Perceptual Function/Color Vision Flashcards
At which age do children begin to distinguish between different colored stimuli?
3 months
Information received by the PRs of the retina from the ganglions cells is an example of what type of pathway?
The centrifugal pathway
-feedback loop
What is the centripital pathway?
Info tranmitting from PRs to bipolar cells to ganglion cells in a forward fashion
Amacrine and horizontal cells are responsible for what?
Lateral integration of data
Scotopic vision is mediated primarily by which type of receptor in the retina?
Rods
How much light is needed to trigger a single molecule of rhodopsin?
1 quanta
What is Weber’s law?
Law that states that as the background brightness is increased, the increment threshold of the test stimulus must also increase, such that the ratio of the incrememnt intensity to the background intensity remains the same
The scotopic system posesses (good/poor) spatial summation.
Good spatial summation
What colors are the background and target of short wavelength perimetry?
Blue stimulus
Yellow background
Which photoreceptors may be more susceptible to early glaucoma damage, thus making the use of SWAP potentially important?
S-cones
What type of contact lens would benefit a dichromat?
X-Chrome
Is the X-Chrome lens worn in one eye, or both eyes?
One eye
Peak PR sensitivity occurs when light passes through which part of the pupil as it enters the eye?
Slightly nasal to the center of the pupil
-PR inner and outer segments act as optic fibers with TIR, directing all the light inward
How is it that a monovision patient can report good retained depth perception?
Monocular depth cues
Name 3 things that could cause a false superior field defect on HVF.
Deep set eyes and large brow ridge
Trial lens set too low
Pt with head tilted back
The change in peak spectral sensitivity from higher wavelengths to lower wavelengths as the surrounding illumination decreases is the basis for which theory?
Purkinje shift
-As illumination increases, we shift from scotopic to photopic
Color vision tests are best administered under which type of illumination?
A MacBeth lamp
Which type of visual acuity is most affected by defocus?
Resolution acuity
Ricco’s law holds only for stimuli that are below a critical ___.
Diameter
What is the critical diameter in Ricco’s law?
10’ arc
Weber’s law deals with what?
Just noticeable difference
Bloch’s law applies to what?
Temporal summation
UV coating on lenses act as what type of filter?
Long-pass filter
What do long-pass filters absorb?
Short wavelengths
- let the long wavelengths pass
How are broad-band and narrow-band filters similar?
They only transmit wavelengths within a certain selected range
Brodmann’s area 17 is part of what?
Primary visual cortex
The primary visual cortex is also known as what?
Striate cortex
Where does the striate cortex send its projections?
Extrastriate cortex, consisting of: IT, MT, V2, V4, V5
Illuminance is directly related to what?
The total amount of lumens emitted from a source
-total illuminance doesn’t depend on any properties of the surface, only the source
A sign that gives the illusion of a person drinking a soda through the use of apparent motion caused by flashing lights it an example of what?
Phi phenomenon
Phi phenomenon is also known as what?
Stroboscopic motion
What are Mach bands?
Perceived bands within transitions zones of a smooth transition between gray/white/to black
What causes Mach bands?
Visual system, due to the augmentation of high spatial frequencies
A typical human contrast sensitivity function is a band-pass function with a peak of how many cycles per degree?
4 cycles/degree
While performing a VF using FDT, what correction should be worn by the pt?
Distance correction
-FDT simulates optical infinity
What makes up a cortical hypercolumn?
Ocular dominance columns for both eyes, and a complete set of orientation columns
A person missing the chlorolabe photopigment is called what?
A deuteranope
A tritanope is missing which photopigment?
Cyanolabe
A person missing erythrolabe is considered what?
Protanope
What is the difference between dichromacy and anomalous trichromacy?
In anomalous trichromacy, the person has all three types of cones, but one doesn’t function correctly.
Dichromats are mission a cone type
In the signal detection theory, what occurs as the detectability of the stimulus is increased?
There is less overlap between the signal and the signal plus noise curves
Spatial summation of the scotopic system follows Ricco’s law, so long as the test spot is not greater than 10’ arc. What is the relationship between stimulus intensity and stimulus area according to Ricco’s law?
