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TMTV final > Pyschophysical methodology > Flashcards

Pyschophysical methodology Flashcards

1
Q

why do we check VA/visual functions as optometrists

A
  1. to chekc if pts vision is normal
  2. to check if a disease has progressed
  3. to check whether a treatment is effective
  4. for legal purposes
  5. for occupational purposes
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2
Q

what are objective tests

examples?

A

a test that doesnt require any feedback or action for a pt

  • ret
  • electroretinography (ERGs)
  • visual evoked potentials (VEPs)
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3
Q

what are subjective tests

A

a tests that requires feedback or action from a pt

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4
Q

what does an electroretinography do

A

the function of the retina is assessed w/ means of electrophysiology
-the pts eye is stimulated by light and the retinal neuron’s electrical impulses are collected w/ electrodes

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5
Q

what does a visual evoked potention (VEP) do

A
  • the electrode collects the electrical activity of the retina which then can be used to assess the retinal function
  • fucntion of the visual pathway (from retina to V1) is assesed w/ means of electroretinography and compared to normal values
  • pts eye is stimulated w/ patterns of light and the elctrical responses from neurons from the primary visual cortex are collected w/ electrods
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6
Q

why are subjective tests called psychophysics

A

perceptual processes are involved in subjective testing
-psychophysics is a procedure that correlates a physical stimulus w/ mechanisms of the visual system after a pt has given a feedback or taken an actoin

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7
Q

what are some visual processes that can be asssessed by psychophysics

A
  1. detection-the minimum amt of energy so as to perceive light
  2. discrimination-ability to differentiate btwn 2 wavelengths of light
  3. recognition-min letter size you can recognize
  4. speed of response-min amount of time needed to respond to a stimulus
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8
Q

what is the central concept to psychophysics? what does this mean

A

sensory threshold: the threshold is the idea that mental events have to be stronger than some critical amount in order to be perceived

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9
Q

what are some examples of psychophysical tests

A 
VA
vf
accomadative tests (perimetry)
color vision tests
steroscopic acuity 
refraction
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10
Q

what is absolute threshold or RL (Reiz Limen)

-how do you measure it

A

the smallest amount of stimulus energy necessary to produce sensation
-measured in spectral sensitivity curves or dark adaptation curves

ex. need at least 1 cd/m^2 of 500 nm stimulus so as to be able to see it

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11
Q

what is the difference threshold?

what do you use to measure it

A

amount of change in a stimulus required to produce a just noticeable difference (jnd) in the sensation
-measured in light adapatation curve, refers to Weber fraction

ex. need to add 2 cd/m^2 on a stimulus of 10 cd/m^2 so as to see the change

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12
Q

what is threshold

A

the intensity for which we perceive 50% of the stimuli

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13
Q

what are the classical psychophysical methods for measuring threshold

A

method of constant stimuli
method of limits
method of adjustment

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14
Q

what is the method of limits

A

finds the transition or ‘limit’ btwn yes and no responses

2 types: ascedning and descednign

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15
Q

what is the ascending method of limits

A

on the ascending method of limits, the stimulus characteristic (ex. intensity or size) changes from values that are below threshold to values that are above threshold
-point where there is a transition from yes to no is considered to be threshold

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16
Q

what is the subthreshold

what is the suptrathreshold

A

subthreshold: stimulus below threshold
suprathreshold: stimulus above threshodl

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17
Q

what are the advantages to ascending limits

what are the disadvantages

A

advt: does not disrupt the adaptation of the subject (preferred for dark adaptation)
disadv: patient’s anticipation, habituation, practice, fatigue

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18
Q

what are some precautions you must take for the ascending limits

A
  1. make sure pt undertsands the test
  2. test the pt multiple times for reliability
  3. vary the starting point
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19
Q

what visual test uses the ascending limits

A

visual fields

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20
Q

what is the descending method of limits

A

the stimulus characteristic changes from values that are above threshold to values that are below threshold

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21
Q

what are the advantages and disadvantes of the method of descending limits

A

advantages: the pt is familiarized w/ the stimulus
- obtains practice before reaches the threshold

disadvantages: disrupts adaptattion (not good for dark adapt)
- pts anticipation
- habituation
- fatigue

