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Pupil-based binary communication

Augmentative alternative communicationBrain-computer interfaceComplete locked-in syndrome

Introduction

Complete locked-in state is a pathological condition that may derive from neurological disorders, such as amyotrophic lateral sclerosis or brain stem stroke. Due to the complete muscle paralysis, the patient cannot communicate with the external word, even if sensory and cognitive functions are preserved. Current EEG-based brain-computer interfaces have not yet proven adequate to solve the problem.

Technical features

A new communication system is proposed, based on the pupil accommodative response (PAR), a robust pupil constriction that takes place when the gaze is shifted from a far to a near object. No eye movement is required if the objects are aligned with the gaze in monocular view. PAR is easy to detect and implement in a binary communication system: the patients may be asked to shift the focus in a first/second time interval to answer YES/NO to a question. More complex protocols and interfaces implementing writing tasks may also be designed. Information transfer rate above 10 bits/min can been reached. Notably, pupil constriction is governed by the autonomic nervous system, which appears to be largely preserved in the relevant clinical conditions, as confirmed in preliminary results from amyotrophic lateral sclerosis patients in locked-in state. PAR may constitute a robust communication channel to un-lock the complete locked-in state.

Possible Applications

  • Eye-based communication;
  • Augmentative and alternative communication;
  • Assistive technology for locked-in state;
  • Gaming for movement-impaired patients;
  • Additional communication channel for existing brain-computer interfaces.

Advantages

  • Robust response, quite independent of eye illuminance, mono/binocular view, type of visual target;
  • non-invasive and simple set-up;
  • No or little learning process required;
  • No expensive equipment required.