Five Shades of Grey: Exploring Quintary m-Sequences for More User-Friendly c-VEP-Based BCIs

Figure 4

α-Values of the stimulus object for the six tested flickering patterns. Displayed are the α-values derived from binary and quintary code patterns at different monitor refresh rates. The α-values range from 0 to 1: 0 denotes “fully transparent” and 1 denotes “fully opaque.” The red line indicates the end of a full stimulation cycle. (a) Stimulus pattern of the binary 63-digit m-sequence, refresh rate 60 Hz, 2 cycles. (b) Stimulus pattern of the binary 63-digit m-sequence, refresh rate 120 Hz, 4 cycles. (c) Stimulus pattern of the binary 63-digit m-sequence, refresh rate 240 Hz, 8 cycles. (d) Stimulus pattern of the quintary 124-digit m-sequence, refresh rate 60 Hz, 1 cycle. (e) Stimulus pattern of the quintary 124-digit m-sequence, refresh rate 120 Hz, 2 cycles. (f) Stimulus pattern of the quintary 124-digit m-sequence, refresh rate 240 Hz, 4 cycles.

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