Merger within an individual

The merger of vowels in a language over time has been a productive area of study, yet how these changes arise remains an ongoing matter of debate. A generally accepted hypothesis is that mergers arise within individuals, who are thought to become merged over time as a result of contact with other merged individuals. A further prediction states that unconditioned mergers, such as the low back merger of /a/ and /ɔ/ in American English, are particularly vulnerable to change, whereas conditioned mergers, such as pre-velar raising of /æ/ before /g/, where the vowels of bag and beg are similar, are more resistant to change within the individual. Neither prediction has been tested against longitudinal data from the same speakers over time. Here, a study is reported showing some support for the predictions of change over time, but with a caveat: individuals are more likely to show change related to unconditioned mergers than conditioned ones, opposite the expected pattern.