Non-binary m-sequences for more comfortable brain–computer interfaces based on c-VEPs

Martínez-Cagigal, Víctor; Santamaría-Vázquez, Eduardo; Pérez-Velasco, Sergio; Marcos-Martínez, Diego; Moreno-Calderón, Selene; Hornero, Roberto

doi:10.1016/j.eswa.2023.120815

Cited by 13 publications

(16 citation statements)

References 35 publications

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“…Since the refresh rate of the monitor allowed up to 144 Hz, the stimuli were presented at 120 Hz. Several studies have shown that the higher the frequency of stimulus presentation, the greater the user comfort (Gembler et al, 2018 ; Baaklar and Ider, 2019 ; Martnez-Cagigal et al, 2023 ). Therefore, a higher frequency has been opted for over the standard 60 Hz to improve system speed and enhance the satisfaction of users (Martnez-Cagigal et al, 2023 ).…”

Section: Methodsmentioning

confidence: 99%

“…Several studies have shown that the higher the frequency of stimulus presentation, the greater the user comfort (Gembler et al, 2018 ; Baaklar and Ider, 2019 ; Martnez-Cagigal et al, 2023 ). Therefore, a higher frequency has been opted for over the standard 60 Hz to improve system speed and enhance the satisfaction of users (Martnez-Cagigal et al, 2023 ). Thus, the duration of a complete cycle of the sequence corresponds to 0.525 s (i.e., 63/120).…”

Section: Methodsmentioning

confidence: 99%

“…The standard deviation (STD) of the signal was calculated for each channel. Then, an epoch was discarded if at least the STD in one channel exceeded three times the STD of that channel (Martnez-Cagigal et al, 2023 ).…”

Section: Methodsmentioning

confidence: 99%

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Combining brain-computer interfaces and multiplayer video games: an application based on c-VEPs

Moreno-Calderón

Martínez-Cagigal

Santamaría-Vázquez

et al. 2023

Front. Hum. Neurosci.

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Introduction and objectiveVideo games are crucial to the entertainment industry, nonetheless they can be challenging to access for those with severe motor disabilities. Brain-computer interfaces (BCI) systems have the potential to help these individuals by allowing them to control video games using their brain signals. Furthermore, multiplayer BCI-based video games may provide valuable insights into how competitiveness or motivation affects the control of these interfaces. Despite the recent advancement in the development of code-modulated visual evoked potentials (c-VEPs) as control signals for high-performance BCIs, to the best of our knowledge, no studies have been conducted to develop a BCI-driven video game utilizing c-VEPs. However, c-VEPs could enhance user experience as an alternative method. Thus, the main goal of this work was to design, develop, and evaluate a version of the well-known ‘Connect 4' video game using a c-VEP-based BCI, allowing 2 users to compete by aligning 4 same-colored coins vertically, horizontally or diagonally.MethodsThe proposed application consists of a multiplayer video game controlled by a real-time BCI system processing 2 electroencephalograms (EEGs) sequentially. To detect user intention, columns in which the coin can be placed was encoded with shifted versions of a pseudorandom binary code, following a traditional circular shifting c-VEP paradigm. To analyze the usability of our application, the experimental protocol comprised an evaluation session by 22 healthy users. Firstly, each user had to perform individual tasks. Afterward, users were matched and the application was used in competitive mode. This was done to assess the accuracy and speed of selection. On the other hand, qualitative data on satisfaction and usability were collected through questionnaires.ResultsThe average accuracy achieved was 93.74% ± 1.71%, using 5.25 seconds per selection. The questionnaires showed that users felt a minimal workload. Likewise, high satisfaction values were obtained, highlighting that the application was intuitive and responds quickly and smoothly.ConclusionsThis c-VEP based multiplayer video game has reached suitable performance on 22 users, supported by high motivation and minimal workload. Consequently, compared to other versions of “Connect 4” that utilized different control signals, this version has exhibited superior performance.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Combining brain-computer interfaces and multiplayer video games: an application based on c-VEPs

Moreno-Calderón

Martínez-Cagigal

Santamaría-Vázquez

et al. 2023

Front. Hum. Neurosci.

