Early visual processing in adults with ADHD: evidence from contrast sensitivity, spatial integration, and external noise

Attention-Deficit/Hyperactivity Disorder (ADHD) is typically conceptualized as a disorder of executive control; however, accumulating evidence suggests that early sensory processing may also be atypical. The present study examined contrast sensitivity (CS) and noise processing in a sample of 45 adults (21 with ADHD and 24 neurotypical controls). In Experiment 1, foveal CS was measured across spatial frequencies (4-12 cpd) using standard-size targets presented at stimulus durations of 40 and 80 ms. A three-way ANOVA revealed a significant main effect of group, indicating overall lower contrast sensitivity in the ADHD group, but no significant interactions between Group, Spatial Frequency, and Stimulus Duration. To examine the effect of stimulus size, an enlarged stimulus condition was introduced at the highest spatial frequency (12 cpd). At the 40 ms duration, a significant Group × Stimulus Size interaction suggested reduced spatial integration in the ADHD group, with controls showing greater improvement when stimulus size increased. At 80 ms, this interaction was not significant, although the main effect of group remained present. In Experiment 2, perceptual noise exclusion was assessed; overall performance did not significantly differ between groups across noise levels and stimulus durations. Together, these findings suggest that visual differences in ADHD are selective, emerging primarily under conditions requiring efficient integration of high spatial frequency information at short stimulus durations, while robust group differences in external noise exclusion were not detected.