[6] Although two-point testing is commonly used clinically, evidence accumulated from many research studies indicates that 2PD is a flawed measure of tactile spatial acuity.

Research studies have shown that the two-point test may have low sensitivity, failing to detect or underestimating sensory deficits,[7][8] that it only poorly tracks recovery of function following nerve injury and repair,[9][8][10] that it has poor test-retest reliability,[11] and that it fails to correlate with validated measures of tactile spatial acuity such as grating orientation discrimination.

Pointing to “the enormous and implausible variability in reported 2PD levels after nerve repair,” the authors of one article “conclude that ... 2PD ... as the sole test for tactile gnosis recovery should be seriously questioned.”[15] Comparing 2PD thresholds to functional recovery in patients following nerve repair, another author states "The conclusion to be drawn from this data is that 2 P.D.

"[9] The author of a book on nerve repair concludes that 2PD is a “convenient but critically flawed procedure” that “presents nonspatial cues that can be learned to improve performance without physiologic change”.

[13][16] In psychophysics research laboratories, a favored test of tactile spatial acuity has for many years been the grating orientation task (GOT).

The GOT is considered to yield a valid measure of tactile spatial acuity and has been used in many research studies, with both manual and automated stimulus delivery protocols.

[8] Although it is very popular in tactile research labs, the GOT is admittedly less practical for clinical use, as it requires specialized pre-constructed stimulus objects, which span a fixed spatial range, rather than a single continuously adjustable calipers.

[13][21][16] The following figure, from a study that evaluated both 2PD and 2POD on the fingertip, finger base, palm and forearm,[16] demonstrates that 2PD is contaminated by non-spatial cues, whereas 2POD provides an uncontaminated measure of tactile spatial acuity.