Other dialects are Northern Khmer dialect, called "Surin Khmer" by Khmers, spoken by over a million Khmer native to Northeast Thailand and Khmer Krom spoken by the millions of Khmer native to the Mekong Delta regions of Vietnam adjacent to Cambodia and their descendants abroad. A little-studied dialect known as Western Khmer, or Cardamom Khmer, is spoken by a small, isolated population in the Cardamom Mountain range extending from Cambodia into eastern Central Thailand. Although little studied, it is unique in that it maintains a definite system of vocal register that has all but disappeared in other dialects of modern Khmer.