1
Q
What is psychophysics
A
The study of the relationship between physical stimuli and perceptual responses
2
Q
What is threshold
A
The minimum quantity of a stimulus that can be detected
3
Q
What is psychometric function
A
The percentage of a stimuli detected is plotted as a function of stimulus intensity to produce a Frequency of Seeing Curve (FOS)
4
Q
What does an ideal observer manifest?
A
An unambiguous Threshold
5
Q
What is seen below the threshold for ideal patients
A
No stimulus
6
Q
What is seen above the threshold for ideal patients
A
Stimulus is always seen
7
Q
What occurs in a real observer
A
As the intensity of stimulus is increases, the probability of seeing the stimulus increases
There is no clear defined intensity below which the stimulus is never seen and above which it is always seen
8
Q
What is threshold based on
A
Theoretical considerations
9
Q
What is threshold defined as
A
The intensity that results n detection of the stimulus 50% of the presentations
10
Q
T/F a diseased visual system is noisier than a healthy one
A
True
11
Q
How does a diseased visual system’s FOS curve look
A
Less steep (more flat)
12
Q
What is the method of ascending limits?
A
- The stimulus is initially not visible
- the stimulus intensity is increased until it is visible
- several trials are done the average is taken
13
Q
What are the advantages of ascending limits?
A
Dark adaptometry (retinal adaptation is minimally affected by the stimulus)
14
Q
What are the disadvantages of the ascending limits
A
Observer anticipation
Mitigation Potential bias
15
Q
What is the method of descending limits
A
- stimulus is clearly visible at beginning
- stimulus intensity in decreased until it is no longer seen
- serval trials, average taken
16
Q
What are the advantages of descending limit
A
Determination of VA (Snellen)
17
Q
How is Threshold MAR determined
A
When optotypes are too small to be resolved
18
Q
What are the disadvantages of descending limit
A
Observer anticipation
Mitigation of potential bias
19
Q
What is the staircase method of determination of threshold
A
Combines ascending and descending limits
- stimulus starts low, increased until visible
- intensity is decreased until no longer seen
- thanks average of a few reversals to determine threshold
20
Q
What are the advantages of staircase method
A
Quick and reliable
Psychophysical method
Automated VF testing
21
Q
What is the method of constant stimuli
A
- Stimulus visibility is varied randomly from presentation to presentation
- FOS curve is plotted based on subjects responses
Yes/No, blank trial, false positive, and false positive
22
Q
What is yes/no procedure
A
Observer is asked whether stimulus is seen or not
23
Q
What is blank trial
A
When no stimulus s presented, even though the observer is asked
24
Q
What is false positive
A
The number of times the observer reports seeing the stimulus during a blank trial
25
What is false negative
When the stimulus is clearly above threshold and the subject reports that a stimulus is not seen
26
What are the advantages of constant stimuli
Maintains overseers expectation at the same level
27
What are the disadvantages of constant stimuli
Time consuming
Not prescribed from clinical applications
False positives and negatives affect FOS curve
Mitigation: forced choice method
28
What is the method of adjustment
Subject adjusts the stimulus until it barely visible or invisible
29
What are advantages of adjustment
Allows for relatively quick Threshold determination
30
What are the disadvantages of adjustment
Repeatability is not high
31
What is the strict threshold criterion for forced choice method
Do NOT report seeing a stimulus until they are absolutely certain they see it
High threshold (low sensitivity)
32
What is the lax threshold criterion for forced choice method
DO report seeing a stimulus even though they may have a great deal of uncertainty regarding their decision
Low threshold (high sensitivity)
33
What are the observers criterion for forced choice method
1. Not all observers use the same criteria when defined whether or not they see a stimulus
2. Threshold criteria may vary from trial to trail for the same observer
3. An observer may use one set of criteria for one type o stimulus and another set for a different stimulus
34
How is forced choice method done
The observers criteria are minimized by forcing a choice
- The stimulus is randomly presented in one of 2 windows. The other window does not have a stimulus
- the observer is FORCED to choose which window contains the stimulus
The patient CANNOT say they do not see a stimulus
Threshold criteria is reduced
35
What is the 2-alternative forced choice (2AFC) method
The observer is forced to choose between 2 alternatives
The lowest percentage correct is 50% (the observer is expected to guess correctly 50% of the time)
Threshold is typically assumed to be the point midway between chance performance(50%) and perfect performance (100%)
36
What is the threshold for 2-alternative forced choice method
75%
37
What is the 4-alternative forced choice (4AFC) method
Stimulus is randomly presented in one of 4 windows
-the psychometric function of the experiment has chance performance of 25%
38
What is the threshold of 4AFC method
62.5%
39
Why is 4AFC better than 2AFC?
