Temporal dissociation of semantic degradation and interference in Alzheimer's disease: Evidence from Chinese character processing.

Chinese characters serve as the psychological entry point for lexical recognition in reading. Over 80% of these characters are phonetic compounds containing a semantic radical. Understanding how individuals with Alzheimer's disease (AD) process these structurally distinct characters is crucial for revealing the underlying nature of their cognitive decline. This study examined 180 older adults (60 Healthy Controls, 60 Mild AD, 60 Moderate AD) in a semantic categorization task across four radical-character relationships: fully related (FR), fully unrelated (FU), radical-only related (RR) and radical-only, related (RO-R). To disentangle semantic degradation from executive control demands, this study employed signal detection theory (SDT) and mixed-effects modelling. Results demonstrated significant group-by-condition interactions for accuracy, reaction time and perceptual sensitivity (d'). AD patients exhibited globally reduced d' and prolonged reaction times. Crucially, an error pattern analysis revealed that Mild AD patients produced significantly more false alarms in the RR condition, a deficit strongly correlated with their Stroop Interference scores (r = .58), reflecting a pronounced susceptibility to semantic interference, exacerbated by atypical executive inhibitory control. Furthermore, a temporal dissociation emerged: while explicit semantic sensitivity (d') collapsed early in the disease, Mild AD patients partially preserved the automatic reaction time advantage for isolated radicals (RO-R), yet suffered an exacerbated reaction time interference effect when resolving radical-related semantic interference (RR > FU). These findings suggest that explicit semantic boundaries and executive conflict resolution abilities degrade early in AD, whereas automatic semantic spreading activation is briefly preserved but highly susceptible to multifaceted semantic interference.