Temporal-order processing of American-English vowel sequences by native and non-native English-speaking listeners

Abstract

To understand the development of native-like proficiency in speech processing, we must consider the apparent ease with which native speakers process speech sounds under a variety of conditions. In the present study, auditory temporal-order processing of American-English vowel sequences was compared across three listener groups: monolingual English speakers and relatively early vs. later learners of English as a second language. Using the methods of Fogerty, Humes and Kewley-Port [2010, J. Acoust. Soc. Am., 127, 2509-2520], 70-ms resynthesized versions of the syllables “pit, pet, put,” and “pot” were presented in a two-syllable temporal-order processing task. Task difficulty was increased by decreasing syllable-onset asynchrony (SOA), i.e., the duration between syllable onsets. SOA thresholds for accuracy of syllable-sequence identification were estimated using the method of constant stimuli on each of four 72-trial blocks. Similar SOA thresholds were obtained for native English speakers and early learners of English, but SOA thresholds increased by a factor of two or more for later learners of English. Furthermore, the average SOA threshold of the later learners is similar to that of the older listeners in Fogerty et al. (2010), suggesting that increased processing time partially accounts for both groups’ increased difficulty in processing speech in noisy environments.