TABLE 2.

Experimental conditions, variables, and tasks.

Phase	Baseline	Comparison	Comparison	Comparison
Condition	Communicator 1.2 (C1.2)	Communicator 2.5 (C2.5)	Shuffle Speller Eye Tracking (SSET)	Shuffle Speller SSVEP BCI (SSBCI)
Independent variable state (typing system)	3-step speller in Communicator 5 with standard Tobii eye tracking and 1.2-second dwell time	3-step speller in Communicator 5 with standard Tobii eye tracking and 2.5-second dwell time	Shuffle Speller with modified eye tracking	Shuffle Speller with SSVEP BCI
Primary dependent variable	Typing accuracy (% correct character selections/total selections)	Typing accuracy (% correct character selections/total selections)	Typing accuracy (% correct character selections/total selections)	Typing accuracy (% correct character selections/total selections)
Additional dependent variables	Number of correct letter selections, correct backspace selections, and incorrect selections Characters per minute (total CPM, correct CPM for letters and backspace, correct CPM for letters only) User experience questionnaire responses	Number of correct letter selections, correct backspace selections, and incorrect selections Characters per minute (total CPM, correct CPM for letters and backspace, correct CPM for letters only) User experience questionnaire responses	Number of correct letter selections, correct backspace selections, and incorrect selections Characters per minute (total CPM, correct CPM for letters and backspace, correct CPM for letters only) User experience questionnaire responses	Number of correct letter selections, correct backspace selections, and incorrect selections Characters per minute (total CPM, correct CPM for letters and backspace, correct CPM for letters only) User experience questionnaire responses SSVEP trial length
Calibration task	Communicator 5 Gaze Interaction Calibration with 9 target locations	Communicator 5 Gaze Interaction Calibration with 9 target locations	EyeX calibration followed by SSET calibration (20 three-second trials of eye tracking data collected for each of four onscreen targets)	SSBCI calibration (20 six-second trials of SSVEP data collected for each of four LED panel targets positioned at edges of screen)
Copy-spelling task	Copy five five-letter English words	Copy five five-letter English words	Copy five five-letter English words	Copy five five-letter English words
Copy-spelling character selection	Participant selects a box by gazing steadily at it for 1.2 seconds. Each character selection requires three box selections (large group, small group, and individual character).	Participant selects a box by gazing steadily at it for 2.5 seconds. Each character selection requires three box selections (large group, small group, and individual character).	Participant selects a box by gazing at it for two seconds. Shuffle Speller queries the user as many times as necessary, rearranging the characters among boxes, until one character’s probability exceeds 85%.	Participant selects a box by gazing at the neighboring LED panel for the duration determined by the adaptive trial length feature. Shuffle Speller queries the user as many times as necessary, rearranging the characters among boxes, until one character’s probability exceeds 85%.