Threshold

 Threshold

            A threshold is the point of intensity at which the participant can just detect the presence of a stimulus. Stimuli with intensities below the threshold are not detectable. However, a subject does not detect the same stimulus every time; thus, thresholds are considered as an average of trials rather than an absolute limit.

Types of Threshold

·         Absolute Threshold

Absolute threshold is the smallest intensity of a stimulus that must be present for a stimulus to be detected.

·         Difference Threshold

The minimum change in intensity required to produce a detectable change in sensory experience (this is also known as a Just Noticeable Difference or JND).

·         Taste Threshold

The minimum concentration at which taste sensitivity to a particular substance or food can be perceived.

Determining the Absolute Threshold

There are three basic methods for determining the absolute threshold; the method of limits; adjustment; and constant stimulus (kimble, 1994).

Method of limit

The method of limits was well suited to determine absolute or detection threshold in the method of limits the physical stimulus is changed by successive discrete steps until a change in response is noted e.g. when the stimulus is increasing in intensity, the response will change from no sensation to detect something (kimble, 1994).

Method of constant stimuli

In the method of constant stimuli, the test stimulus is always compared against a constant reference level (a standard), usually the middle point on a series of physical intensity level (kimble, 1994).

Method of adjustment

The method could be used to determine difference threshold based on variability of the subject over many attempts at matching e.g. using the standard deviation as a measure of difference threshold a modern application is in measuring tradeoff relationship (kimble, 1985).

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