Merged productions of /ɪ/ and /ɛ/ before nasal consonants is well documented in Southern U.S. English, but perception studies on this merger are limited. A two-alternative forced-choice perception task asked U.S. listeners from inside and outside the South to respond to stimuli on continua from bid to bed and bin to Ben. Vowel nasality and coda nasality were fully crossed in the stimuli. The results confirm that Southern speakers are to some degree merged in perception, and that the presence of a nasal coda, and not vowel nasality, conditions merger in perception.
Smith et al. (Fri,) studied this question.