Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
85 Cards in this Set
- Front
- Back
The energy within the electromagnetic spectrum that humans can perceive is known as what?
|
Visible light
|
|
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.
|
pupil
cornea lens retina receptors |
|
What are the two kinds of visual receptors?
|
cones and rods
|
|
What light sensitive chemicals do rods and cones contain? And what do they do?
|
visual pigments
They react to light and trigger electrical signals |
|
What two parts of the eye are responsible for focus and what percentage are each responsible for?
|
Cornea 80%
Lens 20% |
|
What is the name of the process where the ciliary muscles to tighten, increasing the curvature of the lens so that it gets thicker.
|
Accomodation
|
|
Accommodation allows a person to bring ___ and ____ objects into ____.
|
near
far focus |
|
Define the Near Point.
|
It is the distance at which your lens can no longer adjust to bring objects into focus.
|
|
What is the name of the condition which results in an increase in your near point as you age? And why does it occur?
|
presbyopia
it occurs because the lens hardens and the ciliary muscles become weaker with age |
|
As a result of presbyopia what is the normal point ages 20, 30, 40 and 60
|
10
14 22 100 |
|
What is myopia otherwise known as nearsightedness?
|
the inability to see distant objects clearly
|
|
Explain the two forms of myopia?
|
1. refractive myopia - where the cornea/lens bend the light too much
2. axial myopia - the eyeball is too long |
|
In relation to the retina, where does the myopic focus the light and where to hyperopic focus the light?
|
myopia - in front of the retina
hyperopia - behind the retina |
|
What part of the eye does laser treatment concern?
|
cornea
|
|
A sharp image on the retina is essential for what?
|
clear vision
|
|
What key part of the rod is responsible for transduction?
|
the outer segment
|
|
What occurs when light hits the outer segment of a rod"?
|
transduction
|
|
What does the outer segment of the rod contain?
|
stacks of discs containing visual pigment molecules
|
|
Visual pigment molecules are one long strand of protein called what that loops back and forth across the disk membrane several times?
|
Opsin
|
|
Each visual pigment molecule contains only one ____ ____
|
retinal molecule
|
|
Which molecule in the visual pigment is crucial for transduction? why?
|
retinal molecule
because it is the part of the visual pigment that is sensitive to light |
|
Transduction occurs when the light-sensitive retinal does what?
|
absorbs one photon of light
|
|
What is a photon?
|
the smallest packet of light energy
|
|
Explain isomerization.
|
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
|
|
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? |
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 |
|
What the the biological chemical that in small amounts facilitates chemical reaction?
|
enzyme
|
|
What is the sequence of chemical reactions triggered by the activated visual pigment molecule called?
|
Enzyme cascade
|
|
Vision can only occur if the rod and cone visual pigments transformt eh light entering the eye into what?
|
electricity
|
|
Are there more rods or more cones?
|
rods
|
|
What area of the retina contains only cones?
|
fovea
|
|
What part of the retina does the image we look directly at fall on?
|
the fovea
|
|
What is the peripheral retina?
|
The area of the retina outside the fovea.
|
|
What is the common condition that occurs in older people in which the cone-rich fovea and a small area surrounding it are detroyed?
|
macular degeneration
|
|
What happens to a persons vision if they are suffering macular degeneration?
|
They have a blind spot in their central vision. When they looks at something they lose sight of it.
|
|
Explain retinitis pigmentosa?
|
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.
|
|
What can happen in sever cases of retinitis pigmentosa?
|
the foveal cone receptors are attacked resulting in complete blindness.
|
|
Why does everyone have a blind spot?
|
there are no receptors as it is where the optic nerve leaves the eye
|
|
What process is triggered when eyes are kept in the dark?
|
Dark adaption
|
|
What is dark adaption?
|
when the eye increase its sensitivity to the dark
|
|
What are the two stages of dark adaption?
|
1. and initial rapid stage -adaption of the cone receptors
2. later slower stage - adaption of the rod receptors |
|
What is the plot of how visual sensitive changes in the dark when the lights are tuned out called?
|
Dark adaption curve
|
|
What is the first step in measuring dark adaption?
|
light adapt the observer by exposure to light
|
|
The dark adaption curve indicates that sensitivity increases in two phases. Explain the timing of these phases.
|
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
|
|
What is dark adapted sensitivity and how many times greater is it than light-adapted sensitivity measured before dark adaption begins.
