Phonological mergers have systemic phonetic consequences: palm, trees, and the Low Back Merger Shift

Abstract This paper provides a unified phonologically motivated explanation for the movement of trap, dress, and kit following the low-back merger in North American English (i.e., the Canadian Shift, California Shift, Low Back Merger Shift, Third Shift, etc.). The explanation puts forth that the three-way merger of lot, palm, and thought results in the loss of the [+Front] feature specification for trap, opening the door for dispersion focalization to pull trap toward the low central region of the vowel space. Analogy then prompts all other [−Peripheral] vowels, including strut and foot, to centralize. Crucial to this explanation is that the low-back merger includes palm, not just lot and thought. Evidence for this requirement is presented in a phonetic analysis of older speakers from conservative Victoria, British Columbia. The explanation presented here reconciles an earlier proposal (Roeder & Gardner, 2013) with Fruehwald's (2017) observation that parallel movement requires a shared feature specification.