chapter 2/3

Question 1

wavelength

Answer 1

distance between the peaks of electromagnetic waves in the electromagnetic spectrum

Question 2

visible light

Answer 2

wavelength of light that humans can perceive - ranges from about 400 to 700 nanometers and is associated with different colours of the spectrum

Question 3

colours and wavelength

Answer 3

blue - short
green - middle
yellow, orange, red - long

Question 4

what makes up the electromagnetic spectrum

Answer 4

different wavelengths of light - continuum of electromagnetic energy that is produced by electric charges and is radiated as waves

Question 5

examples of animals that perceive things we don’t

Answer 5

snakes that have holes in their faces (pit organs) which allow them to detect infrared radiation from their prey at night - example of how humans are only able to perceive a small portion of what is out there compared to other animals and things

Question 6

rods vs cones

Answer 6

rods: scotopic vision - used in low light because they are very sensitive to light, low acuity and not good w colour

cones: photopic vision - less sensitive to light, used when a lot of light is available - high acuity, colour detail, mostly concentrated in the fovea

Question 7

light pathway through the eye

Answer 7

light enters through pupil and is focused onto the retina by the cornea and lens. It travels all the way back to the retina to the photoreceptors -(rods and cones) which then send it back the way it came (but transduced to electrical energy) , through bipolar and finally ganglion cells

Question 8

optical infinity

Answer 8

a quality of the lens that makes it so that anything further away from us than 20ft doesn’t need to be focused before entering the eye

Question 9

accomodation

Answer 9

process by which the lens thickens or thins to keep an object in focus

Question 10

macular degeneration

Answer 10

blurred central vision related to age

Question 11

myopia

Answer 11

nearsightedness, meaning trouble seeing distant objects - images get projected in front of the retina instead of onto the retina

Question 12

refractive myopia

Answer 12

cornea and lens overbend the light

Question 13

axial myopia

Answer 13

eyeball is too long

Question 14

hyperopia

Answer 14

farsightedness, meaning trouble seeing near objects - objects get focused beyond the retina because the eyeball is too short

Question 15

presbyopia

Answer 15

trouble seeing near objects due to aging - lens becomes more rigid due to age

Question 16

transduction in the eye

Answer 16

photoreceptors contain visual pigments in their rod/cone shaped outer segments - these pigments contain an opsin protein bound to retinal - when light hits the pigments, they change their binding configuration, triggering electrical signals

Question 17

fovea

Answer 17

area of the retina that contains only cones - when we look directly at an object the object’s image falls on the fovea

Question 18

peripheral retina

Answer 18

includes all of the retina outside of the fovea and contains both rods and cones, but many more rods (still a lot of cones)

Question 19

retinitis pigmentosa

Answer 19

degeneration of the retina - in peripheral rod receptors = bad vision in peripheral field - is passed from one generation to the next, as opposed to macular degeneration which is usually caused by ageing

Question 20

why don’t we see our blind spot?

Answer 20

because the brain fills in the places we don’t see - and its located off to the side of the visual field, where objects are not in sharp focus

Question 21

how does the lens change shape

Answer 21

ciliary muscles increase its curvature when we need to bend/focus light

Question 22

what happens when we look at an object 20ft away

Answer 22

the eye doesn’t have to do anything - rays of light enter the eye parallel to each other and focus on the back of the retina

Question 23

what happens when we look at an object closer than 20ft

Answer 23

the focus point gets pushed back, past the retina so that the eye has to accomodate, by increasing the curvature of the lens (fatter) to increase its focusing power in order to bring the focus point of the object closer forward

Question 24

accommodation

Answer 24

change in the len’s 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 25

refractive errors

Answer 25

errors that affect the ability of the cornea and/or lens to focus the visual input onto the retina - presbyopia, myopia, hyperopia

Question 26

visual pigment

Answer 26

light sensitive molecule contained in the outer segments of photoreceptors - contains opsins and retinal

Question 27

isomerization

Answer 27

The process by which retinal molecules change shape when hit by light (bent to straight)- this results in a chemical chain reaction that activates thousands of charged molecules to create electrical signals in receptors, making it so that the isomerization of just one visual pigment molecule can lead to the activation of an entire photoreceptor

Question 28

dark adaptation

Answer 28

process of increasing sensitivity in the dark, measured by a dark adaptation curve

Question 29

how do we measure the dark adaptation curve?

