chapter 3: the eye and retina

Question 1

What are the 4 steps of the visual process

Answer 1

1. distal stimuli
2. proximal stimuli
3. receptor transforms light into electric signal
4. signals travel through a network of neurons

Question 2

what are wavelengths

Answer 2

distance between the peaks of the electromagnetic waves

Question 3

Classify these lights from shortest to longest wavelengths
1. visible light
2. radio waves
3. gamma rays
4. X rays
5. infrared light

Answer 3

2, 5, 1, 4, 3

Question 4

visible light has wavelengths ranging from ___ to ___ nanometers

Answer 4

400 to 700

Question 5

Describe what light goes through when it enters the eye

Answer 5

focused by cornea
enters through pupil
focused more by lens
forms images on the retina

Question 6

What are the two types of photoreceptors responsible for vision

Answer 6

rods and cone cells

Question 7

what are called the light-sensitive chemicals that react to light and trigger electrical signals and where are they found

Answer 7

visual pigments are found in the outer segments

Question 8

define the condition called macular degeneration

Answer 8

condition that destroys the cone-rich fovea and a small area that surrounds it which creates a blind region in central vision

Question 9

which area contains only cones and what is its function

Answer 9

fovea: responsible for sharp central vision

Question 10

True or false? the peripheral retina contains only rod cells

Answer 10

false, it contains both rod and cone cells but has MANY more rod cells

Question 11

what is retinitis pigmentosa

Answer 11

degenerative condition that attacks the peripheral rod receptors and results in poor vision in the peripheral visual field

Question 12

What is the blind spot

Answer 12

area where there is an absence of photoreceptors

Question 13

how does the cornea and the lens work together to focus light

Answer 13

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

Question 14

what happens to the lens when an image focuses behind the retina

Answer 14

it becomes bigger

Question 15

what are refractive errors

Answer 15

errors that can affect the ability of the cornea and/or lens to focus visual input onto the retina

Question 16

what is presbyopia

Answer 16

age-related loss of ability to accomodate

Question 17

define accommodation

Answer 17

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

Question 18

what happens in the eye when someone has myopia

Answer 18

parallel rays of light focus in front of the retina so the image that reaches the retina is blurred

Question 19

what are the two factors that can result in myopia

Answer 19

1. refractive myopia: cornea and/or lens bends the light too much
2. axial myopia: eyeball too long

Question 20

what is hyperopia and how can it be corrected in young people and older people

Answer 20

trouble seeing nearby objects because image focuses behind the retina.
- young people can correct it by accommodation
- older people use corrective lenses

Question 21

define transduction

Answer 21

transformation of one form of energy into another form of energy

Question 22

what are the two parts of visual pigments

Answer 22

opsin: long protein
retinal: smaller light-sensitive component

Question 23

what is isomerization

Answer 23

the change of shape of the retinal from bent to straight when the light hits the retina

Question 24

dark adaption is…

Answer 24

process by which the eyes become more sensitive to low levels of lights

Question 25

explain the experiment done to measure the dark adaptation curve

Answer 25

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

Question 26

how do researchers measure only cones and only rods in dark adaptation

Answer 26

cones: fovea rods: in person with no cones

Question 27

what is the rod-cone break

Answer 27

the place where the rods begin to determine the dark adaptation curve instead of the cones

Question 28

define the process called visual pigment bleaching

Answer 28

- 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

Question 29

define visual pigment regeneration

Answer 29

retinal returning to its bent shape and reattaching itself to the opsin

Question 30

explain how visual pigment regeneration increases our sensitivity during dark adaptation

Answer 30

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

Question 31

what are the two important connections between perception and physiology

Answer 31

1. our sensitivity to light depends on the concentration of a chemical: visual pigment 2. speed at which our sensitivity increases in the dark depends on chemical reaction: regeneration of the visual pigment

Question 32

what is called the condition where a person's retina becomes detached from the pigment epithelium

Answer 32

detached retina

Question 33

define spectral sensitivity

Answer 33

eye's sensitivity to light as a function of the light's wavelength

Question 34

true or false? more light is needed to see wavelengths in the middle of the spectrum than to see wavelengths at either ends

Answer 34

false, middle wavelengths are more sensitive

Question 35

what is the purkinje shift

Answer 35

tendency for the peak sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels

Question 36

what is a pigment's absorption spectrum

Answer 36

plot of the amount of light absorded versus the wavelength of the light

Question 37

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

Answer 37

d. switching to the rod system

Question 38

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

Answer 38

b. regenerate in the dark

Question 39

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

Answer 39

c. has 2 phases; they correspond to adaptation in cones and in the rods

Question 40

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

Answer 40

d. all of the above

Question 41

True or false? Rods are responsible for visual acuity, while cones are responsible for light sensitivity

Answer 41

false, its the inverse

Question 42

in order, name the 5 cells that connect the signals from the retina to the optic nerve

Answer 42

1. photoreceptors 2. horizontal cells 3. bipolar cells 4. amacrine cells 5. ganglion cells

Question 43

True or false? receptors, bipolar cells and ganglion cells all have axons

Answer 43

false, only ganglion cells do

Question 44

define neural convergence

Answer 44

occurs when several neurons synapse onto a single neuron

Question 45

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

Answer 45

b. not see colour and have poor visual acuity

Question 46

explain how convergence causes the rods to be more sensitive than the cones

Answer 46

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

Question 47

explain how less convergence causes the cones to have better acuity than the rods

Answer 47

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

Question 48

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

Answer 48

b. better light sensitivity

Question 49

define receptive field

Answer 49

the region of the retina that must receive illumination in order to obtain a response in any given fiber

Question 50

define center-surround antagonism

Answer 50

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

Question 51

define lateral inhibition

Answer 51

capacity of excited neurons to reduce the activity of their neighbors

Question 52

what is edge enhancement

Answer 52

increase in perceived contrast at borders between regions of the visual field

Question 53

explain the Chevreul illusion

Answer 53

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

Question 54

what are called the light and dark bands created at the fuzzy borders

Answer 54

mach bands

Question 55

rhodopsin is found on the ... and iodopsin is found on the ...

Answer 55

rods, cones

Question 56

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

Answer 56

d. their eyes will have more rods than cones

Question 57

what is the stimulus required for vision? a. electromagnetic energy b. electrostatic energy c. electroconvulsive energy d. electrovisual energy

Answer 57

a. electromagnetic energy

Question 58

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)

Answer 58

d. there are no light-sensitive cells there (optic nerve connects to retina)