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Perception > Block 11 > Flashcards

Block 11 Flashcards

1
Q

What is psychophysics

A

The study of the relationship between physical stimuli and perceptual responses

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2
Q

What is threshold

A

The minimum quantity of a stimulus that can be detected

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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)

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4
Q

What does an ideal observer manifest?

A

An unambiguous Threshold

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5
Q

What is seen below the threshold for ideal patients

A

No stimulus

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6
Q

What is seen above the threshold for ideal patients

A

Stimulus is always seen

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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

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8
Q

What is threshold based on

A

Theoretical considerations

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9
Q

What is threshold defined as

A

The intensity that results n detection of the stimulus 50% of the presentations

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10
Q

T/F a diseased visual system is noisier than a healthy one

A

True

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11
Q

How does a diseased visual system’s FOS curve look

A

Less steep (more flat)

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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
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13
Q

What are the advantages of ascending limits?

A

Dark adaptometry (retinal adaptation is minimally affected by the stimulus)

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14
Q

What are the disadvantages of the ascending limits

A

Observer anticipation

Mitigation Potential bias

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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
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16
Q

What are the advantages of descending limit

A

Determination of VA (Snellen)

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17
Q

How is Threshold MAR determined

A

When optotypes are too small to be resolved

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18
Q

What are the disadvantages of descending limit

A

Observer anticipation

Mitigation of potential bias

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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
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20
Q

What are the advantages of staircase method

A

Quick and reliable
Psychophysical method

Automated VF testing

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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

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22
Q

What is yes/no procedure

A

Observer is asked whether stimulus is seen or not

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23
Q

What is blank trial

A

When no stimulus s presented, even though the observer is asked

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24
Q

What is false positive

A

The number of times the observer reports seeing the stimulus during a blank trial

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25
Q

What is false negative

A

When the stimulus is clearly above threshold and the subject reports that a stimulus is not seen

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26
Q

What are the advantages of constant stimuli

A

Maintains overseers expectation at the same level

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27
Q

What are the disadvantages of constant stimuli

A

Time consuming

Not prescribed from clinical applications

False positives and negatives affect FOS curve

Mitigation: forced choice method

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28
Q

What is the method of adjustment

A

Subject adjusts the stimulus until it barely visible or invisible

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29
Q

What are advantages of adjustment

A

Allows for relatively quick Threshold determination

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30
Q

What are the disadvantages of adjustment

A

Repeatability is not high

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31
Q

What is the strict threshold criterion for forced choice method

A

Do NOT report seeing a stimulus until they are absolutely certain they see it

High threshold (low sensitivity)

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32
Q

What is the lax threshold criterion for forced choice method

A

DO report seeing a stimulus even though they may have a great deal of uncertainty regarding their decision

Low threshold (high sensitivity)

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33
Q

What are the observers criterion for forced choice method

A
  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
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34
Q

How is forced choice method done

A

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

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35
Q

What is the 2-alternative forced choice (2AFC) method

A

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%)

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36
Q

What is the threshold for 2-alternative forced choice method

A

75%

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37
Q

What is the 4-alternative forced choice (4AFC) method

A

Stimulus is randomly presented in one of 4 windows

-the psychometric function of the experiment has chance performance of 25%

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38
Q

What is the threshold of 4AFC method

A

62.5%

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39
Q

Why is 4AFC better than 2AFC?

A

The 4AFC psychometric function is steeper, the threshold can be ascertained wth more confidence

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40
Q

What are the advantages of forced choice method?

A

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

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41
Q

T/F this is D.r Martin’s last lecture

A

True

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42
Q

What can influence the threshold determination

A

Decision criteria
Attention
Motivation
Internal neural noise

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43
Q

What does signal detection theory provide

A

A useful model to predict the facets of certain of these factors

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44
Q

T/F a stimulus produces a neural signal that is superimposed on this neural noise

A

True

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45
Q

What is the observers task in detection

A

To differentiate the signal and noise combination from the background noise alone

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46
Q

What is neural noise

A

Activation present in the absence of a stimulus

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47
Q

What is true of neural noise (2 things)

A
  1. Randomly distributed over time

2. Randomly fluctuating over time

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48
Q

What happens when a signal is presented in the presence of noise

A

A stimulus ashes constant level of neural activation (a signal) yo be added to the noise.

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49
Q

T/F neural noise can be present in the absence of a signal

A

True

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50
Q

When there is a signal presented with noise the signal is superimposed on the noise

A

True

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51
Q

Look at slide 7 graph

A

Lecture part 2

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52
Q

T/F as the signal becomes larger, the distributions of N and N+S become further apart

And detectabiloty of the stimulus increases

A

True

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53
Q

What is low dectability of a signal

A

When a stimulus is weak, there is a substantial overlap of the N and N=S distributions

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54
Q

When the level of neural activation is above criteria line the subject will report…..

