Lexical frequency and voice assimilation

Acoustic duration and degree of vowel reduction are known to correlate with a word's frequency of occurrence. The present study broadens the research on the role of frequency in speech production to voice assimilation. The test case was regressive voice assimilation in Dutch. Clusters from a corpus of read speech were more often perceived as unassimilated in lower-frequency words and as either completely voiced (regressive assimilation) or, unexpectedly, as completely voiceless (progressive assimilation) in higher-frequency words. Frequency did not predict the voice classifications over and above important acoustic cues to voicing, suggesting that the frequency effects on the classifications were carried exclusively by the acoustic signal. The duration of the cluster and the period of glottal vibration during the cluster decreased while the duration of the release noises increased with frequency. This indicates that speakers reduce articulatory effort for higher-frequency words, with some acoustic cues signaling more voicing and others less voicing. A higher frequency leads not only to acoustic reduction but also to more assimilation.     

Changing only the probability that spoken words will be distorted changes how they are recognized

An eye-tracking experiment examined contextual flexibility in speech processing in response to distortions in spoken input. Dutch participants heard Dutch sentences containing critical words and saw four-picture displays. The name of one picture either had the same onset phonemes as the critical word or had a different first phoneme and rhymed. Participants fixated on onset-overlap more than rhyme-overlap pictures, but this tendency varied with speech quality. Relative to a baseline with noise-free sentences, participants looked less at onset-overlap and more at rhyme-overlap pictures when phonemes in the sentences (but not in the critical words) were replaced by noises like those heard on a badly tuned AM radio. The position of the noises (word-initial or word-medial) had no effect. Noises elsewhere in the sentences apparently made evidence about the critical word less reliable: Listeners became less confident of having heard the onset-overlap name but also less sure of having not heard the rhyme-overlap name. The same acoustic information has different effects on spoken-word recognition as the probability of distortion changes.     

Adapting to suprasegmental lexical stress errors in foreign-accented speech

Can native listeners rapidly adapt to suprasegmental mispronunciations in foreign-accented speech? To address this question, an exposure-test paradigm was used to test whether Dutch listeners can improve their understanding of non-canonical lexical stress in Hungarian-accented Dutch. During exposure, one group of listeners heard a Dutch story with only initially stressed words, whereas another group also heard 28 words with canonical second-syllable stress (e.g., EEKhorn, "squirrel" was replaced by koNIJN "rabbit"; capitals indicate stress). The 28 words, however, were non-canonically marked by the Hungarian speaker with high pitch and amplitude on the initial syllable, both of which are stress cues in Dutch. After exposure, listeners' eye movements were tracked to Dutch target-competitor pairs with segmental overlap but different stress patterns, while they listened to new words from the same Hungarian speaker (e.g., HERsens, herSTEL, "brain," "recovery"). Listeners who had previously heard non-canonically produced words distinguished target-competitor pairs better than listeners who had only been exposed to Hungarian accent with canonical forms of lexical stress. Even a short exposure thus allows listeners to tune into speaker-specific realizations of words' suprasegmental make-up, and use this information for word recognition.     

The role of vowel and consonant fundamental frequency, envelope, and temporal fine structure cues to the intelligibility of words and sentences

The speech signal contains many acoustic properties that may contribute differently to spoken word recognition. Previous studies have demonstrated that the importance of properties present during consonants or vowels is dependent upon the linguistic context (i.e., words versus sentences). The current study investigated three potentially informative acoustic properties that are present during consonants and vowels for monosyllabic words and sentences. Natural variations in fundamental frequency were either flattened or removed. The speech envelope and temporal fine structure were also investigated by limiting the availability of these cues via noisy signal extraction. Thus, this study investigated the contribution of these acoustic properties, present during either consonants or vowels, to overall word and sentence intelligibility. Results demonstrated that all processing conditions displayed better performance for vowel-only sentences. Greater performance with vowel-only sentences remained, despite removing dynamic cues of the fundamental frequency. Word and sentence comparisons suggest that the speech envelope may be at least partially responsible for additional vowel contributions in sentences. Results suggest that speech information transmitted by the envelope is responsible, in part, for greater vowel contributions in sentences, but is not predictive for isolated words.     

