Glottal Pulse Rate Research Articles

Speech comprehension in the context of speaker changes: The importance of voice-feature continuity at the cocktail party

In this talk, I will show how different groups of listeners use voice acoustics to enhance speech comprehension under adverse listening conditions, specifically when the auditory scene comprises a multitude of sounds heard at once. These “cocktail-party”-like situations pose a difficult conceptual problem: To comprehend target speech, listeners need to attend to the target voice while at the same time ignoring other irrelevant sounds. The cocktail-party problem is made considerably easier when all target sounds are spoken by the same talker. Previous work suggests that such benefits from voice continuity can be—in large part—attributed to two prominent voice features: Glottal-pulse rate (GPR) and vocal-tract length (VTL). GPR determines the fundamental frequency of a speech sound and is perceived as vocal pitch; VTL determines the spectral envelope of a speech sound and is perceived as an aspect of vocal timbre. Apart from being important voice identity cues, GPR and VTL have been shown to play a crucial role in cocktail-party listening. Here, I will present data from a series of experiments highlighting the importance of voice-feature continuity for speech comprehension at the cocktail party.

Intelligibility benefit for familiar voices is not accompanied by better discrimination of fundamental frequency or vocal tract length

Speech is more intelligible when it is spoken by familiar than unfamiliar people. If this benefit arises because key voice characteristics like perceptual correlates of fundamental frequency or vocal tract length (VTL) are more accurately represented for familiar voices, listeners may be able to discriminate smaller manipulations to such characteristics for familiar than unfamiliar voices. We measured participants’ (N = 17) thresholds for discriminating pitch (correlate of fundamental frequency, or glottal pulse rate) and formant spacing (correlate of VTL; ‘VTL-timbre’) for voices that were familiar (participants’ friends) and unfamiliar (other participants’ friends). As expected, familiar voices were more intelligible. However, discrimination thresholds were no smaller for the same familiar voices. The size of the intelligibility benefit for a familiar over an unfamiliar voice did not relate to the difference in discrimination thresholds for the same voices. Also, the familiar-voice intelligibility benefit was just as large following perceptible manipulations to pitch and VTL-timbre. These results are more consistent with cognitive accounts of speech perception than traditional accounts that predict better discrimination.

Phonological but not lexical processing alters the perceptual weighting of mean fundamental frequency and vocal-tract length cues for voice gender categorisation

Listeners use various voice cues to segregate different speakers, or to infer speaker-related information such as perceived gender. Two important anatomically related voices cues used for speaker identification, including perceived gender, are mean fundamental frequency (F0), related to the glottal pulse rate, and vocal-tract length (VTL), correlating with body size. Voice cue processing seems to be affected by linguistic processes, such that voice perception is more precise when listeners hear speakers in their native language compared to a non-native language. In addition, recent research shows that F0 and VTL sensitivity is lower for words compared to time-reversed words, either because time-reversed words are unintelligible or phonemes are distorted in voice-onset times and aspirations, pointing to effects of lexical or phonological processing. However, voice cue sensitivity and using these cues to infer speaker-related information may rely on different mechanisms. Here, we studied effects of lexical and phonological processing on F0 and VTL cue weighting for one aspect of speaker identification, namely voice gender categorisation, by manipulating these cues in three linguistic conditions: meaningful words; phonotactically plausible nonwords; and phonotactically implausible time-reversed nonwords. We found that F0 and VTL weighting for voice gender categorisation was affected by phonological but not by lexical processing.

Development of voice perception is dissociated across gender cues in school-age children

Children’s ability to distinguish speakers’ voices continues to develop throughout childhood, yet it remains unclear how children’s sensitivity to voice cues, such as differences in speakers’ gender, develops over time. This so-called voice gender is primarily characterized by speakers’ mean fundamental frequency (F0), related to glottal pulse rate, and vocal-tract length (VTL), related to speakers’ size. Here we show that children’s acquisition of adult-like performance for discrimination, a lower-order perceptual task, and categorization, a higher-order cognitive task, differs across voice gender cues. Children’s discrimination was adult-like around the age of 8 for VTL but still differed from adults at the age of 12 for F0. Children’s perceptual weight attributed to F0 for gender categorization was adult-like around the age of 6 but around the age of 10 for VTL. Children’s discrimination and weighting of F0 and VTL were only correlated for 4- to 6-year-olds. Hence, children’s development of discrimination and weighting of voice gender cues are dissociated, i.e., adult-like performance for F0 and VTL is acquired at different rates and does not seem to be closely related. The different developmental patterns for auditory discrimination and categorization highlight the complexity of the relationship between perceptual and cognitive mechanisms of voice perception.