The 4AFC psychometric function is steeper, the threshold can be ascertained wth more confidence
40
What are the advantages of forced choice method?
Lower thresholds
When the observer is forced to guess, they often do remarkably well despite claims they cannot see the stimulus
-used effectively to determine the VA and other visual capabilities of infants
41
T/F this is D.r Martin's last lecture
True
42
What can influence the threshold determination
Decision criteria
Attention
Motivation
Internal neural noise
43
What does signal detection theory provide
A useful model to predict the facets of certain of these factors
44
T/F a stimulus produces a neural signal that is superimposed on this neural noise
True
45
What is the observers task in detection
To differentiate the signal and noise combination from the background noise alone
46
What is neural noise
Activation present in the absence of a stimulus
47
What is true of neural noise (2 things)
1. Randomly distributed over time
| 2. Randomly fluctuating over time
48
What happens when a signal is presented in the presence of noise
A stimulus ashes constant level of neural activation (a signal) yo be added to the noise.
49
T/F neural noise can be present in the absence of a signal
True
50
When there is a signal presented with noise the signal is superimposed on the noise
True
51
Look at slide 7 graph
Lecture part 2
52
T/F as the signal becomes larger, the distributions of N and N+S become further apart
And detectabiloty of the stimulus increases
True
53
What is low dectability of a signal
When a stimulus is weak, there is a substantial overlap of the N and N=S distributions
54
When the level of neural activation is above criteria line the subject will report.....
Seeing a stimulus
55
When teh level of neural activation is below the criterion line the subject will report...
Not seeing the stimulus
56
What is the subjects repsonse determined by
The level of neural activation
57
What is a hit
Occurs when the stimulus results in neural activity that exceeds the threshold criterion
58
What is a miss
The activity does not exceed the criterion
59
What is a false positive
Occurs when the neural activity accedes the threshold criterion in the absence of a stimulus
60
What is a correct reject
When the activity is below the criterion during a blank trial
61
What does a lax criterion result look like
Many. Hits
Few misses
Large number of false positives
62
What does a lax criterion result look like
Fewer hits
More misses
Low number of false positives
63
What does the receiver operating characteristics (ROC) curve show
The probability of a hit as a function of the probability of a false positive for different threshold criteria
64
What is the task of Weber's law
To discriminate between the combination of stimulus and background and background alone
65
How is Weber's Law understood
By using an increment threshold experiment (see slide 14)
66
As the background intensity increases, the JND _____
What happens to the JND and background ration?
Increases
the ratio between the JND an background stays constant
67
What is light constancy
The visual system detects contrast, rather than absolute luminance. The appearance of E is the same under bright and dim lighting conditions.
