place assimilation in the persian coronal nasal: categorical or gradient?

this study focuses on one particular sound change common in conversational speech, in which coronal nasal consonants undergo place assimilation toward the following syllable- or word-initial labial consonants. f2 and f3 formant frequency measurements were taken from, and compared between words involving the sequences /vnb/ and /vmb/ across syllable boundary as well as word boundary in assimilating sentence context. the same formant frequencies were measured for word final coronal nasals in non-assimilatory context.  the frequency of the second formant at vowel offset and during nasal closure was found to be sufficient to discriminate between underlying forms across the word boundary. the obtained mean formant frequencies were, indeed, intermediate between those of unassimilated alveolar and labial sounds. across the syllable boundary, however, there was no significant effect for any of the formant frequencies. the acoustic evidence suggests that an alveolar nasal which assimilates to a following labial consonant across the syllable boundary shows complete lack of coronal closure and full labial contact, while an alveolar nasal assimilating a following labial across word boundary often shows evidence of both alveolar place of articulation and labial place of articulation to varying degrees. the result supports an articulation-based theory of assimilation that allows for assimilation to be a gradient process, with a continuum of realizations between unchanged surface forms and complete feature substitutions.