Color-modulated olfactory testing using RAPPIT: An innovative tool for early detection of cognitive decline

Background: Olfactory and visual processing are sensitive biomarkers for cognitive impairment; however, unimodal assessments may fail to capture early deficits in higher order cognitive integration. When sensory cues are mismatched, multisensory processing induces crossmodal conflict that requires inhibitory control, which is particularly vulnerable in early neurodegeneration. Objective: We developed RAPPIT (Rapid, massively APPlicable Identification Test), a color-modulated olfactory test to assess multisensory interference as an early marker of cognitive decline. Methods: RAPPIT includes 16 physically presented odors, with a digital application for task control and response recording. Answer options are displayed on color backgrounds derived from the MONEX-40 color profile, either congruent or incongruent with the presented odors. A total of 163 participants from the German population completed the assessment. Odor identification accuracy, effects of color congruence (ΔE00), associations with cognitive performance (Montreal Cognitive Assessment, MoCA), hedonic ratings, and depressive symptoms were analyzed. Results: Odor identification declined with age. Participants aged ≥ 60 years, a group at increased risk for neurodegenerative disorders including Alzheimer's disease, showed reduced performance under incongruent conditions. Performance exhibited a non-linear relationship with color difference (ΔE00), declining at mid-range values. Accuracy was significantly associated with MoCA scores. Hedonic ratings varied with color cues, while no associations were found with depressive symptoms. Conclusions: These findings demonstrate that differences between congruent and incongruent odor-color conditions capture cognitively relevant interference effects beyond unimodal olfactory or visual performance, supporting the utility of this approach for early detection of cognitive impairment in older adults, in clinical and home settings.