chemical: visual pigment
- speed at which our sensitivity increases in the dark depends on chemical reaction: regeneration of the visual pigment
what is called the condition where a person’s retina becomes detached from the pigment epithelium
detached retina
define spectral sensitivity
eye’s sensitivity to light as a function of the light’s wavelength
true or false? more light is needed to see wavelengths in the middle of the spectrum than to see wavelengths at either ends
false, middle wavelengths are more sensitive
what is the purkinje shift
tendency for the peak sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels
what is a pigment’s absorption spectrum
plot of the amount of light absorded versus the wavelength of the light
photoreceptors in the eye adapt to lower light levels by:
a. decreasing the proportion of isomerized retinal molecules
b. decreasing the convergence to ganglion cells
c. stopping the release of NT
d. switching to the rod system
d. switching to the rod system
The visual photopigments…
a. are the same in rods and cones
b. regenerate in the dark
c. are located in the inner segments of rods and cones
d. become transparent in the dark
b. regenerate in the dark
the time course of dark adaptation:
a. is fast; it only requires pupil adaptation
b. is fast; rhodopsin molecules regenerate quickly
c. has 2 phases; they correspond to adaptation in cones and in the rods
d. is slow; only rods are required for dark adaptation
c. has 2 phases; they correspond to adaptation in cones and in the rods
the Purkinje shift is when
a. vision goes from photopic (day) to scotopic and we lose colour perception
b. cone functioning decreases and rod functioning increases
c. colour sensitivity fades from long wavelengths to shorter ones
d. all of the above
d. all of the above
True or false? Rods are responsible for visual acuity, while cones are responsible for light sensitivity
false, its the inverse
in order, name the 5 cells that connect the signals from the retina to the optic nerve
- photoreceptors
- horizontal cells
- bipolar cells
- amacrine cells
- ganglion cells
True or false? receptors, bipolar cells and ganglion cells all have axons
false, only ganglion cells do
define neural convergence
occurs when several neurons synapse onto a single neuron
someones with only rods and no cones in the retina would:
a. not see colour
b. not see colour and have poor visual acuity
c. see better in the dark than someone with rods and cones
d. have poor visual acuity
b. not see colour and have poor visual acuity
explain how convergence causes the rods to be more sensitive than the cones
rod ganglion cells receive input from many rods at a time. it, therefore, needs less incoming light to be stimulated since the light received by each rod is added up towards the one ganglion cell
explain how less convergence causes the cones to have better acuity than the rods
stimulating two neighboring cones will cause two neighboring ganglion cells to fire since cones converge less than rods.
on the contrary, stimulating two neighboring rod will cause the same ganglion cell to fire because they have higher convergence
the advantage of many rods converging to few ganglion cells is:
a. better frequency discrimination
b. better light sensitivity
c. better spatial resolution
d. better colour vision
b. better light sensitivity
define receptive field
the region of the retina that must receive illumination in order to obtain a response in any given fiber
define center-surround antagonism
happens when the light’s size becomes large enough that it begins to cover the inhibitory area, causing a decrease in the neuron’s firing rate
define lateral inhibition
capacity of excited neurons to reduce the activity of their neighbors
what is edge enhancement
increase in perceived contrast at borders between regions of the visual field
explain the Chevreul illusion
on the light side, the receptive field’s center is fully illuminated (+1) but only 3/4 of the inhibitory region is illuminated (-0.75). it will send a +0.25 signal indicating there is light (compared to 0 if receptive field is fully in the light part)
on the dark side, center not illuminated, but 1/4 of inhibitory region is (-0.25). it will send a (-0.25) signal making it darker
what are called the light and dark bands created at the fuzzy borders
mach bands
rhodopsin is found on the … and iodopsin is found on the …
rods, cones
coyotes hunt. what prediction could you make about their retina?
a. they do not have blind spots
b. their eyes will have more cones than rods
c. the retina will be thicker
d. their eyes will have more rods than cones
d. their eyes will have more rods than cones
what is the stimulus required for vision?
a. electromagnetic energy
b. electrostatic energy
c. electroconvulsive energy
d. electrovisual energy
a. electromagnetic energy
the reason we cannot see light that falls on the blind spot is:
a. photoreceptors in that region of the retina are light adapted
b. the cortex suppresses vision in this area
c. photoreceptors in that region of the retina are dark adapted
d. there are no light-sensitive cells there (optic nerve connects to retina)
d. there are no light-sensitive cells there (optic nerve connects to retina)
