Psy3051 - Perception - Chpt 3 - Introduction To Vision

Front 1

The energy within the electromagnetic spectrum that humans can perceive is known as what?

Back 1

Visible light

Front 2

Light reflected fro objects in the environment enters the eye through the ______ and is focused by the _____ and _____ to form sharp images of the objects on the _____ which contain the _____ for vision.

Back 2

pupil
cornea
lens
retina
receptors

Front 3

What are the two kinds of visual receptors?

Back 3

cones and rods

Front 4

What light sensitive chemicals do rods and cones contain? And what do they do?

Back 4

visual pigments
They react to light and trigger electrical signals

Front 5

What two parts of the eye are responsible for focus and what percentage are each responsible for?

Back 5

Cornea 80%
Lens 20%

Front 6

What is the name of the process where the ciliary muscles to tighten, increasing the curvature of the lens so that it gets thicker.

Back 6

Accomodation

Front 7

Accommodation allows a person to bring ___ and ____ objects into ____.

Back 7

near
far
focus

Front 8

Define the Near Point.

Back 8

It is the distance at which your lens can no longer adjust to bring objects into focus.

Front 9

What is the name of the condition which results in an increase in your near point as you age? And why does it occur?

Back 9

presbyopia
it occurs because the lens hardens and the ciliary muscles become weaker with age

Front 10

As a result of presbyopia what is the normal point ages 20, 30, 40 and 60

Back 10

10
14
22
100

Front 11

What is myopia otherwise known as nearsightedness?

Back 11

the inability to see distant objects clearly

Front 12

Explain the two forms of myopia?

Back 12

1. refractive myopia - where the cornea/lens bend the light too much
2. axial myopia - the eyeball is too long

Front 13

In relation to the retina, where does the myopic focus the light and where to hyperopic focus the light?

Back 13

myopia - in front of the retina
hyperopia - behind the retina

Front 14

What part of the eye does laser treatment concern?

Back 14

cornea

Front 15

A sharp image on the retina is essential for what?

Back 15

clear vision

Front 16

What key part of the rod is responsible for transduction?

Back 16

the outer segment

Front 17

What occurs when light hits the outer segment of a rod"?

Back 17

transduction

Front 18

What does the outer segment of the rod contain?

Back 18

stacks of discs containing visual pigment molecules

Front 19

Visual pigment molecules are one long strand of protein called what that loops back and forth across the disk membrane several times?

Back 19

Opsin

Front 20

Each visual pigment molecule contains only one ____ ____

Back 20

retinal molecule

Front 21

Which molecule in the visual pigment is crucial for transduction? why?

Back 21

retinal molecule
because it is the part of the visual pigment that is sensitive to light

Front 22

Transduction occurs when the light-sensitive retinal does what?

Back 22

absorbs one photon of light

Front 23

What is a photon?

Back 23

the smallest packet of light energy

Front 24

Explain isomerization.

Back 24

when the retinal changes shape so that it is sticking out from the opsin in response to a photon of light hitting the retinal. It is this process that triggers transduction

Front 25

Answer the following questions in relation to Selig Hechts experiement:
1. What approach to studying perception did he use?
2. How many photons must be flashed in order for humans to see?
3. What % of photons are bounced of the cornea or absorbed by the lens?
4. How many are reach the retinals?
5. How many photons are required to activate a rod?
6. How many rods must be activated simultaneously in order for a person to see?

Back 25

1. Approach - Psychophysical
2. Total photons flashed - 100
3. % bounced - 50%
4. Reach retinals - 7
5. Number of rods - 7
6. Rods to see - 7

Front 26

What the the biological chemical that in small amounts facilitates chemical reaction?

Back 26

enzyme

Front 27

What is the sequence of chemical reactions triggered by the activated visual pigment molecule called?

Back 27

Enzyme cascade

Front 28

Vision can only occur if the rod and cone visual pigments transformt eh light entering the eye into what?

Back 28

electricity

Front 29

Are there more rods or more cones?

Back 29

rods

Front 30

What area of the retina contains only cones?

Back 30

fovea

Front 31

What part of the retina does the image we look directly at fall on?

Back 31

the fovea

Front 32

What is the peripheral retina?

Back 32

The area of the retina outside the fovea.

Front 33

What is the common condition that occurs in older people in which the cone-rich fovea and a small area surrounding it are detroyed?

