Comparing visual and auditory cued eyeblink conditioning in humans

Delay eyeblink conditioning is widely used to study cerebellar function and has been considered a biomarker of cerebellar dysfunction in neurological and psychiatric disorders. A major challenge for repeated testing is transfer of learning across sessions. We tested whether using conditioned stimuli (CSs) from different modalities reduces transfer in humans, whether participants can be stratified into Fast and Slow learners, and whether pupillometry-based blink detection can serve as an alternative to electromyography (EMG). In Experiment 1 (N = 32), participants completed a short screening and two task sessions with auditory and visual CSs paired with an air puff as unconditioned stimulus, followed by extinction training. Learning occurred in both sessions with no difference in overall conditioned response incidences (CRIs) between sessions. However, auditory CSs led to stronger conditioning than visual CSs. In Experiment 2 (N = 16), no screening session was performed, and both task sessions used visual CSs. Here, specific transfer was evident, with high CRIs from the first block of session 2 and a significant session effect. Similarly, transfer occurred from screening to task sessions in Experiment 1 when CSs matched in modality. Across experiments, participants could be stratified into Fast and Slow learners based on median CRIs in the second acquisition training block during screening (Experiment 1) or first task (Experiment 2) sessions. CRIs derived from EMG and pupillometry were highly correlated, confirming pupillometry-based blink detection as a valid MRI-compatible alternative. In sum, transfer is substantial with same-modality CSs, whereas cross-modal designs reduce transfer and enable repeated testing.