OUCH: Objective, Uniform, Controlled Haptic Stimulation for Automated Neurological Assessment

Sherry Choi, Sitao Sunny Li, Joseph Romero, Lillian Chin, Ashwin G. Ramayya, Allison M. Okamura, Ava Chen

November 2026

TL;DR A wrist-worn pneumatic cuff that presses a pointed indenter into the skin to give a repeatable painful stimulus for bedside neurological assessment. At 200 kPa it reaches an estimated 18,500 kPa contact pressure, against 707 kPa for a clinical algometer tip, and in a four-person pilot it caused discomfort at about 89% lower force.

What they do

Bedside coma assessments judge how a patient moves in response to a painful pinch or press. A clinician applies that stimulus by hand, so its force, duration and location vary between examiners. OUCH is a wrist cuff that delivers the stimulus pneumatically. Inflating a pouch drives a small rigid indenter into the back of the wrist, and an IMU in the cuff is meant to track the evoked movement. The authors test it on rigid and tissue-like surfaces and compare it with the tip of a clinical handheld algometer (AlgoMed).

How it works

Actuator. Two stacked 30x30 mm single-layer pouches of TPU-coated nylon. They replaced folded pouches, which leaked and did not reliably give more force. At 200 kPa the stack gives 39.7 N of blocked force.
Indenter. A 3D-printed pointed tip with a 2.27 mm² contact area. The algometer’s flat tip has 78.5 mm².
Compliant spacer. An elastomer shaped like a suction cup holds the indenter off the skin at rest and buckles under load. FEA and a compression test agree that it buckles at 4.3 N.
Testbed. A silicone metamaterial block with air channels 18 mm and 34 mm below the surface. Pressure changes in the channels measure deformation.

Results

Blocked force at 200 kPa: 42.0 N with the OUCH indenter against 55.5 N with the algometer tip. The estimated contact pressure is 18,500 kPa against 707 kPa.
On the testbed at 200 kPa, the shallow channel read 1.72 kPa (OUCH) against 2.25 kPa (algometer), while the deep channels differed by at most 0.04 kPa. OUCH concentrates deformation near the surface.
Four team members felt discomfort at 1.47-4.12 N with OUCH against 16.18-37.56 N with the algometer tip, about 89% less force. Clinicians who wore the device rated its stimulus comparable to current bedside assessments.

Limitations

Discomfort thresholds come from four members of the research team rather than a formal user study, and no patients were tested. Creep in the spacer, which lowered the shallow reading by up to 9% during a 5 s hold, was not characterized. The testbed only approximates skin, and blocked force likely overstates what the cuff delivers on a real wrist.

Figures

From Figure 1: OUCH on the wrist from the side and the front, and a schematic of the device at rest and during assess... — From Figure 1: OUCH on the wrist from the side and the front, and a schematic of the device at rest and during assessment. Pouch expansion buckles the compliant spacer and drives the indenter into the skin while the IMU tracks motion.

From Figure 2: The blocked force test setup, pouch designs with zero, one and two folds, and the final stack of two s... — From Figure 2: The blocked force test setup, pouch designs with zero, one and two folds, and the final stack of two single-layer pouches with and without the OUCH indenter. Plots show blocked force against inflation pressure for each.

From Figure 5: The stepwise 120-200 kPa inflation profile and the top and bottom testbed sensor readings for the AlgoMed and OUCH indenters. Photos show how the testbed deforms under each at 120, 160 and 200 kPa.

From Figure 7: Blocked force and estimated contact pressure (log scale) against inflation pressure for the AlgoMed ti... — From Figure 7: Blocked force and estimated contact pressure (log scale) against inflation pressure for the AlgoMed tip and the OUCH indenter, and the applied force at the discomfort threshold for four research team members.

Abstract

Motor responses evoked by noxious stimulation are used to assess neurological function in hospitalized patients with disorders of consciousness. In standard bedside assessments, these stimuli are applied manually, resulting in substantial variation in force, duration, frequency, and location. Here, we present OUCH (Objective, Uniform, Controlled Haptic stimulation), a wrist-worn device that uses pneumatic actuation to deliver noxious mechanical stimuli. OUCH combines stacked pneumatic pouch actuators, a rigid indenter, and a compliant spacer designed to buckle at a set load, so that the indenter contacts the skin only during actuation. We characterize the device using blocked force tests, clinician evaluation, finite element analysis, and a deformable pressure testbed, and benchmark it against a commercially available handheld pressure algometer. At 200 kPa pouch inflation pressure, our indenter concentrated its load into an estimated contact pressure of 18,500 kPa, over 25 times that of the algometer tip, while requiring less total force. On the deformable testbed, it localized deformation near the surface, while deformation at depth remained comparable to the algometer. As a result, in preliminary perceptual testing, our indenter elicited discomfort at approximately 89% lower applied force than the algometer, demonstrating the feasibility of evoking discomfort with a compact, wearable soft actuator. These results show that combining pneumatic actuation with designed contact geometry enables controlled, repeatable noxious stimulation at the wrist, providing a foundation for objective neurological assessment.

Summaries are written automatically from each paper's text. Figures and videos come from the paper and its project page; all credit goes to the authors.

Matt Strong