1
Q
How does wavelength and amplitude differ in terms of perception
A
-wavelength is used for perception of colour
- amplitude is used for perception of brightness
- > eg; high amplitude of 700 nm wave is a bright red light
2
Q
How much of the outer eye does the cornea make? What is the rest of the outer eye made up of?
A
- makes up 15% of the outer eye
- > it is where light first enters the eye
-rest of the eye is made of the sclera(opaque)
3
Q
Where is the pupil?
A
- it is a hole in the middle of the iris
- iris are a ring of muscles behind the cornea
4
Q
How does size of pupil change in response to illumination? Also describe acuity and sensitivity in this regard. Note pupil is involved in the amount of light entering the eye.
A
Bright-light
- > constriction
- > creates sharper image
- > higher acuity but decreased sensitivity
Low illumination
- > dilation
- > lets in more light
- > decreased acuity but increased sensitivity
5
Q
What is the role of the lens? Describe the ciliary muscles contraction and relaxation in terms of nearby objects or distant ones. Also describe the tension on the ligaments. Note lenses have a cylindrical shape.
A
- role of lens is to focus light on the retina
- > does this through accommodation
When objects are nearby
- > ciliary muscles contract
- > less tension on ligaments holding lens in shape
- > lens is natural shape(fat)
When objects are distant
- > ciliary muscles relax with focus on distant objects
- > increase the tension on the ligaments
- > the lens is flattened
6
Q
What is binocular disparity and does it construct 3D or 2D images? Note binocular disparity helps with perception of distance
A
- binocular disparity is the creation of difference in the same image on two different retinas
- construction of 3D image from two slightly different 2 D retinal images
7
Q
Where is the site of transduction in the eyes
A
-it is at the retinas
8
Q
What are the 5 layers of the retina?
A
1) Photoreceptors
- >located at the back of the retina
2) Horizontal cells
- >lateral communication
3) Bipolar cells
- >third layer
4) Amacrine cells
- >lateral communication
5) Retinal ganglion cells
- >axons projecting from surface of retina
- >gather at optic disk to exit eye
- >create blind spot
9
Q
Is the fovea indented? Where is the indentation located?
A
- fovea is indented
- >this indentation exists in the macula
10
Q
How does completion work to get rid of the blind spot?
A
- it uses info from receptors around the blind spot
- >note visual system may not always represent true image of the world
11
Q
What kind of system are cones considered to be a part of
A
- it is considered to be part of a photopic system
- > provides high acuity and coloured perception
- > found in daytime animals
12
Q
How do cones work in terms of convergence onto retinal ganglionic cells?
A
- few cone cells converge on a single retinal ganglionic cell
- > gives higher acuity
- > easier to distinguish between 2 stimuli
13
Q
Describe the three types of cones
A
S cones
- > short wavelength
- > least abundant
- > blue
- > high sensitivity
- > less concentrated in fovea
M cones
- > medium wavelength
- > green
L cones
- > long wavelength
- > ref
14
Q
Are there genetic differences in cones? And what is dichromatic vision
A
- there are genetic differences in cone types
- >note dichromatic vision is colour blindness
15
Q
What kind of a system are rods a part of
A
- it is a scotopic visual system
- >lacks detail and colour
16
Q
How do rods work in terms of their convergence onto retinal ganglionic cells?
A
- several hundred rods converge onto one retinal ganglionic cell
- > dim light stimulates several rods to activate RGC
- > but poor acuity as there are a lot of rods firing
- > 1000 x more sensitivity than cones
17
Q
What kind of vision do rods result in?
A
- they result in achromatic vision
- > shades of grey from black to white
- > not colour sensitive
18
Q
What is rhodopsin made up of
A
-it is made up of opsin and retinal
19
Q
How does rhodopsin work in terms of sodium channels and bleaching
A
- 500 nm light colour bleaches and it stops absorbing light
- > activates cGMP which closes sodium channels
- in dark red light hits and it begins to absorb light again
- sodium channels open only in the dark
- > this induces rods to keep releasing neurotransmitters in the dark
20
Q
Describe the ipsilateral and contralateral visual processing in the retina
A
- ipsilaterally via the temporal hemiretina
- contralaterally via the nasal hemiretina
21
Q
How many layers in the LGN? What layers does it receive input from and how many from each layer?
