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Introduction Cognitive models implicate attentional bias towards sleep-related cues in the perpetuation of chronic insomnia. However, the influence of psychiatric comorbidities on the specific cognitive mechanisms underlying such bias remains underexplored. This study employed Hierarchical Drift Diffusion Modelling (HDDM), a computational framework quantifying evidence accumulation speed (drift rate, v), to examine attentional processing in insomnia stratified by psychiatric symptomatology.Methods A total of 201 clinically diagnosed insomnia patients (aged 15–24 years) completed a validated sleep-related dot-probe task. Participants were stratified into four subgroups: insomnia only (IO), insomnia with high anxiety symptoms (IA), insomnia with high depressive symptoms (ID), and insomnia with both anxiety and depressive symptoms (IAD). HDDM was applied to model drift rates during congruent (sleep-related) and incongruent (neutral) trials, with subgroup comparisons conducted via Bayesian estimation.Results Across the cohort, faster drift rates in congruent versus incongruent trials (q = .036) confirmed sleep-related attentional bias. The IAD group exhibited significantly higher v than the ID group in both congruent (q = .035) and incongruent (q = .027) trials, and marginally higher v than the IA group (q = .061), reflecting generalised hyperarousal. Notably, ID group demonstrated a relative increase in v for incongruent over congruent trials (q = .064), indicative of disengagement from sleep-related stimuli. IO and IA groups showed intermediate patterns ( figure 1).Discussion Findings suggest distinct neurocognitive profiles across insomnia subtypes. Comorbid depression was associated with globally reduced evidence accumulation, consistent with attentional disengagement and cognitive hypoarousal. The combination of anxiety and depression yielded a hyperarousal signature with indiscriminate enhancement of attentional gain, potentially reflecting an agitated affective phenotype. Interestingly, IA showed slightly lower drift rates than IO, which may indicate attentional interference or fragmentation driven by internal preoccupation, rather than enhanced salience processing. These exploratory findings suggest disorder-specific attentional dynamics and heterogeneity of cognitive-affective processing in insomnia.Abstract P36 Figure 1