EXPRESS: Selective and divided listening in a dual-language context.

Background speech can reduce intelligibility of target speech because of masking effects. However, masking can be mitigated by presenting target and masker dichotically, an effect we refer to as the dichotic advantage. Because masking, and signal degradation in general, is often shown to negatively impact second language (L2) more than first language (L1) processing, we hypothesised that L2 might accrue a greater dichotic advantage than L1 when listener must selectively attend to the target and ignore the masker. Under divided attention, however, dichotic presentation might introduce cognitive costs due to the need for binaural attentional control. Such costs might be particularly pronounced for L2 given the already high cognitive demands associated with L2 processing and therefore mitigate the L2 dichotic advantage. Using a dual-language context, Spanish (L1)-English (L2) bilinguals heard one English sentence and one Spanish sentence simultaneously, either diotically or dichotically. They completed a selective-attention task (track one talker - Experiment 1) and a divided-attention task (track both talkers - Experiment 2). In both experiments, performance was higher for L1 than L2. The dichotic advantage (better performance in dichotic than diotic listening) was similar for L1 and L2. It was smaller under divided than selective attention, suggesting that increased the cognitive costs incurred by divided listening reduced the dichotic advantage. The results demonstrate that bilinguals experience a dichotic advantage of a similar size in each language (L1 and L2), even in dual-language contexts and under high cognitive load.