Comparing tactile and visual gaze-independent brain–computer interfaces in patients with amyotrophic lateral sclerosis and healthy users

• ALS patients with mild to moderate disabilities can control a visual gaze-independent BCI spelling system.
• The visual Hex-o-Spell outperforms the tactile speller in both healthy participants and ALS patients.
• Subjective assessment shows that attending to visual stimuli is easier than attending to tactile stimuli, even if the stimuli are in the peripheral visual field.

ObjectiveBrain–computer interfaces (BCI) tested in patients often are gaze-dependent, while these intended users could possibly lose the ability to focus their gaze. Therefore, a visual and a tactile gaze-independent spelling system were investigated.MethodsFive patients with amyotrophic lateral sclerosis (ALS) tested a visual Hex-o-Spell and a tactile speller. Six healthy participants were also included, mainly to evaluate the tactile stimulators.ResultsA significant attentional modulation was seen in the P300 for the Hex-o-Spell and in the N2 for the tactile speller. Average on-line classification performance for selecting a step in the speller was above chance level (17%) for both spellers. However, average performance was higher for the Hex-o-Spell (88% and 85% for healthy participants and patients, respectively) than for the tactile speller (56% and 53%, respectively). Likewise, bitrates were higher for the Hex-o-Spell compared with the tactile speller, and in the subjective usability a preference for the Hex-o-Spell was found.ConclusionsThe Hex-o-Spell outperformed the tactile speller in classification performance, bit rate and subjective usability.SignificanceThis is the first study showing the possible use of tactile and visual gaze-independent BCI spelling systems by ALS patients with mild to moderate disabilities.