Tablet-based SDMT: Digital metric validation and within-task learning in MCI and dementia

Background Scalable, process-sensitive tools are needed to address the gap between neuropathological onset and clinical recognition of cognitive decline. Tablet-based assessments can capture behavioral and temporal data beyond conventional test metrics, but require validation in target populations. Objective To evaluate whether a tablet-based Symbol Digit Modalities Test (SDMT) and a response-time-based Performance Index capture clinically relevant cognitive performance in a memory-clinic population with mild cognitive impairment (MCI) or dementia. Methods In a cross-sectional validation study, forty-one adults (mean age 73.7 years, 51% scoring below the CERAD cutoff for likely major cognitive impairment) completed a tablet-based SDMT alongside standard neuropsychological assessments (CERAD battery, MoCA). Digital response counts were compared with oral SDMT scores, the Performance Index was evaluated against clinical reference measures, and exploratory analyses examined within-task response-time patterns across repeated symbol exposures. Results Digital and oral SDMT scores showed strong rank-order agreement ( ρ = 0 . 77 – 0 . 80 , p < . 001 ), with systematically lower absolute digital scores, indicating preserved inter-individual ranking but non-interchangeable modalities. The Performance Index and correct response count showed comparable associations with MoCA ( ρ = 0 . 59 and 0 . 62 ) and CERAD ( ρ = 0 . 49 for both; all p ≤ . 001 ); their convergence was attributable to near-ceiling response accuracy (mean 95.6%, excluding skipped items). Exploratory analyses revealed within-task response-time facilitation across repeated symbol exposures. Conclusion The tablet-based SDMT preserves inter-individual ranking relative to the oral format, and the Performance Index generalizes to a memory-clinic population. Within-task response-time facilitation was observed even among participants with impaired declarative memory. Whether it reflects implicit or procedural learning rather than explicit mediation remains a hypothesis for controlled study.