Practice makes imperfect: stronger implicit interference with practice in individuals at high risk of developing Alzheimer's disease.

Early screening to determine patient risk of developing Alzheimer's will allow better interventions and planning but necessitates accessible methods such as behavioral biomarkers. Previously, we showed that cognitively healthy older individuals whose cerebrospinal fluid amyloid/tau ratio indicates high risk of cognitive decline experienced implicit interference during a high-effort task, signaling early changes in attention. To further investigate attention's effect on implicit interference, we analyzed two experiments completed sequentially by the same high- and low-risk individuals. We hypothesized that if attention modulates interference, practice would affect the influence of implicit distractors. Indeed, while both groups experienced a strong practice effect, the association between practice and interference effects diverged between groups: stronger practice effects correlated with more implicit interference in high-risk participants, but less interference in low-risk individuals. Furthermore, low-risk individuals showed a positive correlation between implicit interference and EEG low-range alpha event-related desynchronization when switching from high- to low-load tasks. This suggests that lower attention on the task was correlated with stronger interference, a typical phenomenon in the younger population. These results demonstrate how attention impacts implicit interference and highlight early differences in perception between high- and low-risk individuals.