Attention-deficit/hyperactivity disorder (ADHD) is commonly characterized by impulsiveness and hyperactivity. Previous studies report that individuals with ADHD exhibit higher-than-normal intrusive saccades during prolonged visual fixation. However, little is known about the characteristics of fixational eye movements in ADHD. To address this question, we measured fixational eye movements for 11 young adults (aged: 18 – 30) previously diagnosed with ADHD (4 on ADHD medication), and 6 age-matched control observers. A self-report ADHD screening questionnaire was administered before eye movement measurement to confirm ADHD diagnosis. Observers were asked to fixate a high-contrast, black 1° cross displayed against a uniform gray background on a 32” display for trials of 70 s while the positions of both eyes were sampled at 1000 Hz using an Eyelink 1000 Plus eye tracker. Observers completed 10 trials, split into two blocks. After blink removal and denoising, a velocity-based algorithm was used to detect saccades and slow-drifts. Consistent with previous reports, on average, ADHD observers (with or without medication) exhibited more intrusive saccades (defined as amplitude > 3°) during fixation than control observers. However, group differences in fixation stability, frequency, amplitude and peak velocity of microsaccades (defined as saccades of amplitude ≤ 3°), and diffusion constants (amount of eye displacements due to slow-drifts), were not statistically significant. These data imply that characteristics of fixational eye movements were largely similar between observers with and without ADHD. Our small sample size, coupled with substantial within-group variability, may partly explain this result.
Acknowledgements: Koret Discovery Scholarship