Block 11 Flashcards
Study of the relationship between the physical stimuli and perceptual responses
Psychophysics
The minimum quantity of a stimulus that can be detected
Threshold
Percentage of stimuli detected is plotted as a function of stimuli intensity to produce
FOS curve (frequency of seeing) or (psychometric function)
Type of observer that’s manifests an unambiguous threshold (never seen below threshold, above threshold is always seen)
Ideal observer
Type of observer: As the intensity of stimulus in creased, the probability of seeing it increases
Real observer
Type of observer: no clearly defined intensity below which the stimulus is never seen and above which it is always seen
Real observer
A diseased visual system in _______ than a healthy one
Noises
A noiser visual system makes the FOS curve
Less steep (more flat)
6 mothers to measure the threshold
Ascending limits Descending limits Staircase Constant stimuli Adjustment Forced choice
How the the method for finding threshold determined
By the nature of the experiment or procedure
Stimulus is initially not visible, intensity increased until visible, done several times and averaged to determine threshold
Method of ascending limits
Advantage of method of ascending limits
Dark adaptometry
Disadvantage of method of ascending limits
Observer anticipation (Begin each trial at a different intensity)
Reverse method of ascending limits (stimulus clearly visible and decreased until no longer seen)
Method of descending limits
Advantage of method of descending limits
Determination of VA
Disadvantage of method of descending limits
Observer anticipation
Combo of ascending and descending limits
Staircase method
Advantages of staircase method
Quick and reliable
Psychophysical experimentation
Automated visual field testing
A “yes/no” procedure where the stimulus is varied randomly and the curve is plotted based on response
- involved blank trials, false positive and false negatives
Method of constant stimuli
Advantage of method of constant stimuli
Maintains observers expectation at same level
Diadvantage of method of constant stimuli
Time consuming
False pos/neg affect curve and must be adjusted
When no stimulus is presented, even though the observer is asked
Blank trials
Observer reports seeing the stimulus during a blank trial
False positive
Stimulus is above threshold and the subject reports the stimulus is not seen
False negative
The subject adjusts the stimulus intensity until it is barely visible/invisible
Method of adjustment
Advantage of method of adjustment
Pretty quick
Disadvantage of method of adjustment
Repeatability is not as high as other methods
What are the 3 observer’s criterion involved in forced choice method
1- not all use the ‘same criteria’
2- threshold criteria may vary trial to trial for same observer
3- observer Amy use one set of criteria for one type of stimulus and another set for a different stimulus
Criterion: do not report seeing a stimulus until absolutely certain (give high threshold)
Strict threshold criterion
Criterion: do report seeing a stimulus even though they may have a great deal of uncertainly (give low threshold)
Lax threshold criterion
Effects of observer’s criteria are minimized by forcing a choice
Forced choice method
Example of a 2 forced choice method
Vector vision CSV chart
Threshold for a 2AFC (2 alternative forced choice)
75%
Threshold is assumed to be the point midway between what
Chance performance and perfect performance
How to determine chance performance
The chance that they will get it correct
Threshold for 4AFC
62.5%
The steeper the curve, the more or less confident?
More
Advantages of forced choice method
- lower thresholds
- used effectively to determine the VA and other visual capabilities of infants
- when forced to guess, they do well despite claiming they cannot see the stimulus
4 things that influence the determination of threshold
Decision criteria
Attention
Motivation
Internal neural noise
What does signal detection theory provide
A useful model to predict the effects of certain factors
How are the neural signal produced by the stimulus and neural noise related
Superimposed
What is the task of the observer
To differentiate the signal and noise combo FROM background noise
Present in the absence of a stimulus
Neural noise
Randomly distributed over time and randomly fluctuates over time
Neural noise
Stimulus causes a constant level of neural activation to be added to the noise
Noise + signal
As the signal becomes larger, what happens to the noise and noise+signal
Get further apart
As the signal becomes larger, what happens to detectability
Increases
It is easer for observer to determine noise+signal if the signal is: large or small
Larger
When there is a large detectability (d), how does a viewer see it
No uncertainty regarding whether it was presented or not
How strong is the signal when there is overlap of the N and N+S
Weak stimulus
If the stimulus is delivered what the noise is low, what is the resulting level of neural activation
Ambiguous
- no way to be certain if the stimulus is absent or present
If the stimulus is delivered when the noise is high, what is the resulting level of neural activation
Unambiguous
- neural noise only occurs when stimulus is present
When the level of neural activation is above the criterion line, will the subject see the stimulus?