Perceptual grouping in the cocktail party: Contributions of voice-feature continuity.

Cocktail parties pose a difficult yet solvable problem for the auditory system. Previous work has shown that the cocktail-party problem is considerably easier when all sounds in the target stream are spoken by the same talker (the voice-continuity benefit). The present study investigated the contributions of two of the most salient voice features-glottal-pulse rate (GPR) and vocal-tract length (VTL)-to the voice-continuity benefit. Twenty young, normal-hearing listeners participated in two experiments. On each trial, listeners heard concurrent sequences of spoken digits from three different spatial locations and reported the digits coming from a target location. Critically, across conditions, GPR and VTL either remained constant or varied across target digits. Additionally, across experiments, the target location either remained constant (Experiment 1) or varied (Experiment 2) within a trial. In Experiment 1, listeners benefited from continuity in either voice feature, but VTL continuity was more helpful than GPR continuity. In Experiment 2, spatial discontinuity greatly hindered listeners' abilities to exploit continuity in GPR and VTL. The present results suggest that selective attention benefits from continuity in target voice features and that VTL and GPR play different roles for perceptual grouping and stream segregation in the cocktail party.

Familiar Voices Are More Intelligible, Even if They Are Not Recognized as Familiar

We can recognize familiar people by their voices, and familiar talkers are more intelligible than unfamiliar talkers when competing talkers are present. However, whether the acoustic voice characteristics that permit recognition and those that benefit intelligibility are the same or different is unknown. Here, we recruited pairs of participants who had known each other for 6 months or longer and manipulated the acoustic correlates of two voice characteristics (vocal tract length and glottal pulse rate). These had different effects on explicit recognition of and the speech-intelligibility benefit realized from familiar voices. Furthermore, even when explicit recognition of familiar voices was eliminated, they were still more intelligible than unfamiliar voices—demonstrating that familiar voices do not need to be explicitly recognized to benefit intelligibility. Processing familiar-voice information appears therefore to depend on multiple, at least partially independent, systems that are recruited depending on the perceptual goal of the listener.

Comparison of performance with voiced and whispered speech in word recognition and mean-formant-frequency discrimination

There has recently been a series of studies concerning the interaction of glottal pulse rate (GPR) and mean-formant-frequency (MFF) in the perception of speaker characteristics and speech recognition. This paper extends the research by comparing the recognition and discrimination performance achieved with voiced words to that achieved with whispered words. The recognition experiment shows that performance with whispered words is slightly worse than with voiced words at all MFFs when the GPR of the voiced words is in the middle of the normal range. But, as GPR decreases below this range, voiced-word performance decreases and eventually becomes worse than whispered-word performance. The discrimination experiment shows that the just noticeable difference (JND) for MFF is essentially independent of the mode of vocal excitation; the JND is close to 5% for both voiced and voiceless words for all speaker types. The interaction between GPR and VTL is interpreted in terms of the stability of the internal representation of speech which improves with GPR across the range of values used in these experiments.

The mutual roles of temporal glimpsing and vocal characteristics in cocktail-party listening

At a cocktail party, listeners must attend selectively to a target speaker and segregate their speech from distracting speech sounds uttered by other speakers. To solve this task, listeners can draw on a variety of vocal, spatial, and temporal cues. Recently, Vestergaard et al. [J. Acoust. Soc. Am. 125, 1114-1124 (2009)] developed a concurrent-syllable task to control temporal glimpsing within segments of concurrent speech, and this allowed them to measure the interaction of glottal pulse rate and vocal tract length and reveal how the auditory system integrates information from independent acoustic modalities to enhance recognition. The current paper shows how the interaction of these acoustic cues evolves as the temporal overlap of syllables is varied. Temporal glimpses as short as 25 ms are observed to improve syllable recognition substantially when the target and distracter have similar vocal characteristics, but not when they are dissimilar. The effect of temporal glimpsing on recognition performance is strongly affected by the form of the syllable (consonant-vowel versus vowel-consonant), but it is independent of other phonetic features such as place and manner of articulation.

