Interaction of Intrinsic Vowel and Consonant Durational Correlates with Foreigner Directed Speech

Foreigner-directed and Lombard speech are two examples of speech modes that have increased intelligibility compared to normal speech. Investigating the interactions between altered speech modes and phonological contrasts may throw light on the question of which details are vital in intelligibility enhancement. The present study compares the production of vowel shortening in English, a duration-based voicing correlate, realized in a listener-directed speech style (foreigner-directed speech) with native adult-directed speech and another listener-directed speech mode (Lombard speech). British speakers completed a communicative task in cooperation with an adult native speaker or adult foreigner, in quiet and in noisy conditions. Speaker productions were analyzed to examine the changes in the duration of the target vowels and following plosive consonants. The results show that vowel shortening was present in the three speech styles. The durational voicing correlate was maintained in foreigner-directed and reduced in Lombard speech when compared with native adult-directed speech. Consonant durational differences were enhanced in foreigner-directed but reduced in Lombard speech relative to native adult-directed speech. The results suggest that foreigner-directed speech may be more intelligible in quiet conditions than Lombard speech, but less when both are presented with the same amount of noise.