Yes
When the level of neural activation is below the criterion line, will the subject see the stimulus?
No
The subjects response is determined by what
The level of neural activation
Is the subjects response determined by whether the stimulus is presented or not?
No
When the stimulus results in a neural activity that exceeds the threshold criterion
Hit
When the activity does no exceed the criterion
Miss
When the neural activity exceeds the threshold criterion in the absence of a stimuli
False positive
When the activity is below the criterion during a blank trial
Correct reject
Large number of hits, few misses, but lots of false positive
Lax threshold criterion
Few hits, more misses, but few false positives
Strict threshold criterion
Curve showing the probability of a hit as a function of the probability of a false positive
ROC curve (receiver operating characteristic)
Probability of a high is high, so the probability of a false positive is high
Lax criterion
Probability of a hit is low, so the probability of a false positive is low
Strict criterion
Weber’s law deals with
Contrast
Which system is more sensitive when it comes to contrast
Photopic (.015…….scotopic is .14)
Discriminate between the combination of stimulus+background and background alone
Weber’s law
Can be understood using an increment threshold experiment
Weber’s law
The threshold increment is referred to as
JND (just noticeable difference)
As the background intensity increases, what happens to the JND
Increases
What happens to the ratio of JND to background intensity as the background intensity increases
The JND increases as well, so the ratio remains constant
The ratio of the optotypes to the background luminance (contrast) is the same, no matter the illumination
Lightness constancy
Why is the appearance of the E the same under both dim and bright lights
Because of lightness constancy (visual system detects contrast, no absolute luminance)
What is the appearance of a stimulus of constant luminance when viewed against backgrounds of various luminance
Brightness depends on background
The phenomenon regarding the brightness something appears when viewed against backgrounds of various luminances
Simultaneous contrast
Key factor in predicting the brightness of a stimulus (its appearance)
The contrast of the stimulus
When no stimulus is presented, even though the observer is asked if they saw
Blank trial
during a VF test, pt is reluctant to signal that she sees stimulus even when she may see it. The threshold criteria used by patient is
Strict
When determining a clinical threshold, which psychophysical method most minimizes the importance of the patients criterion
Forced choice
Common used during automated VF testing
Staircase
Which forced choice clinical procedure is expected to result in least steep (flatter)
2AFC
Response in which subject reports not seeing a clearly visible, Supra-threshold stimulus is referred to as
False negative
If sub threshold and they see
False positive e
If sub threshold and they dont see
Correct reject
The JCC test for measuring astigmatism is an example of which method
Forced choice
If the chance performance of 4AFC is 25%, what is threshold
62.5%
When a patient adopts a strict criterion during clinical tests, the result is
Few false positives and few hits
Ocular disease is expected to cause the slop of function to
Decrease (get flatter)
Weber’s law predicts as background intensity increases, contrast threshold
Remains constant
When measuring VA with snellen, which method will provide most reliable results
Descending with forced choice
As the intensity of background increases, the brightness of a patch inside the background
Decreases
According to signal selection theory, a stimulus produces a normal activity that is
Constant
Ass the probability of a hit increases, the probability of FP
Increases
The method of constant stimuli is designed to keep what constant from trial to trial
Stimulus intensity
Subject’s expectations
As stimulus size increased, the detectability
Increases
The retinal analyzes data and encodes it into what
A neural signal
What cells in the retina produce action potentials
Ganglion and amacrine
Small light on center of ganglion receptive field does what to the AP firing
Increases firing
Small light on surround of receptive field of ganglion cell does what to AP firing
Decrease firing
Large light that covers the entire center of the ganglion cells receptive field does what to AP firing
Increases firing