Location and acoustic scale cues in concurrent speech recognition.

Location and acoustic scale cues have both been shown to have an effect on the recognition of speech in multi-speaker environments. This study examines the interaction of these variables. Subjects were presented with concurrent triplets of syllables from a target voice and a distracting voice, and asked to recognize a specific target syllable. The task was made more or less difficult by changing (a) the location of the distracting speaker, (b) the scale difference between the two speakers, and/or (c) the relative level of the two speakers. Scale differences were produced by changing the vocal tract length and glottal pulse rate during syllable synthesis: 32 acoustic scale differences were used. Location cues were produced by convolving head-related transfer functions with the stimulus. The angle between the target speaker and the distracter was 0 degrees, 4 degrees, 8 degrees, 16 degrees, or 32 degrees on the 0 degrees horizontal plane. The relative level of the target to the distracter was 0 or -6 dB. The results show that location and scale difference interact, and the interaction is greatest when one of these cues is small. Increasing either the acoustic scale or the angle between target and distracter speakers quickly elevates performance to ceiling levels.

A statistical, formant-pattern model for segregating vowel type and vocal-tract length in developmental formant data

This paper investigates the theoretical basis for estimating vocal-tract length (VTL) from the formant frequencies of vowel sounds. A statistical inference model was developed to characterize the relationship between vowel type and VTL, on the one hand, and formant frequency and vocal cavity size, on the other. The model was applied to two well known developmental studies of formant frequency. The results show that VTL is the major source of variability after vowel type and that the contribution due to other factors like developmental changes in oral-pharyngeal ratio is small relative to the residual measurement noise. The results suggest that speakers adjust the shape of the vocal tract as they grow to maintain a specific pattern of formant frequencies for individual vowels. This formant-pattern hypothesis motivates development of a statistical-inference model for estimating VTL from formant-frequency data. The technique is illustrated using a third developmental study of formant frequencies. The VTLs of the speakers are estimated and used to provide a more accurate description of the complicated relationship between VTL and glottal pulse rate as children mature into adults.

The interaction of location with acoustic scale in concurrent speech recognition.

Location and acoustic scale cues have been shown to have a significant effect on the recognition of speech in multispeaker environments. The interaction of these two cues is less well understood. In this study, subjects are presented with two triplets of concurrent speech syllables with similar temporal envelopes, and asked to recognize a specific target syllable. The task was made more or less difficult by changing the location of the distracting speaker, the scale difference between the two speakers and the relative level of the two speakers. Scale differences were produced by changing the vocal tract length and glottal pulse rate of resynthesized speech: 32 scale differences were used. Location cues were produced by convolving heat‐related transfer functions with the stimulus. The target speaker was located directly to the front of the listener and the distracting/masking speaker located from one of five locations (0, 4, 8, 16, 32 deg) on the 0 deg horizontal plane. Target‐to‐masker ratios of 0 and −6 ...

The interaction of vocal characteristics and audibility in the recognition of concurrent syllables.

In concurrent-speech recognition, performance is enhanced when either the glottal pulse rate (GPR) or the vocal tract length (VTL) of the target speaker differs from that of the distracter, but relatively little is known about the trading relationship between the two variables, or how they interact with other cues such as signal-to-noise ratio (SNR). This paper presents a study in which listeners were asked to identify a target syllable in the presence of a distracter syllable, with carefully matched temporal envelopes. The syllables varied in GPR and VTL over a large range, and they were presented at different SNRs. The results showed that performance is particularly sensitive to the combination of GPR and VTL when the SNR is 0 dB. Equal-performance contours showed that when there are no other cues, a two-semitone difference in GPR produced the same advantage in performance as a 20% difference in VTL. This corresponds to a trading relationship between GPR and VTL of 1.6. The results illustrate that the auditory system can use any combination of differences in GPR, VTL, and SNR to segregate competing speech signals.

