Variability attenuates sensitivity to acoustic detail in cross-language speech production

In the production of non-native consonant clusters, speakers' systematic errors have been attributed to the influence of native-language phonotactics (Dupoux et al., 1999). However, recent models of non-native speech production suggest that speakers are also sensitive to acoustic details (Davidson et al., 2012). We examine whether speakers' sensitivity to phonetic detail is modulated by variability in the speech signal, and whether they abstract away from subphonemic detail given sufficient variability. This was tested by presenting English speakers with ill-formed clusters (e.g. bdafa, tmape, zgade) containing systematically manipulated sub-phonemic acoustic properties: burst duration and amplitude for stop-initial clusters, and the presence/absence of pre-obstruent voicing (POV) for voiced clusters. In Experiment 1, which presented stimuli produced by one Russian talker, significant effects were found for the duration manipulations on the rates of epenthesis, the amplitude manipulation on consonant change/deletion errors, and the POV manipulation on the rate of prothesis. In Experiment 2, which contained stimuli produced by three talkers, there was a substantial attenuation of the influence of the acoustic manipulations on speakers? productions. These results suggest that an account of non-native speech production that models the relative contribution of phonotactics and phonetic detail must incorporate information about variability in the environment.