Method Of Limits
Psychophysical research is focused on the influence and relationship between physical stimuli (such as sounds, visual stimuli such as lights, and tactile stimuli) and the sensation and perception of these stimuli by an organism. There are three methods that are traditionally used to test perception of stimuli.
The first type of testing is method of limits which is used in psychophysical research in order to measure a subject's perception of stimuli by determining at what level a stimulus is perceived by a subject. A stimulus is presented and increased or decreased until it is perceivable by the subject. An ascending method of limits study is when the stimulus is presented initially at a very low level and gradually increased until the subject can perceive it. The opposite of this is descending order and that is when the stimulus is present at a high level and gradually decreased until the subject can no longer perceive it. Ascending and descending trials are typically used in conjunction with each other in method of limits testing. Issues with this type of testing are that subjects can predict when the stimulus is close to being imperceptible and will sometimes respond too early and also habituation (decreasing sensitivity to the stimulus).
The second type of testing is method of constant in which the stimulus is presented randomly instead of ascending or descending order. This prevents the subjects from expectations and responding too hastily because they are anticipating the stimulus to increase or decrease.
The third type of testing is method of adjustment in which the subject is in control of the stimulus level and is typically asked to alter it until it is barely there. The stimulus will not be present and the subject is asked to adjust it until it is noticeable. This is usually repeated several times and an average is taken of all of the scores. Which method of testing to use depends on the experiment and what resources the researchers have.