Task-Dependent Modulation of Medial Geniculate Body Is Behaviorally Relevant for Speech Recognition

SummaryRecent work has shown that responses in first-order sensory thalamic nuclei are modulated by cortical areas [1–5]. However, the functional role of such corticothalamic modulation and its relevance for human perception is still unclear. Here, we show in two functional magnetic resonance imaging (fMRI) studies that the neuronal response in the first-order auditory thalamus, the medial geniculate body (MGB), is increased when rapidly varying spectrotemporal features of speech sounds are processed, as compared to processing slowly varying spectrotemporal features of the same sounds. The strength of this task-dependent modulation is positively correlated with the speech recognition scores of individual subjects. These results show that task-dependent modulation of the MGB serves the processing of specific features of speech sounds and is behaviorally relevant for speech recognition. Our findings suggest that the first-order auditory thalamus is not simply a nonspecific gatekeeper controlled by attention [6]. Together with studies in nonhuman mammals [4, 5], our findings imply a mechanism in which the first-order auditory thalamus, possibly by corticothalamic modulation, reacts adaptively to features of sensory input.

The interaction of glimpsing, pitch and vocal tract length in the recognition of concurrent syllables

In multispeaker environments, human listeners use the temporal misalignment of competing speech signals to improve recognition‐ an effect referred to as “glimpsing.” When the temporal envelopes of concurrent syllables pairs are carefully matched to preclude glimpsing, listeners were observed to use vocal tract length (VTL) and glottal pulse rate (GPR) cues to improve recognition. This paper reports an investigation of the interaction between glimpsing and these vocal cues. Syllables were synthesized with a vocoder to simulate speakers with widely different combinations of GPR and VTL. Recognition of one syllable in the presence of a concurrent syllable was measured as the vocal cues and the temporal alignment of the syllables were varied. The effect of glimpsing was most pronounced when the vocal cue differences between the target and distracter syllables were small. Furthermore, there was a strong effect of consonant type (stops, fricatives, or sonorants) and an asymmetry between consonant‐vowel (CV) and vowel‐consonant (VC) syllables. The lowest recognition rate was observed, not at perfect temporal alignment but rather at a distracter lag of ‐50 ms for CVs and 100 ms for VCs. The results are analyzed with confusion matrices. Research supported by the UK MRC [G0500221, G9900369].

Discrimination of speaker sex and size when glottal-pulse rate and vocal-tract length are controlled.

A recent study [Smith and Patterson, J. Acoust. Soc. Am. 118, 3177-3186 (2005)] demonstrated that both the glottal-pulse rate (GPR) and the vocal-tract length (VTL) of vowel sounds have a large effect on the perceived sex and age (or size) of a speaker. The vowels for all of the "different" speakers in that study were synthesized from recordings of the sustained vowels of one, adult male speaker. This paper presents a follow-up study in which a range of vowels were synthesized from recordings of four different speakers--an adult man, an adult woman, a young boy, and a young girl--to determine whether the sex and age of the original speaker would have an effect upon listeners' judgments of whether a vowel was spoken by a man, woman, boy, or girl, after they were equated for GPR and VTL. The sustained vowels of the four speakers were scaled to produce the same combinations of GPR and VTL, which covered the entire range normally encountered in every day life. The results show that listeners readily distinguish children from adults based on their sustained vowels but that they struggle to distinguish the sex of the speaker.

Comparison of relative and absolute judgments of speaker size based on vowel sounds

Judgments of speaker size are largely determined by two acoustic variables: glottal pulse rate (GPR) and resonance scale [i.e., vocal tract length (VTL)]. Both variables change with age (or height), but the rate is governed by different factors. The interaction of the variables was previously measured using absolute judgments of speaker size [D.R.R Smith and R.D. Patterson, J. Acoust. Soc. Am. 118, 3177–3186 (2005)]. The resulting size surface (over the GPR‐VTL plane) bends down outside the normal range. In this paper, a method is developed for deriving the surface using size‐discrimination data. In a two‐alternative forced‐choice experiment, listeners compared sequences of vowels scaled in GPR and VTL to represent speakers with slightly different sizes; they were required to choose the interval with the smaller speaker. Comparisons about a point in the plane reveal the gradient vector, and the vectors across the GPR‐VTL plane can be integrated to estimate the size surface. The results indicate that the size surface would be essentially planar if determined by size discrimination. This indicates that relative size judgments are different from absolute size judgments, probably because some source knowledge is required for the absolute judgements. [Research supported by the UK Medical Research Council (G9900369).] a)Currently at the Gatsby Computational Neuroscience Unit, Alexandra House, 17 Queen Square, London, WC1N 3AR, UK.

