**3.2. P300-SSVEP hybrid**

**Hybrid type Subj. Modes of** 

122 Evolving BCI Therapy - Engaging Brain State Dynamics

**operation**

P300 + SSVEP 8 Simultaneous SVM and

P300 + SSVEP 12 Simultaneous SWLDA and

SSVEP + MI 6 Sequential Filter and

P300 + SSVEP 10 Simultaneous BLDA and

P300 + SSVEP 10 Simultaneous SWLDA and

P300 + SSVEP 10 Sequential FLDA and

P300 + SSVEP 10 Simultaneous BLDA and

P300 + MI 4 Sequential SVM and

**Classifiers Acc.** 

DFT

CCA

SSVEP + MI 14 Simultaneous LDA 81 — Reduction in BCI

SSVEP + MI 12 Simultaneous CCA 80 15 False activations

SSVEP + MI 3 Simultaneous SVM & CCA 90 295 Time reduction

SSVEP + MI 24 Sequential CSP & CCA 87 — Enhanced MI

CCA

CCA

BLDA

CCA

FLDA

P300 + MI 4 Sequential FLDA 82 — Less exhaustive

P300 + SSVEP 12 Simultaneous SWLDA 93 34 Transformed

SSVEP + MI 17 Simultaneous LDA 85 — Improved

Threshold

**(%)**

**ITR (bits/ min)**

90 22 "Go/stop" control

93 56 Classification

78 — Improved

90 22 Improved

93 31 Reduced

88 19 Improved

**Improvements Reference**

[54]

[55]

[61]

[62]

[63]

[64]

[65]

[66]

[56]

[67]

[68]

[69]

[51]

[70]

[71]

signal with higher accuracy

accuracy and ITR

reduction with binary decision

with higher reliability

performance

performance over conventional FET

performances with single channel

performance and easiness for users

stimulation time for P300 and improved ITR

classification accuracy and ITR

speller

but not P300

complex tasks in virtual environment

and reliable control of robotic devices

83 12 Improved SSVEP

82 — Finished more

frequency locked SSVEP to time locked in a single

illiteracy

An asynchronous control of wheelchair was proposed by [54] combining SSVEP and P300 in which four groups of buttons were displayed, each group having one large central button surrounding eight small buttons with 45° spacing in a circumference of 60 mm radius. The four groups flickered at frequencies 6, 6.67, 7.5, and 8.57 Hz to evoke SSVEP, while 100 ms interval was used to intensify and change the color of large central button to elicit P300. SVM and discrete Fourier transform (DFT) were used for classification of P300 and SSVEP, respectively, with an overall classification accuracy of about 90% from eight healthy subjects (20–31 years) performing "go/stop" control task using a real wheelchair.

In [51], SSVEP and P300 were combinedly evoked to improve accuracy using four red boxes with black background participating 10 healthy male subjects of age 21–25 years for three runs of 80 trials each in pseudorandom order. P300 was elicited by counting 32 flashings of the four red boxes for 8 times in each trial in the order: top, down, left, and right, and box changed from red to white for 100 ms during each flash while SSVEP was evoked by focusing on the target box which flickered at particular frequencies 9, 6, 10, and 8 Hz for 4 sec in the same order as of flashing, and the subjects needed to count the flashes and focus on flickering simultaneously for the hybrid paradigm. The P300 and SSVEP signals were analyzed separately and the average performances are mentioned in **Table 1**. This experiment highlighted the need for efficient hybrid as the hybrid performances improved relative to SSVEP but not

Hybrid Brain-Computer Interface Systems: Approaches, Features, and Trends

http://dx.doi.org/10.5772/intechopen.75132

125

A hybrid SSVEP-P300 BCI generating dual-frequency SSVEP was proposed by [67] using 9 panels speller, each panel with 4 characters flickering at different frequencies, and flickering panel and periodically updating characters evoked dual-frequency SSVEP. Ten graduate students (8 male, 2 female subjects, and average age 26 years) participated in both the offline and

A hybrid P300-MI was used in [70] to control appliances in a virtual environment, in which P300 was used as a device control to operate control panel of virtual devices and MI as a navigation tool to turn left/right in the virtual environment, and the detection was sequential based on the activation of either MI or P300. Four healthy adults (1 male, 3 female subjects, age 23–25 years) participated and P300 was elicited using oddball paradigm, and MI using left-hand/right-hand movement imagination. The average online classification accuracy was achieved around 82% and authors claimed that more complex tasks in virtual environment

