Stability in perceiving non-native segmental length contrasts
Previous studies have demonstrated that listeners show high sensitivity in discriminating non-native prosodic contrasts thanks to auditory memory (Hayes and Masuda 2008; Hirano 2011). We tested the limits of discriminating Japanese consonantal length contrasts with three groups of listeners (German learners of Japanese, German non-learners and Japanese natives) under increasing task demands. We increased auditory memory load through a longer inter-stimulus interval (=ISI) (2500ms vs. 300ms) and added psycho-acoustic complexity (trials with task-irrelevant pitch falls that occurred simultaneously with the consonant vs. with m onotonous pitch). Results showed very good discrimination in all groups when task demands were lowest. With increasing task demands, only non-natives’ discrimination abilities decreased: non-learners were strongly affected by both ISI and pitch, while learners only by pitch. The psycho-acoustic complexity of the stimuli had a stronger impact on performance than increased memory load. Our findings suggest that L2 learners can establish novel phonological representations, but the ability to use them can be applied still only under favorable listening conditions with no distracting acoustic information. The non-native listeners’ reduced sensitivity under increasing task demands appears to be the reason why even advanced learners still face difficulties in natural learning situations.