Control Interfaces for Operating Assistive Devices

Various control interfaces (CIs) are used to capture user intent for operating assistive devices. In recent years, several methods have been developed to detect user intent for controlling invasive motor neuroprostheses for upper limbs. The Freehand System® utilized an external shoulder position sensor on the contralateral side to detect user intent and control hand grasp stimulation. In some studies, a switch was integrated with the sensor to turn the system on and off and to select the type of grasp (palmar or lateral). Brain-computer interface (BCI) systems based on electroencephalography (EEG) have also been employed. The Implantable Stimulator-Telemeter ('IST-10'), the second generation of the Freehand, had ten stimulation channels and was used with an implantable joint angle sensor. The third generation, the Implanted Stimulator Telemeter (IST-12), used myoelectric signals. However, no direct comparison has been made between these different modalities, nor has their relevance been determined.

Therefore, this study aims to evaluate the performance (efficacy: reliability and precision) of six non-invasive control interfaces. The efficacy criterion is defined by the ability to reliably and accurately control a motor action as illustrated by software on a screen. The six control interfaces are: (1) inertial measurement unit (IMU) sensors that record movements of the contralateral shoulder; (2) surface electromyography (EMG) sensors that capture voluntary muscle contractions of the contralateral limb; (3) a pressure sensor button (switch sensor); (4) a pressure sensor joystick (joystick sensor); (5) a voice recognition sensor (voice sensor) that incorporates a machine learning model capable of recognizing specific words spoken by the participant; and (6) an Ear-Switch® sensor that detects movements of a muscle inside the ear, the tensor tympani.

The study will be conducted over six sessions:

• (V1) Selection Visit: The selection visit will be conducted by the coordinating investigator, who will monitor the participant throughout the trial.
• (V2) Inclusion Visit: This visit will include:

• Clinical examination
• Collection of the signed consent form
• Audio recordings of key words to personalize the speech recognition algorithms
• (V3 to V5) Experimental Visits:

• V3: Evaluation of all six control interfaces.
• V4: Detailed assessment of the two best-mastered control interfaces, both separately and in combination (bimodal use).
• V5: Intensity modulation visit, assessing the participant's ability to reliably and accurately reach target static and dynamic intensity levels (as shown on a screen) using two of the interfaces.
• (V6) End-of-Study Visit: This final visit will consist of a clinical and psychological follow-up consultation to ensure the absence of any adverse effects.

Inclusion criteria

• Spinal cord injury defined by an AIS A, B or C score (AIS A, B or C): complete or incomplete motor deficit below the lesion. This is a standard for describing spinal cord injuries that has been internationally agreed upon.
• Spinal cord injury at the neurological level > C7
• Age greater than or equal to 18 and less than or equal to 80 years
• A history of more than 3 months of neurological stability, with no changes in muscle testing.
• Participants capable of following instructions for testing and providing feedback on the use of the device.
• Participants who have signed the informed consent form to participate in the study after being fully informed.
• Participants affiliated with a social security system (either as a beneficiary or a dependent), excluding those covered by State Medical Aid (AME).

Exclusion criteria

• Participant deprived of liberty (by judicial or administrative decision).
• Adult participants are under legal protection or unable to provide informed consent.
• Participation in another ongoing clinical trial.
• Unstable psychiatric condition.
• Severe cognitive impairment.
• Unstable acute medical condition
• Insufficient proficiency in spoken and written French.