Alterations in fine-grained eye movements during reading as early indicators of cognitive decline in mild cognitive impairment

Eye-tracking provides a non-invasive way to measure subtle changes in cognitive processing. Although global reading outcomes, such as total reading time and error count, may remain unchanged in mild cognitive impairment (MCI), fine-grained eye-movement features may provide more sensitive markers of decline. We investigated whether detailed oculomotor features recorded during an oral reading task differentiate individuals with MCI from cognitively healthy controls. We examined 174 participants, including 122 cognitively healthy controls and 52 individuals clinically classified with MCI. Eye movements were recorded during an oral reading task and analyzed for fixation dynamics, word-skipping behavior, re-reading patterns, and regressive eye-movement measures. Group differences were first evaluated using independent-samples t-tests or Mann–Whitney U tests, with effect sizes reported, and were further examined using age-adjusted and mixed-effects models. Several fine-grained eye-movement metrics differed between groups. Compared with controls, participants with MCI showed shorter fixation durations, higher word-skipping rates, and more frequent re-reading episodes, whereas global performance measures, including total reading time and error count, did not differ significantly between groups. The strongest and most age-robust evidence was observed for fixation timing, while evidence for altered regressive-saccade frequency or saccade amplitude was inconclusive. Fine-grained eye-movement features extracted during a controlled oral reading task differed between individuals with MCI and healthy controls under identical stimulus conditions, suggesting that reading-based eye-tracking measures can capture subtle changes in cognitive processing before global reading performance is affected.