68
What does brightness depend on
The background
| Simultaneous contrast
69
What is teh key to predicting the appearance of a stimulus
The contrast
NOT the luminance
70
What is the retina an extension of
The brain
71
What are the roles of the retina
Analyze data
Encodes data into a neural signal
Data transmitted to higher visual centers
72
How do you measure the receptive fields of ganglion cells
Electrophysiology
Fovea aligned with a point on screen
Microelectrode placed in extracellular fluid next to ganglion cell
Action potentials are read
Spot elicits response from cell
73
T/F a stimulus in the receptive fields will either increase or decrease the firing rate of the neuron
True
It depends on the location
74
What does a small light in the center of an ON center receptive field cause
Increase in frequency of AP
75
What does a small light in the periphery of an ON center ganglion cell cause
Reduction in AP
76
What does a large stimulus that covers the entire center of ON ganglion cause
Increase AP due to spatial summation in the center
77
What does a large stimulus that covers the entire ganglion receptive field cause
Same as if no stimulus was presented
78
T/F sine wave gratings are another strong stimulus for ganglion cells
True
79
What happens when the bright bar of a sine wave grating falls on the excitatory center
Increased AP
80
What happens when dark bars of a sine wave grating fall in the inhibitory surround
Increase AP
81
T/F eventually a point is reached where further increases in the stimulus diameter have no effect on the cells response
True
82
Look at the flow of information of the cell types
Slide 14-16
83
What are photoreceptors
Specialized sensory receptor
Contain photosensitive pigment that covert light into electrical activity
They are slightly depolarization at rest (-50mV)
They hyperpolarize when exposed to light (-70mV)
84
What kind of potential do photoreceptors have
Graded potential
85
What is a graded potential
Greater intensity causes a greater hyperpolarization
86
What is the Dark current
Na ions flow through ion channels into rod outer segment
| Producing a slight -50mV depol
87
11-cis is transformed into all-trans retinal
Yes
88
What are the 2 portions of rhodopsin
Opsin
| Chromophore
89
What is opsin
Inert chain of a.a.
| Determines the absorption profile of photopigment
90
What is chromophore
Responsive to light
| Consists of retinal
91
What is the phototransduction cascade
- Unbleached retinal is in the 11-cis state
- absorption of a quantum of light. Retinal isomerizes to all-trans. Transducin activates PDE. PDE breaks down cGMP into GMP. Closes rod outer segment Na channels. Rod hyperpol
Constrains the potential magnitude of rid hyperpol.
92
T/F when even a small amount of rods rhodopsin is bleached, all the sodium channels are closed
True
93
What are horizontal cells
Widely dispersed dendritic tree synapses with many photoreceptors
Substantial spatial summation
Graded potentials
H1- M/L cones
H2- S cones
94
Describe bipolar cells
Graded potentials
Spatial antagonism
On-center and Off center
95
Describe ON-center bipolar cells
Invaginiating synapse
Inner layer of IPL
Glutamate is inhibitory
96
Describe OFF center bipolar cells
Flat synapse
Outer IPL
Glutamate is excitatory
97
Describe amacrine cells
Center surround
Action potentials
Brief transient response at stimulus onset and offset
98
Midget bipolar cells
Small soma
Small dendritic tree
Small receptive field (1:1)
99
Diffuse bipolar cells
5-10 m/l cones
100
What is another name for Midget GCs
Retinal parvo cells
101
What do diffuse bipolar cells synapse with
Parasol GCs (retinal magno cells)
102
Parasol GCs: ____% of GCs in central 20 degrees and up to ____% more peripheral
10%
| 15%
103
Describe parasol cells
Large dendritic tres
Large surround receptive field
Center formed by several cones
104
Describe ganglion cells
Receive input from S cone bipolar cells
8%
On-center
105
What are the ganglion cell projections
LGN
Superior Colliculus
Pulvinar
106
LGN
Parvo-midget GC
Magno- parasol GC
Kongo- bistratified GCs
107
Superior colliculus
Eye movements
108
Pulvinar
Visual attention
Motion processing
Visually guided movement
109
Pretectum
Reflex control of the pupil
110
Tell me about AMD
Devastating foveal damage
Damages choriocapillaris and Bruchs membrane
Loss of overlying sensory tissue
Leading cause of blindness
111
What is used to treat AMD
Angiogenesis blocking drugs help with wet AMD
112
What is the limit to retinal prosthesis
They have been designed to stimulate GCs with a photoreceptor signal
113
T/F GC can contain photopigment
True
114
What pigment molecule can be in GCs
Melanopsin
115
What do melanopsin containing GCs project to?