Why is there an increase in AP firing with the light covers the entire center of the ganglion cells receptive field
Due to spatial summation in the field’s center
Stimulus that covers the entire receptive field of the ganglion cells will do what to AP
Nothing, acts the same as if there were no stimulus
What type of ganglion cells do not respond well to diffuse illumination
Spatially antagonistic GCs
What is an example of a strong stimulus for ganglion cells
Sine wave grating
The the bright bar of the sine wave grating falls on the center and the dark bars fall on the surround, what does that do to APs
Increase firing
Spatial grating does what to a ganglion cell
Vigorously excites
When do you reach max firing of AP in a ganglion cell
When the entire center of the receptive field is covered
When the stimulus covers the entire receptive field of a GC plus some more area, does this have an affect on the cell’s response
No
First cell to respond with an action potential in phototransduction
Amacrine cells
What is the order than info is sent in the phototransduction path
PR Horizontal Bipolar Amacrine Ganglion
Which cells convert light quanta into electrical activity
PRs
Resting membrane potential of PR
-50 mV
When exposed to light, what happens to PRs
They hyperpolarize and go to -70 mV
Which cells produce graded potentials
PR, horizontal, bipolar
What does graded potential mean
The more intense the stimulus, the greater the hyperpolarization
What does action potential mean
No matter the intensity of the stimulus, the hyperpolarization is the same
Steps of phototransduction cascade
1) light converts 11 cis retinal to 11 trans retinal (all-trans retinal)
2) activates transducin
3) activates PDE
4) cGMP to GMP
5) Na+ pores close (no more Na comes in)
6) rod hyperpolarizes
Visually inert chain of amino acids
Opsin
Rhodopsin consists of 2 portions
Opsin and chromosphere
What part of rhodopsin determines the absorption profile of the photopigment
Opsin
T or F: rod outer segment sodium channel quantity is limited
True
When even a small amount of a rod’s rhodopsin in bleached, what happens to the Na channels
They close
Widely dispersed dendritic tree synapses with many PRs
Horizontal cells
Type of cell with substantial spatial summation
Horizontal
H1 cells have input from which PRs
M and L cones
H2 cells have input from which PRs
S cones
Type of cell displaying spatial antagonism
Bipolar cells
Bipolar cell: Invaginating synapse
On center bipolar
Bipolar cell: flat synapse
Off center bipolar
Bipolar cell: in the inner sublayer of the IPL
On center bipolar
Bipolar cell: in the outer sublayer of the IPL
Off center bipolar
Bipolar cell: glutamate is inhibitory
On center bipolar
Bipolar cell: glutamate is excitatory
Off center bipolar
Bipolar cell: smaller soma, dendritic tree and receptive field
Midget bipolar cell
Bipolar cell: center formed by 5-10 M/L cones and center spectral sensitivity is similar to the surround
Diffuse bipolar cells
Midget ganglion cells are also called
Parvo cells
Diffuse bipolar cells synapse with
Parasol GCs
Parasol GCs are also called
Magno cells
Are there more parasol GCs in the central 20 degrees or the periphery
Periphery
8% of GC, on center formed only by S cones
Small bistratified cells
3 places GCs project to
LGN
Superior colliculus
Pulvinar
Where to MOST GC projections go to
LGN
The superior colliculus controls
Eye movements
The pulvinar controls
Visual attention
Motion processing
Visually guided movement
Damages choriocapillaris and Bruch’s membrane
ARMD
A leading case of blindness
ARMD
What type of drugs may help wet ARMD
Angiogenesis blocking drugs
Photopigment containing GCS
Melanopsin containing GCs
Where to melanopsin GCs project and what are they responsible for
Suprachiasmic nucleus (SCN Circadian rhythm
Seasonal affective disorder is often treated with
Bright light therapy
Extracellular recording techniques may be used to record the activity of which cells
Ganglion and amacrine
- need an AP to do this
LGN: magno cells
2 most ventral layers
LGN: parvo cells
4 most dorsal layers
LGN: Konio cells
Interlaminar regions
Smallest of the LGN cells
Konio cells
Where does the LGN primarily project to
Visual cortex
Cells sensitive to r/g color contras
Parvo cells
Cells making up 70% of the retinogeniculate path
Parvo cells
Cells sensitive to rapid movement
Magno cells
Cells making up 10% of the retinogeniculate path
Magno cells
Which PR primarily feeds into the Magno path
Rods