The possibility of combining various brain signals for hybrid BCI was discussed by [71] merging P300 and ERD to control a robotic device such that additional features of one system could be used to improve classification accuracy of another. In this case, object selection from various options, called discrete decision, was done using P300 and movement control of the robot was done using ERD from motor imagination. EEG was filtered to a band 0–10 Hz for P300 classification. Optimum filter band varied with subject for ERD and the filter band was obtained from training data. Principal component analysis (PCA) and CSP was used in feature extraction for P300 and MI, respectively, and the discriminant classification was done by FLDA. Four healthy subjects were experimented with at least three MI trainings before the experiment by each subject with tasks: one out of five P300 symbols (1–5) and one out of two MI hand movements (left/right). Each subject performed one experimental session consisting of 60 trials, 30 trials for P300 in which targets were 1–5 numbers random flashings, and remaining 30 trials for MI where subjects needed to focus only one either on P300 or MI during each trial. Hybrid classification accuracy achieved was about 82% with average MI

online experiments and there were improvements in stimulation time and ITR.

to P300, and the subjects were comfortable with the hybrid.

could be performed compared to single pattern BCI.

**3.3. P300-MI hybrid**

classification accuracy of 71%.

A hybrid SSVEP-P300 BCI was proposed by [55] as mentioned earlier to improve spelling accuracy combining random flashing and periodic flickering to evoke P300 and SSVEP, respectively. All the cells of 6x6 matrix were flickered on black background with six frequencies 8.18, 8.97, 9.98, 11.23, 12.85, and 14.99 Hz, and selection of these frequencies were based on the higher SSVEP amplitude and easier target detection while orange crosses were flashed for 120 ms in random manner. Twelve healthy subjects (5 male and 7 female subjects, age 21–29 years) with good visions were used and the performance of the hybrid system was evaluated online using single trial. This experiment claimed to have the best performance.

In [56], a BCI with shape changing and flickering speller was designed, rather than traditional color changing as in [67], combining SSVEP and P300 in which the classification accuracy was improved in each of the individual systems. Shape changing of red boxes to arrows was used for P300 and flickering of those four boxes with frequencies 6, 8, 9, and 10 Hz for SSVEP. Ten healthy right-handed subjects with normal vision (9 male and 1 female subjects, age 22–27 years) were used for five offline experimental sessions having 20 runs of each sessions lasting for 4 s so the one session was 40 min including 10 min rest. The subjects found the new hybrid less annoying.

An asynchronous hybrid BCI combining P300 and SSVEP was proposed by [68] where the information transfer and control state (CS) detection was accomplished using P300 and SSVEP, respectively. This system operated in sequential manner in both offline and online experiments. Ten healthy subjects (7 males and 3 females aged 19–28 years) were participated in both experiments where P300 was elicited from flashing of a 6x6 matrix of 36 characters (A-Z and 0–9), and SSVEP was obtained from flickering of the characters black and white alternatively with frequency around 17.7 Hz. Two classifiers: Fisher's linear discriminant analysis (FLDA) for first three subjects and Bayesian linear discriminant analysis (BLDA) for remaining subjects were used for P300 classification. Inclusion of SSVEP into P300 improved the classification accuracy.

In [69], same target stimulus was used to elicit P300 and SSVEP blocking (SSVEP-B). A new speller of 3x3 matrix with characters 1–9 was proposed while all the characters flickered at a constant repetitive rate, and each character stopped flickering randomly within a short time. The repetitive flickering elicited SSVEP and the interrupted flickering of a character would elicit SSVEP-B and P300, a rare event at the same time which was detected simultaneously. Twelve right-handed healthy subjects (7 male and 5 female subjects, age 23–36 years) were participated in the experiment. The size and font of characters were changed with a variance of 0.49 ms for event-related potential, and brightness altered between light and dark with about 14.96 Hz for evoked potential. Stepwise linear discriminant analysis (SWLDA) was used for classification and the hybrid system produced better result than the individual systems.

In [51], SSVEP and P300 were combinedly evoked to improve accuracy using four red boxes with black background participating 10 healthy male subjects of age 21–25 years for three runs of 80 trials each in pseudorandom order. P300 was elicited by counting 32 flashings of the four red boxes for 8 times in each trial in the order: top, down, left, and right, and box changed from red to white for 100 ms during each flash while SSVEP was evoked by focusing on the target box which flickered at particular frequencies 9, 6, 10, and 8 Hz for 4 sec in the same order as of flashing, and the subjects needed to count the flashes and focus on flickering simultaneously for the hybrid paradigm. The P300 and SSVEP signals were analyzed separately and the average performances are mentioned in **Table 1**. This experiment highlighted the need for efficient hybrid as the hybrid performances improved relative to SSVEP but not to P300, and the subjects were comfortable with the hybrid.

A hybrid SSVEP-P300 BCI generating dual-frequency SSVEP was proposed by [67] using 9 panels speller, each panel with 4 characters flickering at different frequencies, and flickering panel and periodically updating characters evoked dual-frequency SSVEP. Ten graduate students (8 male, 2 female subjects, and average age 26 years) participated in both the offline and online experiments and there were improvements in stimulation time and ITR.
