 The low-back merger is a sound change which describes the merging of the two low-backed vowels uh and or through this process which such as caught and caught have become homophones. Let us listen. In North America, the low-backed merger is complete in the majority of Canada, the west of the US, Western Pennsylvania and in Eastern New England. However, in the upper Midwest, the low-backed merger is in a transition stage where the merging of the two vowels has yet not been completed. As we can see here, the low-backed merger has opened a new space on the vowel chart, with the effect that low front vowels can now be retracted to a low central position. For example, the Canadian shift affects words such as stack which are now pronounced like stock in the north of the US. Even though the low-backed merger affects the speech of a large number of people, over the borders of the US it is not prestigious. In teaching, American English varieties without the low-backed merger are preferred. A different type of low-backed merger can be found in standard Scottish English where the same vowels are affected but the result is a short mid-low-back or.