# Visual ERP-based brain–computer interface use with severe physical, speech and eye movement impairments: case studies

## TL;DR

This study explores a visual BCI for people with severe physical and speech impairments, showing that it can work even with limited eye movement.

## Contribution

The study introduces a gaze-independent visual BCI that can be used for communication despite eye movement limitations.

## Key findings

- Covert VSA with central fixation leads to decreased BCI accuracy.
- Free VSA performance is comparable to overt VSA for some participants.
- Training with overt VSA improves performance for users with gaze control difficulties.

## Abstract

Individuals who experience severe speech and physical impairment face significant challenges in communication and daily interaction. Visual brain–computer interfaces (BCIs) offer a potential assistive solution, but their usability is limited when facing restrictions in eye motor control, gaze redirection and fixation. This study investigates the feasibility of a gaze-independent visual oddball BCI for use as an augmentative and alternative communication (AAC) device in the presence of limited eye motor control.

Seven participants with varying degrees of eye motor control were recruited and their conditions were thoroughly assessed. Visual oddball BCI decoding accuracy was evaluated with multiple decoders in three visuospatial attention (VSA) conditions: overt VSA, with fixation cued on the target, covert VSA, with fixation cued on the center of the screen, and free VSA without gaze cue.

covert VSA with central fixation leads to decreased accuracy, whereas free VSA is comparable to overt VSA for some participants. Furthermore, cross-condition decoder training and evaluation suggests that training with overt VSA may improve performance in BCI users experiencing gaze control difficulties.

These findings highlight the need for adaptive decoding strategies and further validation in applied settings in the presence of gaze impairment.