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      New approach for designing cVEP BCI stimuli based on superposition of edge responses

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      Author
      Yasinzai, Muhammad Nabi
      İder, Yusuf Ziya
      Date
      2020-06
      Source Title
      Biomedical Physics and Engineering Express
      Print ISSN
      2057-1976
      Publisher
      Institute of Physics Publishing
      Volume
      6
      Issue
      4
      Language
      English
      Type
      Article
      Item Usage Stats
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      Abstract
      The purpose of this study is to develop a new methodology for designing stimulus sequences for Brain Computer Interfaces that utilize code modulated Visually Evoked Potentials (cVEP BCIs), based on experimental results regarding the behavior and the properties of the actual EEG responses of the visual system to binary-coded visual stimuli, such that training time is reduced and possible number of targets is increased. EEG from 8 occipital sites is recorded with 2000 sps, in response to visual stimuli presented on a computer monitor with 60 Hz refresh rate. EEG responses of the visual system to black-to-white and white-to-black transitions of a target area on the monitor are recorded for 500 ms, for 160 trials, and signal-averaged to obtain the onset (positive edge) and offset (negative edge) responses, respectively. It is found that both edge responses are delayed by 50 ms and wane completely within 350 ms. These edge responses are then used to generate (predict) the EEG responses to arbitrary binary stimulus sequences using the superposition principle. It is found that the generated and the measured EEG responses to certain (16) simple short sequences (16.67–350 ms) are highly correlated. These 'optimal short patterns' are then randomly combined to design the long (120 bit, 2 sec) 'Superposition Optimized Pulse (SOP)' sequences, and their EEG response templates are obtained by superposition of the edge responses. A SOP sequence-based Visual Speller BCI application yielded higher accuracy (95.9%) and Information Transfer Rate (ITR) (57.2 bpm), compared to when superposition principle is applied to conventional m-sequences and randomly generated sequences. Training for the BCI application involves only the acquisition of the edge responses and takes less than 4 min. This is the first study in which the EEG templates for cVEP BCI sequences are obtained by the superposition of edge responses.
      Keywords
      Brain computer interface
      Coded visually evoked response
      EEG
      Stimulus design
      BCI speller
      Permalink
      http://hdl.handle.net/11693/75531
      Published Version (Please cite this version)
      https://dx.doi.org/10.1088/2057-1976/ab98e7
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      • Department of Electrical and Electronics Engineering 3605
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