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It is conventional to examine vowel systems by their acoustic correlates, specifically formants. In the International Phonetic Alphabet (IPA) vowel chart, vowels are placed according to their relative positions determined by the first two formant values. This two-dimensional plane makes possible the calculation of the articulatory working space of vowels. Variations in the size and shape of the vowel space exist across gender, dialects, and languages. The present study focuses on comparing the vowel space area (VSA) in English and German produced by native Swiss German speakers, attempting to shed light on whether VSAs differ significantly with different calculation methods cross-linguistically. Given the fact that absolute formant values vary tremendously across gender, Hertz values are converted to z-scores, allowing for more direct and meaningful comparisons. While vowel normalization mitigates gender-related differences within specific languages to a large extent, there remains a significant cross-linguistic gender difference. The results reveal that for 3- and 4-vowel space there is no significant effect in language but an effect is observed in gender and vowel combination on VSA, specifically in terms of individual area and overlapping ratio. This suggests that Swiss German speakers tend to utilize the same amount of vowel space in both languages, with the only difference being the expansion of English VSA in higher F2 dimension and lower F1 dimension, as observed across all calculation methods. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the use of Visible Vowels to detect formant and durational differences between L2 and L1 speakers. We used a dataset that contains vowel measures from L1 speakers of French and from L2 learners of French, with Italian, Spanish and English as L1. We found that vowels that are not part of the L1 phonological system are often pronounced differently by L2 speakers. Inspired by the Native Language Magnet Theory which was introduced by Patricia Kuhl in 2000, we introduced magnet plots that relate vowels shared by the French phonological system and the learners' phonological system—the magnet vowels—to the vowels found only in the French phonological system. At a glance, it can be seen which vowels are attracted to the magnets and which vowels become further away from the magnets. When comparing vowel spaces, we found that the shape of the French vowel space of the English learners differed most from the shape of L1 speakers' vowel space. Finally, it was found that the vowel durations of the L2 speakers are greater than that of the L1 speakers of French, especially those of the English learners of French. [ABSTRACT FROM AUTHOR]

Talkers vary in the phonetic realization of their vowels. One influential hypothesis holds that listeners overcome this inter-talker variability through pre-linguistic auditory mechanisms that normalize the acoustic or phonetic cues that form the input to speech recognition. Dozens of competing normalization accounts exist--including both accounts specific to vowel perception and general purpose accounts that can be applied to any type of cue. We add to the cross-linguistic literature on this matter by comparing normalization accounts against a new phonetically annotated vowel database of Swedish, a language with a particularly dense vowel inventory of 21 vowels differing in quality and quantity. We evaluate normalization accounts on how they differ in predicted consequences for perception. The results indicate that the best performing accounts either center or standardize formants by talker. The study also suggests that general purpose accounts perform as well as vowel-specific accounts, and that vowel normalization operates in both temporal and spectral domains. [ABSTRACT FROM AUTHOR]

Talkers vary in the phonetic realization of their vowels. One influential hypothesis holds that listeners overcome this inter-talker variability through pre-linguistic auditory mechanisms that normalize the acoustic or phonetic cues that form the input to speech recognition. Dozens of competing normalization accounts exist—including both accounts specific to vowel perception and general purpose accounts that can be applied to any type of cue. We add to the cross-linguistic literature on this matter by comparing normalization accounts against a new phonetically annotated vowel database of Swedish, a language with a particularly dense vowel inventory of 21 vowels differing in quality and quantity. We evaluate normalization accounts on how they differ in predicted consequences for perception. The results indicate that the best performing accounts either center or standardize formants by talker. The study also suggests that general purpose accounts perform as well as vowel-specific accounts, and that vowel normalization operates in both temporal and spectral domains.

The resonant frequencies of the vocal tract during vowel production convey information about the linguistic vowel intended by the talker - whether they mean to say ‘hey’ or ‘hoe’, for example - while also conveying information about the talker. One particularly salient bit of talker information that partially determines the frequencies of the vowel formants is the length of the talker’s vocal tract. Vowel formant normalization aims to remove the effects of talker differences without also removing important linguistic information. This paper presents a study of vocal tract length normalization using a new ΔF method, and compares this method to other vowel normalization methods. A key point of comparison in this study is the number of vowel tokens that are needed in order to derive a stable estimate of vocal tract length. Several of the vowel normalization methods that are most commonly used in phonetic studies are shown to need a full set of vowels in order to be reliable, while methods that derive vocal tract length information from the full acoustic spectrum are much more stable and may even provide a length-normalized representation that could be cognitively computed and used in human speech perception.

