Temporal Vision (Sensory) Flashcards
The length of time for one complete cycle of light and dark of a flickering stimulus is what?
Period
The number of light-dark cycles per second of a flickering stimulus is what?
Flicker rate (or flicker frequency)
UNITS: Herts (cycles/second)
The highest flicker frequency at which the flicker is perceived is what?
Critical Flicker Frequency (CFF)
The brightness of a fused flickering stimulus is equal to the brightness of a steady stimulus with the same time-averaged luminance is what law?
Talbot-Plateau Law
NOTE: a strobe lights time-averaged luminance is also known as TALBOT brightness
Brightness enhancement in which a flickering stimulus appears brighter than the Talbot brightness at some flicker frequencies below the CFF (5-20 Hz) is considered what law?
Brucke-Bartley Phenomenon
NOTE: even though the time-average luminance of 2 lights is the same, the flickering light is perceived to be brighter without adjustment
Why is the temporal resolution limit (CFF) reached?
Due to retinal neurons lagging in their responses
NOTE: NT travelling from pre-synaptic to post-synaptic cleft does NOT occur instantly
CFF is proportional to log luminance (as one goes up, the other goes up too) according to what law?
Ferry-Porter Law
Describes relationship btwn CFF and stimulus luminance
The slope for the Ferry-Porter law in the periphery is steeper or shallower?
STEEPER out in the mid-periphery or periphery
The Ferry-Porter function is STRONGER out there UNLESS in scotopic levels where CFF is flat and the same across entire retina
NOTE: the FP law works EVERYWHERE though
CFF is proportional to the log of stimulus area is described as which law?
Granit-Harper Law
NOTE: larger the stimuli = better temporal acuity and the FP function shifts UP!!!! Slope does NOT change
Do cones or rods follow flicker well?
Cones > Rods
Cones greatest in mid-periphery
NOTE: 30 Hz flicker ERG ONLY measures cone function bc rods cannot perceive flicker > 20 Hz
Michaelson Contrast equation?
(Lmax-Lmin)/(Lmax+Lmin)
Peak contrast sensitivity for temporal CSF?
5-20 Hz
What is the longest flash duration for which bloch’s law holds true called?
Critical Duration which varies from 30ms (photopic) to 100ms (scotopic)
NOTE: the critical duration DEC as luminance of background OR area INCREASES
Increased temporal resolution at shorter or longer critical durations?
SHORTER critical duration
NOTE: resolution and summation are inversely related
A short-duration (50-100 ms) suprathreshold flash can appear bright than a longer or shorter flash of the same physical intensity is explained by what effect?
Broca-Sulzer effect
10 Hz to 5 Hz basically
Masking is a _____ phenomenon while crowding is a ____ phenomenon
Temporal; spatial
Masking does what to threshold?
Increases threshold bc there is another stimulus presented before, during, or after a target
If test stimulus is brought closure to the mask during forward masking, how is threshold effected?
It is elevated
Which has greater threshold elevation: forward masking or simultaneous masking?
Simultaneous masking bc a test flash is presented while the masking flash is turned on
Which type of masking has the greatest threshold elevation?
Backwards masking bc the mask comes so quickly after the target that both the target and mask are temporally summed!!!
Metacontrast involves:
a. Backwards masking
b. Simultaneous masking
c. Forward masking
a. Backwards masking
Paracontrast involves:
a. Backwards masking
b. Simultaneous masking
c. Forward masking
c. Forward masking
What is the spatial extent of masking?
~3 degrees
Falls off after that
Which type of masking occurs when the test flash is presented to one eye and the masking flash to the other?
Dichoptic masking
NOTE: this indicates that masking is a cortical phenomenon and not at the retinal level
You need at least how many retinal points to detect motion?
At least TWO!!!
Dynamic visual acuity (DVA) breaks down above what for 20/40 letters?
60 degrees/sec
NOTE: for smaller letters, DVA may break down earlier (~30 degrees/sec)
Which direction are neurons MOST sensitive?
UP!!!
79 AP’s
Makes sense something falling on you
Which direction are neurons LEAST sensitive?
DOWN!!
2 AP’s
What is 1st order motion?
Motion detection due to LUMINANCE changes
NOTE: example is TV
What is 2nd order motion?
Motion detection due to CONTRAST or TEXTURE changes
NOTE: nothing is actually moving the contrast change makes it look like things are. EX boxes change from black to white, giving appearance of a bar moving
What is the minimum displacement threshold (detection of displacement) threshold?
10”
Hyperacuity bc center-to-center PR spacing is 30”
The % of dots needed to move for perception of movement in a direction is called what?
Motion coherence
NOTE: threshold is 5-10% in order to tell
Where is motion processed in the brain?
Middle temporal region of the cortex known as V5
NOTE: MT contains specialized neurons for detection of motion
What is Akinetopsia?
Loss of motion perception, but other visual functions are intact (i.e. spatial vision, color vision, etc)
NOTE: can occur due to a stroke in the MT