Self Cite

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“…EEG signals were processed in real-time using a pipeline mainly based on the reference processing for circular shifting (Martinez-Cagigal et al, 2023). A pre-processing step consisting on a series of 7-th order infinite impulse response Butterworth filters was employed to enable real-time processing.…”

Section: Data Acquisition and Signal Processingmentioning

confidence: 99%

“…The initial filter covered a wide frequency range of 1-60 Hz, capturing all frequency bands. The second filter focused on the beta and gamma frequency bands (12-60 Hz), while the third filter specifically targeted the gamma band (30-60 Hz) (Martinez-Cagigal et al, 2023). The upper cutoff of 60 Hz was chosen based on the maximum frequency that can be represented in the EEG due to the refresh rate of the monitor (120 Hz).…”

Section: Data Acquisition and Signal Processingmentioning

confidence: 99%

Influence of spatial frequency in visual stimuli for cVEP-based BCIs: evaluation of performance and user experience

Fernández-Rodríguez,

Martínez-Cagigal,

Santamaría-Vázquez

et al. 2023

Front. Hum. Neurosci.

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Code-modulated visual evoked potentials (c-VEPs) are an innovative control signal utilized in brain-computer interfaces (BCIs) with promising performance. Prior studies on steady-state visual evoked potentials (SSVEPs) have indicated that the spatial frequency of checkerboard-like stimuli influences both performance and user experience. Spatial frequency refers to the dimensions of the individual squares comprising the visual stimulus, quantified in cycles (i.e., number of black-white squares pairs) per degree of visual angle. However, the specific effects of this parameter on c-VEP-based BCIs remain unexplored. Therefore, the objective of this study is to investigate the role of spatial frequency of checkerboard-like visual stimuli in a c-VEP-based BCI. Sixteen participants evaluated selection matrices with eight spatial frequencies: C001 (0 c/°, 1×1 squares), C002 (0.15 c/°, 2×2 squares), C004 (0.3 c/°, 4×4 squares), C008 (0.6 c/°, 8×8 squares), C016 (1.2 c/°, 16×16 squares), C032 (2.4 c/°, 32×32 squares), C064 (4.79 c/°, 64×64 squares), and C128 (9.58 c/°, 128×128 squares). These conditions were tested in an online spelling task, which consisted of 18 trials each conducted on a 3×3 command interface. In addition to accuracy and information transfer rate (ITR), subjective measures regarding comfort, ocular irritation, and satisfaction were collected. Significant differences in performance and comfort were observed based on different stimulus spatial frequencies. Although all conditions achieved mean accuracy over 95% after 2.1 s of trial duration, C016 stood out in terms user experience. The proposed condition not only achieved a mean accuracy of 96.53% and 164.54 bits/min with a trial duration of 1.05s, but also was reported to be significantly more comfortable than the traditional C001 stimulus. Since both features are key for BCI development, higher spatial frequencies than the classical black-to-white stimulus might be more adequate for c-VEP systems. Hence, we assert that the spatial frequency should be carefully considered in the development of future applications for c-VEP-based BCIs.

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Toward Early Stopping Detection for Non-binary c-VEP-Based BCIs: A Pilot Study

Martínez-Cagigal,

Santamaría-Vázquez,

Hornero

2023

Lecture Notes in Computer Science

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Non-binary m-sequences for more comfortable brain–computer interfaces based on c-VEPs

Cited by 13 publications

References 35 publications

Combining brain-computer interfaces and multiplayer video games: an application based on c-VEPs

Combining brain-computer interfaces and multiplayer video games: an application based on c-VEPs

Influence of spatial frequency in visual stimuli for cVEP-based BCIs: evaluation of performance and user experience

Toward Early Stopping Detection for Non-binary c-VEP-Based BCIs: A Pilot Study

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