Answer 29

using the method of adjustment - we have ps look at a fixation point while a light flashes in their periphery - they turn down the flight until it is just barely perceptible - this is their threshold. The same thing is done in the dark - as the p becomes more sensitive to light in the dark, we track how low they are able to dim the light

Question 30

dark adapted sensitivity

Answer 30

sensitivity at the end of dark adaptation - about 100,000 times greater than the beginning

Question 31

phases of the dark adaptation curve

Answer 31

first phase: sensitivity increases during the first 3 to 4 minutes then levels out
second phase: sensitivity starts to increase again at about 7 to 10 minutes and finally stops at around 20 or 30

Question 32

cone adaptation

Answer 32

cones only go through the first phase - we can tell by measuring the threshold for light that falls only in the fovea

Question 33

rod adaptation

Answer 33

rods adapt slower than cones and go through both stages - can tell by measuring the threshold for rod monochromats (people who have no cones)

Question 34

rod cone break

Answer 34

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

Question 35

visual pigment bleaching

Answer 35

when retinal changes shape due to light (bent to straight) it detaches from the opsin causing it to become lighter in colour - in this state visual pigments are no longer useful for vision

Question 36

visual pigment regeneration

Answer 36

process of reforming the visual pigment molecule - the increase in visual pigment concentration that occurs as the pigment regenerates in the dark is responsible for the increase in sensitivity we measure during dark adaption - happens faster in cones (6 min) than rods (30 min)

Question 37

what determines our sensitivity to light

Answer 37

the concentration of visual pigment

Question 38

what determines the speed at which our sensitivity increases in the dark

Answer 38

the regeneration of the visual pigment

Question 39

detached retina

Answer 39

when the retina becomes detached from the pigment epithelium, a layer that contains enzymes necessary for pigment regeneration

Question 40

spectral sensitivity

Answer 40

the eye’s sensitivity to light as a function of the light’s wavelength - measured by determining the spectral sensitivity curve

Question 41

how do we measure a spectral sensitivity curve

Answer 41

we determine a person’s threshold for seeing monochromatic light across the spectrum at regular intervals - amount of light that is needed to see certain wavelengths - we often plot our curve in terms of wavelength, using sensitivity =1/threshold

Question 42

how do we measure cone spectral sensitivity

Answer 42

by having participants look directly at the test light so that it stimulates only the cones in the fovea

Question 43

how do we measure rod spectral sensitivity

Answer 43

we measure sensitivity after the eye is dark adapted so that only the rods control vision, and we present test flashes in the peripheral retina

Question 44

what is the difference in rod and cone spectral sensitivity?

Answer 44

rods are more sensitive to short wavelength light (blue green) than cones -they are most sensitive to 500nm, while cones are most sensitive to 560 nm light - this means that as vision shifts from cones to rods in dark adapted eyes, our vision becomes more sensitive to short wavelength light

Question 45

purkinje shift

Answer 45

enhanced perception of short wavelengths during dark adaptation

Question 46

absoption spectrum

Answer 46

the plot of light absorbed by a pigment versus the wavelength of the light

Question 47

absoption spectra for cones

Answer 47

short wavelength pigment: 419 nm
medium wavelength pigment: 531 nm
long wavelength pigement: 558nm

add together to result in a psychophysical spectral sensitivity curve that peaks at 560nm

rod is same to spectral sensitivity curve

Question 48

horizontal cells and amacrine cells

Answer 48

signal travels between photoreceptors and bipolar cells in horizontal cells and between bipolar and ganglion cells through amacrine cells