Cells responding to b/y color contrast
Konio cells
Which neuron(s) are characterized by color opponency
Parvo and Konio
Excited by certain wavelengths and inhibited by others
Color opponenecy
Cells showing weak or no color opponency
Magno cells
Cells with a sustained response to long duration stimulus
Parvo cells
Cells with transient response to long duration stimulus
Magno cells
When do you see bursts of activity at the onset and offset, which cells is firing
Magno
When you see rapid firing of APs through the entire stimulus, what cell is firing
Parvo
Cells with spatial properties similar to retinal midget cells
Parvo
Cells with spatial properties similar to retinal parasol cells
Magno
Cells with smaller receptive field centers providing higher spatial resolution
Parvo
Cells with larger diameter axons, transmitting APs faster
Magno
Cells with shorter visual latency
Magno
Is there a clear division into distinct parvo and magno in the cortex
No
Is there a clear division into distinct parvo and magno in the retinogeniculate path
Yes
Lesion of the parvocellular region of LGN
Reduced wavelength discrimination
Reduced high spatial frequency contrast sensitivity
Lesion in magnocellular region of LGN
Reduction of high temporal frequency flicker
Reduction of low spatial frequency contrast sensitivity
Which path is key to color discrimination and visual acuity
Parvo path
Pathway encoding fast movement and low spatial frequencies
Magno path
Isoluminant gratings isolate which system
Parvo system
The bars on isoluminant gratings are only visible due to
Chromatic Contrast
Visual field loss indications what kind of cells have died
Ganglion cells
Which pathway is more susceptible to damage in glaucoma
Magno
Why is the magno path more susceptible to damage in glaucoma
Axons of larger neurons ar damaged earlier than smaller
As temporal rate is increased, the healthy patient will note the apparent spatial frequency of the grating doubles
Frequency doubling
POAG impairs the perception of
Frequency doubling
What type of procedure does the original FDT perimeter threshold testing employ
4-reversal staircase procedure
- MOBS
In the N30-1 screening test, what is the first stimuli presented
One that can be detected by 99% of normal population
If the first presented stimulus in the N30-1 screening test is not seen after repeated presentations, what level is then presented
99.5% of the normal population can detect
If the target at 99.5% detectibility is not seen in the N30-1 screening test, what is next
Stimulus is presented as max contrast
Sensitivity for the N30-1 test
78-92%
Specificity of N30-1 screening test
85-100%
What makes the N30-1 screening test a useful option for large population screening
The high specificity
The first stimulus in the N30-5 screening test
Can be detected by 95% of normal population
If the first stimulus in the N30-5 test is not seen after repeated presentations, the next stimulus is
Detected by 98% of population
If the 98% detected stimulus is not seen in the N30-5 test, the next stimulus is
Detected by 99%
Sensitivity for the N30-5 test
85-95%
Specificity of N30-5 test
80-90%
The high sensitivity of the N30-5 tests suggests what
It is better for detecting earlier VF loss in glaucoma pts
How long to the N30-1 and N30-5 tests take in normal eyes
30 seconds per eye
How long does the N30-1 and N30-5 tests take in eyes with VF defects
2 minutes each eye
The Humphrey matrix 800 is good for what
Early VF loss detection
Data suggests that developmental dyslexics manifest deficits in the processing of
Temporal info
- MAGNO path
Which path encodes motion and low spatial frequencies
Magno path
With path encodes r/g chromaticity and high spatial frequencies (VA)
Parvo path
Which path processes b/y color info
Konio path
Where does the end of the bipolar cell with flat/invaginating synapses occur
OPL
Isoluminant gratings are thought to be detect by
Parvo cells
Located in the 2 ventral layers of the LGN
Magno cells
Have transient neural response
Magno cels
Have strong color opponency
Parvo
Konio
Synapse in layer 4Calpha of the cortex
Magno
Synapse in layer 4Cbeta of the cortex
Parvo
Sustained neural response
Parvo
Parvo cells continue about what percentage of ganglion cells
70%
Magno cells constitute about what percentage of ganglion cells
10%
An on center magno neuron is least responsive to
Isoluminant grating
A lesion on in the parvocelluar region of the LGN is expected to result in a reduction in
Visual acuity
