Previous research by speech scientists on the acoustic characteristics of American English vowel systems has typically focused on a single regional variety, despite decades of sociolinguistic research demonstrating the extent of regional phonological variation in the United States. In the present study, acoustic measures of duration and first and second formant frequencies were obtained from five repetitions of 11 different vowels produced by 48 talkers representing both genders and six regional varieties of American English. Results revealed consistent variation due to region of origin, particularly with respect to the production of low vowels and high back vowels. The Northern talkers produced shifted low vowels consistent with the Northern Cities Chain Shift, the Southern talkers produced fronted back vowels consistent with the Southern Vowel Shift, and the New England, Midland, and Western talkers produced the low back vowel merger. These findings indicate that the vowel systems of American English are better characterized in terms of the region of origin of the talkers than in terms of a single set of idealized acoustic-phonetic baselines of "General" American English and provide benchmark data for six regional varieties.

The perception of phonological differences between regional dialects of American English by naïve listeners has received little attention in the speech perception literature and is still a poorly understood problem. Two experiments were carried out using the TIMIT corpus of spoken sentences produced by talkers from a number of distinct dialect regions in the United States. In Experiment 1, acoustic analysis techniques identified several phonetic features that can be used to distinguish different dialects. In Experiment 2, recordings of the sentences were played back to naïve listeners who were asked to categorize talkers into one of six geographical dialect regions. Results showed that listeners are able to reliably categorize talkers using three broad dialect clusters (New England, South, North/West), but that they have more difficulty categorizing talkers into six smaller regions. Multiple regression analyses on the acoustic measures, the actual dialect affiliation of the talkers, and the categorization responses revealed that the listeners in this study made use of several reliable acoustic-phonetic properties of the dialects in categorizing the talkers. Taken together, the results of these two experiments confirm that naïve listeners have knowledge of phonological differences between dialects and can use this knowledge to categorize talkers by dialect.

Listeners can explicitly categorize unfamiliar talkers by regional dialect with above-chance performance under ideal listening conditions. However, the extent to which this important source of variation affects speech processing is largely unknown. In a series of four experiments, we examined the effects of dialect variation on speech intelligibility in noise and the effects of noise on perceptual dialect classification. Results revealed that, on the one hand, dialect-specific differences in speech intelligibility were more pronounced at harder signal-to-noise ratios, but were attenuated under more favorable listening conditions. Listener dialect did not interact with talker dialect; for all listeners, at a range of noise levels, the General American talkers were the most intelligible and the Mid-Atlantic talkers were the least intelligible. Dialect classification performance, on the other hand, was poor even with only moderate amounts of noise. These findings suggest that at moderate noise levels, listeners are able to adapt to dialect variation in the acoustic signal such that some cross-dialect intelligibility differences are neutralized, despite relatively poor explicit dialect classification performance. However, at more difficult noise levels, participants cannot effectively adapt to dialect variation in the acoustic signal and cross-dialect differences in intelligibility emerge for all listeners, regardless of their dialect.

Early linguistic experience has been shown to affect speech perception in a variety of ways. The present experiment investigated the effects of early linguistic experience on dialect perception. Two groups of participants listened to sentences read by talkers from six American English dialects and were asked to identify where they thought the talkers were from using a forced-choice categorization task. We found that "army brats," who had lived in at least three different states, performed better than "homebodies," who had lived only in Indiana, in terms of overall categorization accuracy. Army brats who had lived in a given region also categorized talkers from that region more accurately than army brats who had not lived there. Clustering analyses on the stimulus-response confusion matrices revealed significant differences in the perceptual similarity spaces for the two listener groups. These results suggest that early exposure to linguistic variation affects how well listeners can identify where unfamiliar talkers are from.

A speaker's regional dialect is a rich source of information about that person. Two studies examined five- to six-year-old children's perception of regional dialect: Can they perceive differences among dialects? Have they made meaningful social connections to specific dialects? Experiment 1 asked children to categorize speakers into groups based on their accent; Experiment 2 asked them to match speakers to (un)familiar cultural items. Each child was tested with two of the following: the child's Home dialect, a Regional variant of that dialect, and a Second-Language variant. Results showed that children could successfully categorize only with a Home vs. Second-Language dialect contrast, but could reliably link cultural items with either a Home vs. Second-Language or a Regional vs. Second-Language dialect contrast. These results demonstrate five- to six-year-old children's developing perceptual skill with dialect, and suggest that they have a gradient representation of dialect variation.