Effects of acoustic variability in the perceptual learning of non-native-accented speech sounds

This study addressed whether acoustic variability and category overlap in non-native speech contribute to difficulty in its recognition, and more generally whether the benefits of exposure to acoustic variability during categorization training are stable across differences in category confusability. Three experiments considered a set of Spanish-accented English productions. The set was seen to pose learning and recognition difficulty (experiment 1) and was more variable and confusable than a parallel set of native productions (experiment 2). A training study (experiment 3) probed the relative contributions of category central tendency and variability to difficulty in vowel identification using derived inventories in which these dimensions were manipulated based on the results of experiments 1 and 2. Training and test difficulty related straightforwardly to category confusability but not to location in the vowel space. Benefits of high-variability exposure also varied across vowel categories, and seemed to be diminished for highly confusable vowels. Overall, variability was implicated in perception and learning difficulty in ways that warrant further investigation.