Fig 1.
General scheme of the BCI system used in the experiment.
Fig 2.
To begin the session, each patient was first presented with the command ‘We are going to start.’ After the command ‘To make it beep faster keep opening and closing your right hand’, the patient was expected to try moving his/her right hand. After the command ‘To make it beep slower stop opening and closing your right hand’, the patient was expected to stop his/her right-hand motion. To ensure patients did not forget the task, each command was repeated every 10 seconds. Duration of each motion/no motion period was randomly chosen from the interval [15, 50] seconds.
Fig 3.
(A) Auditory feedback. Each time the motion intention pattern was detected in the EEG signal, the pace of the sound (beets per second, bps) and sound frequency were increased (Δbps = 0.15, ΔkHz = 0.15) until 2 bps and 2 kHz were reached. If the pattern was not detected, both were decreased (Δbps = -0.15, ΔkHz = -0.15) until reaching 0.5 bps and 0.5 kHz. When reaching a pace of 2 bps and a 2 kHz frequency during the motion task the auditory feedback “you have succeeded” was provided to the patient. (B) Visual feedback. Each time the motion intention was detected, the size of the bar was increased by 0.1 until reaching of 1. Otherwise, it was decreased by 0.1, until reaching 0. Motion intention periods were indicated with a green arrow pointing up and a red hourglass was pictured when no motion intention patterns were detected. A smiley face was displayed when the bar reached 1 (full size).
Fig 4.
For each time t, to form the explanatory variable x(t), EEG signal from the electrodes was mapped by continuous wavelet transform with 35 frequencies (1, 2, …, 35 Hz). Then, the absolute values of the wavelet coefficients were decimated along the temporal modality to receive 10 points. The response variable y(t) was equal to 1 during the command “Keep opening and closing …” and was equal to 0 during the command “Stop opening and closing …”. The next epoch was taken with a time step of 100 ms.
Fig 5.
Signal decoding during calibration and validation sessions of the BCI experiment.
The model was updated every 10 seconds during the calibration session and fixed during the validation session.
Table 1.
Characteristics of the healthy volunteers.
Fig 6.
(A) Patient 1, (B) Patient 2, (C) Patient 3, (D) Patient 4, (E) Patient 5. Both auditory and visual feedback were provided for the cases of (A) and (B); only auditory feedback was provided for the cases of (C), (D), and (E). For all the cases, value 1 of y-axis corresponds to the task “… keep opening and closing …”, and 0 corresponds to the task “… stop opening and closing …”.
Table 2.
Characteristics of the ICU patients.