Midterm Questions Flashcards
A threshold can be defined arbitrarily as some particular level on a frequency-of-seeing curve. The form of such a curve would probably be described as:
a. step function
b. logarithmic
c. u-shaped
d. s-shaped
e. bell-shaped
d. s-shaped
curve is also known as an ogive and represents a cumulative probability distribution
An observer continually varies the intensity of one light up and down until its brightness matches that of a second light. This is an example of the utilization of the psychophysical method of:
a. limits
b. constant stimuli
c. adjustment
d. staircase
c. adjustment
simplest and most direct way to estimate thresholds
Signal-detection theory is useful in the analysis of psychophysical threshold data because:
a. observer’s noise level can be determined
b. sensitivity is not confounded by response criterion
c. observers can discriminate between responses due to signal or noise
d. an observer’s threshold is independent of the response criterion
b. sensitivity is not confounded by response criterion
experimentor can manipulate the inherent bias
A fundamental assumption made in receiver operating characteristic (ROC) analysis is:
a. noise, and signal + noise distributions are Gaussian
b. both distributions have same variance
c. the distributions could overlap
d. response is determined by where criterion line is set
e. all of the above
e. all of the above
If Steven’s law is plotted in log-log coordinates, we can determine the power as the value of:
a. x-intercept
b. y-intercept
c. slope
d. curvature
e. peak position
c. slope
forms a straight line with p = slope
The psychophysical method that gives the most stable data is:
a. constant stimuli
b. staircase
c. limits
d. adjustment
e. forced choice
a. constant stimuli
considered the most accurate psychophysical method
In an ROC curve, the d’ = 0 line:
a. represents complete overlap of the noise (N) and signal + noise (S+N) distribution
b. implies that the N and (S+N) distributions have different variances
c. implies that the N and (S+N) distributions are infinitely far apart
d. implies that no noise distribution is present
a. represents complete overlap of the noise (N) and signal + noise (S+N) distribution
d’ line represents the distance between the means of the noise and the signal + noise distributions, so if this equals zero the two distributions completely overlap
Let us assume that two observers require different levels of stimulation for a 50% threshold response. Which of the following conclusions is valid?
a. one observer may be more willing to say “yes” than the other
b. one observer is more sensitive than the other
c. one observer is more cautious than the other
d. all of the above
d. all of the above
According to signal-detection theory:
a. as the hit rate goes up, the false-alarm rate goes up
b. as the hit rate goes up, the false-alarm rate goes down
c. as the hit rate goes up, the correct reject rate goes up
d. as the hit rate goes up, the miss rate goes down
a. as the hit rate goes up, the false-alarm rate goes up
If the criterion line is set at a low level of excitation:
a. the hit rate goes up
b. the miss rate goes up
c. the false-alarm rate goes up
d. a and c
e. b and c
d. a and c - the hit rate goes up and the false-alarn rate goes up
In a psychophysical experiment, how can you correct for guessing?
a. use the forced-choice method
b. make an assumption about the guess rate
c. use the method of constant stimuli
d. use random-catch trials
d. use random-catch trials
catch trials are trials in which either a stimulus that should not be detected or should be detected are shown
Variability in measured thresholds can be due to:
a. subject’s alertness/attention level
b. pscyhological bias
c. random fluctuation in both stimulus and the neural system
d. all of the above
d. all of the above
For a five-alternative forced-choice experiment, what is the percentage used to determine the threshold?
a. 50%
b. 20%
c. 25%
d. 75%
b. 20%
100/5 = 20%
At suprathreshold levels, what is the relation between stimulus intensity and magnitude of sensation?
a. Weber’s law
b. Law of unvariance
c. Fechner’s law
d. Law of Malus
c. Fechner’s law
S = klog I
s = magnitude of sensation
I = stimulus intensity
k = constant
When measuring absolute thresholds, we must take into account:
a. dark light
b. ovserver’s adaptation state
c. pupil image
d. guess rate
a. dark light
represents noise in the visual system, responsible for the limit set on absolute threshold
The psychometric function is really a(n):
a. linear function
b. cumulative probability distribution
c. ogive
d. b and c
d. b and c - cumulative probability distribution, ogive
In ROC analysis, we plot:
a. hit rate versus miss rate
b. hit rate versus correct-reject rate
c. false-alarm rate versus correct-reject rate
d. hit rate versus false-alarm rate
d. hit rate vs false-alarm rate
- Which of the following curves respresents the probability of photon catch as a function of wavelength?
