Transcript Absolute Threshold Demonstration

Absolute Threshold
PSY 3203 - Perception – Appalachian State University
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.
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 %)
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.
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.
The Stimuli
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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).
Method of Constant Stimuli
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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.
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.