| What affect does this have
SCN
Circadian rhythm
Stimulating these cells suppresses release of melanin
116
What is Seasonal Affective Disorder
Depression thought to be caused by reduction in daylight hours during winter months
Treated wth bright light therapy
117
What affects can tablets and bright lights have on us
They emit blue light
Suppresses melatonin
May interfere with sleep patterns
118
What is the LGN composed of
```
Magno cells (2 ventral layers)
Parvo cells (4 dorsal layers)
Konio cells (intrlaminar regions, between principle cells) (the smallest)
```
119
Where does the LGN project to
Visual cortex
120
What are parvo cells sensitive to
R.G color contrast
70% of retinogeniculate pathway
Not sensitive to movement
121
What are Magno cells sensitive to
Rapid movement
10% of retinogeniculate path
Mostly monochromatic (rods)
122
What are koni cells sensitive to
B/Y contrast
123
What is characterized by both parvo and konio
Color opponency
They are excited by certain wavelengths and inhibited by others
The sign of the response encodes info about the wavelength
124
What do parvo and koni cells play a critical role in
Wavelength based discrimination
125
Why do many cells in the parvo layers manifest R-G opponency
Because of input from ganglion cells
126
Why do konio cells exhibit B-Y opponency
Input from small bistratified ganglion cells
Konio cells are not confined to the interlaminar region of LGN
127
Magno cells
Weak/no color opponency
Gives response of the are sign regardless of wavelength
Do not contribute to wavelength based discrimination
128
Parvo cells responses are
Sustained response to long duration stimulus
129
Magno cell repsonse
Transient repsonse to long-duration stimulus
Brief burst of activity at onset and offset
May be due to input from transient amacrine cells
130
Partial properties of parvo cells
Similar to midget cells
| Small receptive field centers provide higher spatial resolution
131
Magno cells
Similar to parasol cells
Larger diamter axons transit APs faster than konio/parvo (myelin)
Have shorter visual latency
132
T/F the clear division into distinct parvo and magno paths seen in the retinogeniculate path is not as apparent in the cortex
True
133
Thy is the clear division into distinct parvo and magno paths seen in the retinogeniculate path is not as apparent in the cortex
P and M retinocortical paths may be the predominant inputs to the cortical ventral and dorsal processing streams
Neither retinogeniculate path appears to communicate exclusively with a particular cortical stream
134
Study in monkeys
| Lecture 4
Slide 11-13
135
Parvo path is key for
Color discrimination
| Visual acuity
136
Magno path is key to
Fast movement
| Low spatial frequencies
137
Human study slide 14-17
Isoluminant grating
138
Why do isoluminant gratings isolate the parvo system
Green and red bar activates magno to same extent
| Magno is silenced by isoluminant stimuli
139
T/F certain disease processes may differently impact the P, M, and K paths
Tru
140
What is glaucoma diagnosis based on
VF loss
ONH appearance
IOP
141
What does visual field loss indicate in the glaucoma
A substantial proportion of ganglion cells have died
142
What can glaucoma lead to
Blindness
143
In autopsies of POAG patients it is seen that axons of _____ neurons are damaged earlier than those of ____ neurons
What does this suggest?
Larger> smaller
This suggests that the magno pathway is more susceptible to glaucoma damage
144
What path is more affected by glaucoma
M
145
Perception of ____ is impaired in POAG
Frequency doubling
146
What is frequency doubling
When viewing a flickering sine wave grating
| As the temporal rate s increased the patient will note the apparent spatial frequency of the grating doubles
147
Frequency doubling study 22-24
Look at it. A lot of info
148
What is the use of HUmphrey VF good for in glaucoma
Early detection of visual field loss
| By using a the frequency doubling technique it can detect damage to M cells
149
What is developmental dyslexia
Selective impairment of reading skills in spite of normal intelligence, vision, hearing, instruction, and motivation
150
What causes dyslexia?
Unknown really
Maybe due to sensory effects or a cognitive disorder
Deficits in processing of temporal information. They cannot temporally resolve 2 consecutive stimuli. Defect of the M path
151
Tests with lower contrast are
More sensitive
152
Tests with higher contrast targets are
More specific for detecting VF defects
153
T/F each lobe of the brain is organized into different function areas
True
154
How many functional areas are devoted to analyzing visual information
About 20
155
Where is the striate cortex located
Occipital lobe
156
What are the other names for the striate cortex
Primary visua cortex
Visual area 1
V1
Brodmans’ area 17
157
What is contains in the striate a cortex
A representation of the entire visual field
158
What input dominates the striate cortex
Fovea input
159
What is cortical magnification of foveal vision due to
Increased area of cortex devoted to individual foveal ganglion cells, rather than solely to the high density of foveal ganglion cells
160
Where does the striate cortex project to
Extrastriate cortex
161
What is contained in the extrastriate cortex
V2
V4
IT
MT (V5)
162
What are the 2 processing streams
Ventral
| Dorsal
163
Ventral processing stream
What?
