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Absolute Threshold

Absolute Threshold. PSY 3203 - Perception – Appalachian State University. Method of Limits. A range of stimuli are selected, from below threshold to above threshold.

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Absolute Threshold

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  1. Absolute Threshold PSY 3203 - Perception – Appalachian State University

  2. Method of Limits • A range of stimuli are selected, from below threshold to above threshold. • The stimuli are ordered and presented in a sequence that corresponds to either an ascending or descending series of the “amount” of the physical dimension under investigation. • Forced Choice: The observer is to judge only whether the stimulus was detected (Yes) or not detected (No). • The trial is ended when there is a transition.

  3. Method of Limits • The observer will need to make many judgments over several repetitions of the ascending and descending series. • The psychophysical function is created in the following fashion: • X-axis contains the information about the physical dimension. • Stimuli are ordered from less to more. • Interval size reflects size of increment from stimulus to stimulus. • Y-axis contains the information about the observer’s judgment of the experience. • Responses are reported as Percent(Yes). • Scale goes from 0.00 (0%) to 1.0 (100 %)

  4. Let’s try an example • The following slide contains a series of music icons. • Clicking on an icon will cause a 2-second tone to be played. • You should record Y if you hear the tone and N if you do not hear the tone. • The number on the icon indicates the “amount” of volume. • Each increment in number is an equal increment in volume.

  5. Let’s try an example • First, the speaker volume will be adjusted so that the range of stimuli goes from inaudible to audible. • Second, you will make judgments with ascending and descending series. • Third, we will compute the psychophysical function and discuss the location of the absolute threshold.

  6. The Stimuli

  7. Method of Constant Stimuli • A range of stimuli are selected, from below threshold to above threshold. • The stimuli are ordered and presented in a randomized series of the “amount” of the physical dimension under investigation. • Forced Choice: The observer is to judge only whether the stimulus was detected (Yes) or not detected (No).

  8. Method of Constant Stimuli

  9. Method of Adjustment • Observer makes adjustment to stimulus source until threshold is achieved. • A production method. (more Behavioral?) • Method works very quickly. • Greater variability hence less accuracy.

  10. Staircase Method • Presents and notes response (“Yes” or “No”) • If “No” then increase stimulus intensity on next trial. • If “Yes” then decrease stimulus intensity on next trial. • Direction of change is reversed when answer changes.

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