Rocio Asperilla¹, Liubov Ardasheva², Anna Montagnini³, Pilar Aivar⁴; ¹Universidad Autónoma de Madrid, ²Aix-Marseille University

Sensory Processing Sensitivity (SPS) may influence how individuals integrate sensory information, yet its role in controlled perceptual decision-making remains largely unexplored. Here, we examined how SPS—as measured by the Highly Sensitive Person Scale—interacts with stimulus ambiguity and cognitive priors during motion discrimination of an ambiguous, bistable rotating sphere. Across three experiments with independent participant samples, we manipulated stimulus ambiguity (variants of the Kinetic Depth Effect stimulus) and expectations about motion direction (probabilistic cues), while recording behavioral responses and high-precision eye movements (not analyzed here). In Experiment 1 (continuous 3-min bistable viewing), SPS correlated positively with perceptual switch frequency (Spearman ρ = .47, p = .002), indicating that individuals higher in SPS experienced more frequent alternations. Pearson correlations were nonsignificant, suggesting a nonlinear association. In Experiment 2 (trial-based unbiased direction judgments), mixed-effects models showed robust effects of stimulus ambiguity on both perceptual choices and reaction times (Ambiguous > Mid-Ambiguous > Non-Ambiguous; all p < .001). SPS influenced response promptness: higher-SPS individuals responded faster and more consistently when stimuli were less ambiguous. Within-trial switches were strongly reduced for non-ambiguous stimuli (p < .001) and did not interact with SPS. In Experiment 3 (priming with 50/70/90% cue validity), prior cues biased perceived direction but did not reliably affect reaction times or switching. Ambiguity again dominated perceptual stability, and SPS did not modulate cue-induced biases. These findings provide initial evidence linking SPS to individual variability in bistable motion perception, with greater reactivity to ambiguous sensory input but not to externally imposed probabilistic priors. Given the modest sample sizes and the subjective nature of SPS assessment, interpretations should remain cautious. Nonetheless, the results identify a novel connection between trait sensitivity and perceptual decision-making.