Editing Psychophysics (section)

===Discrimination===
A difference threshold (or [[just-noticeable difference]], JND) is the magnitude of the smallest difference between two stimuli of differing intensities that a participant can detect a certain proportion of the time, with the specific percentage depending on the task. Several methods are employed to test this threshold. For instance, the subject may be asked to adjust one stimulus until it is perceived as identical to another (method of adjustment), to describe the direction and magnitude of the difference between two stimuli, or to decide whether the intensities in a pair of stimuli are the same or different (forced choice). The just-noticeable difference is not a fixed quantity; rather, it varies depending on the intensity of the stimuli and the specific sense being tested.<ref>Schacter, Daniel L.; Gilbert, Daniel t.; Wegner, Daniel M. (2010). Psychology (2nd ed.)</ref> According to [[Weber–Fechner law|Weber's Law]], the just-noticeable difference for any stimulus is a constant proportion, regardless of variations in intensity.<ref>Gustav Theodor Fechner (1860). Elemente der Psychophysik (Elements of Psychophysics), Kap. IX: Das Weber’sche Gesetz.</ref>

In discrimination experiments, the experimenter seeks to determine at what point the difference between two stimuli, such as two weights or two sounds, becomes 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 indicate that the two weights are the same. At the point of subjective equality (PSE), the subject perceives both weights as identical. The just-noticeable difference, or difference limen (DL), is the magnitude of the difference in stimuli that the subject notices some proportion {{math|''p''}} of the time; typically, 50% is used for {{math|''p''}} in the comparison task.<ref>''Psychology: the Science of Behaviour''. 4th ED. Neil R. Carlson, C. Donald Heth</ref> Additionally, the [[two-alternative forced choice]] (2AFC) paradigm is used to assess the point at which performance reduces to chance in discriminating between two alternatives; here, {{math|''p''}} is typically 75%, as a 50% success rate corresponds to chance in the 2AFC task.

Absolute and difference thresholds are sometimes considered similar in principle because background noise always interferes with our ability to detect stimuli.<ref name=Snodgrass/><ref name=GescheiderChap4>{{cite book |author=Gescheider G |year=1997 |title=Psychophysics: the fundamentals | edition=3rd |publisher=Lawrence Erlbaum Associates | chapter=Chapter 4: Classical Psychophysical Theory |isbn=978-0-8058-2281-6 }}</ref>