|
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.
|
|
What method is used to measure dark adaption?
|
method of adjustment
|
|
What must be done before measuring dark adaption?
|
must measure light-adapted sensitivity
|
|
Why do we measure light-adapted sensitivity before dark adaption?
|
To adapt the person to light
|
|
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?
|
down
|
|
What are three ways to measure dark adaption?
|
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 |
|
In dark adaption of rods and cones what is the positioning of the test light and the fixation position on the retina?
|
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.
|
|
When measuring dark adaption of the cones only what is the positioning of the test light and fixation point?
|
The observer looks directly at the light, this is the fixation point, so that the light will fall directly on the cone only fovea.
|
|
Who can we measure dark adpation of rods in and why?
|
Rod monochromats because they have no cones
|
|
What is the condition Rod Monochromat?
|
A rare genetic defect where people are born without cones.
|
|
On the dark adaption curve what is the point called where the rod begin to determine the dark adaption curve?
|
rod- cone break
|
|
Why do rods tale 20 to 30 minutes to reach their maximum sensitivity compared to 3 to 4 minutes for cones?
|
because visual pigment regeneration occurs more rapidly in cones than in rods
|
|
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?
|
visual pigment bleaching
|
|
Does all our pigment eventually become bleached if we are continuously exposed to light? Why?
|
No. because of visual pigment regeneration
|
|
What is visual pigment regeneration?
|
The process where the retinal molecule and the opsin molecule are rejoined.
|
|
What two process occur simultaneously in the retina in order to help us continually see and maintain the retina?
|
visual pigment bleaching and visual pigment regeneration
|
|
How long does cone pigment take to regenerate compared to rods?
|
Cone pigment take 6 minutes and rods take 30 minutes
|
|
In Rushton's assertion about dark adaption what two important points did his results demonstrate about the connection between perception and physiology?
|
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 |
|
What is the condition where the visual pigment can't regenerate? How does this condition commonly occur and what are the consequences?
|
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 |
|
What are the five layers of the retina?
|
1. Rod and cone receptors
2. Horizontal cells 3. Bipolar cells 4. Amacrine cells 5. Ganglion cells |
|
Which cells in the retina transmit signals out of the retina to the optic nerve?
|
Ganglion cells
|
|
Which cells in the retina are the receptors?
|
Rod and cone cells
|
|
Which two sets of cells connect neurons across the retina?
|
horizontal and amacrine cells
|
|
Which three cells form the pathway from the receptors to the optic nerver?
|
1. Rod and cone receptor cells
2. Bipolar cells 3. Ganglion cells |
|
A great degree of what process occurs in the retina because there are 126 millions cells and only 1 million ganglion cells?
|
convergence
|
|
On average how many rods and how many cones pool their signal to each ganglion cell?
|
120 rods and 6 cones
|
|
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?
|
1. the rods results in better sensitivity than the cones and
2. the cones result in better detail vision than the rods |
|
What are the two reasons why rods have greater sensitivity than cones?
|
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) |
|
How does convergence of the rod cells impact sensitivity?
|
The more rods attached to each ganglion cell the more likely it is to received the required excitatory input needed in order to fire
|
|
What do cones have better visual acuity?
|
because they have less convergence, less competing information
|
|
Why do we use the Limulus (horshoe carb) to study lateral inhibition?
|
Because the structure of the limulus eye makes it possible to stimulate individual receptors.
|
|
What are the structures in the limulus called that make it easier to study lateral inhibition?
|
Ommatidia
|
|
What is lateral inhibition?
|
information from every bipolar cell inhibits every other one
|
|
What are the three perceptual phenomena explained by lateral inhibition?
|
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 |
|
What illusion do people see in the Hermann Grid?
|
People see an illusion of grey at the intersection of white areas
|
|
Which type of cell in the retina is responsible for lateral inhibition?
|
bipolar cells
|
|
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?
|
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
|
|
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?
|
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.
|
|
Why do we need lateral inhibition?
|
To detect edges in the environment.
|
|
What activity demonstrates that lateral inhibition does not fully explain simultaneous contrast?
|
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.
|
|
What occurs in whites illusion that that is contrary to what we would expect if lateral inhibition was at play?
|
That the grey rectangle bordered by white would appear darker and not lighter and vice versa for the black boarded rectangle
|
|
What concept did Adam Gilchrist and colleagues offer to explain white illusion? Explain.
|
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. |