Role of glottal-pulse rate, vocal-tract length, and original talker upon judgements of speaker sex and age

Glottal-pulse rate (GPR) and vocal-tract length (VTL) are important determinants of the perceived sex and age of the speaker [D. R. R. Smith and R. D. Patterson, J. Acoust. Soc. Am. 118, 3177–3186 (2005)]. Our previous research simulated the voices of variously-sized speakers of both sexes by manipulating the recorded vowels of one adult male talker. The current study explored whether there are additional cues in the voices of men, women, and children that influence judgements of speaker sex and age. We manipulated the recorded vowels of an adult man, adult woman, young boy, and young girl, and determined the effect upon the distribution of sex and age responses (man, woman, boy, girl). Results show that the distribution of sex and age judgements across the GPR-VTL plane is heavily influenced by GPR and VTL, but it is also affected by the original talker’s size (or age). The effect of original talker appears to be mainly due to the consistent difference between oral-pharyngeal length ratios of children and adults. We also report gender differences in male and female listeners across the GPR-VTL plane; adult men and women listeners show somewhat different biases. [Research supported by UK MRC (G9900369, G0500221) and German Volkswagen Foundation (1/79 783).]

Processing the acoustic effect of size in speech sounds

The length of a vocal tract is reflected in the sound it is producing. The length of the vocal tract is correlated with body size and humans are very good at making size judgments based on the acoustic effect of vocal tract length only. Here we investigate the underlying mechanism for processing this main auditory cue to size information in the human brain. Sensory encoding of the acoustic effect of vocal tract length (VTL) depends on a time-stabilized spectral scaling mechanism that is independent of glottal pulse rate (GPR, or voice pitch); we provide evidence that a potential neural correlate for such a mechanism exists in the medial geniculate body (MGB). The perception of the acoustic effect of speaker size is influenced by GPR suggesting an interaction between VTL and GPR processing; such an interaction occurs only at the level of non-primary auditory cortex in planum temporale and anterior superior temporal gyrus. Our findings support a two-stage model for the processing of size information in speech based on an initial stage of sensory analysis as early as MGB, and a neural correlate of the perception of source size in non-primary auditory cortex.

The interaction of glottal-pulse rate and vocal-tract length in judgements of speaker size, sex, and age.

Glottal-pulse rate (GPR) and vocal-tract length (VTL) are related to the size, sex, and age of the speaker but it is not clear how the two factors combine to influence our perception of speaker size, sex, and age. This paper describes experiments designed to measure the effect of the interaction of GPR and VTL upon judgements of speaker size, sex, and age. Vowels were scaled to represent people with a wide range of GPRs and VTLs, including many well beyond the normal range of the population, and listeners were asked to judge the size and sex/age of the speaker. The judgements of speaker size show that VTL has a strong influence upon perceived speaker size. The results for the sex and age categorization (man, woman, boy, or girl) show that, for vowels with GPR and VTL values in the normal range, judgements of speaker sex and age are influenced about equally by GPR and VTL. For vowels with abnormal combinations of low GPRs and short VTLs, the VTL information appears to decide the sex/age judgement.

Perception of speaker size and sex of vowel sounds

Glottal-pulse rate (GPR) and vocal-tract length (VTL) are both related to speaker size and sex—however, it is unclear how they interact to determine our perception of speaker size and sex. Experiments were designed to measure the relative contribution of GPR and VTL to judgements of speaker size and sex. Vowels were scaled to represent people with different GPRs and VTLs, including many well beyond the normal population values. In a single interval, two response rating paradigm, listeners judged the size (using a 7-point scale) and sex/age of the speaker (man, woman, boy, or girl) of these scaled vowels. Results from the size-rating experiments show that VTL has a much greater influence upon judgements of speaker size than GPR. Results from the sex-categorization experiments show that judgements of speaker sex are influenced about equally by GPR and VTL for vowels with normal GPR and VTL values. For abnormal combinations of GPR and VTL, where low GPRs are combined with short VTLs, VTL has more influence than GPR in sex judgements. [Work supported by the UK MRC (G9901257) and the German Volkswagen Foundation (VWF 1/79 783).]