Toward a reliable PWM-based light-emitting diode visual stimulus for improved SSVEP response with minimal visual fatigue

TL;DR

This paper proposes a PWM-based LED stimulus with high duty-cycles to enhance SSVEP responses while minimizing visual fatigue, improving the practicality of brain-computer interfaces.

Contribution

It introduces a novel approach using extremely high duty-cycle PWM stimuli with precise hardware, demonstrating reduced fatigue and improved SSVEP responses across subjects.

Findings

Higher duty-cycles reduce visual strain.

Peak SSVEP response at 85% duty-cycle.

Potential for more practical BCI applications.

Abstract

Steady state visual evoked response (SSVEP) is widely used in visual-based diagnosis and applications such as brain computer interfacing due to its high information transfer rate and the capability to activate commands through simple gaze control. However, one major impediment in using flashing visual stimulus to obtain SSVEP is eye fatigue that prevents continued long term use preventing practical deployment. This combined with the difficulty in establishing precise pulse-width modulation (PWM) that results in poorer accuracy warrants the development of appropriate approach to solve these issues. Various studies have suggested the usage of high frequencies of visual stimulus to reduce the visual fatigue for the user but this results in poor response performance. Here, the authors study the use of extremely high duty-cycles in the stimulus in the hope of solving these constraints. Electroencephalogram data was recorded with PWM duty-cycles of 50 to 95% generated by a precise custom-made light-emitting diode hardware and tested ten subjects responded that increasing duty-cycles had less visual strain for all the frequency values and the SSVEP exhibited a subject-independent peak response for duty-cycle of 85%. This could pave the way for increased usage of SSVEP for practical applications.