A
- there are 6 layers in the LGN
- > it receives input from 3 layers of the ipsilateral temporal hemiretina
- > it receives input from 3 layers of the contralateral nasal hemiretina
22
Q
Where do top areas of the visual field and bottom areas of the visual field end up on the striate?
A
- all areas at top of the visual field end up at bottom portion of the striate
- > below calcarine fissure
- all areas at the bottom of the visual field end up in striate above calcarine fissure
23
Q
What are the 2 independent channels in the LGN
A
-it is the P channels and the M channels
24
Q
Describe the parvocellular layer of the LGN. Where is it in the LGN? What does it respond to? Where does it get input from?
A
- small cell bodies
- > top 4 layers of the lgn
- > responds to colour and gets input from cones
- > projects to bottom of striate layer(4 neurons)
25
Describe the magnocellular layer of the LGN. Where is it in the LGN? What does it respond to? Where does it get input from?
- big cell bodies
- >bottom 2 layers of the lgn
- >responds to movement and gets input from the rods
- >projects to top part of striate layer
26
What is a visual edge? How is it useful
-perception of contrast between 2 adjacent areas of the visual field
- it is useful for:
- >defining position of objects
- >perception of edge=perception of contrast
- >common across species
27
What are Mach bands
-non existent stripes of brightness and darkness
28
Describe lateral inhibition in horseshoe crabs
- large receptor ommatidium with own axon
| - when single ommatidium fires it inhibits neighbouring ones via the lateral plexus
29
What shape receptive fields do neurons at levels of striate cortex, LGN and RGC have?
-they all have round circular receptive fields
30
What is most common type of cell in visual system?
- it is the center-surround cells
| - >they have an excitatory and an inhibitory area
31
Describe the on center of neurons vs the off center of neurons. How they respond in terms of the light being in the periphery and how that relates to activity bursts.
On center
->when light in the periphery is turned off, it responds with activity bursts
Off center
->when light in the periphery is turned on, responds with activity bursts.
32
Do neurons responding to fovea have larger or smaller receptive fields than periphery? Is there more or less convergence?
- neurons responding in the fovea have smaller receptive fields than the periphery
- >there is less convergence
33
What do receptive field of simple cortical cells respond to? Straight or circular edges? Are they monocular? What is the shape of the receptive fields?
- striate neurons(simple cortical cells) respond to straight edges instead of circular ones
- >different from lower layer 4 neurons
-on and off region for straight lines
- they are monocular
- >respond to lines of particular orientation or position
-rectangular receptive fields
34
What is the convergence of cells starting from LGN to complex cells. Note overall the pattern is that neurons with simple preference converge onto those with more complex preference.
- so the levels of processing start with the LGN
- >then go to lower layer 4
- >then to simple cells
- >finally move on to complex cells
35
What is the shape of the complex cortical cells shape? And what are the numbers like compared to the simple cells?Is it responsive to diffuse light?
- it is more numerous than simple cells
- >has a rectangular field receptive field
- it does not respond to diffused light
36
Compare receptive fields of complex cells to that of simple cells. Also do complex cells have ocular dominance?
Complex cells
- >larger receptive fields
- >no static on and off regions
- >many are binocular
-complex cells do have ocular dominance and respond more strongly to stimulation in one eye than the other eye
37
What was found when the electrode was lowered vertically into striate cortex
- common characteristics of cells in a column were discovered
- >receptive fields in the same area of the visual field exist
- >half from each eye
-note each cell prefers lines that are in the same direction
38
What was found when the electrode was lowered horizontally into the striate cortex?
- each successive cell receptive field is in slightly different location in the visual field
- >each cell therefore responds to different orientations
-note successive cells alternate with respect to left or right eye dominance
39
How can the V1 cortex be divided into independent columns? How can these columns be further divided for ocular dominance? Then from that how can you divide each column to smaller columns that prefer a particular location?