A

Seeing a stimulus

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55
Q

When teh level of neural activation is below the criterion line the subject will report…

A

Not seeing the stimulus

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56
Q

What is the subjects repsonse determined by

A

The level of neural activation

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57
Q

What is a hit

A

Occurs when the stimulus results in neural activity that exceeds the threshold criterion

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58
Q

What is a miss

A

The activity does not exceed the criterion

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59
Q

What is a false positive

A

Occurs when the neural activity accedes the threshold criterion in the absence of a stimulus

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60
Q

What is a correct reject

A

When the activity is below the criterion during a blank trial

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61
Q

What does a lax criterion result look like

A

Many. Hits
Few misses
Large number of false positives

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62
Q

What does a lax criterion result look like

A

Fewer hits
More misses
Low number of false positives

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63
Q

What does the receiver operating characteristics (ROC) curve show

A

The probability of a hit as a function of the probability of a false positive for different threshold criteria

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64
Q

What is the task of Weber’s law

A

To discriminate between the combination of stimulus and background and background alone

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65
Q

How is Weber’s Law understood

A

By using an increment threshold experiment (see slide 14)

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66
Q

As the background intensity increases, the JND _____

What happens to the JND and background ration?

A

Increases

the ratio between the JND an background stays constant

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67
Q

What is light constancy

A

The visual system detects contrast, rather than absolute luminance. The appearance of E is the same under bright and dim lighting conditions.

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68
Q

What does brightness depend on

A

The background

Simultaneous contrast

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69
Q

What is teh key to predicting the appearance of a stimulus

A

The contrast

NOT the luminance

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70
Q

What is the retina an extension of

A

The brain

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71
Q

What are the roles of the retina

A

Analyze data
Encodes data into a neural signal
Data transmitted to higher visual centers

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72
Q

How do you measure the receptive fields of ganglion cells

A

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

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73
Q

T/F a stimulus in the receptive fields will either increase or decrease the firing rate of the neuron

A

True

It depends on the location

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74
Q

What does a small light in the center of an ON center receptive field cause

A

Increase in frequency of AP

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75
Q

What does a small light in the periphery of an ON center ganglion cell cause

A

Reduction in AP

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76
Q

What does a large stimulus that covers the entire center of ON ganglion cause

A

Increase AP due to spatial summation in the center

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77
Q

What does a large stimulus that covers the entire ganglion receptive field cause

A

Same as if no stimulus was presented

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78
Q

T/F sine wave gratings are another strong stimulus for ganglion cells

A

True

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79
Q

What happens when the bright bar of a sine wave grating falls on the excitatory center

A

Increased AP

80
Q

What happens when dark bars of a sine wave grating fall in the inhibitory surround

A

Increase AP

81
Q

T/F eventually a point is reached where further increases in the stimulus diameter have no effect on the cells response

A

True

82
Q

Look at the flow of information of the cell types

A

Slide 14-16

83
Q

What are photoreceptors

A

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
Q

What kind of potential do photoreceptors have

A

Graded potential

85
Q

What is a graded potential

A

Greater intensity causes a greater hyperpolarization

86
Q

What is the Dark current

A

Na ions flow through ion channels into rod outer segment

Producing a slight -50mV depol

87
Q

11-cis is transformed into all-trans retinal

A

Yes

88
Q

What are the 2 portions of rhodopsin

A

Opsin

Chromophore

89
Q

What is opsin

A

Inert chain of a.a.

Determines the absorption profile of photopigment

90
Q

What is chromophore

A

Responsive to light

Consists of retinal

91
Q

What is the phototransduction cascade

A
  • 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
Q

T/F when even a small amount of rods rhodopsin is bleached, all the sodium channels are closed

A

True

93
Q

What are horizontal cells

A

Widely dispersed dendritic tree synapses with many photoreceptors

Substantial spatial summation

Graded potentials

H1- M/L cones
H2- S cones

94
Q

Describe bipolar cells

A

Graded potentials
Spatial antagonism

On-center and Off center

95
Q

Describe ON-center bipolar cells

A

Invaginiating synapse
Inner layer of IPL
Glutamate is inhibitory

96
Q

Describe OFF center bipolar cells

A

Flat synapse
Outer IPL
Glutamate is excitatory

97
Q

Describe amacrine cells

A

Center surround
Action potentials
Brief transient response at stimulus onset and offset

98
Q

Midget bipolar cells

A

Small soma
Small dendritic tree
Small receptive field (1:1)

99
Q

Diffuse bipolar cells

A

5-10 m/l cones

100
Q

What is another name for Midget GCs

A

Retinal parvo cells

101
Q

What do diffuse bipolar cells synapse with

A

Parasol GCs (retinal magno cells)