Back 33

macular degeneration

Front 34

What happens to a persons vision if they are suffering macular degeneration?

Back 34

They have a blind spot in their central vision. When they looks at something they lose sight of it.

Front 35

Explain retinitis pigmentosa?

Back 35

degeneration of the retina that is passed fro generation to generation which attackes the peripheral rod recptors and results in poor vision in the peripheral field, tunnel vision.

Front 36

What can happen in sever cases of retinitis pigmentosa?

Back 36

the foveal cone receptors are attacked resulting in complete blindness.

Front 37

Why does everyone have a blind spot?

Back 37

there are no receptors as it is where the optic nerve leaves the eye

Front 38

What process is triggered when eyes are kept in the dark?

Back 38

Dark adaption

Front 39

What is dark adaption?

Back 39

when the eye increase its sensitivity to the dark

Front 40

What are the two stages of dark adaption?

Back 40

1. and initial rapid stage -adaption of the cone receptors
2. later slower stage - adaption of the rod receptors

Front 41

What is the plot of how visual sensitive changes in the dark when the lights are tuned out called?

Back 41

Dark adaption curve

Front 42

What is the first step in measuring dark adaption?

Back 42

light adapt the observer by exposure to light

Front 43

The dark adaption curve indicates that sensitivity increases in two phases. Explain the timing of these phases.

Back 43

Sensitivity increase rapidly for the first 3 to 4 minutes after the light is extinguished and then it levels off; it begins increasing again as about 7 to 10 minutes and continues to do so until about 20 to 30 minutes

Front 44

What is dark adapted sensitivity and how many times greater is it than light-adapted sensitivity measured before dark adaption begins.

Back 44

It is the sensitivity at the end of the dark adaption and it is 100,000 times more sensitive that light-adapted sensitivity measured before dark adaption begins.

Front 45

What method is used to measure dark adaption?

Back 45

method of adjustment

Front 46

What must be done before measuring dark adaption?

Back 46

must measure light-adapted sensitivity

Front 47

Why do we measure light-adapted sensitivity before dark adaption?

Back 47

To adapt the person to light

Front 48

The course of dark adaption is measured by have the observer turn a knob to adjust the intensity of the light. As the person is adapting to the dark do they turn the light up or down?

Back 48

down

Front 49

What are three ways to measure dark adaption?

Back 49

1. measure dark adaption caused by both rods and cones
2. measure dark adaption caused by cones alone
3. measure dark adaption caused by rods alone

Front 50

In dark adaption of rods and cones what is the positioning of the test light and the fixation position on the retina?

Back 50

The person looks directly at a fixation point just to the side of the test light so that the test light falls on the peripheral area and not on the fovea.

Front 51

When measuring dark adaption of the cones only what is the positioning of the test light and fixation point?

Back 51

The observer looks directly at the light, this is the fixation point, so that the light will fall directly on the cone only fovea.

Front 52

Who can we measure dark adpation of rods in and why?

Back 52

Rod monochromats because they have no cones

Front 53

What is the condition Rod Monochromat?

Back 53

A rare genetic defect where people are born without cones.

Front 54

On the dark adaption curve what is the point called where the rod begin to determine the dark adaption curve?

Back 54

rod- cone break

Front 55

Why do rods tale 20 to 30 minutes to reach their maximum sensitivity compared to 3 to 4 minutes for cones?

Back 55

because visual pigment regeneration occurs more rapidly in cones than in rods

Front 56

When the visual pigment molecule, retinal, is isomerised triggering transduction it seperated frot eh opsin part of the molecule which cause the retina to become lighter in colour. What is this process called?

Back 56

visual pigment bleaching

Front 57

Does all our pigment eventually become bleached if we are continuously exposed to light? Why?

Back 57

No. because of visual pigment regeneration

Front 58

What is visual pigment regeneration?

Back 58

The process where the retinal molecule and the opsin molecule are rejoined.

Front 59

What two process occur simultaneously in the retina in order to help us continually see and maintain the retina?

Back 59

visual pigment bleaching and visual pigment regeneration

Front 60

How long does cone pigment take to regenerate compared to rods?

Back 60

Cone pigment take 6 minutes and rods take 30 minutes

Front 61

In Rushton's assertion about dark adaption what two important points did his results demonstrate about the connection between perception and physiology?

