Pupil dilation as a measure of processing load in simultaneous interpretation and other language tasks.

The present study tested whether the pupillary response can be applied to study the variation in processing load during simultaneous interpretation. In Experiment 1, the global processing load in simultaneous interpretation as reflected in the average pupil size was compared to that in two other language tasks, listening to and repeating back an auditorily presented text. Experiment 1 showed clear differences between the experimental tasks. In Experiment 2, the task effect was replicated using single words as stimuli. Experiment 2 showed that momentary variations in processing load during a lexical translation task are reflected in pupil size. Words that were chosen to be more difficult to translate induced higher levels of pupil dilation than did easily translatable words. Moreover, repeating back words in a non-native language was accompanied by increased pupil dilations, in comparison to repetition in the subject's native language. In sum, the study lends good support to the use of the pupillary response as an indicator of processing load.