Different Between Threshold and Absolute Threshold in Psychology

A difference threshold (or just-noticeable difference) is the magnitude of the smallest difference between two stimuli of differing intensities that the participant is able to detect some proportion of the time (again, 50% is often used). To test this threshold, several different methods are used. The subject may be asked to adjust one stimulus until it is perceived as the same as the other, may be asked to describe the magnitude of the difference between two stimuli, or may be asked to detect a stimulus against a background.

The just noticeable difference is not a fixed quantity, rather it depends on how intense the stimuli being measured are and the particular sense being measured. Weber’s Law (Weber Fechner Law) states that the just noticeable difference of a stimulus is a constant proportion despite variation in intensity.

In discrimination experiments, the experimenter seeks to determine at what point the difference between two stimuli, such as two weights or two sounds, is detectable. The subject is presented with one stimulus, for example a weight, and is asked to say whether another weight is heavier or lighter (in some experiments, the subject may also say the two weights are the same).

At the Point of Subjective Equality (PSE), the subject perceives the two weights to be the same. The Just-Noticeable Difference (JND), or Difference Limen (DL) is the magnitude of the difference in stimuli that the subject notices some proportion p of the time (50% is usually used for p). In addition, a Two-alternative forced choice paradigm can be used to assess the point at which performance reduces to chance on a discrimination between two alternatives.

Absolute and difference thresholds are sometimes considered similar because there is always background noise interfering with our ability to detect stimuli, however study of difference thresholds still occurs, for example in pitch discrimination tasks.

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