Block 10 Flashcards
Changes in luminance across space
Spatial vision
Changes in luminance over time
Temporal vision
What is the difference between low and high modulation depth with looking at a graph
High modulation depth appear taller than low modulation depth
Resolution of low modulation depth
Low
How does low modulation depth appear: flicker or steady
Steady
Resolution of high modulation depth
High
How does high modulation depth appear: flicker or steady
Flicker
How does high and low temporal frequency differ on a graph
High appears as more periods than low
Which frequency flickers at a low rate
Low temporal frequency
Which frequency may flicker at a higher rate
Higher temporal frequency
Unit for temporal frequency
Hertz
1 Hz equals
1 cycle/second
What is the CFF
Frequency at which the flicker can no longer be resolved
Where the stimulus first appears stead
CFF
What represents the high temporal resolution limit of the visual system
CFF
Can be though of as temporal acuity
CFF
Is CFF higher for photopic or scotopic
Photopic
Why is the CFF higher under photopic conditions
Due to speeding up of retinal processes that occurs at increasing levels of light adaptation
What happens to CFF as the retinal illumination increases
CFF increases
Max TMTF?
10 Hz
Max sensitive is to what frequencies
Moderate
Reduced sensitivity to what frequencies
Low and high
What happens to CFF as the stimulus area increases
CFF increases
How are temporal properties of the retina related across eccentricity
Similar
Why do stimuli at the fovea appear steady, but may flicker in the periphery
Higher temporal resolution in periphery
Flickering does what the nearby retinal blood vessels
Dilate
Visual system’s reduced sensitivity to low temporal frequencies is the inability to perceive stationary or stabilized retinal images
Troxler phenomenon
What keeps us aware of our world as we focus on a target
Small, involuntary eye movements (saccades)
Are we sensitive to low temporal frequencies; what happens to borders
No; they disappear
Are we sensitive to moderate temporal frequencies? What happens to the border
Yes; border stays
What frequencies does lateral inhibition affect
Low temporal frequencies
High frequency TMTF is due to
Neural constraints
Provides info regarding both spatial and temporal processing
Masking
Mask and target presented at the same time
Simultaneous masking
More pronounced in amblyopia patients
Simultaneous masking
Reduction in acuity caused by surrounding spatial patterns is sometimes referred to as
Crowding phenomenon
Target precedes the mask
Backward masking
Mask is brighter and interferes with detection of the target
Backward masking
Backward masking where mask and target are spatially adjacent
Metacontrast
Visibility of a briefly presented target is reduced by subsequent presentation of a spatially adjacent mask
Metacontrast
Mask precedes the target
Forward masking
Mask reduces the visibility of a subsequently presented, spatially adjacent target
Paracontrast
When optotypes are surrounded by spatial patterns, the visual acuity
Decreases
When a mask reduces sensitivity to previously presented spatially adjacent stimuli, the phenomenon is referred to as
Metacontrast
The VA of amblyopia patients is poorer when measured using a snellen chart than when measured with isolated optotypes because of
Simultaneous masking
When flicker light falls on retina, nearby vessels
Dilate
What prevents our visual world from disappearing when we fixate on an object
Small, inhibitory eye movements (microsaccades)
When the modulation depth is very small, the screen appears
Steady
The maximal TMTF value of a young healthy eye is
10 Hz
At which temporal frequencies does the TMTF show max sensitivity
Moderate temporal frequencies
The reduction in sensitivity to low temporal frequencies is caused by
Lateral inhibition
The detection of high temporal frequency is limited by
Speed of neural processing
As the area of the stimulus increases, the CFF
Increases
Beyond CFF, the stimuli appears steady bc
It cant be resolved
A high temporal frequency stimulus may appear flickering at what rate
Higher
The CFF for a given percentage modulation is 50 Hz. A stimulus of 55 Hz, presented at the given percentage modulation, is seen as
Steady
Unit for temporal frequency
1 Hz
1 Hz is equal to
1 cycle/second
When testing under scotopic conditions, CFF is expected to be closest to
20 Hz
When testing under photopic conditions, CFF is expected to be closest to
60-70 Hz
Changes in what can lead to the perception of motion
Changes in the spatial distribution of light
Which pathway processes motion
Dorsal processing stream
Tests of motion perception can be useful in the diagnosis of what
Certain neurological disorders
In real motion, the image slides across
The retina
What is apparent motion dependent on
Spatially separated stimuli AND appropriate time interval
Sense of motion elicited by apparent motion is known as
Stroboscopic motion (phi phenomenon)
Example of stroboscopic motion
Movies/tv/computer monitors
How many different images are presented per second
