Flat F0 Contour Research Articles

Effects of F0 contour depth differences on school-age children’s speech recognition in a two-talker masker

This study investigated the extent to which children (ages 5–17) can take advantage of differences in fundamental frequency (F0) contour between target and masker speech to improve speech-in-speech recognition. A number of studies show that differences in F0 and F0 contour between talkers support better speech-in-speech recognition for adults, suggesting it is an important cue for recognizing speech in multitalker environments. However, children’s use of F0 contour differences during speech-in-speech recognition is less well understood. In the present study, sentence recognition was measured adaptively in a two-talker speech masker. Target and masker sentences were recorded with either normal, flat, or exaggerated F0 contours. Results revealed that children’s sentence recognition was impacted by differences in F0 contour depth in both target and masker speech, but the pattern of results differed between children and adults in some conditions. For children, the consistent nature of the flat F0 contour often had a greater impact on speech recognition thresholds (SRTs) than target/masker differences in F0 contour depth. Observed age effects did not appear to be due to limitations in children’s ability to use F0 contour differences in general but are likely related to the perceptual salience of the target contour relative to the masker.

Sentence Context Differentially Modulates Contributions of Fundamental Frequency Contours to Word Recognition in Chinese-Speaking Children With and Without Dyslexia.

Previous work has shown that children with dyslexia are impaired in speech recognition in adverse listening conditions. Our study further examined how semantic context and fundamental frequency (F0) contours contribute to word recognition against interfering speech in dyslexic and non-dyslexic children. Thirty-two children with dyslexia and 35 chronological-age-matched control children were tested on the recognition of words in normal sentences versus wordlist sentences with natural versus flat F0 contours against single-talker interference. The dyslexic children had overall poorer recognition performance than non-dyslexic children. Furthermore, semantic context differentially modulated the effect of F0 contours on the recognition performances of the two groups. Specifically, compared with flat F0 contours, natural F0 contours increased the recognition accuracy of dyslexic children less than non-dyslexic children in the wordlist condition. By contrast, natural F0 contours increased the recognition accuracy of both groups to a similar extent in the sentence condition. These results indicate that access to semantic context improves the effect of natural F0 contours on word recognition in adverse listening conditions by dyslexic children who are more impaired in the use of natural F0 contours during isolated and unrelated word recognition. Our findings have practical implications for communication with dyslexic children when listening conditions are unfavorable.

The effect of F0 contour on the intelligibility of Mandarin Chinese for hearing-impaired listeners.

Dynamic F0 contour plays an important role in recognizing speech. The present work examined the effect of F0 contour on speech intelligibility for hearing-impaired listeners for Mandarin Chinese in quiet, in steady noise, and in two-talker competing speech. The intelligibility of two types of natural speech was measured: single-Tone speech with relatively flat F0 contours and multi-Tone speech with time-varying F0 contours. The speech rate and mean F0 of speech materials were carefully controlled to avoid effects other than F0 contour on the speech intelligibility. Results showed that intelligibility was significantly higher for speech with a flat F0 contour than that with a dynamic F0 contour at a low signal-to-masker ratio in both speech-spectrum noise and two-talker masker.

Understanding low-pass-filtered Mandarin sentences: Effects of fundamental frequency contour and single-channel noise suppression.

The present work assessed the effects of flattening the fundamental frequency (F0) contour and processing by single-channel noise suppression on the intelligibility of low-pass (LP)-filtered (LPF) sentences. The original F0 contour was replaced by an average flat F0 contour or treated by single-channel noise suppression, followed by application of LP filtering to Mandarin sentences. Processed stimuli were presented to normal-hearing listeners to recognize. Flattening the F0 contour significantly affected the understanding of LPF sentences. Noise suppression by existing single-channel algorithms did not improve the intelligibility of LPF sentences.

The effect of F0 contour on the intelligibility of speech in the presence of interfering sounds for Mandarin Chinese.

In Mandarin Chinese, the fundamental frequency (F0) contour defines lexical "Tones" that differ in meaning despite being phonetically identical. Flattening the F0 contour impairs the intelligibility of Mandarin Chinese in background sounds. This might occur because the flattening introduces misleading lexical information. To avoid this effect, two types of speech were used: single-Tone speech contained Tones 1 and 0 only, which have a flat F0 contour; multi-Tone speech contained all Tones and had a varying F0 contour. The intelligibility of speech in steady noise was slightly better for single-Tone speech than for multi-Tone speech. The intelligibility of speech in a two-talker masker, with the difference in mean F0 between the target and masker matched across conditions, was worse for the multi-Tone target in the multi-Tone masker than for any other combination of target and masker, probably because informational masking was maximal for this combination. The introduction of a perceived spatial separation between the target and masker, via the precedence effect, led to better performance for all target-masker combinations, especially the multi-Tone target in the multi-Tone masker. In summary, a flat F0 contour does not reduce the intelligibility of Mandarin Chinese when the introduction of misleading lexical cues is avoided.

Mandarin-Speaking Children's Speech Recognition: Developmental Changes in the Influences of Semantic Context and F0 Contours.

The goal of this developmental speech perception study was to assess whether and how age group modulated the influences of high-level semantic context and low-level fundamental frequency (F0) contours on the recognition of Mandarin speech by elementary and middle-school-aged children in quiet and interference backgrounds. The results revealed different patterns for semantic and F0 information. One the one hand, age group modulated significantly the use of F0 contours, indicating that elementary school children relied more on natural F0 contours than middle school children during Mandarin speech recognition. On the other hand, there was no significant modulation effect of age group on semantic context, indicating that children of both age groups used semantic context to assist speech recognition to a similar extent. Furthermore, the significant modulation effect of age group on the interaction between F0 contours and semantic context revealed that younger children could not make better use of semantic context in recognizing speech with flat F0 contours compared with natural F0 contours, while older children could benefit from semantic context even when natural F0 contours were altered, thus confirming the important role of F0 contours in Mandarin speech recognition by elementary school children. The developmental changes in the effects of high-level semantic and low-level F0 information on speech recognition might reflect the differences in auditory and cognitive resources associated with processing of the two types of information in speech perception.

