Table 4.

Overall satisfaction ratings expressed with a visual analog scale (VAS) and answers to the custom usability questionnaire (system design).

	Healthy (Gel)	Healthy (Dry)	User 3 (Dry)	User 5 (Gel)
	Visual analog scale (VAS) overall device satisfaction (0 = not satisfied at all, 10 = extremely satisfied)
	7.5	7.8	3.8	4.5
CUSTOM USABILITY QUESTIONNAIRE (SYSTEM DESIGN)
Did you feel in control, while using the system?	Yes (N = 9)	Yes (N = 10)	Yes	Yes
Would you describe the system as intuitive?	Yes (N = 9)	Yes (N = 9)	Yes	No (regarding the functionality of some icons), otherwise yes
Operating the interface was…	Easy (4), ok (5), partly difficult (1)	Easy (6), ok (4)	Ok	Ok
Did you like the symbols/icons of the interface?	Yes (N = 7)	Yes (N = 7)	No	Yes
Did you like the colors of the interface?	Yes (N = 6)	Yes (N = 7)	n/a	Yes
Positive experience	“Success if attentive,” “spelling works quite well,” “one can reliably reach the overall goal,” “many senses of achievements,” “I would have never thought that something like this was possible,” “that the system recognizes the fixated icons and to control the program,” “I could write,” “positive how easy commands could be executed with the system,” “much was recognized correctly,” “controlling the interface”	“Control with eyes,” “weight of the cap,” “exciting to give commands basically just using the brain,” “control via eye gaze,” fascinating how well it worked, and I am happy if persons with paralysis could gain quality of life using this technology,” “writing with eyes,” “being able to test the usefulnes of this technology,” “control over systems without using hands possible,” “good cause, interesting, was fun,” “worked well,” “to control things just using gaze and attention”	“Should be 100% accuracy”	“Helping others by testing it”
Negative experience	“Tiring, because of repetitive flashing, constricting cap,” “controlling menu difficult,” “long time needed for selections,” “frustrating if wrong symbol gets selected,” “very tiring,” “the gel in my hairs,” “often it [the intended symbol] was not recognized correctly,” “did not work 100%,” “some symbols were not recognized,” “wrong selections”	“If wrong items are selected,” “I got tired quickly,” “takes a long time,” “attention difficulties,” “three wrong selections in a row,” “eyes ache slightly if one fixates a symbol for too long,” “dissatisfaction if repeatedly a wrong icon was selected,” “electrodes painful after a while,” “high effort needed,” “to realize how diificult it is to focus attention”	“Frustrated if selection wrong”	“Cumbersome, time consuming”
Suggestions for improvements	“Reduce speed of flashing,” “diversify design, so that less tiring,” “no gel,” “quicker text entry method (auto complete function),” “use consistent symbol size”	“Selections could be quicker,” “design,” “design could be optimized,” “improve wearing comfort of electrodes to enable long usage without pain”	“No cap, no wires”	“Might be a help for ALS patients [in the current state]”