Toward a model for lexical access based on acoustic landmarks and distinctive features

This article describes a model in which the acoustic speech signal is processed to yield a discrete representation of the speech stream in terms of a sequence of segments, each of which is described by a set (or bundle) of binary distinctive features. These distinctive features specify the phonemic contrasts that are used in the language, such that a change in the value of a feature can potentially generate a new word. This model is a part of a more general model that derives a word sequence from this feature representation, the words being represented in a lexicon by sequences of feature bundles. The processing of the signal proceeds in three steps: (1) Detection of peaks, valleys, and discontinuities in particular frequency ranges of the signal leads to identification of acoustic landmarks. The type of landmark provides evidence for a subset of distinctive features called articulator-free features (e.g., [vowel], [consonant], [continuant]). (2) Acoustic parameters are derived from the signal near the landmarks to provide evidence for the actions of particular articulators, and acoustic cues are extracted by sampling selected attributes of these parameters in these regions. The selection of cues that are extracted depends on the type of landmark and on the environment in which it occurs. (3) The cues obtained in step (2) are combined, taking context into account, to provide estimates of "articulator-bound" features associated with each landmark (e.g., [lips], [high], [nasal]). These articulator-bound features, combined with the articulator-free features in (1), constitute the sequence of feature bundles that forms the output of the model. Examples of cues that are used, and justification for this selection, are given, as well as examples of the process of inferring the underlying features for a segment when there is variability in the signal due to enhancement gestures (recruited by a speaker to make a contrast more salient) or due to overlap of gestures from neighboring segments.     

The role of the mora in the timing of spontaneous Japanese speech

This study investigates whether the mora is used in controlling timing in Japanese speech, or is instead a structural unit in the language not involved in timing. Unlike most previous studies of mora-timing in Japanese, this article investigates timing in spontaneous speech. Predictability of word duration from number of moras is found to be much weaker than in careful speech. Furthermore, the number of moras predicts word duration only slightly better than number of segments. Syllable structure also has a significant effect on word duration. Finally, comparison of the predictability of whole words and arbitrarily truncated words shows better predictability for truncated words, which would not be possible if the truncated portion were compensating for remaining moras. The results support an accumulative model of variance with a final lengthening effect, and do not indicate the presence of any compensation related to mora-timing. It is suggested that the rhythm of Japanese derives from several factors about the structure of the language, not from durational compensation.     

Formant movements of Dutch vowels in a text, read at normal and fast rate.

Speaking rate in general, and vowel duration more specifically, is thought to affect the dynamic structure of vowel formant tracks. To test this, a single, professional speaker read a long text at two different speaking rates, fast and normal. The present project investigated the extent to which the first and second formant tracks of eight Dutch vowels varied under the two different speaking rate conditions. A total of 549 pairs of vowel realizations from various contexts were selected for analysis. The formant track shape was assessed on a point-by-point basis, using 16 samples at the same relative positions in the vowels. Differences in speech rate only resulted in a uniform change in F1 frequency. Within each speaking rate, there was only evidence of a weak leveling off of the F1 tracks of the open vowels /a a/ with shorter durations. When considering sentence stress or vowel realizations from a more uniform, alveolar-vowel-alveolar context, these same conclusions were reached. These results indicate a much more active adaptation to speaking rate than implied by the target undershoot model.     

Frequent word section extraction in a presentation speech by an effective dynamic programming algorithm

Word frequency in a document has often been utilized in text searching and summarization. Similarly, identifying frequent words or phrases in a speech data set for searching and summarization would also be meaningful. However, obtaining word frequency in a speech data set is difficult, because frequent words are often special terms in the speech and cannot be recognized by a general speech recognizer. This paper proposes another approach that is effective for automatic extraction of such frequent word sections in a speech data set. The proposed method is applicable to any domain of monologue speech, because no language models or specific terms are required in advance. The extracted sections can be regarded as speech labels of some kind or a digest of the speech presentation. The frequent word sections are determined by detecting similar sections, which are sections of audio data that represent the same word or phrase. The similar sections are detected by an efficient algorithm, called Shift Continuous Dynamic Programming (Shift CDP), which realizes fast matching between arbitrary sections in the reference speech pattern and those in the input speech, and enables frame-synchronous extraction of similar sections. In experiments, the algorithm is applied to extract the repeated sections in oral presentation speeches recorded in academic conferences in Japan. The results show that Shift CDP successfully detects similar sections and identifies the frequent word sections in individual presentation speeches, without prior domain knowledge, such as language models and terms.     

