Discriminating Non-Native Segmental Length Contrasts Under Increased Task Demands

The present study examines how vulnerable perception of second language prosody is to increased task demands. German learners of Japanese, German non-learners without exposure to Japanese, and Japanese native listeners were tested in their ability to discriminate consonant length contrasts (compared to vowel length contrasts that served as a control condition). Memory load was increased by a longer inter-stimulus interval (2500 ms compared to 300 ms) and the demand on attention control was enhanced through the addition of the acoustic complexity of the stimuli (i.e., through a task-irrelevant pitch fall that occurred simultaneously with a consonant length contrast). The results showed high discrimination abilities, in all groups, when task demands were lowest. With increased task demands, only non-native listeners' discrimination abilities decreased: non-learners were strongly affected by both increased memory load and higher demand on attention control, while learners were only affected by the latter. The task-irrelevant acoustic complexity of the stimuli had a stronger impact on performance than increased memory load did. The findings suggest that second language learners established novel phonological representations but that the ability to use them could only be applied in the absence of distracting acoustic information. The non-native listeners' reduced sensitivity under increased task demands explains why even advanced learners still face difficulties in daily listening situations with numerous distractions.