Visual orientation discrimination in adults with ADHD and ASD: the differential impact of clinical diagnosis and trait severity

Objectives: This study aimed to clarify whether clinical diagnosis, as opposed to trait severity alone, differentiates sensory processing profiles in adults with ADHD and ASD. Specifically, we compared clinical and non-clinical cohorts matched on standardized self-report measures to test the impact of diagnosis on visual orientation discrimination. Methods: A total of 152 adults were assigned to four matched groups: clinical ADHD, non-clinical ADHD, clinical ASD, and non-clinical ASD (n = 38/group). ADHD and ASD traits were assessed using the Adult ADHD Self-Report Scale (ASRS) and Broad Autism Phenotype Questionnaire (BAPQ). Sensory performance was measured using a visual orientation discrimination task (with vertical and oblique conditions). Propensity score matching and ANCOVAs (controlling for age/gender) were used to ensure comparability between the clinical and non-clinical groups. Results: Clinically diagnosed ADHD participants displayed significantly poorer oblique orientation sensitivity than non-clinical controls, while clinical ASD participants exhibited superior vertical orientation discrimination compared to their matched non-clinical group. No significant differences were found for vertical thresholds in ADHD and oblique thresholds in ASD. These patterns remained after controlling for age and gender, indicating disorder-specific sensory trajectories, with bidirectional effects of severity and/or clinical diagnosis on sensory performance. Conclusions: Findings suggest that clinical diagnosis captures qualitative as well as quantitative differences not reflected by trait severity alone. Within visual orientation discrimination, ADHD and ASD showed different patterns of diagnostic modulation that are consistent with dimensional and dimensional-categorical (hybrid) interpretative frameworks, respectively.