Low-back-merger shift
The low-back-merger shift is a chain shift of vowel sounds found in several accents of North American English, beginning in the last quarter of the 20th century and most significantly involving the low back merger (which collapses together the low-back vowel sounds: , , and in words like PALM, LOT, and THOUGHT respectively) accompanied by the lowering and backing of each of the front-lax vowels: , , and (in words like TRAP, DRESS, and KIT respectively). The back and downward movement of all the front lax vowels was first noted as distinguishing certain California English speakers in 1987, and it was soon known by linguists as the California vowel shift.