Changing the way you learn

Visual Testing

Method of Adjustments
1. Subjective
  1. Observer must adjust limits
    1. Stops when just visible
    2. Continuous instead of discrete
2. Trials
  1. 50%
    1. Descending Series
      1. Stimulus above threshold
  2. 50%
    1. Ascending Series
      1. Stimulus below threshold
3. Advantages
  1. Quick
  2. Constant error less likely
  3. Precise for the practiced observer
4. Disadvantages
  1. Sloppiness due to individual diff. b/w observers
    1. Don't trust naive subjects!!!
  2. More variability
5. Examples
  1. Goldmann Tonometry
    Annotations:
    - Inner mire edges align
  2. Keratometry
    Annotations:
    - Markers superimpose; singleness judgment
Method of Limits
1. Controlled by experimenter
  1. Use ascending & descending b/c observers have diff. thresholds
    1. Descending Trial
      1. Clearly noticeable
    2. Ascending Trial
      1. Clearly too weak
    3. Start at various stimulus values
      1. Average transition level is threshold
2. Examples
  1. Measuring near point of convergence
    1. Target moves toward patient
      1. Double = "break"
    2. Target moves away from patient
      1. Single = recovery
  2. Measuring near point of accomodation
3. Errors
  1. Nonrandomizes
    1. Observer can count!!!
  2. Guessing
  3. Practice
  4. Fatigue
Method of constant stimulus
1. effect being measured is transient
  1. Avoid presentation in ordered sequence
    1. Random order
      1. 5-9 stimuli
        weakest
        Clearly below
        Strongest
        Clearly above
2. Constant set
  1. Constant number
    1. Designed to maintain observer's expectations from presentation to presentation
3. Advantages
  1. Precise
4. Disadvantages
  1. Time consuming

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Visual Testing

Description

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	Created by catdees1 almost 11 years ago