a. frequency-of-seeing curve
b. luminosity function
c. an ogive
d. Poisson distribution
b. luminosity function
luminosity refers to the luminous effect, based on photon catch of radiant energy
- The patient makes a classic intensity-difference discrimination in:
a. kinetic perimetry
b. dark adaptometry
c. static perimetry
d. the color lantern test
c. static perimetry
patient must detect a test target against a constant background luminance
- To hasten dark adaptation, the final briefing of pilots about to fly at night is held in a room illuminated by:
a. red light
b. green light
c. white light
d. blue light
a. red light
red light has little to no effect on the photopigment in the rods, so the rods can being dark adaptation in the presence of red light
- The background is 100 cd/m2 and a central stimulus spot has to be 12 cd/m2 brighter than the background to be just visible. The background is now increased to 150 cd/m2. Which of the following would you use to determine the stimulus spot brightness now necessary for threshold detection?
a. Ricco’s law
b. Weber’s law
C. Fechner’s law
d. Bloch’s law
b. Weber’s law
sets forth that a constant proportional relation exists betweent the increment threshold and the background luminance
- If the period of preadaptation is extended, what is the extended change in the dark-adaptation recording?
a. the secondary portion of the curve will be larger
b. the kink in the recording will be earlier
c. the initial portion of the curve will be larger
d. the total amount of adaptation recorded will be less
c. the initiation portion of the curve will be larger
longer preadaptation period increase light adaptation and renders the initial (cone) portion of the dark adaptation curve more prominent
- Which of the following is true for complete temporal summation (flash duration less than the critical duration)?
a. the longer the flash, the more total quanta needed for threshold
b. the effects of quanta delivered early in the critical period are less than those delivered later
c. the effects of all quanta delivered during the critical period sum
d. within the critical period, the shorter the flash, the more quanta needed for threshold
c. the effects of all quanta delivered during the critical period sum
- You are attempting to measure the smallest amount of light necessary to stimulate the rods so that light is perceived. What color should the fixation stimulus be to affect minimally the rods to be tested?
a. red
b. blue
c. white
d. green
a. red
when the fixation light is red, it permits the subject to fixate as the cones are well stimulated, and the rods are insensitive to red
20.The maximal change in pupil size can account for about how much dark adaptation?
a. 3 log units
b. 1 log unit
c. 8 log units
d. none
b. 1 log unit
the smallest possible pupil is 2 mm and teh largest is 8mm - difference betweent the two is approx. 1 log unit
- When dark adaptation is measured strictly foveally with a red light:
a. the kink in the curve occurs sooner
b. no kink appears
c. the total amount of threshold decrease is the same as when dark adaptation is measured peripherally
d. the kink appears later than usual
b. no kink appears
when dark adaptation is measured foveally with a red light, the rods play no role and only the initial cone branch results
- Which of the following plays no role in signaling luminosity?
a. L-cones
b. S-cones
c. M-cones
d. all of the above play a role
b. S-cones
short-wavelength-sensitive cones do not contribute to the perceptino of luminance
- In measuring dark adaptation, the larger the field, the:
a. larger the initial portion for the dark adaptation curve
b. later the rod-cone break will occur
c. larger the second portion of the dark adaptation curve
d. earlier the rod-cone break will occur
c. larger the second portion of the dark adaptation curve
more rods are involved, so the second (rod) portion of the curve increases in size
- A brighter, longer preadaptation light will cause a:
a. higher initial threshold
b. later rod-cone break
c. longer time to complete adaptation
d. all of the above
d. all of the above
- You have a light flash of 50 units on for 20 msec. If you now double the light flash luminance, what should the time duration be? Assume Bloch’s law to be valid.
