Gradient and categorical patterns of spoken-word recognition and processing of phonetic details

The speech signal is inherently rich, and this reflects complexities of speech articulation. During spoken-word recognition, listeners must process time-dependent perceptual cues, and the role that these cues play varies depending on the phonological status of the sounds across languages. For example, Canadian French has both phonologically nasal vowels (i.e., contrastive) and coarticulatorily nasalized vowels, as opposed to English, which only has coarticulatorily nasalized vowels. We investigated how vowel nasalization duration, a time-dependent phonetic cue to the French nasal contrast, affects spoken-word recognition. Using eye tracking in two visual world paradigm experiments, the results show that fine-grained phonetic information is important for lexical recognition, and that lexical access is dependent on small variations in the signal. The results also show gradient interpretation of ambiguous vowel nasalization despite the phonemic distinction between phonological nasal vowels and coarticulatorily nasalized vowels in Canadian French. Gradience was found when words were ambiguous, and interpretation was more categorical when words were unambiguous. These results support the hypothesis of gradient interpretation of phonetic cues for ambiguously produced stimuli and the storage of coarticulatory information in phono-lexical representations for a language that has a phonological contrast for nasality (i.e., French).