The influence of final-syllable position on the vowel and word duration of deaf talkers

Hearing talkers produce shorter vowel and word durations in multisyllabic contexts than in monosyllabic contexts. This investigation determined whether a similar effect occurs for deaf talkers, a population often characterized as lacking coarticulation in their speech. Four prelingually deafened adults and two hearing controls produced three sets of word sequences. Each set included a kernel word and six derived forms (e.g., "speed," "speedy," "speeding," etc.). The derived forms were created by adding unstressed and stressed syllables to the kernel form. A spectrographic analysis indicated that the deaf subjects did not always decrease word and vowel durations for the derivatives. Unlike hearing speakers, they often did not reduce vowel segments more than consonant segments. Three explanations are forwarded for the shortening effects. One relates to the implementation of temporal rules, the second concerns the organization imposed upon the articulators to produce speech, and the third suggests a language-independent vocal tract characteristic. The role of auditory information in developing the shortening effects is also considered.     

Speech intonation and focus location in matched statements and questions

An acoustical study of speech production was conducted to determine the manner in which the location of linguistic focus influences intonational attributes of duration and fundamental voice frequency (F0) in matched statements and questions. Speakers orally read sentences that were preceded by aurally presented stimuli designed to elicit either no focus or focus on the first or last noun phrase of the target sentences. Computer-aided acoustical analysis of word durations showed a localized, large magnitude increase in the duration of the focused word for both statements and questions. Analysis of F0 revealed a more complex pattern of results, with the shape of the F0 topline dependent on sentence type and focus location. For sentences with neutral or sentence-final focus, the difference in the F0 topline between questions and statements was evident only on the last key word, where the F0 peak of questions was considerably higher than that of statements. For sentences with focus on the first key word, there was no difference in peak F0 on the focused item itself, but the F0 toplines of questions and statements diverged quite dramatically following the initial word. The statement contour dropped to a low F0 value for the remainder of the sentence, whereas the question remained quite high in F0 for all subsequent words. In addition, the F0 contour on the focused word was rising in questions and falling in statements, regardless of focus location. The results provide a basis for work on the perception of linguistic focus.     

Acoustical Correlates of Affective Prosody

The word "Anna" was spoken by 12 female and 11 male subjects with six different emotional expressions: "rage/hot anger," "despair/lamentation," "contempt/disgust," "joyful surprise," "voluptuous enjoyment/sensual satisfaction," and "affection/tenderness." In an acoustical analysis, 94 parameters were extracted from the speech samples and broken down by correlation analysis to 15 parameters entering subsequent statistical tests. The results show that each emotion can be characterized by a specific acoustic profile, differentiating that emotion significantly from all others. If aversive emotions are tested against hedonistic emotions as a group, it turns out that the best indicator of aversiveness is the ratio of peak frequency (frequency with the highest amplitude) to fundamental frequency, followed by the peak frequency, the percentage of time segments with nonharmonic structure ("noise"), frequency range within single time segments, and time of the maximum of the peak frequency within the utterance. Only the last parameter, however, codes aversiveness independent of the loudness of an utterance.     

Acoustics of children's speech: developmental changes of temporal and spectral parameters

Changes in magnitude and variability of duration, fundamental frequency, formant frequencies, and spectral envelope of children's speech are investigated as a function of age and gender using data obtained from 436 children, ages 5 to 17 years, and 56 adults. The results confirm that the reduction in magnitude and within-subject variability of both temporal and spectral acoustic parameters with age is a major trend associated with speech development in normal children. Between ages 9 and 12, both magnitude and variability of segmental durations decrease significantly and rapidly, converging to adult levels around age 12. Within-subject fundamental frequency and formant-frequency variability, however, may reach adult range about 2 or 3 years later. Differentiation of male and female fundamental frequency and formant frequency patterns begins at around age 11, becoming fully established around age 15. During that time period, changes in vowel formant frequencies of male speakers is approximately linear with age, while such a linear trend is less obvious for female speakers. These results support the hypothesis of uniform axial growth of the vocal tract for male speakers. The study also shows evidence for an apparent overshoot in acoustic parameter values, somewhere between ages 13 and 15, before converging to the canonical levels for adults. For instance, teenagers around age 14 differ from adults in that, on average, they show shorter segmental durations and exhibit less within-subject variability in durations, fundamental frequency, and spectral envelope measures.     

