Across somatosensory and pain literature, there exist several methods of characterizing the location and extent of perceived sensations, and quantifying how these sensory maps may differ. However, these measures of somatosensory intensity and similarity can give non-unique results, creating challenges in literature review and meta-analysis across different methods. In this paper, we propose novel and unifying measures to quantify the similarity and intensity of pain maps and somatosensory percepts. These measures are generalizable and can be applied to any application of somatosensory maps, and are usable with both discretized and free-hand drawings in both 2D and 3D representations. Somatosensory Percept Intensity (SPI) is inspired by Piper's Law, which describes the phenomenon of incomplete spatial summation wherein changes in pain area do not yield linearly proportional changes in perceived intensity. Somatosensory Percept Deviation (SPD) is derived from optimal transport theory, which quantifies differences between two probability distributions or somatosensory maps. Mathematical derivations for both measures are provided. The utility of these measures is demonstrated using data from two studies - one characterizing elicited somatosensory percepts, and one investigating neuropathic pain drawings. The proposed measures strongly agree with the validation studies, illustrating their potential as agnostic measures for characterizing somatosensory percepts in studies and meta-analyses. Ultimately, our work yields powerful unified measures for use in the fields of perception and pain, and may aid in improved pain characterization within healthcare, granting a better understanding of the needs and progression of patients experiencing pain.

The authors have declared no competing interest.

This work was supported by the Promobilia Foundation (Stiftelsen Promobilia), the IngaBritt and Arne Lundbergs Foundation (IngaBritt och Arne Lundbergs Forskningsstiftelse), and the Swedish Research Council (Vetenskapsradet).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

De-identified somatosensory data from two different previous studies were used to validate the proposed measures. The study by Collu et al., 2023, was approved by the Swedish regional ethical committee in Gothenburg (Dnr: 2019-05,446) and the research was performed in accordance with the relevant guidelines and regulations in compliance with the Declaration of Helsinki. The study by Rosner et al., 2021, was approved by the local ethics board, "Kantonale Ethikkommission Zurich" (reference number: EK-04/2006).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

No original data were generated as part of this study. All data used in this study can be requested from the respective corresponding authors.