Back 61

1. our sensitivity of light depends on the concentration of visual pigment
2. The speed of our sensitivity is adjusted in the dark depends on a chemical reaction - visual pigment regeneration

Front 62

What is the condition where the visual pigment can't regenerate? How does this condition commonly occur and what are the consequences?

Back 62

detached retina
commonly occurs through trauma to the eye or head and the results are that the person becomes blind in the detached part of the retina

Front 63

What are the five layers of the retina?

Back 63

1. Rod and cone receptors
2. Horizontal cells
3. Bipolar cells
4. Amacrine cells
5. Ganglion cells

Front 64

Which cells in the retina transmit signals out of the retina to the optic nerve?

Back 64

Ganglion cells

Front 65

Which cells in the retina are the receptors?

Back 65

Rod and cone cells

Front 66

Which two sets of cells connect neurons across the retina?

Back 66

horizontal and amacrine cells

Front 67

Which three cells form the pathway from the receptors to the optic nerver?

Back 67

1. Rod and cone receptor cells
2. Bipolar cells
3. Ganglion cells

Front 68

A great degree of what process occurs in the retina because there are 126 millions cells and only 1 million ganglion cells?

Back 68

convergence

Front 69

On average how many rods and how many cones pool their signal to each ganglion cell?

Back 69

120 rods and 6 cones

Front 70

The greater convergence of the rods compared to cones (manly because of the foveal cones private line to ganglion cells) translates into what two differences in perception?

Back 70

1. the rods results in better sensitivity than the cones and
2. the cones result in better detail vision than the rods

Front 71

What are the two reasons why rods have greater sensitivity than cones?

Back 71

1. it takes less light to generate a response from an individual rod receptor than it does from an individual cone receptor
2. the rods have greater convergence than cones (more information)

Front 72

How does convergence of the rod cells impact sensitivity?

Back 72

The more rods attached to each ganglion cell the more likely it is to received the required excitatory input needed in order to fire

Front 73

What do cones have better visual acuity?

Back 73

because they have less convergence, less competing information

Front 74

Why do we use the Limulus (horshoe carb) to study lateral inhibition?

Back 74

Because the structure of the limulus eye makes it possible to stimulate individual receptors.

Front 75

What are the structures in the limulus called that make it easier to study lateral inhibition?

Back 75

Ommatidia

Front 76

What is lateral inhibition?

Back 76

information from every bipolar cell inhibits every other one

Front 77

What are the three perceptual phenomena explained by lateral inhibition?

Back 77

1. The Hermann Grid - seeing spots at an intersection
2. Mach Bands - seeing borders more sharply
3. Simultaneous contrast - seeing areas of different brightness due to adjacent areas

Front 78

What illusion do people see in the Hermann Grid?

Back 78

People see an illusion of grey at the intersection of white areas

Front 79

Which type of cell in the retina is responsible for lateral inhibition?

Back 79

bipolar cells

Front 80

In the Hermann Grid what are the bipolar cells doing with the information from the receptors in the white corridors of the grid? and what is the outcome of this process?

Back 80

The bipolar cells are transferring inhibiting signals from the receptors in the white corridor to the receptors at the intersection, this lateral inhibition causes a reduced response of the cell at the intersection leading to the perception of grey instead of white

Front 81

In the mach band example of lateral inhibition explain how the bands appear to change intensity just before there actually is a change in intensity?

Back 81

The receptors perceiving the light band exhibit a greater response and therefore a greater % of inhibitory responses. The receptors perceiving he dark band exhibit a smaller response and therefore a smaller % of inhibitory responses. When these receptors are next to each other the light receptor is inhibited less and the dark receptor is inhibited more. Therefore highlighted edges appear where the light moves to dark and vice versa.

Front 82

Why do we need lateral inhibition?

Back 82

To detect edges in the environment.

Front 83

What activity demonstrates that lateral inhibition does not fully explain simultaneous contrast?

Back 83

Moving focus from one side of the square in the centre to the other does not change the lightness of the square as would be expected if only lateral inhibition was implicated.

Front 84

What occurs in whites illusion that that is contrary to what we would expect if lateral inhibition was at play?

Back 84

That the grey rectangle bordered by white would appear darker and not lighter and vice versa for the black boarded rectangle

Front 85

What concept did Adam Gilchrist and colleagues offer to explain white illusion? Explain.

Back 85

the principle of belongingness
which states that an areas appearance is influenced by the part of the surroundings to which the area appears to belong.