A color-coded SSVEP-based brain–computer interface

Objective. Steady-state visual evoked potential (SSVEP) based brain–computer interfaces (BCIs) predominantly employ frequency, phase, or spatial coding. This study proposes a color-dimension SSVEP encoding scheme and evaluates its feasibility and elicited response characteristics. Approach. Seven isoluminant colors were paired to form 21 combinations, and four stimulation paradigms (sliding checkerboard, reversing checkerboard, flickering checkerboard, and solid-color flicker) were used to investigate the modulatory effects of color on SSVEP. Offline simulations and an online four-target SSVEP-BCI were conducted for validation purposes. Main results. Under identical frequencies and initial phases, different color combinations produced separable SSVEP patterns in amplitude, topography, and phase, enabling reliable classification. At a stimulation frequency of 10 Hz, the four-target online system using the solid-color flicker paradigm achieved an average information transfer rate (ITR) of 80 ± 0 bits/min, and its user experience was favorable compared with the classic black-white stimulation. Additionally, the system employing the flickering checkerboard paradigm obtained an average ITR of 68.76 ± 1.79 bits/min while delivering even better user experience, with a comfort score of 3.10 ± 0.21, a flicker perception score of 3.07 ± 0.21, and a preference score of 2.78 ± 0.21. Significance. The proposed approach introduces an additional encoding dimension for SSVEP-BCI, expanding stimulus design options and supporting broader applications.