The relationship between visual stimulus frequency and steady-state visually evoked potential (SSVEP) frequency and amplitude is a foundational principle of electrophysiology and frequency-tagging paradigms, requiring no citation.
The claim that visual stimulus frequency directly modulates steady-state visually evoked potential characteristics is a definitional core of how SSVEPs operate and are utilized in vision science (where periodic visual stimuli at specific frequencies elicit neural responses at matching frequencies). Because this is a foundational observation of visual neuroscience and everyday methodological application in EEG research, it is classified as common knowledge.