The effect of background speech on attentive sound processing: A pupil dilation study

Abstract

Listening to task-irrelevant speech while performing a cognitive task can involuntarily deviate our attention and lead to decreases in performance. One explanation for the impairing effect of irrelevant speech is that semantic processing can consume attentional resources. In the present study, we tested this assumption by measuring performance in a non-linguistic attentional task while participants were exposed to meaningful (native) and non-meaningful (foreign) speech. Moreover, based on the tight relation between pupillometry and attentional processes, we also registered changes in pupil diameter size to quantify the effect of meaningfulness upon attentional allocation. To these aims, we recruited 41 native German speakers who had neither received formal instruction in French nor had extensive informal contact with this language. The focal task consisted of an auditory oddball task. Participants performed a duration discrimination task containing frequently repeated standard sounds and rarely presented deviant sounds while a story was read in German or (non-meaningful) French in the background. Our results revealed that, whereas effects of language meaningfulness on attention were not detectable at the behavioural level, participants' pupil dilated more in response to the sounds of the auditory task when background speech was played in non-meaningful French compared to German, independent of sound type. In line with the initial hypothesis, this suggested that semantic processing of the native language required attentional resources, which lead to fewer resources devoted to the processing of the sounds of the focal task. Our results highlight the potential of the pupil dilation response for the investigation of subtle cognitive processes that might not surface when only behaviour is measured.