| Predominant input from P path
164
Dorsal processing path
Where?
| Predominates input from M path
165
T/F there is significant communication between the 2 cortical processing streams. They are not independent
True
166
What is the reciprocal project of the striate nucleus
LGN
| Pulvinar
167
Pulvinar processes
Visual attention
Motion processing
Visually guided movement
168
T/F information can flow backward toward the striate cortex from extrastriate cortex via reciprocal paths
True
| Acts as feedback
169
Simple cells
Most sensitive to an edge or bar of specific orientation
Stimulus must be a specific width
Bar/edge must be properly positioned within the cells receptive field
Receptive field can be mapped out with small spots of light which will allow to divide into excitatory and inhibitory regions
170
What do simple cell receptive fields results from
Input to LGN neurons whose receptive fields lie along a straight line
171
What is heirarchical processing
Formation of increasingly complicated receptive field arrangements
172
Complex cells respond best.
To an elongated stimulus of specific orientation
173
Stimulus position with receptive field of a simple cell is ____
Critical
174
t/F stimulus can be postponed anywhere in a complex cells receptive field
True
175
many complex cells are characterized by direction selectivity. What does this mean?
For a cell to be stimulated the stimulus must move in a specific direction. A stimulus moving in the opposites direction does not elicit a response
176
Can the receptive fields of complex cells be divided into excitatory and inhibitory regions
No
177
Complex cell theory
Slide 18-21
178
Based on Hubel and Wiesels model it shows that receptive fields of higher neurons are made of what??
Those of preceding neurons
This shows why stimulus parameters are more specific to activate a neuron at higher levels of the visual system
179
T/F the higher up in the visual system, the more stringent are the requirements to drive a visual neuron
True
180
T/F cortical neurons respond well to sine-wave gratings and are selective for a particular spatial frequency
True
181
Information from the 2 eyes is first combined here
In the striate cortex
182
Most cortical cells are binocular or monocular
Binocular, they revive input from both eyes
183
Can binocular cortical cells mediate stereopsis?
A cortical cells receptive field is determined by stimulating the right eye may be in a different potion that for the left eye.
The cortical receptive fields do not overlap at a critical distance from the eyes, because the inputs from both eyes are summed, a stimulus at this critical distance maximally activates the cortical neuron
184
What is a horopter
A line of surface contains all those points in space whose images fall on corresponding points of each eyes retina
185
T/F the majority of striate cortical neurons are binocular BUT most are dominated by one eye
True
Stimulation of the dominant eye causes a stronger repsonse than stimulation through the fellow eye
186
Ocular domaine is laid out in what pattern
A regular pattern of alternating right and left ocular dominance bands. Called ocular dominance slabs/columns . These bands run through the cortex perpendicular to its surface
187
What is teh striate correct organized according to
Orientation and ocular dominance
188
What is a hypercolumn
A complete set of ocular dominance columns and orientation columns
Each hyper-column has dimensions of 1x1 mm
189
The development of standard corral architecture requires what
Normal visual input early in life
Cortical architecture can be altered by environmental deprivation early in life
Can result in anisometropia and strabismus
190
Orientation sensitivity of the cortex is arranged in what pattern
Pinwheel pattern
191
What are striate blobs rich in
Color opponent neurons
| Manifest color contrast
192
What does the magno path bypass
The blob and interblob regions
193
Secondary to a lesion that has destroyed all striate cortex, a patient will lose what
No conscious vision
Blindsight vision, will respond to a stimulus but claim they dont see it
194
V1 projects where
To higher visual areas that are specialized to analyzing specific visual attributes
195
The receptive fields of striate cortical neurons are more complicated than those of neurons situated earlier in the visual system, largely due to hierarchical processing, with the P and M retinogeniculate paths feeding into the cortical processing streams
Yes
Perception
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