The Effect of Duty Cycle and Brightness Variation of Visual Stimuli on SSVEP in Brain Computer Interface Systems

Stimulation methods are very significant for the performance of electroencephalogram (EEG)-based brain-computer interface (BCI) systems. This study aims to investigate methods for obtaining higher information transfer rate (ITR) through duty cycle and brightness variation of visual stimuli for steady-state visual evoked potential-based BCI. Although previous studies were concentrated on either duty cycle or brightness of stimuli separately, our study focused on the change of duty cycle and brightness of stimuli at the same time. Duty cycle values of 20%, 40%, 50%, 60%, and 80% were used. During the experiment, 16 flickering stimuli with a frequency range between 5 and 20Hz were used on liquid crystal display. Subjects gazed to the flickers which had frequencies of 6, 12 and 15Hz. Canonical correlation analyses (CCA), a multivariate statistical method, was used for channel selection and frequency detection. According to the CCA, the maximum average accuracy of the experiment was 96.88% when the frequency of flicker was in beta band and its duty cycle was 40% with a brightness tuning wave. Under the same conditions stated above, average ITR was improved 25.38% according to the most commonly used flicker model which is square wave and has 50% duty cycle.Stimulation methods are very signi!cant for the performance of electroencephalogram (EEG)-based brain!computer interface (BCI) systems. This study aims to investigate methods for obtaining higher information transfer rate (ITR) through duty cycle and brightness variation of visual stimuli for steadystate visual evoked potential-based BCI. Although previous studies were concentrated on either duty cycle or brightness of stimuli separately, our study focused on the change of duty cycle and brightness of stimuli at the same time. Duty cycle values of 20%, 40%, 50%, 60%, and 80% were used. During the experiment, 16 "ickering stimuli with a frequency range between 5 and 20 Hz were used on liquid crystal display. Subjects gazed to the "ickers which had frequencies of 6, 12 and 15 Hz. Canonical correlation analyses (CCA), a multivariate statistical method, was used for channel selection and frequency detection. According to the CCA, the maximum average accuracy of the experiment was 96.88% when the frequency of "icker was in beta band and its duty cycle was 40% with abrightness tuning wave. Under the same conditions stated above, average ITR was improved 25.38% according to the most commonly used "icker model which is square wave and has 50% duty cycle.