Wavelength discrimination
Low temporal frequency
A lesion in the magnocellualr region of the LGN is expected to result in a redction in
High frequency temporal resolution
In frequency doubling, what aspect of the stimulus appears to double as the temporal frequency increase
Spatial frequency
Neurons in the 4 most dorsal layers of the primate LGN manifest what property
Color opponency
Max sensitivity to low spatial frequencies
Magno
4 most dorsal layers of LGN
Parvo
2 most ventral alyers of LGN
Magno
Thicker/larger diameter axons
Magno
Action potentials faster or shower in parvo
Slower
What are the smallest cells
Konio
Which cells are noncolor opponent
Magno
Cytochrome oxidase blobs are located in
Striate cortex
The more superficial layers of striate cortex projec to
Higher cortical area
Double color opponent neurons are located in the
Blobs
Info from the 2 eyes is first combined in cells within
Striate cortex
The receptive fields of which cells cannot be mapped out with small spots of light
Complex
The receptive fields of which cells can be mapped out with small spots of light
Simple
Spatially nonlinear magno cells are thought to provide input to
Complex cortical cells
A hypercolum contains a complete set of
Ocular dominance columns
Orientation columns
Simple cell receptive field properties
Distant on and off region
Orientation selectivity
Position selectivity
Cells that mediate stereopsis are found in
Cortex
Neuron expected to be most responsive to an isoluminant grating
Double color opponent cortical cell
May be demonstrated using forced choice methodology
Blindsight
The cortex contains about how many areas predominantly devoted to analyzing visual info
20
Striate cortex projects to
Extra striate cortex
LGN
Pulvinar
Striate cortex receives input from
Extra striate cortex
LGN
Optical imaging of intrinsic signals in striate cortex reveals that orientation sensitivity is arranged in formations that appear as
Pinwheels
Which lobe is the striate cortex in
Occipital lobe
Other names fro the striate cortex
Primary visual cortex
Visual area 1
V1
Brodmann area 17
A representation of the entire visual field
Striate cortex
Comprises only .01% of retinal area
Fovea
Represented in at least 8% of striate cortex
Fovea
The temporal path
Ventral stream
The what system
Ventral processing stream
Relieves input form parvo path
Ventral processing
Parietal path
Dorsal processing stream
The where system
Dorsal processing stream
Recieves input from magno path
Dorsal processing
Are the 2 cortical processing streams independent
No
Projections to lower visual centers originate from what layers of the striate cortex
Deeper layers (layer 6)
The projections to the extra striate cortex originate more from what layers of the striate cortex
Superficial layers (layers 2/3)
Cells most sensitive to a bar or edge of a specific orientation
Simple cells
Receptive fields are divided into antagonistic excitatory and inhibitory regions
Simple cells
Type of processing used by simple cells
Serial processing
Cells responding best to an elongated stimulus of a specific orientation
Complex cells
With which cells are certain cortical neurons sensitive to stimulus length
Complex cells
With which cells must the stimulus be a specific width and orientation
Simple cells
Which cells respond to diffuse light
PRs
Which cells respond to a spot of light of a specific diameter
Ganglion cells
What cells respond to a bar of light moving in the proper direction
Complex cells
Both pathways (parvo and magno) have what kind of processing
Hierarchical
Which neurons respond well to sine wave grating and are selective for a particular spatial frequency
Cortical neurons
Line or surface content all points in space whose images fall on corresponding points of each eye retina
Horopter
Stimulation of a neuron through the dominant eye causes
A stronger response
A complete set of ocular dominance columns(both eyes) and orientation columns(all orientations)
Hyper column
The development of standard cortical architecture requires
Normal visual input early in life
Optimally responsive to stimuli that manifest color contrast
Striate blobs
Superficial region of striate cortex between bobs that recieves substantial parvo input
Interblob region
Pathway that bypasses blobs
Magno
Which path feeds exclusively into one of the cortical processing streams
Neither parvo nor magno
Why are receptive fields of striate cortical neurons more complicated
Due to hierarchical processing
