Effects of simulated visual acuity and ocular motility impairments on SSVEP brain-computer interface performance: an experiment with Shuffle Speller

Individuals with severe speech and physical impairments may have concomitant visual acuity impairments (VAI) or ocular motility impairments (OMI) impacting visual BCI use. We report on use of the Shuffle Speller typing interface for SSVEP BCI copy-spelling with simulated VAI, simulated OMI, and unimpaired vision. To mitigate the effects of visual impairments, we introduce a method that adaptively selects user-specific trial lengths to maximize expected information transfer rate (ITR), which is shown to closely approximate correct letter selection rate. All participants could type under the unimpaired and simulated VAI conditions, without significant differences in typing accuracy or speed. Most participants (31 of 37) could not type under the simulated OMI condition; some achieved high accuracy with slower typing speeds. Reported workload and discomfort were low, and satisfaction high, under the unimpaired and simulated VAI conditions. Implications and future directions for exploration of visual impairment in BCI use are discussed.

伴有重度言语与肢体障碍的个体，可能同时存在视敏度损伤（visual acuity impairments, VAI）或眼球运动损伤（ocular motility impairments, OMI），此类损伤会对视觉脑机接口（Brain-Computer Interface, BCI）的使用造成影响。本研究采用Shuffle Speller打字界面，针对稳态视觉诱发电位脑机接口（steady-state visual evoked potential BCI, SSVEP BCI）的抄写式拼写任务，在模拟视敏度损伤、模拟眼球运动损伤以及视力正常三种条件下开展测试。为缓解视觉损伤带来的不利影响，本研究提出一种自适应选择适配用户试次时长的方法，以最大化预期信息传输速率（information transfer rate, ITR），该方法经证实可与正确字符选择率高度拟合。实验结果显示：所有受试者均可在视力正常与模拟视敏度损伤条件下完成打字任务，且打字准确率与速度无显著差异；37名受试者中有31名无法在模拟眼球运动损伤条件下完成打字，仅少数受试者可实现较高的字符识别准确率，但打字速度较慢。在视力正常与模拟视敏度损伤条件下，受试者报告的任务负荷与不适感较低，满意度较高。最后，本文讨论了脑机接口使用场景中视觉损伤相关研究的启示与未来探索方向。