102
Q

Parasol GCs: ____% of GCs in central 20 degrees and up to ____% more peripheral

A

10%

15%

103
Q

Describe parasol cells

A

Large dendritic tres
Large surround receptive field
Center formed by several cones

104
Q

Describe ganglion cells

A

Receive input from S cone bipolar cells
8%
On-center

105
Q

What are the ganglion cell projections

A

LGN
Superior Colliculus
Pulvinar

106
Q

LGN

A

Parvo-midget GC
Magno- parasol GC
Kongo- bistratified GCs

107
Q

Superior colliculus

A

Eye movements

108
Q

Pulvinar

A

Visual attention
Motion processing
Visually guided movement

109
Q

Pretectum

A

Reflex control of the pupil

110
Q

Tell me about AMD

A

Devastating foveal damage
Damages choriocapillaris and Bruchs membrane
Loss of overlying sensory tissue
Leading cause of blindness

111
Q

What is used to treat AMD

A

Angiogenesis blocking drugs help with wet AMD

112
Q

What is the limit to retinal prosthesis

A

They have been designed to stimulate GCs with a photoreceptor signal

113
Q

T/F GC can contain photopigment

A

True

114
Q

What pigment molecule can be in GCs

A

Melanopsin

115
Q

What do melanopsin containing GCs project to?

What affect does this have

A

SCN
Circadian rhythm

Stimulating these cells suppresses release of melanin

116
Q

What is Seasonal Affective Disorder

A

Depression thought to be caused by reduction in daylight hours during winter months

Treated wth bright light therapy

117
Q

What affects can tablets and bright lights have on us

A

They emit blue light
Suppresses melatonin
May interfere with sleep patterns

118
Q

What is the LGN composed of

A 
Magno cells (2 ventral layers)
Parvo cells (4 dorsal layers)
Konio cells (intrlaminar regions, between principle cells) (the smallest)
119
Q

Where does the LGN project to

A

Visual cortex

120
Q

What are parvo cells sensitive to

A

R.G color contrast
70% of retinogeniculate pathway
Not sensitive to movement

121
Q

What are Magno cells sensitive to

A

Rapid movement
10% of retinogeniculate path
Mostly monochromatic (rods)

122
Q

What are koni cells sensitive to

A

B/Y contrast

123
Q

What is characterized by both parvo and konio

A

Color opponency

They are excited by certain wavelengths and inhibited by others

The sign of the response encodes info about the wavelength

124
Q

What do parvo and koni cells play a critical role in

A

Wavelength based discrimination

125
Q

Why do many cells in the parvo layers manifest R-G opponency

A

Because of input from ganglion cells

126
Q

Why do konio cells exhibit B-Y opponency

A

Input from small bistratified ganglion cells

Konio cells are not confined to the interlaminar region of LGN

127
Q

Magno cells

A

Weak/no color opponency
Gives response of the are sign regardless of wavelength
Do not contribute to wavelength based discrimination

128
Q

Parvo cells responses are

A

Sustained response to long duration stimulus

129
Q

Magno cell repsonse

A

Transient repsonse to long-duration stimulus

Brief burst of activity at onset and offset

May be due to input from transient amacrine cells

130
Q

Partial properties of parvo cells

A

Similar to midget cells

Small receptive field centers provide higher spatial resolution

131
Q

Magno cells

A

Similar to parasol cells
Larger diamter axons transit APs faster than konio/parvo (myelin)

Have shorter visual latency

132
Q

T/F the clear division into distinct parvo and magno paths seen in the retinogeniculate path is not as apparent in the cortex

A

True

133
Q

Thy is the clear division into distinct parvo and magno paths seen in the retinogeniculate path is not as apparent in the cortex

A

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
Q

Study in monkeys

Lecture 4

A

Slide 11-13

135
Q

Parvo path is key for

A

Color discrimination

Visual acuity

136
Q

Magno path is key to

A

Fast movement

Low spatial frequencies

137
Q

Human study slide 14-17

A

Isoluminant grating

138
Q

Why do isoluminant gratings isolate the parvo system

A

Green and red bar activates magno to same extent

Magno is silenced by isoluminant stimuli

139
Q

T/F certain disease processes may differently impact the P, M, and K paths

A

Tru

140
Q

What is glaucoma diagnosis based on

A

VF loss
ONH appearance
IOP

141
Q

What does visual field loss indicate in the glaucoma

A

A substantial proportion of ganglion cells have died

142
Q

What can glaucoma lead to

A

Blindness

143
Q

In autopsies of POAG patients it is seen that axons of _____ neurons are damaged earlier than those of ____ neurons

What does this suggest?

