Probing the visual system with frequency tagging: new insights from a systematic EEG study

Frequency tagging – presenting stimuli at a fixed rate and measuring the brain’s resonance at the exact same frequency – is a widely used tool for probing the human visual system, yet what drives the strength of this response remains poorly understood. We conducted an EEG study where we systematically varied flicker frequency, stimulus contrast, waveform type, and visual complexity, while participants provided trial-by-trial ratings of perceived flicker intensity. We uncovered several striking and previously overlooked effects that challenge common assumptions about frequency tagging and offer concrete guidelines for paradigm design, while raising broader questions about the distinct neural mechanisms engaged across the frequency spectrum.