In the research on semantic processing and brain activity, the N400-paradigm has been long known to reflect a reaction to unexpected events, for instance the incongruence between visual and verbal information when subjects are presented with a picture and a mismatching word. In the present study, we investigate whether an N400-like reaction to unexpected events can be captured with pupillometry. While earlier research has firmly established a connection between changes in pupil diameter and arousal, the findings have not been so far extended to the domain of semantic processing.
Consequently, we measured pupil size change in reaction to a match or a mismatch between a picture and an auditorily presented word. We presented 120 trials to ten native speakers of Swedish. In each trial a picture was displayed for six seconds, and 2.5 seconds into the trial the word was played through loudspeakers. The picture and the word were matching in half of the trials, and all stimuli were common high-frequency monosyllabic Swedish words.
For the analysis, the baseline pupil size at the sound playback onset was compared against the maximum pupil size in the following time window of 3.5 seconds. The results show a statistically significant difference (t(746)=-2.8, p < 0.01) between the conditions. In line with the hypothesis, the pupil was observed to dilate more in the incongruent condition (on average by 0.03 mm). While the results are preliminary, they suggest that pupillometry could be a viable alternative to existing methods in the field of language processing, for instance across different ages and clinical groups. In the future, we intend to validate the results on a larger sample of participants as well as expand the analysis with a view to locating temporal regions of greatest differences between the conditions. In the future, we intend to validate the results on a larger sample of participants as well as expand the analysis with a functional analysis accounting for temporal changes in the data. This will allow locating temporal regions of greatest differences between the conditions.
24th Biennial Meeting of the International Society for the Study of Behavioural Development