The foundational ADHD noise study (Soderlund et al., 2007) used silence as the control condition. The key finding was asymmetric: ADHD children performed worse in silence than with white noise, while non-ADHD children performed best in silence.
A 2024 study by Soderlund et al. added an important nuance: ADHD individuals with elevated hyperactivity/impulsivity scores actually performed worse with noise, while those with higher inattention scores benefited. The correlation between inattention score and noise benefit was positive (r = .64, p < .001), but the correlation between hyperactivity score and noise benefit was negative.
This means noise is not universally helpful even within the ADHD population. Silence is included as a deliberate option because it is the optimal condition for some users. Offering the choice, rather than defaulting everyone to noise, lets each person find their own peak performance environment.