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Towards an optimization of stimulus parameters for brain-computer interfaces based on steady state visual evoked potentials.

Duszyk A, Bierzyńska M, Radzikowska Z, Milanowski P, Kuś R, Suffczyński P, Michalska M, Łabęcki M, Zwoliński P, Durka P - PLoS ONE (2014)

Bottom Line: Brighter colours and larger dimensions of flickering fields resulted in a significantly stronger SSVEP response.The distance between stimulation fields and the presence or absence of the fixation point had no significant effect on the response.Contrary to a popular belief, these results suggest that absence of the fixation point does not reduce the magnitude of SSVEP response.

View Article: PubMed Central - PubMed

Affiliation: University of Social Sciences and Humanities, Warsaw, Poland.

ABSTRACT
Efforts to construct an effective brain-computer interface (BCI) system based on Steady State Visual Evoked Potentials (SSVEP) commonly focus on sophisticated mathematical methods for data analysis. The role of different stimulus features in evoking strong SSVEP is less often considered and the knowledge on the optimal stimulus properties is still fragmentary. The goal of this study was to provide insight into the influence of stimulus characteristics on the magnitude of SSVEP response. Five stimuli parameters were tested: size, distance, colour, shape, and presence of a fixation point in the middle of each flickering field. The stimuli were presented on four squares on LCD screen, with each square highlighted by LEDs flickering with different frequencies. Brighter colours and larger dimensions of flickering fields resulted in a significantly stronger SSVEP response. The distance between stimulation fields and the presence or absence of the fixation point had no significant effect on the response. Contrary to a popular belief, these results suggest that absence of the fixation point does not reduce the magnitude of SSVEP response. However, some parameters of the stimuli such as colour and the size of the flickering field play an important role in evoking SSVEP response, which indicates that stimuli rendering is an important factor in building effective SSVEP based BCI systems.

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Related in: MedlinePlus

Time course of the experimental paradigm.
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pone-0112099-g001: Time course of the experimental paradigm.

Mentions: Four stimuli were presented simultaneously and subjects were asked to concentrate on the one indicated by an auditory cue. The schematic sequence of events is presented in Fig. 1. Experiment I consisted of 4 s long stimulation periods interleaved by 6 s long resting periods. The screen was black during the rest period. In order to create experimental conditions corresponding to the SSVEP paradigm used in BCI systems, all four fields were simultaneously active (each flickering at a different frequency) during the stimulation intervals. Four frequencies of stimulation (14, 17, 25, and 30 Hz) were chosen on the basis of the results obtained by Kuś [21]. Investigated parameters (colour, size, etc.) were software controlled and randomly presented on an LCD screen, while the flickering was generated by the underlaid LEDs. Stimuli were presented on a hybrid device [22] constructed at the Faculty of Physics, University of Warsaw in order to optimize stability of stimuli rendering. The device consists of an array of LEDs underlaid below an LCD screen (195 mm high and 350 mm wide), where the LEDs highlight precisely determined area of the screen. Each of the four squares displayed on the LCD screen is highlighted by a group of LEDs, flickering with frequencies controlled by the software. Using such a device eliminates problems with monitor refresh rate and at the same time enables full control of stimulus appearance.


Towards an optimization of stimulus parameters for brain-computer interfaces based on steady state visual evoked potentials.

Duszyk A, Bierzyńska M, Radzikowska Z, Milanowski P, Kuś R, Suffczyński P, Michalska M, Łabęcki M, Zwoliński P, Durka P - PLoS ONE (2014)

Time course of the experimental paradigm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4232393&req=5

pone-0112099-g001: Time course of the experimental paradigm.
Mentions: Four stimuli were presented simultaneously and subjects were asked to concentrate on the one indicated by an auditory cue. The schematic sequence of events is presented in Fig. 1. Experiment I consisted of 4 s long stimulation periods interleaved by 6 s long resting periods. The screen was black during the rest period. In order to create experimental conditions corresponding to the SSVEP paradigm used in BCI systems, all four fields were simultaneously active (each flickering at a different frequency) during the stimulation intervals. Four frequencies of stimulation (14, 17, 25, and 30 Hz) were chosen on the basis of the results obtained by Kuś [21]. Investigated parameters (colour, size, etc.) were software controlled and randomly presented on an LCD screen, while the flickering was generated by the underlaid LEDs. Stimuli were presented on a hybrid device [22] constructed at the Faculty of Physics, University of Warsaw in order to optimize stability of stimuli rendering. The device consists of an array of LEDs underlaid below an LCD screen (195 mm high and 350 mm wide), where the LEDs highlight precisely determined area of the screen. Each of the four squares displayed on the LCD screen is highlighted by a group of LEDs, flickering with frequencies controlled by the software. Using such a device eliminates problems with monitor refresh rate and at the same time enables full control of stimulus appearance.

Bottom Line: Brighter colours and larger dimensions of flickering fields resulted in a significantly stronger SSVEP response.The distance between stimulation fields and the presence or absence of the fixation point had no significant effect on the response.Contrary to a popular belief, these results suggest that absence of the fixation point does not reduce the magnitude of SSVEP response.

View Article: PubMed Central - PubMed

Affiliation: University of Social Sciences and Humanities, Warsaw, Poland.

ABSTRACT
Efforts to construct an effective brain-computer interface (BCI) system based on Steady State Visual Evoked Potentials (SSVEP) commonly focus on sophisticated mathematical methods for data analysis. The role of different stimulus features in evoking strong SSVEP is less often considered and the knowledge on the optimal stimulus properties is still fragmentary. The goal of this study was to provide insight into the influence of stimulus characteristics on the magnitude of SSVEP response. Five stimuli parameters were tested: size, distance, colour, shape, and presence of a fixation point in the middle of each flickering field. The stimuli were presented on four squares on LCD screen, with each square highlighted by LEDs flickering with different frequencies. Brighter colours and larger dimensions of flickering fields resulted in a significantly stronger SSVEP response. The distance between stimulation fields and the presence or absence of the fixation point had no significant effect on the response. Contrary to a popular belief, these results suggest that absence of the fixation point does not reduce the magnitude of SSVEP response. However, some parameters of the stimuli such as colour and the size of the flickering field play an important role in evoking SSVEP response, which indicates that stimuli rendering is an important factor in building effective SSVEP based BCI systems.

Show MeSH
Related in: MedlinePlus