Within the critical diameter, as the stimulus intensity increases, the stimulus area decreases
What is the formula for Ricco’s law?
IA=K
I = stimulus intensity
A = stimulus area
K = Constant
What is the Stiles-Crawford effect?
Rods and cones respond differently to incident light that is not perpendicular to their surface
According to the Stiles-Crawford effect, light that strikes cones perpendicularly to their surface will have (maximal/minimal) absorption.
Maximal
-will be reported as brighter
The Stiles-Crawford effect is not noted with which system (Photopic/Scotopic)?
Scotopic
What is the contrast of a projected VA chart in which the target luminance is measured as 50 units of light, and the background luminance measures 100 units of light?
33%
-(target luminance - background luminance)/(target luminance +background luminance)
= (50-100)/(50+100) = 33
Which color vision test is able to differentiate between a dichromat and an anomalous trichromat?
Anomaloscope
What is the most likely reason that a patient is able to retain good VA despite the fact that they are missing a photopigment (anomalous trichromacy)?
The missing photopigment is replaced by the remaining photopigments that are present
As applied to color vision, what is the proper term for two stimuli that appear the same, but are physically different?
Metamers
A patient with a cvisual acuity of 20/30 will likely display a high spatial frequency cut-off of how many cycles per degree?
20 cycles per degree
How do you convert from Snellen to cycles per degree?
Divide 600 by the Snellen denominator
Ex: 20/30 = 600/30 = 20
A person can just detect the difference between two weights: one 12 lbs, and the other 10 lbs. What is the JND for 70 lbs?
14 lbs
What 3 things can be determined from a CIE diagram?
Excitation purity of a stimulus
Dominant wavelength of a stimulus
Complimentary colors
Which form of VA possesses the smallest threshold?
Detection acuity
What is detection acuity?
The ability to determine presence or absence of a target in an empty field
What is the threshold of detection acuity?
1 second of arc
The fact that 100 quanta of 507nm and 200 quanta of 580nm produce the same effect on rhodopsin is known as which of the following?
The principal of univariance
What is the Purkinje shift?
The shift in peak spectral sensitivities during the change from scotopic to photopic vision
-as lighting increases, longer wavelengths appear brighter because the peak spectral sensitivity for scotopic conditions is 507nm, and 555 nm for photopic
A piece of paper is held 2 feet away from a point source of light with an intensity of 60 candelas. What is the resultant illumination on the surface of the paper?
15 candelas
-The illumination of a surface will decrease by the square of the distance
What is the unit for luminous power?
Lumens
Which filter essentially transmits a single wavelength of light?
Interference filter
Which term is used for the event where an observer correctly reports the lack of stimulus on a threshold test
Correct reject
An observer is presented with left-tilted bars seen exclusively by the left eye, and bars that are tilted to the right viewed only by the right eye. The observer reports seeing alternating images of the right and left tilted bars, but the images do not fuse. What phenomenon explains this?
Binocular rivalry
You measure a patients contrast sensitivity. She is able to correctly identify 20/20 with a 1 percent contrast. What is her contrast sensitivity?
100
- take the reciprocal of the contrast threshold
Snellen is a type of which acuity?
Resolution
The scotopic system is more sensitive than the photopic system for all wavelengths except those of which color?
Red
What is the photochromatic interval?
Measure of the difference in sensitivities between the photopic and scotopic system for a given wavelength
The photopic system is more sensitive than the scotopic system for wavelengths greater than what?
650nm
How is the human contrast sensitivity function expected to change for a myope who is uncorrected?
The high spatial frequency cut-off will shift to a lower frequency
-high spatial frequency most affected without correction
During a saccadic movement, which pathway is suppressed?
Magno
-During a saccade, vision is suppressed just before, during, and just after the motion
When looking at an image depicting light gray on sone side, black on the other, and a smooth transition in between, observers report the appearance of light and dark bars. What is the name of this phenomenon?
Mach Bands
What is the high-spatial frequency cut-off for a young adult free of ocular pathology?
60 cycles per degree (20/10)
-limited by anatomy
A typical human contrast sensitivity function is a band-pass function with a peak of how many cycles per degree?
4 cycles per degree