Vowel intelligibility in clear and conversational speech for normal-hearing and hearing-impaired listeners

Several studies have demonstrated that when talkers are instructed to speak clearly, the resulting speech is significantly more intelligible than speech produced in ordinary conversation. These speech intelligibility improvements are accompanied by a wide variety of acoustic changes. The current study explored the relationship between acoustic properties of vowels and their identification in clear and conversational speech, for young normal-hearing (YNH) and elderly hearing-impaired (EHI) listeners. Monosyllabic words excised from sentences spoken either clearly or conversationally by a male talker were presented in 12-talker babble for vowel identification. While vowel intelligibility was significantly higher in clear speech than in conversational speech for the YNH listeners, no clear speech advantage was found for the EHI group. Regression analyses were used to assess the relative importance of spectral target, dynamic formant movement, and duration information for perception of individual vowels. For both listener groups, all three types of information emerged as primary cues to vowel identity. However, the relative importance of the three cues for individual vowels differed greatly for the YNH and EHI listeners. This suggests that hearing loss alters the way acoustic cues are used for identifying vowels.     

Speech processing studies using an acoustic model of a multiple-channel cochlear implant

The speech perception of two multiple-channel cochlear implant patients was compared with that of three normally hearing listeners using an acoustic model of the implant for 22 different speech tests. The tests used included a minimal auditory capabilities battery, both closed-set and open-set word and sentence tests, speech tracking and a 12-consonant confusion study using nonsense syllables. The acoustic model represented electrical current pulses by bursts of noise and the effects of different electrodes were represented by using bandpass filters with different center frequencies. All subjects used a speech processor that coded the fundamental voicing frequency of speech as a pulse rate and the second formant frequency of speech as the electrode position in the cochlea, or the center frequency of the bandpass filter. Very good agreement was found for the two groups of subjects, indicating that the acoustic model is a useful tool for the development and evaluation of alternative cochlear implant speech processing strategies.     

Effects of the salience of pitch and periodicity information on the intelligibility of four-channel vocoded speech: implications for cochlear implants

Recent simulations of continuous interleaved sampling (CIS) cochlear implant speech processors have used acoustic stimulation that provides only weak cues to pitch, periodicity, and aperiodicity, although these are regarded as important perceptual factors of speech. Four-channel vocoders simulating CIS processors have been constructed, in which the salience of speech-derived periodicity and pitch information was manipulated. The highest salience of pitch and periodicity was provided by an explicit encoding, using a pulse carrier following fundamental frequency for voiced speech, and a noise carrier during voiceless speech. Other processors included noise-excited vocoders with envelope cutoff frequencies of 32 and 400 Hz. The use of a pulse carrier following fundamental frequency gave substantially higher performance in identification of frequency glides than did vocoders using envelope-modulated noise carriers. The perception of consonant voicing information was improved by processors that preserved periodicity, and connected discourse tracking rates were slightly faster with noise carriers modulated by envelopes with a cutoff frequency of 400 Hz compared to 32 Hz. However, consonant and vowel identification, sentence intelligibility, and connected discourse tracking rates were generally similar through all of the processors. For these speech tasks, pitch and periodicity beyond the weak information available from 400 Hz envelope-modulated noise did not contribute substantially to performance.     

