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Design and Implementation of a P-300 Speller using RSVP Paradigm

Mijani, Amir Mohammad | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51250 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Shamsollahi, Mohammad Bagher
  7. Abstract:
  8. The brain-computer interface is an advanced technology in human-machine interaction. The Speller system is a typical use of BCI, in which the target stimulation is detected by the induced signal in the brain. The most commonly speller system, the matrix Speller, has a major disadvantage, and it is Gaze-dependent. Research has proven that target-character selection in the matrix Speller is dependent on eye movement, or as referred to in technical terminology, it is gaze dependent. Therefore, the Speller matrix is not usable for users suffering from unimpaired oculomotor control. Many researchers attempted to overcome this issue, and their results led to two solutions; 1) changing the type of modality, and using touch and audio instead of vision 2) Changing the Paradigm. One of the suggested protocols is RSVP, in which target-character selection is not dependent on eye movement. In this protocol, characters are displayed one by one at random at a fast rate on the center of the screen. In this study, in order to increase time efficiency and decrease the number of repetitions required to identify each target-character, two other protocols named Dual and Triple RSVP paradigms are introduced. Compared to the primary RSVP paradigm which displayed one character at a time, the Dual and Triple RSVP paradigms display two and three characters at a time, respectively. The mean of character selection accuracy for the single, dual and triple paradigms was 0.78, 0.63 and 0.64, respectively. The mean of ITR for the three paradigms was 3.91, 7.72 and 11.5, in the same order as mentioned above. As observed, the single protocol yields a higher mean accuracy by 15.39% compared to the dual protocol, and 14% compared to the triple. However, displaying a high number of stimulations in the single protocol lengthens the time of the experiment, and results in a relatively low ITR. To prove this point, the ITR for the single protocol is 3.81 bit/min lower than the dual and 7.59 bit/min lower than the triple protocol. As previously mentioned, this problem can be viewed as a tradeoff between accuracy and ITR, and from the mean results obtained it can be concluded that the increase in ITR compared to the decrease in accuracy justifies the choice to opt for dual or triple protocols. All EEGs have been recorded using an EMOTIV device which affects the quality and accuracy of the system.
    Another set of protocols that have been tested, called Shifted RSVP paradigm. Shifted RSVP paradigm include a Single protocol, a shifted Dual protocol, and a Shifted Triple Protocol. In the shifted Dual and Triple RSVP paradigms, two and three characters appear on the screen each time slot respectively. The second and third character are shifted characters of the first characters string. The accuracy of the character detection and the information transfer rate of the three protocols for one subject were {0.93%, 5.16 (bits / min)}, {0.97%, 7.61 (bits / min)} and {0.77%, 7.39 (bits / min}}. The data of these three protocols are recorded with the 32-channel g.HIamp device
  9. Keywords:
  10. Signal Processing ; Machine Learning ; Brain-Computer Interface (BCI) ; Event Related Potential (ERP) ; Brain Signal ; Rapid Serial Visual Presentation (RSVP) Paradiym

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