How Semantic Processing of Words Evokes Changes in Pupil

This paper investigates the relationship between semantic processing of words and modifications in pupil size. Variations in pupil diameter reflect cognitive processing, as has been widely demonstrated in literature. We designed an experiment in which semantic association between words was manipulated in order to disclose potential differences in cognitive processing. Moreover, we measured the concurrent pupil diameter changes. Results showed faster pupil dilation in trials in which words were semantically associated. As changes in pupil diameter do not occur under voluntary control, they could reflect processing of preconscious information. We believe that a better symbiotic relationship between humans and machines is achievable once systems are able to make us aware of these "involuntary" changes.