hearing exam6

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hearing exam6
2010-11-29 22:21:18

exam 6
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  1. Classical Measurement Methods
    • 1.Method of Limits
    • 2.Method of Adjustment
    • 3.Method of Constant Stimuli
  2. Method of Limits
    • –Stimulus is presented
    • –Subject indicates whether or not they heard it
    • –Tester manipulates the level of the stimulus based on the subjects response
  3. Run:
  4. Number of individual presentations of a stimulus
  5. –Ascending run:
    stimulus level begins below threshold and is raised until the subject can barely hear the tone
  6. Method of Adjustments
    • –The subject controls the stimulus level by turning an unmarked knob
    • –Stimulus changes in a continuous fashion (rather than in fixed steps)
  7. Method of Constant Stimuli
    • Presents various stimulus levels in random order
    • •Like the Method of Limits but not sequential
    • –No ascending or descending runs
    • -Results are tabulated and plotted as a “psychometric function”
  8. –Psychometric Function:
    • a plot which shows the percentage of times the stimulus was heard at each level
    • –Threshold
  9. Direct Scaling
  10. subject establishes the relationship between a standard and comparison stimulus
    • -
    • Major Approaches to Direct Scaling:
    • •Ratio Scales
    • •Magnitude Scales
  11. Ratio Estimation:
  12. expresses subjective magnitude of one stimulus as a ratio of the other stimulus
    –For example: compared to the standard tone, the comparison tone might be twice as loud
  13. Ratio Production:
  14. adjusts the magnitude of a stimulus to produce a specific ratio of the other
    –For example: the subject adjusts the intensity of the stimulus until it is twice as loud as the standard tone
  15. Magnitude Estimation:
    • –A series of stimuli are presented that vary in some dimension such as intensity or frequency.
    • –The subject assigns a number to each stimulus to represent its loudness or pitch.
  16. Magnitude Production:
    –Physical magnitude adjusted to correspond with numbers indicating perceived magnitude
  17. Human Hearing Thresholds
    • Humans have sensitivity over a broad range of frequencies: 10 Hz – 20,000 Hz
    • •Hearing sensitivity is best between 2000 – 5000 Hz
    • •Hearing sensitivity is poor below 100 Hz and above 10,000 Hz
  18. 1.Minimum Audible Pressure (MAP):
    • based on monaural (one ear) thresholds with earphones
    • –Measure sound pressure in the ear canal at threshold
  19. Minimum Audible Field (MAF):
    • based on binaural (two ears) thresholds from loudspeakers
    • –Measure sound pressure in sound field at head level
    • -MAF thresholds tend to be 6 dB lower (better) than MAP thresholds due to binaural summation
  20. Upper Limits of Hearing
    • •Sounds become uncomfortably loud at a level of about 100 dB SLP
    • –This level is fairly constant across frequencies
    • •Sounds that evoke feeling or pain occur at levels of 120 – 140 dB SPL
    • –Tactile sensations rather than auditory
  21. Temporal Summation/Integration def
    • -trading of duration and intensity
    • -When sounds are shorter than approximately 300 ms, threshold (or loudness) depends on duration
  22. Temporal Summation/Integration
    • •As a sound gets shorter
    • –Threshold becomes higher (less sensitivity)
    • –The sound is perceived as being softer
    • •As the sound get longer
    • –Threshold becomes lower (better sensitivity)
    • –The sound is perceived as being louder
  23. integration
    –a 10-fold decrease in duration is offset by a 10 dB increase in intensity
  24. Just Noticeable Difference (JND) or Difference Limen (DL):
    -the smallest perceptible difference between two sounds
  25. Absolute Difference Limens:
    • –ΔI: smallest intensity change that can be detected
    • –ΔF: smallest frequency change that can be detected
    • -they specify the absolute physical difference needed to tell two sounds apart
  26. Relative Difference Limen or Weber Fraction:
  27. -considers both the absolute DL and the starting point
    • -Weber’s Fraction = absolute DL / starting point
    • = ΔI/I or Δ F/F