Autistic traits are associated with suboptimal decision Bias strategies in subsecond timing

Time perception difficulties are frequently reported in Autism Spectrum Disorder(ASD), yet empirical findings remain inconsistent: some studies document impaired timing, while others find no such deficit. This lack of consensus may reflect a key methodological limitation, failing to separate perceptual sensitivity from decision-making strategies. We applied Signal Detection Theory (SDT) to a sub-second duration discrimination task (100 and 500 ms) in 65 non-clinical adults varying in autistic traits, assessed via the Autism-Spectrum Quotient (AQ) and its five subscales. Autistic traits showed no reliable association with reduced perceptual sensitivity (d'): temporal discrimination remained intact across the subclinical range, with Bayesian analyses providing converging evidence against a perceptual deficit. Instead, trial-level generalized linear mixed modeling including all five AQ subscales revealed that higher scores on the Imagination subscale were uniquely associated with a systematic shift in decision bias (c). While observers generally exploited the statistical regularity of the repeated standard stimulus to build a stabilized internal reference consistent with the Internal Reference Model (IRM), individuals with higher Imagination scores (reflecting reduced imaginative flexibility) showed a shift toward positional anchoring, favoring whichever stimulus appeared first. These findings suggest that temporal differences along the autistic-trait dimension do not reflect a core perceptual deficit, but rather a suboptimal decision-making strategy favoring immediately available within-trial information over accumulated representational knowledge.