Spatiotemporal frequency characteristics of cerebral oscillations during the perception of fundamental frequency contour changes in one-syllable intonation

Accurate perception of fundamental frequency (F0) contour changes in the human voice is important for understanding a speaker's intonation, and consequently also his/her attitude. In this study, we investigated the neural processes involved in the perception of F0 contour changes in the Japanese one-syllable interjection “ne” in 21 native-Japanese listeners. A passive oddball paradigm was applied in which “ne” with a high falling F0 contour, used when urging a reaction from the listener, was randomly presented as a rare deviant among a frequent “ne” syllable with a flat F0 contour (i.e., meaningless intonation). We applied an adaptive spatial filtering method to the neuromagnetic time course recorded by whole-head magnetoencephalography (MEG) and estimated the spatiotemporal frequency dynamics of event-related cerebral oscillatory changes in the oddball paradigm. Our results demonstrated a significant elevation of beta band event-related desynchronization (ERD) in the right temporal and frontal areas, in time windows from 100 to 300 and from 300 to 500ms after the onset of deviant stimuli (high falling F0 contour). This is the first study to reveal detailed spatiotemporal frequency characteristics of cerebral oscillations during the perception of intonational (not lexical) F0 contour changes in the human voice. The results further confirmed that the right hemisphere is associated with perception of intonational F0 contour information in the human voice, especially in early time windows.

Intelligibility of accented American English isolated vowel: Effects of fundamental frequency (F0) contour and formant structures.

Our previous studies have shown that Chinese and Korean accented English vowels deviated in fundamental and formant frequency values and gross spectral shape properties when compared to English-native productions. The present study proposed to examine the intelligibility of accented English vowel by manipulating the fundamental frequency, formant frequencies, and/or entire spectrum shape in an effort to measure the specific contribution of each of these discrete acoustical parameters on accented vowel perception. There were six sets of vowel stimuli: original vowels produced by native and non-native speakers, flat F0 contour with original spectrogram of native and non-native speakers, hybrid vowels mixing non-native F0 contour and native spectrogram, and hybrid vowels mixing native F0 contour and non-native spectrogram. Preliminary results showed that intelligibility was significantly improved for foreign-accented vowels when the non-native spectrogram was replaced with native spectrogram. On the other hand, effects of F0 contour were dependent on talker intelligibility. For non-native speakers with low vowel intelligibility, replacement of F0 contour with native F0 contour slightly increased vowel intelligibility while for non-native speakers with high vowel intelligibility, replacement of F0 contour degraded rather than improved vowel intelligibility.

The effects of flattening fundamental frequency contours on sentence intelligibility in speakers with dysarthria

This study explored the relationship between F0 variability and intelligibility in persons with motor speech disorders. The literature suggests that monopitch may have detrimental effects on the intelligibility of individuals with dysarthria (and other speech disorders), but few studies have examined the independent effect of a flat F0 contour on intelligibility in speakers with articulatory difficulties. An LPC resynthesis technique was used to reduce the speakers' sentence F0 range by 25%, 50% and 100% (flattened F0). Two dysarthric speaker groups were evaluated, one with prosodic inadequacy and imprecise articulation (hypokinetic) and one with imprecise articulation only (UUMN). Speech intelligibility was assessed using a word transcription task and an interval-scaling task. Results argue strongly for the perceptual importance of sentence-level F0 variations on speech intelligibility even when the F0 range is severely restricted. Results also suggest that the contribution of F0 to intelligibility may vary with type of dysarthria.

Rethinking the basics of declination

Declination, the tendency of fundamental frequency to gradually fall over the course of an utterance, has for a long time been treated as if it were a universal principle of speech intonation. Most intonation models adopt declination as a baseline upon which more local F0 patterns reside. A reexamination of the literature related to declination finds, however, that the existence of declination as an independent F0-determining mechanism is far from being firmly established. Instead, some recent as well as earlier studies are found to provide evidence that various linguistic factors may be responsible for generating different local as well as global patterns of intonation, which, taken as a whole, may sometimes give the appearance of declination. These factors include sentence focus, topic initiation, word stress, and lexical tone. When these factors happen to be neutralized, virtually flat F0 contours may occur, as have been observed in some tone languages. Furthermore, the commonly assumed declination rate is found to well exceed the possible rates of pitch decline due to global physiological limitations. It is concluded that, rather than being a basic principle of intonation, declination is more likely to be an artifact of various linguistic factors plus certain local physiological constraints.

The role of voice pitch in the perception of glottal stops

Glottal stops that occur in VCV context are often not realized as stops at all, but rather show voicing that is continuous throughout the ‘‘occlusion’’ interval. Glottal stops that are realized in this way are apparently marked by reductions in intensity and fundamental frequency. In the present study recordings were made of speakers producing glottal stops in utterances such as ‘‘oh–oh’’ in which a glottal stop separates two identical vowels. The utterances were resynthesized in three ways: (1) with a flat F0 contour and an intensity contour matching the original utterance, (2) with a flat intensity contour and an F0 contour matching the original utterance, and (3) with intensity and F0 contours matching the original utterance. Results suggest that either cue alone is sufficient to signal the presence of the glottal stop. The impression of most listeners was that the signals cued by intensity alone were quite similar to those cued by F0 alone. The apparent equivalence of loudness and pitch in signaling the presence of a glottal stop would seem to present difficulties for a straightforward auditory account of phonetic recognition.