Pupil responses by level of valence sensitivity to emotion-evoking pictures

Pupillary change due to emotion-evoking stimuli and the relationship between pupil responses and emotion-rating behaviours were analysed carefully. Chronological pupil responses were compared by level of emotional impression, which was standardised using item response theory. The results show that mean pupil size changes according to the level of emotional impression, and the maximum size depends on the classification level, such as middle-group negative on the valence scale. Also, the duration of appearance of the significant difference between the various levels of the groups depends on the number of levels. These results confirm the results of some of the previous studies. Therefore, they suggest that pupil response consists of the composite reactions mentioned above. The importance of assessment of the individual rating responses was confirmed in a detailed analysis.