Given the acoustic consequences of physiological differences between talkers, there is a practical need for effective and theoretically motivated procedures of vowel normalization to facilitate comparison of speech produced by people who differ by dialect or language. In addition, there is a question whether listeners might utilize a normalization procedure during speech perception. This paper reports the results of two studies that explore these questions—with particular focus on vocal tract length normalization. Drawing on research in speech engineering, where accurate estimates of vocal tract length are needed in some approaches to automatic speech recognition and speaker verification, a new model of vowel normalization is introduced. The model uses a direct measure of average formant spacing (the ΔF) which can be used to measure vocal tract length. The acoustic consequences of vocal tract length differences are removed from vowel measurements by scaling vowel formant measurements by ΔF. Study 1 found that this method is comparable to Nearey’s (1978) uniform normalization method, while providing an explicit vocal tract length interpretation, and a rationalized unit of measure. Study 2 found that uniform normalization measures (which let each formant serve as a noisy estimator of ΔF) improve vowel classification even with only a couple of randomly selected vowel tokens. This suggests that vocal tract length normalization could be involved in speech perception.

This study investigates how listeners associate acoustically different vowels with a single linguistic vowel quality. Listeners were asked to identify vowel sounds as /æ/ or /?/ and to indicate the size of the speaker that produced them. Results indicate that perceived vowel quality trades off with the perception of speaker size: different vowels can sound the same, and the same vowel can sound different when a different speaker is perceived. These findings suggest that vowel normalization is broadly similar to perceptual constancy in other domains, and that social, indexical, and linguistic information play an important role in determining even the most fundamental units of linguistic representation. [ABSTRACT FROM AUTHOR]

Speech sounds are perceived relative to spectral properties of surrounding speech. For instance, target words that are ambiguous between /bɪt/ (with low F1) and /bɛt/ (with high F1) are more likely to be perceived as "bet" after a "low F1" sentence, but as "bit" after a "high F1" sentence. However, it is unclear how these spectral contrast effects (SCEs) operate in multi-talker listening conditions. Recently, Feng and Oxenham (J.Exp.Psychol.-Hum.Percept.Perform. 44(9), 1447–1457, 2018b) reported that selective attention affected SCEs to a small degree, using two simultaneously presented sentences produced by a single talker. The present study assessed the role of selective attention in more naturalistic "cocktail party" settings, with 200 lexically unique sentences, 20 target words, and different talkers. Results indicate that selective attention to one talker in one ear (while ignoring another talker in the other ear) modulates SCEs in such a way that only the spectral properties of the attended talker influences target perception. However, SCEs were much smaller in multi-talker settings (Experiment 2) than those in single-talker settings (Experiment 1). Therefore, the influence of SCEs on speech comprehension in more naturalistic settings (i.e., with competing talkers) may be smaller than estimated based on studies without competing talkers. [ABSTRACT FROM AUTHOR]

Different speakers produce the same speech sound differently, yet listeners are still able to reliably identify the speech sound. How listeners can adjust their perception to compensate for speaker differences in speech, and whether these compensatory processes are unique only to humans, is still not fully understood. In this study we compare the ability of humans and zebra finches to categorize vowels despite speaker variation in speech in order to test the hypothesis that accommodating speaker and gender differences in isolated vowels can be achieved without prior experience with speaker-related variability. Using a behavioural Go/No-go task and identical stimuli, we compared Australian English adults’ (naïve to Dutch) and zebra finches’ (naïve to human speech) ability to categorize /ɪ/ and /ɛ/ vowels of an novel Dutch speaker after learning to discriminate those vowels from only one other speaker. Experiment 1 and 2 presented vowels of two speakers interspersed or blocked, respectively. Results demonstrate that categorization of vowels is possible without prior exposure to speaker-related variability in speech for zebra finches, and in non-native vowel categories for humans. Therefore, this study is the first to provide evidence for what might be a species-shared auditory bias that may supersede speaker-related information during vowel categorization. It additionally provides behavioural evidence contradicting a prior hypothesis that accommodation of speaker differences is achieved via the use of formant ratios. Therefore, investigations of alternative accounts of vowel normalization that incorporate the possibility of an auditory bias for disregarding inter-speaker variability are warranted.

Abstract: This study used an active multiple-deviant oddball design to investigate the time-course of normalization processes that help listeners deal with between-speaker variability. Electroencephalograms were recorded while Dutch listeners heard sequences of non-words (standards and occasional deviants). Deviants were [ipapu] or [ɛpapu], and the standard was [I ɛpapu], where [I ɛ] was a vowel that was ambiguous between [ɛ] and [i]. These sequences were presented in two conditions, which differed with respect to the vocal-tract characteristics (i.e., the average 1st formant frequency) of the [papu] part, but not of the initial vowels [i], [ɛ] or [I ɛ] (these vowels were thus identical across conditions). Listeners more often detected a shift from [I ɛpapu] to [ɛpapu] than from [I ɛpapu] to [ipapu] in the high F1 context condition; the reverse was true in the low F1 context condition. This shows that listeners’ perception of vowels differs depending on the speaker''s vocal-tract characteristics, as revealed in the speech surrounding those vowels. Cortical electrophysiological responses reflected this normalization process as early as about 120ms after vowel onset, which suggests that shifts in perception precede influences due to conscious biases or decision strategies. Listeners’ abilities to normalize for speaker-vocal-tract properties are for an important part the result of a process that influences representations of speech sounds early in the speech processing stream. [Copyright &y& Elsevier]