The method of constant stimuli is the procedure of repeatedly using the same set of stimuli (usually between 5 and 9) throughout the experiment.
The 50% range is located between this range.
- The lower end ⇒ should be a stimulus that is never detected.
- The upper end ⇒ should be always detected
As the intensity level is increased within this range, the likelihood of detecting the stimulus will systematically increase in this way the percentage of detections as a function of stimulus intensity and is determined.
- How can we prepare an experiment with this method?
- Preliminary observation should be done in order to locate the approximate range of values in which the stimulus of lowest intensity is rarely perceived and the stimulus of highest intensity is almost always perceived.
- How can we construct an experiment with this method?
- The procedure requires that each stimulus be presented repeatedly, usually 100 times or more in a random order.
- During the experiment a count of the number of yes or no response for each stimulus intensity level is kept.
- For each stimulus the proportion (p) of yes responses is then computed and a graph called psychometric function is constructed.