24 images
How many times are each image displayed
3 times
How many total presentations per second
72
Why would the a movie flicker
If presentation rate is below the CFF
Example of a simple first-order stimuli for motion
Sine-wave grating
Both stroboscopic stimuli, sine-wave gratings and the aperture problem are used to study what
Local motion processing
Physiological mechanism of first-order stimuli
Neurons respond with different latencies
- initially stimulated (at fovea) respond slower than the following stimulated (in periphery)
- it is because of this that they are all responding at the same time
- responses are added together to encode stimulus speed and direction
More complex first-order stimuli presented with
Random dot kinematograms
Smallest percent coherence that results in the perception of motion in a defined direction
Coherence threshold
Coherence threshold in humans
Close to 1%
Minimum distance dots must move in a given direction to elicit the perception of motion
Dmin (minimum displacement threshold)
Maximum distance the dots can move to still elicit motion perception
Dmax (maximum displacement threshold)
Example of local motion perception
Sine-wave grating (billboard)
Example of global motion perception
Random dot kinematograms (gas molecules in jar)
Why is the random dot kinematograms more complicated than stroboscopic and sine-wave stimuli
Because visual system must integrate information from many dots over a broad expanse of the retina
The aperature problem is caused by
Local motion cues
How do you resolve the aperture problem
Global motion cues (see the entire background)
Cues that help your visual system resolve locally ambiguous motion
Global motion cues
Interocular transfer study proves that the information from 2 eyes are
Combined
Motion perception for more complex stimuli, such as texture defined contours
Second-order stimuli
Which path processes high velocity info
Magno
Which path processes low velocity info
Parvo
Which pathway processes motion
Magno
Which pathway processes objects
Parvo
Which pathway is the “where” system
Magno
Which pathway is the “what” system
Parvo
Which pathway is the dorsal path
Magno
Which path is the parietal lobe
Magno
Which pathway is the ventral path
Parvo
Which pathway is the temporal lobe
Parvo
Lack of percieved movement as we change form one point to another is probably due to suppression of
Magno
Spot of integration Magno and Parvo
V1
Gateway to dorsal and ventral paths
V1
Biological motion activates
Posterior superior temporal sulcus
Which photoreceptors are used in parvo path
Cones
Which photoreceptors are used in magno path
Rods
Pathway with better spatial resolution
Parvo
Pathway selective for color
Parvo
Pathway with better temporal resolution
Magno
Monochromataic pathway
Magno
Midget RGC receptive field tilling in which path
Parvo
Parasol RGCs receptive field tilling in which path
Magno
High contrast movement on sine-wave grating appears - smooth or stepping?
Stepping
Low contrast movement appears : smooth or stepping
Smooth
Do objects move slower or plaster in scotopic
Slower
How much slower do objects appear to move in scotopic compared to photopic
25%
Motion perception is impaired under mesopic condition due to
Incomplete integration of rod and cone signals
As velocity increases, resolution acuity does what
Stays pretty constant until about 60-80 degrees/second
The ability to resolve a moving stimulus
Dynamic visual acuity
As you move beyond the velocity of 60-80 degrees/second, what happens to dynamic visual acuity
Deteriorates
Reduction in dynamic visual acuity as target velocity increases is due to
Inability to track: Smooth pursuit movements
Higher dynamic visual acutiy is associated with
Improved ability to detect hazardous situation while driving
Ballistic eye movement between 2 fixation points
Saccadic eye movement
Vision is suppressed shortly before, during and after saccadic eye movement –> this is called
Saccadic suppression/omission
Enables u to look form one object to another without smearing of our vision
Saccadic suppression
Which pathway is suppressed to avoid smearing during saccadic movement and why
Magno because it is sensitive to high velocity movement
Primary contributor to saccadic suppression is
Extraretinal signal
7 types of pictorial, monocular cues to depth perception
Relative size Familiar size Linear perspective Texture Interposition Clarity Lighting and shadow
Depth cue when comparing object sizes with no reference
Relative size
When comparing to images, which appears closer due to relative size and why
The larger because there is no reference point, so it creates a larger retinal image
Cue used when viewing objects of known size
Familiar size
Illusion of a picture of a railroad
Linear perspective
Illusion formed because all aspects of the photo are the same distance from your eye, but parts appear farther away
Linear perspective
Brains consciously ignore the background, even though we unconsciously notice size changes int he backgrounds
Texture gradient
