Effects of Aversive Classical Conditioning on Pupil Dilation and Microsaccades

Unintentional shifts of gaze and the modulation of pupil size are both highly automated processes that serve to regulate the initial influx of visual information. The present work investigated these mechanisms as they came to differentially respond to initially unthreatening stimuli following aversive conditioning. The classical conditioning experimental paradigm employed simple grating stimuli (Gabor patches) shown individually at various (5) on-screen locations, one of which was paired with a noxious auditory unconditioned stimulus (US). Aversively paired Gabor patches elicited an attenuated initial constriction of the pupil (pupillary light response; PLR) along with more rapid re-dilation compared to otherwise identical but unpaired gratings. Modulation of both the PLR and the rate of re-dilation following conditioning showed pronounced individual differences. Rapid eye movements away from fixation (microsaccades) were suppressed for the aversively associated compared to unassociated stimulus locations at several post-stimulus latencies. Mutual information between pupil dilation and microsaccade rate, meanwhile, did not differ between the aversively associated and unassociated visual on-screen locations. Together, these results suggest that measures of pupil diameter and microsaccade rate supply complementary information on early-stage processes of associative learning through experience.