a. 10 msec
b. 100 msec
c. 1 msec
d. 1000 msec
a. 10 msec
Bloch’s law: L x T = C
L = luminance threshold of flash
T = time duration
C = constant
LxT = 50x20=1000
when L doubles, T should be halved
- Piper’s law describes:
a. temporal summation
b. rhodopsin kinetics
c. spatial summation
d. quantal variability
c. spatial summation
Piper’s law: LxA^1/2
L = luminance
A = area of stimulus
- On an increment threshold curve, quantal fluctuations are reflected by the section of the curve having slope ________ and are expressed by ____________ law.
a. 1; Weber’s
b. 0; Dowling-Rushton
c. 0; Inverse square
d. 1/2; DeVries-Rose
d. 1/2; DeVries-Rose
DeVries-Rose law states that as stimulus luminance icnreases, the minimum descriminable threshold increases in proportion to the square root of the intensity level
- The Weber fraction is affected by:
a. wavelength of stimulus
b. retinal locus
c. size of stimulus
d. all of the above
d. all of the above
- For detecting and recognizing objects, we need:
a. low spatial frequencies
b. middle spatial frequencies
c. high spatial frequencies
d. a and b
d. a and b - low and middle spatial frequencies
- Temporal modulation functions show that at low temporal frequencies, the relative sensitivity remains constant as background illumination changes. This is another example of:
a. Ferry-Porter law
b. Granit-Harper law
c. Weber’s law
d. Talbot-Plateau law
c. Weber’s law
the amplitude remains a constant fraction as background illuminatino is increased, which is a simple manifestation of Weber’s law
- If you are measuring V-lambda, photopic lumiunance functions in a protanope, you will find it to be:
a. shifted toward shorter wavelengths
b. shifted toward longer wavelengths
c. identical to the normal V lambda function
d. the same as that shown by a deutranope
a. shifted towards shorter wavelengths
EX1:6. Threshold contrast, under photopic conditions, is closest to:
a. 1.000
b. 0.1000
c. 0.010
d. 0.001
c. 0.010
EX1:7 To optimize the rod-cone break of the dark adaptation curve for clinical testing, the stimulus should be:
a. 0.50 degree in diameter and green
b. 0.50 degree in diameter and orange
c. 5.0 degrees in diameter and green
d. 5.0 degrees in diameter and orange
c. 5.0 degrees in diameter and green
EX1:8 Consider the region of the light adaptation curve that follows Weber’s law. As the background intensity decreases, contrast sensitivity:
a. decreases
b. increases
c. remains constant
c. remains constant
EX1: 11 Appropriate units for luminous power, illuminance, and luminance are, respectively:
a. candelas, candelas/m2, lumens/m2
b. candelas, foot-candelas, foot-lamberts
c. candelas, foot-lamberts, foot-candles
d. lumens, foot-lamberts, foot-candles
e. lumens, foot-candles, foot-lamberts
e. lumens, foot-candles, foot-lamberts
EX1:12 You are asked to measure the lighting conditions in a classroom to determine if they are adequate. The lighting conditions should be specified in which of the following units?
a. lumens/m2
b. candelas/m2
c. lumens
d. candelas
a. lumens/m2
EX1: 13 When measured at an angle of 30 degrees to its surface, a matte surface with a reflectance factor of 0.70 has a luminance of 50 foot-lamberts. What is the luminance when measured perpendicular to the surface?
a. 25 foot-lamberts
b. 43 foot-lamberts
c. 50 foot-lamberts
d. 75 foot-lamberts
c. 50 foot-lamberts
EX1:22 A yellow background is used when performing short-wavelength automated perimetry because this background:
a. increases the absolute sensitivity of the S-cones
b. suppresses the S-cones
c. suppresses the M- and L-cones
cc. suppresses M and L cones
EX1: 38 When a patient adopts a strict criterion during clinical test, as opposed to a lax criterion, the result is:
a. few false-positives and many hits
b. few false-positivies and few hits
c. many false-positives and many hits
d. many false-positives and few hits
b. few false-positives and few hits
EX1: 39 When deterining a clinical threshold, which psychophysical method most minimizes the importance of a patient’s criterion?