- each column is responsible for analyzing input from different areas of the visual field
- >each cortical column can be further divided into ocular dominance
- >the columns divided for ocular dominance can be further divided into half for columns that prefer particular locations
40
Describe the achromatic colour hues. Name the three
- Black->produced by a lack of light
- White->produced by mixture of wavelengths in equal proportions
- Gray->produced by mixture of wavelengths in equal proportions at lower intensities.
41
Describe the opponent processing theory. Refer to the term complementary colours.
- complementary colours cannot exist together in the same colour
- >no greenish red or yellowish blue
- >when light combined equally, they create white
42
Can trichromatic theory of colour explain afterimages
-NO
43
What is microspectrophotemtry used for? What did it confirm?
- it is a technique used for measuring the absorption spectrum of photopigments contained in one single cone
- >it confirmed the existence of 3 different types of cones
44
What is Land's retinex theory
- colour is determined by reflectance
- >reflectance is the proportion of light of different wavelengths a surface reflects
- note the amount of light absorbed and reflected by a surface is constant
- >so light constancy remains
- cortical neurons calculate contrast
- >they are dual opponent color cells
- >circular receptive field
- >have an on center and an off center
- >concentrated in v1 in peg like columns(blob cells)
45
Do you need all 3 wavelength bands for light constancy
-Yes
46
What is scotoma? How does it result?
- it is damage in one hemisphere in the v1 cortex
- it is a result of combat wounds or migraines
- there is an area of blindness in contralateral visual field of both eyes
47
How do you check for the area of blindness in individuals with scotoma?How does it work?What does it allow the researchers to determine?
you can do a perimetry test
- >it determines area of blindness
- >patient stares at fixation point with one eye open
- >point moves. respond when see the dot
-it allows the researchers to map out the visual field of each eye
48
How does blindsight work or seeing without consciousness? How is this possible
- patients with complete lesions of V1 report total blindness
- >can still perform visually guided tasks
- >eg; grabbed for moving objects or indicated direction of momenent
- note some visual signals bypass v1 and go to prestriate cortex to make up for damaged visual function
- >patients are still unaware they can see
49
Describe the 24 subsections that make up the secondary visual cortex
- each is retinotopic
- each responds to different stimuli
- each has hypercomplex cells
- >responds to stimuli of certain size/shape/length/movement
- >neurons have larger receptive fields earlier in the hierarchy
50
Describe the prestriate cortex and the inferotemporal cortex locations. Note they are part of the secondary visual cortex.
Prestriate cortex
->band surrounding the striate
Inferotemporal cortex
->inferior temporal lobe
51
Where is the association visual cortex? What is its function
- it is outside the primary visual area
- >note each sensory system has its onw association cortices
- it has higher visual functions
- >such as giving meaning to things seen
52
Does the association visual cortex recognize objects or does it merely recognize its features
- it is used more for recognition of objects rather than the features
- cells respond to complex patterns and structure
- >so maybe the involvement of grandmother cells?
53
What is the dorsal stream referred to as?Describe the pathway of the dorsal stream.
- it is the where pathway
- the pathway is:
- >V1->dorsal prestriate->posterior parietal cortex
- >neurons respond to spatial stimuli
54
What pathway input is the dorsal stream fed by?Is it involved in motion perception?
- it is fed by the M pathway input
- it is involved in motion perception
- >V5 of the brain is crucial in processing motion
55
What is the alternative theory for the dorsal stream
-"it is the control of behavior"
56
What is the ventral stream refered to as? Describe the pathway of the ventral stream
- it is the what pathway
- the pathway is:
- >V1->ventral prestriate cortex->inferotemporal cortex
- >neurons respond to perception of objects
57
What pathway input is the ventral stream fed by? Is it involved in perception of shape and colour?
- it is fed by the p pathway
- it is involved in perception fo shape and colour
- >V4 is crucial for processing of color shape and info
Psych 275
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