A pair of experiments examines first the coarticulatory relations among certain stressed and unstressed vowels, and next the perception of coarticulated unstressed vowels. The first study finds the acoustic properties of unstressed medial and, to a substantially lesser extent, of stressed medial, to be assimilated to the properties of their flanking vocalic contexts. Both initial and final flanking vowels coarticulate with medial, but carryover coarticulatory effects tend to exceed anticipatory effects. In a secondary experiment, listeners' manners of perceiving the coarticulated unstressed vowels of the first experiment are shown to be coupled to, or to be compatible with, the talkers' coarticulatory strategies. In particular, perceivers hear acoustically identical vowels to be different when the vowels appear in different contexts of flanking vowels. Similarly, instances of that are acoustically different due to different coarticulatory influences on them sound the same to listeners as long as each appears in its appropriate context of flanking vowels.
Carol A. Fowler (Sun,) studied this question.