A

Larger> smaller

This suggests that the magno pathway is more susceptible to glaucoma damage

144
Q

What path is more affected by glaucoma

A

M

145
Q

Perception of ____ is impaired in POAG

A

Frequency doubling

146
Q

What is frequency doubling

A

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
Q

Frequency doubling study 22-24

A

Look at it. A lot of info

148
Q

What is the use of HUmphrey VF good for in glaucoma

A

Early detection of visual field loss

By using a the frequency doubling technique it can detect damage to M cells

149
Q

What is developmental dyslexia

A

Selective impairment of reading skills in spite of normal intelligence, vision, hearing, instruction, and motivation

150
Q

What causes dyslexia?

A

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
Q

Tests with lower contrast are

A

More sensitive

152
Q

Tests with higher contrast targets are

A

More specific for detecting VF defects

153
Q

T/F each lobe of the brain is organized into different function areas

A

True

154
Q

How many functional areas are devoted to analyzing visual information

A

About 20

155
Q

Where is the striate cortex located

A

Occipital lobe

156
Q

What are the other names for the striate cortex

A

Primary visua cortex
Visual area 1
V1
Brodmans’ area 17

157
Q

What is contains in the striate a cortex

A

A representation of the entire visual field

158
Q

What input dominates the striate cortex

A

Fovea input

159
Q

What is cortical magnification of foveal vision due to

A

Increased area of cortex devoted to individual foveal ganglion cells, rather than solely to the high density of foveal ganglion cells

160
Q

Where does the striate cortex project to

A

Extrastriate cortex

161
Q

What is contained in the extrastriate cortex

A

V2
V4
IT
MT (V5)

162
Q

What are the 2 processing streams

A

Ventral

Dorsal

163
Q

Ventral processing stream

A

What?

Predominant input from P path

164
Q

Dorsal processing path

A

Where?

Predominates input from M path

165
Q

T/F there is significant communication between the 2 cortical processing streams. They are not independent

A

True

166
Q

What is the reciprocal project of the striate nucleus

A

LGN

Pulvinar

167
Q

Pulvinar processes

A

Visual attention
Motion processing
Visually guided movement

168
Q

T/F information can flow backward toward the striate cortex from extrastriate cortex via reciprocal paths

A

True

Acts as feedback

169
Q

Simple cells

A

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
Q

What do simple cell receptive fields results from

A

Input to LGN neurons whose receptive fields lie along a straight line

171
Q

What is heirarchical processing

A

Formation of increasingly complicated receptive field arrangements

172
Q

Complex cells respond best.

A

To an elongated stimulus of specific orientation

173
Q

Stimulus position with receptive field of a simple cell is ____

A

Critical

174
Q

t/F stimulus can be postponed anywhere in a complex cells receptive field

A

True

175
Q

many complex cells are characterized by direction selectivity. What does this mean?

A

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
Q

Can the receptive fields of complex cells be divided into excitatory and inhibitory regions

A

No

177
Q

Complex cell theory

A

Slide 18-21

178
Q

Based on Hubel and Wiesels model it shows that receptive fields of higher neurons are made of what??

A

Those of preceding neurons

This shows why stimulus parameters are more specific to activate a neuron at higher levels of the visual system

179
Q

T/F the higher up in the visual system, the more stringent are the requirements to drive a visual neuron

A

True

180
Q

T/F cortical neurons respond well to sine-wave gratings and are selective for a particular spatial frequency

A

True

181
Q

Information from the 2 eyes is first combined here

A

In the striate cortex

182
Q

Most cortical cells are binocular or monocular

A

Binocular, they revive input from both eyes

183
Q

Can binocular cortical cells mediate stereopsis?

A

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
Q

What is a horopter

A

A line of surface contains all those points in space whose images fall on corresponding points of each eyes retina

185
Q

T/F the majority of striate cortical neurons are binocular BUT most are dominated by one eye

A

True

Stimulation of the dominant eye causes a stronger repsonse than stimulation through the fellow eye

186
Q

Ocular domaine is laid out in what pattern

A

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
Q

What is teh striate correct organized according to

A

Orientation and ocular dominance

188
Q

What is a hypercolumn

A

A complete set of ocular dominance columns and orientation columns

Each hyper-column has dimensions of 1x1 mm

189
Q

The development of standard corral architecture requires what

A

Normal visual input early in life

Cortical architecture can be altered by environmental deprivation early in life

Can result in anisometropia and strabismus

190
Q

Orientation sensitivity of the cortex is arranged in what pattern

A

Pinwheel pattern

191
Q

What are striate blobs rich in

A

Color opponent neurons

Manifest color contrast

192
Q

What does the magno path bypass

A

The blob and interblob regions

193
Q

Secondary to a lesion that has destroyed all striate cortex, a patient will lose what

A

No conscious vision

Blindsight vision, will respond to a stimulus but claim they dont see it

194
Q

V1 projects where

A

To higher visual areas that are specialized to analyzing specific visual attributes

195
Q

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

A

Yes

Perception (6 decks)

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