In a quiet laboratory, fifty children sat before eye-tracking cameras, and what their pupils revealed was not simply whether they could remember shapes and patterns, but how steadily their minds could hold attention from one moment to the next. Researchers found that children with ADHD showed roughly 23 percent greater trial-to-trial pupil variability than their peers — a physiological tremor of attention that standard tests rarely capture. Stimulant medication appeared to calm that tremor, drawing the pupils' behavior closer to those of children without the diagnosis. The study does not yet o