TRACING PUPILS AND PERFORMANCE: TASK DIFFICULTY AND TIMESCALES OF AROUSAL

A century after Yerkes and Dodson proposed that performance peaks at intermediate arousal, the neurobiological conditions under which this relationship emerges in humans remain debated. Arousal is increasingly understood as a multiscale process, expressed in fluctuations unfolding over different timescales, from fast, transient responses to slower changes in global state. These are reflected in pupil dynamics and relate to neuromodulatory influences, including but not limited to locus coeruleus-noradrenergic activity.
We investigated how task difficulty and the timescale of pupil-linked arousal fluctuations shape the arousal-performance relationship in an auditory discrimination task. Sixty participants performed easy and difficult task variants (~90% and 70% accuracy, respectively) while pupil size was measured. Using a hierarchical Bayesian model, we estimated how task difficulty and pre-stimulus pupil-linked arousal predicted sensitivity.
Overall, we found evidence for an inverted-U shaped arousal-performance relationship, but no evidence for a task-dependent shift. Crucially, the strength and form of this relationship depended on the investigated arousal timescale. When infra-slow arousal fluctuations (<0.01 Hz) were removed, the inverted-U relationship became stronger, whereas isolating these infra-slow components abolished the inverted-U.
Sliding-window analyses further showed a temporal dissociation in which the inverted-U relationship emerged later within blocks, coinciding with attenuation of pupil decay. This suggests that early performance might be dominated by slower neuromodulatory fluctuations than intermediate-timescale fluctuations, influencing performance later in the block.
Together, these findings demonstrate that arousal-performance relationships depend on the temporal scale of arousal fluctuations being examined, refining the interpretation of the Yerkes-Dodson law by addressing specificity to specific arousal timescales.