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The pronunciation patterns across dialect regions in the United States are changing. This paper examines acoustic differences between the vowels of old and middle-aged adults produced in spontaneous speech. The new developments in regional vowels systems which differentiate American English dialects found recently in citation-form vowels and in read speech were confirmed in the present analysis. While providing additional evidence for the existence of sound change on the basis of spontaneous speech data, this work brings to light important challenges facing researchers using spontaneous speech in laboratory analyses such as the loss of fine experimental control in the examination of spectral dynamics or the usefulness of statistical assessment.