Numerosity estimation in children with ADHD across space, time, vision and action.

Children with ADHD often experience difficulties in mathematics, but the mechanisms underlying these difficulties remain unclear. One possibility is that they reflect a basic impairment in the "number sense," that is, the ability to approximate the number of objects and temporal events without counting. Here, we tested this hypothesis by asking children with ADHD (N = 20) and typically developing controls (N = 43) to verbally estimate briefly presented dot arrays, temporal sequences of flashes, and self-generated hand actions (button presses). Performance was quantified in terms of precision (Weber fraction) and accuracy (absolute bias). In the unadjusted analysis, children with ADHD showed lower overall estimation precision than controls. The group difference disappeared after adjustment for age, reasoning abilities, and mathematical performance. No group differences emerged for estimation accuracy. Taken together, these findings provide no clear evidence of impaired approximate numerosity processing in ADHD and are consistent with the possibility that mathematical difficulties do not primarily arise from a core deficit in the non-symbolic number sense.