a. staircase
b. adjustment
c. forced choice
d. constant stimuli
e. descending limits
c. forced choice
EX1: 40 When using a ROC to determine if a clinical test is effective, the goal is to:
a. maximize the sensitivity and minimize the specificity
b. maximize the specificity and minimize the sensitividity
c. maximize the specificity and maximize the sensitivity
d. minimize the specificity and minimize the sensitivity
c. maximize specificity, minimize sensitividity
EX1: 41 If the visual acuity of a patient who has a strict criterion is determined with the method of descending limits, the measured VA is likely to be:
a. accurate
b. better than it actually is
c. worse that it actually is
c. worse
EX2:6 Under scotopic conditions, a blue and yellow flower appears equally bright. Under photopic conditions, which flower will most likely appear brighter?
a. blue flower
b. yellow flower
c. equally bright
b. yellow flower
EX2:10 One candela is equal to:
a. 1 lumen per m2
b. 1 lumen per steradian
c. 1 lumen per ft2
b. 1 lumen per steradian
EX2: 33 When compared to photopic conditions, objects viewed under scotopic conditions appear to move:
a. faster
b. slower
c. at the same speed
b. slower
EX2: 38 A yes-no experiment consists of 100 trials. The stimulus is present on 80 of the trials. The subject reports seeing the stimulus on 70 trials, and there are 55 hits. How many false-alarms are there?
a. 5
b. 15
c. 25
d. 55
b. 15
EX2:39 A forced-choice clinical procedure with how many choices is expected to result in the least steep psychometric function?
a. 2 AFC
b. 4 AFC
c. 6 AFC
d. 8 AFC
a. 2 AFC
EX2:40 Which method of threshold determination is commonly used during automated visual field testing?
a. adjustment
b. constant stimuli
c. forced choice
d. staircase
d. staircase
EX2:41 Ocular disease is expected to cause the slope of the psychometric function to:
a. increase
b. decrease
c. remain the same
b. decrease
EX2:42 When a subject reports that he cannot see a clearly visible suprathreshold stimulus, this is called a:
a. false-positive
b. false-negative
c. false-alarm
b. false-negative
EX3:5 Photopic and scoptopic thresholds are most similar to each other for which wavelength?
a. 400 nm
b. 420 nm
c. 507 nm
d. 555 nm
e. 650 nm
e. 650 nm
EX3:6 The percentage of rhosopsin that is bleached at rod saturation is closest to:
a. 10%
b. 30%
c. 50%
d. 70%
e. 90%
a. 10%
EX3:7 The photochromatic interval is expected to be smallest for a:
a. centrally fixated 5.0 degree orange target
b. centrally fixated 0.5 degree orange target
c. peripherally viewed 5.0 degree orange target
d. peripherally viewed 0.5 degree orange target
b
EX3:8 Sensitivity regulation is most associated with the portion of the light adaptation curve that has a slope of:
a. infinity
b. 1
c. 1/2
d. 0
b. 1
EX3:10 The color temperature of an incandescent bulb is 3300K. This means that:
a. the temperature of the bulb is 3300K
b. when the bulb is heated to 3300K, it matches the spectral distribution of a blackbody radiator
c. the bulb matches the spectral distribution of a blackbody radiator whose temperature is 3300K
c
EX3:11 In the minimally distinct border method of photometry, the perception of the border is minimzied when the two surfaces are matched for:
a. radiant intensity
b. radiance
c. luminous intensity
d. luminance
d. luminance
EX3:14 Which of the following classes of cones contributes leas to the photopic spectral sensitivity curve?
a. L-cones
b. M-cones
c. S-cones
c. s-cones
EX3:39 When measuring VA with a typical Snellen test, which psychophysical method is typically used?
a. ascending limits
b. descending limits
c. adjustment
d. constant stimuli
e. staircase
b. descending limits
EX3:39 Steven’s law is based up on the use of:
a. indirect scaling
b. magnitude estimation
c. both a and b are correct
b. magnitude estimation
EX3:42 During a visual field test that patient is reluctant to signal that she sees the stimulus even when she does see it. The threshold criteria used by the patient is:
a. lax
b. moderate
c. strict
c. strict