The distance to any object sitting on the texture can be accurately judged by comparing it to what
The part of the texture the objects happens to be sitting on
Occurs when the view of a scene is partially obstructed
Interposition
Obscuring the view of objects causes them to appear ________; what cue is this
Farther away; clarity
Light falls on an object and casts a shadow; the shadow is interpreted as what; this creates what
Falling behind the object; creates a sense of depth
Visual system uses the angular declination below the horizon to determine
Object distance
What type of depth cue is motion parallax
Kinetic monocular depth cue
When a moving observer fixates on an object while noticing the relative motion of surrounding objects
Motion parallax
In motion parallax, when fixating on a closer target, what do you notice about the distance target
Moves in the same direction of head movement
In motion parallax, when fixating on a distant target, what do you notice about the near target
It appears to move in the opposite direction of your head
What area of the brain encodes motion parallax info
MT/V5
During accommodation, what happens to the power of the lens
It increases
2 binocular depth cues
Retinal disparity
Convergence
In regards to retinal disparity, light rays from a distant target hit what part of the retina
Nasal to fovea
In regards to retinal disparity, light rays from a near target hit what part of the retina
Temporal to fovea
Retinal disparity of a distant target is said to be
Uncrossed
Retinal disparity of a near target is said to be
Crossed
Important contributor to depth perception at near distance
Stereopsis
Is stereopsis important at far distances and why?
No bc the threshold for retinal disparity requires objects to be separated by great distances
Retinal disparity produces stereopsis only if it is small enough to
Allow fusion
If disparity is too large, the images fall on retinal positions that signal grossly different directions, resulting in
Physiological diplopia
Illusions when pictorial depth cues are used to determine object size
Size illusions
Visual system compensates for differences in retinal image size by taking into account the relative distance of an object
Size constancy
When judgements of distance are erroneous, such as when viewing a flat picture, size constancy may fail causing
Size illusion
Size constancy fails because monocular depth cues provide incorrect info regarding relative distance
Corridor illusion
Moon viewed on the horizon appears
Larger (moon illusion)
Illusion with vertical lines
Muller-layer illusion
Line with an outgoing corner appears
Farther –> looks longer
What does a typical stereopsis test test
The minimum amount of disparity required to perceive depth
Threshold disparity is known as the patient’s
Stereoacuity
Stereoacuity can be as small as
3 seconds of arc
Correcting one eye for near and one eye for distance
Monovision
Is a patients stereo messed up with monovision
Yes
Will a patient still have depth perception with monovision correction and why
Yes bc many important depth cues are monocular
Stereopsis is important for depth at which distance
Near
Will monovision affect driving
Many judgements required in driving are for far distances, in which stereo is less important, but other judgements are for relatively near distances
A depth cue that compares sizes of objects to each other
Relative size
The object that produces the smaller retinal image is percieved at what distance
Farther away
Which depth cue is experienced when viewing a photo
Texture
When viewing a railroad, we experience a strong sense of depth because of
The retinal image size of the separation in the background is smaller than the foreground
The distance to any object could be accurately determined by which depth cue
Texture gradient
Interposition occurs when the view of the scene is _____ obstructed
Partially
Which are the only binocular depth cues
Retinal disparity and convergence
Which of the monocular depth cues are not pictorial
Motion parallax
Accommodation
Angular declination
If an object is closer than the fixated target, the retinal disparity is
Crossed
If there is with motion when you focus on an object
It is farther away that what you are focusing on
If there is against motion when you are fixating
It is closer to you than whatever you are fixating on
As the viewing distance increases, the usefulness of stereopsis
Decreases
A monocular individual may use what cues when determining the distance
Angular declination and motion parallax
Is stereo impaired in anisometropia
Yes
Is stereo impaired in strabismus
Yes
Monovision CL typicallly cause stereo to
Worsen bc only 1 eye is working at near, and you need both eyes working together for good stereo
The appearance of the moon in the horizon being bigger than at the zenith is due to
Interposition
Test to determine minimum amount of disparity required to perceived depth
Stereopsis
3 types of first order stimuli for motion
Local - sine wave grating - stroboscopic stimuli Global - random dot kinetomatogram