Statistical properties of Chinese phonemic networks

The study of properties of speech sound systems is of great significance in understanding the human cognitive mechanism and the working principles of speech sound systems. Some properties of speech sound systems, such as the listener-oriented feature and the talker-oriented feature, have been unveiled with the statistical study of phonemes in human languages and the research of the interrelations between human articulatory gestures and the corresponding acoustic parameters. With all the phonemes of speech sound systems treated as a coherent whole, our research, which focuses on the dynamic properties of speech sound systems in operation, investigates some statistical parameters of Chinese phoneme networks based on real text and dictionaries. The findings are as follows: phonemic networks have high connectivity degrees and short average distances; the degrees obey normal distribution and the weighted degrees obey power law distribution; vowels enjoy higher priority than consonants in the actual operation of speech sound systems; the phonemic networks have high robustness against targeted attacks and random errors. In addition, for investigating the structural properties of a speech sound system, a statistical study of dictionaries is conducted, which shows the higher frequency of shorter words and syllables and the tendency that the longer a word is, the shorter the syllables composing it are. From these structural properties and dynamic properties one can derive the following conclusion: the static structure of a speech sound system tends to promote communication efficiency and save articulation effort while the dynamic operation of this system gives preference to reliable transmission and easy recognition. In short, a speech sound system is an effective, efficient and reliable communication system optimized in many aspects.     

Specific features of vowel-like signals of white whales

The set of acoustic signals of White-Sea white whales comprises about 70 types of signals. Six of them occur most often and constitute 75% of the total number of signals produced by these animals. According to behavioral reactions, white whales distinguish each other by acoustic signals, which is also typical of other animal species and humans. To investigate this phenomenon, signals perceived as vowel-like sounds of speech, including sounds perceived as a “bleat,” were chosen A sample of 480 signals recorded in June and July, 2000, in the White Sea within a reproductive assemblage of white whales near the Large Solovetskii Island was studied. Signals were recorded on a digital data carrier (a SONY minidisk) in the frequency range of 0.06–20 kHz. The purpose of the study was to reveal the perceptive and acoustic features specific to individual animals. The study was carried out using the methods of structural analysis of vocal speech that are employed in lingual criminalistics to identify a speaking person. It was demonstrated that this approach allows one to group the signals by coincident perceptive and acoustic parameters with assigning individual attributes to single parameters. This provided an opportunity to separate conditionally about 40 different sources of acoustic signals according to the totality of coincidences, which corresponded to the number of white whales observed visually. Thus, the application of this method proves to be very promising for the acoustic identification of white whales and other marine mammals, this possibility being very important for biology.     

The effect of reduced vowel working space on speech intelligibility in Mandarin-speaking young adults with cerebral palsy

The purpose of this study was to examine the effect of reduced vowel working space on dysarthric talkers' speech intelligibility using both acoustic and perceptual approaches. In experiment 1, the acoustic-perceptual relationship between vowel working space area and speech intelligibility was examined in Mandarin-speaking young adults with cerebral palsy. Subjects read aloud 18 bisyllabic words containing the vowels /i/, /a/, and /u/ using their normal speaking rate. Each talker's words were identified by three normal listeners. The percentage of correct vowel and word identification were calculated as vowel intelligibility and word intelligibility, respectively. Results revealed that talkers with cerebral palsy exhibited smaller vowel working space areas compared to ten age-matched controls. The vowel working space area was significantly correlated with vowel intelligibility (r=0.632, p<0.005) and with word intelligibility (r=0.684, p<0.005). Experiment 2 examined whether tokens of expanded vowel working spaces were perceived as better vowel exemplars and represented with greater perceptual spaces than tokens of reduced vowel working spaces. The results of the perceptual experiment support this prediction. The distorted vowels of talkers with cerebral palsy compose a smaller acoustic space that results in shrunken intervowel perceptual distances for listeners.     

Phonetic variability of stops and flaps in spontaneous and careful speech

Variability is perhaps the most notable characteristic of speech, and it is particularly noticeable in spontaneous conversational speech. The current research examines how speakers realize the American English stops /p, k, b, g/ and flaps (? from /t, d/), in casual conversation and in careful speech. Target consonants appear after stressed syllables (e.g., "lobby") or between unstressed syllables (e.g., "humanity"), in one of six segmental/word-boundary environments. This work documents the degree and types of variability listeners encounter and must parse. Findings show greater reduction in connected and spontaneous speech, greater reduction in high frequency phrases (but not within high frequency words), and greater reduction between unstressed syllables than after a stress. Although highly reduced productions of stops and flaps occur often, with approximant-like tokens even in careful speech, reduction does not lead to a large amount of overlap between phonological categories. Approximant-like realizations of expected stops and flaps in some conditions constitute the majority of tokens. This shows that reduced speech is something that listeners encounter, and must perceive, in a large proportion of the speech they hear.