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22
Q

what are the precautions of the method of descending limits

A
  1. test the pt multiple times for reliability

2. vary the starting point

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23
Q

what are some techniques that use the method of descending limits

A

snellen VA

-test starts w/ letter sizes that are well above threshold and pt is familiarized w/ procedure

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24
Q

by combining the ascending and descending methods of limits, what are cancelled out

A

habituation and anticipation
-pt isnt habituated in the one direction of responses and they dont anticipate a certain response as they dont know what stimlul will b enext

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25
Q

how do you determine the threshold for the method of limits

A

for dtermining the difference threshold you usually need to make a comparison btwn a standard stimulus (reference) and a comparison stimulus

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26
Q

what is the interval of uncertainty

A

the stimulus range over which the subject does not notice a difference btwn the reference and comparison stimulus
-the range of stimulus intensity values in which the subject perceives the values as the same

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27
Q

what is the point of subjective equality

A

the point where the reference and the comparison stimulus are perceived as equal
-midpoint btwn the lower limen and upper limen
PSE=(LL-LU)/2

28
Q

what is the lower limen, what is the upper limen

A

lower limen: the intensity value where the ‘NO’ response transitions to an ‘E’ response or equal (both the comparison and background stimulus are equal)
-upper limen: intensity value where a ‘YES’ response transitions to an E or equal perception

29
Q

what is the difference threshold

A

half of the interval of uncertainty

DL=IU/2

30
Q

what is the point of objective equality

A

the point where the reference and the comparison stimulus are measuured as equal using an objective technique
ex. testing luminous intensities of a light you could measure when the values of the 2 stimuli are the same w/ a photometer

31
Q

what is the constant error (CE)

A

the difference btwn the POE and PSE

CE=POE-PSE

32
Q

what is the staircase method

A

the method changes from ascending and descending method automatically dpeending on the pts response
-general principle is if the pt doesnt see the stimulus make it stronger, if pt sees it, make it weaker

33
Q

how is the threshold determiend for the staircase method

A

the threshold is determined as the avg of the last 3 or 4 reversals

34
Q

what is a disadvantage to the staircase method

A

it can take a long time to reach the first reversal (fatigue or boredom can occur)

35
Q

what is the parameter estimation by sequential testing (PEST)

A

the increase and decrease of stimulus intensity isnt constant throughout the test and is dependent on pt’s response

36
Q

what are the advantages and disadvantages to the parameter estimation by sequential testing (PEST)

A

advantages: much faster than the traditional staircase method bc you need fewer stimuli to elicit a reversal
- stimulus is close to threshold so that pt’s adaptatoin does not get disrupted
disadvantages: boredom, learning effect

37
Q

how can you overcome the disadvantages of the staircase method

A

by using a double random staircase method

-stimuli from the 2 diff staircases are presented randomly to the pt so he/she doesnt know what to epect

38
Q

what is the forced choice method

A

prsents a set of diff stimuli and forces the pt to mak ea choice among the options

  • effect of subject’s criterion is minimized bc forced to make a choice
  • stimuli changes after choice and another is made
  • can be separated in space or tiem
39
Q

what is spatially separated simuli?

what is temporally separated stimuli?

A

spatially: which stimulus is diff? present stimuli that differ in spatial location ex. choose right or left
temporal: present the stimuli at diff points in time, which was diff, the first or second one?

40
Q

what techniques use forced choice

A

jackson cross cylinder

also called a 2 alternative forced choice procedure (2AFC) and preferential looking (in infants)

41
Q

in the forced choice, how many presentations are required?

from the number of correct responses, what kind of function is plotted

A

~100 presentations

psychometric function is plotted => % of correct answers as a function of the stimulus characteristic => forms a sigmoid curve

42
Q

in the forced choice 2AFC, the starting point of a psychometric function is 50% correct response and not at 0, why?
-what is the threshold at?

