Hani Tsruya¹, Maria Lev, Uri Polat; ¹Bar Ilan University

Contrast sensitivity (CS) is a fundamental low-level visual function that serves as a building block for overall visual perception and underlies early visual processing. Recently, we demonstrated that adults with ADHD show increased susceptibility to visual crowding compared to controls. The present study examined whether more basic visual functions, specifically CS and signal extraction under noise, may account for these differences.Forty-five adults participated (23 controls, 22 with ADHD). CS was assessed using a contrast detection task with single Gabor patches (uncrowded condition) at spatial frequencies of 4, 6, 9, and 12 cycles/degree and stimulus durations of 40 and 80 ms. In addition, a letter identification task presented with several levels of external noise and exposure durations of 30 and 60 ms was used to evaluate mechanisms of signal extraction and noise exclusion under constrained conditions. Adults with ADHD showed reduced CS relative to controls, particularly at higher spatial frequencies and shorter stimulus durations. In the noise task, both groups showed a significant decline in performance as external noise increased. A significant main effect of duration was observed, with better identification at 60 ms compared to 30 ms; however, no significant differences were found between the ADHD and control groups. These findings indicate that perceptual processing in ADHD is compromised at early stages of visual processing, particularly in contrast detection under spatial and temporal constraints. The absence of group differences in the noise task suggests that external noise exclusion and internal noise levels may be relatively preserved, although signal strength encoding may be reduced. Overall, the results support the view that visual differences in ADHD reflect limitations in basic sensory encoding rather than solely deficits in higher-level control processes.