Absolute Threshold

PSY 3215 – 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

15 7

14 613 512 411 310 29 18

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

13 15

7 64 1110 145 312 21 98

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.