Two-point discrimination

Two-point discrimination
Different areas of the body have receptive fields of different sizes, giving some better resolution in two-point discrimination. Areas including the fingertips, lips, and tongue have very high resolution, and therefore are the most sensitive. Other areas like the forearms, calves, and back are the least sensitive. This is illustrated as the distance where the two points can be felt as separate.

Two-point discrimination (2PD) is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination[1]: 632 [2]: 71  and is assumed to reflect how finely innervated an area of skin is.

In clinical settings, two-point discrimination is a widely used technique for assessing tactile perception.[3] It relies on the ability and/or willingness of the patient to subjectively report what they are feeling and should be completed with the patient’s eyes closed.[4] The therapist may use calipers or simply a reshaped paperclip to do the testing.[5] The therapist may alternate randomly between touching the patient with one point or with two points on the area being tested (e.g. finger, arm, leg, toe).[4] The patient is asked to report whether one or two points was felt. The smallest distance between two points that still results in the perception of two distinct stimuli is recorded as the patient's two-point threshold.[6] Performance on the two extremities can be compared for discrepancies. Although the test is still commonly used clinically, it has been roundly criticized by many researchers as providing an invalid measure of tactile spatial acuity, and several highly regarded alternative tests have been proposed to replace it.

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