The rare presentation of a sound that deviates from the auditory background tends to capture attention, which is known to impede cognitive functioning. Such disruption is usually measured using performance on a concurrent visual task. Growing evidence recently showed that the pupillary dilation response (PDR) could index the attentional response triggered by a deviant sound. Given that the pupil diameter is sensitive to several vision-related factors, it is unclear whether the PDR could serve to study attentional capture in such contexts. Hence, the present study aimed at verifying whether the PDR can be used as a proxy for auditory attentional capture while a visual serial recall task (Experiment 1) or a reading comprehension task (Experiment 2) – respectively producing changes in luminance and gaze position – is being performed. Results showed that presenting a deviant sound within steady-state standard sounds elicited larger PDRs than a standard sound. Moreover, the magnitude of these PDRs was positively related to the amount of performance disruption produced by deviant sounds in Experiment 1. Performance remained unaffected by the deviants in Experiment 2, thereby implying that the PDR may be a more sensitive attention-capture index than behavioural measures. These results suggest that the PDR can be used to assess attentional capture by a deviant sound in contexts where the pupil diameter can be modulated by the visual environment.