A

bc the subject has a 50% chance on guessing correct even if he doesnt see the stimulus
-the threshold is defined at the 75% correct answers (1/2 btwn 50 and 100%)

43
Q

what is the starting point of a psychometric function for a 4AFC experiment?
what is the threshold

A

25% and not 0 bc the subject has a 25% chance on guessing correct even if he doesnt see stimulus
-threshold defined as 62.5% (1/2 btwn 25 and 100%)

44
Q

why does a forced choice method yield lower threshold

A

bc the subjects are forced to guess

45
Q

what is the method of constant stimuli

A

a set of predefined stimuli are shown in RANDOM ORDER

  • subject asked whether he saw or not the stimulus responding w/ a yes or no
  • usually btwn 5 and 10 stimuli are used, each one is presented in a random order
46
Q

what does the frequency of seeing curve/psychometric curve plot

A

can be plotted once you have the percentage of YES responses for each stimulus intensity
-threshold is the stimulus intensity point on the curve where the subject has a YES response 50% of the time

47
Q

in the method of constant stimuli, why do you have to do prelinary runs

A

to have an idea of approximately where the threshold is

-you don’t want to use stimuli that are a lot below or above threshold

48
Q

what are the advantages and disadvantages to the method of constant stimuli

A

advantages: no habituation (bc stimuli changing randomly)
- no anticipation (dont know whether the next one will be yes or no)

disadvantages: time consuming

49
Q

the frequency of seeing curve might reveal _____ on the detection of a stimulus even if the threshold is caluclated to be w/in normal limits

A

abnormalities

  • the curve itself will show deviations in responses even if the threshold is normal
  • can give us info about disease progression
50
Q

psychometric function often follow a particular S-shaped function, called….

(FOS curve)

A

ogive

51
Q

for measuing the DL (difference threahold) using the method of constant stimuli, what must be shown to the subject

A

a reference stimulus and a comparison stimulus
-the intensity of the comparison stimulus is varied from trial to trial and he must judge whether this value is higher or lower than the ref sitmulus

52
Q

in the method of constant stimuli, what ist he lower limen and upper limen and PSE

A

lower limen: intensity value at 25% higher responses
upper limen: intensity value at 75%
PSE: intensity value at 50% higher responses

53
Q

how do you control for space errror in method of constnat stimuli

A

the reference stimulus must be presented on half of the trials in one retinal location and on the other half on the othe rlocation

54
Q

how do you control for time error for method of constant stimuli

A

reference stimulus must be presented as first on half of the tirals first and as second on the other half of the trials

55
Q

the method of counterbalancing spatial location or temporal order is based on the assumption that…

A

when the results from all the trials are combined the effects of the time and space error will be canclled, providing an unbiased estimate of DL (diff thresholdd)

56
Q

what are the advantages and disadvantages of the method of adjustment

A

advant: natural and straight forward
- not boring for the subjects
disadvantages: experimenter loses control
- may take a long time
- cues in the experiment may allow pt to set threshold

57
Q

what is the method of avg error

where is this used

A

the pt adjusts the comparison stimulus until it is perceived as equal to the reference sitmulus
-used in method of adjustment to find the DL

58
Q

what are catch trials

A

method used to estimate guessing

  • trials where the subject must always be able to detect the stimulus or the reverse
  • subj unaware of the catch trials and therefore will continue to have the same bias and rate of guessing
59
Q

what is the guessing rate for 2AFC

4ACF?

A

50%

25%

60
Q

using ht emthod of constant stimuli, is there a need for catch trials?

A

no-

use 2 stimuli, one well below threshold and one well above will give you the guessing rate, if any

61
Q

what are the 4 diff ways to measure the relationshiop btwn the stimulus strength and the magnitude of sensation

A

ratio production
ratio estimation
magnitude estimation
magnitude production

62
Q

what is ration production

A

subj presented w/ a ref stimulus and asked ot adjuct the test stim so as it appreas to be a ration of the ref stim

ex. adjust test stim so it appears twice as bright as ref

63
Q

what is ratio estimation

A

examiner sets the strength of the ref and test stim to be of a certain ratio and the subj is asked to est the ratio

ex. how much brighter is thet est stim

64
Q

what is magnitude estimation

A
  1. obs presented w/ a ref stim and told that has a certain value. series of test stim then presented and the obs needs to assign a value to indicate his perceived mag in relation to the ref stim
  2. there is no ref stim and the subj prsented w/ a series of stim and asked ot assign a number to them
65
Q

what is magnitude production

A

obs presented w/ a ref stim w/ a certain value. test stim then presented and the obs is asked to adjust the stim to some value relative to the ref stim

ex. here is a stim w/ a value of 100, adjust so as it has a value of 25

TMTV final (10 decks)

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