Sources Of Acoustic Variability Research Articles

Effects of speaker variability and noise on Mandarin tone identification by native and non-native listeners

The purpose of this study was to examine whether speaker variability and noise affect native and non-native listeners differently in Mandarin tone perception. Multi-speaker tone stimuli embedded in speech-shaped noise were presented blocked by speaker or mixed across speakers. The listeners included 20 native listeners and 33 non-native listeners with various degree of Mandarin proficiency, defined by years of Mandarin instruction and baseline performance. The results showed that the mixed-speaker presentation did not affect non-native listeners disproportionately, suggesting that speaker variability did not pose a special challenge to non-native listeners. In contrast, noise disrupted native and non-native perception differently, but it was the listeners with higher Mandarin proficiency that were affected disproportionately. These findings suggest that that not all sources of acoustic variability are equally disruptive to native and non-native speech perception.

The use of auditory and visual context in speech perception by listeners with normal hearing and listeners with cochlear implants

There is a wide range of acoustic and visual variability across different talkers and different speaking contexts. Listeners with normal hearing (NH) accommodate that variability in ways that facilitate efficient perception, but it is not known whether listeners with cochlear implants (CIs) can do the same. In this study, listeners with NH and listeners with CIs were tested for accommodation to auditory and visual phonetic contexts created by gender-driven speech differences as well as vowel coarticulation and lip rounding in both consonants and vowels. Accommodation was measured as the shifting of perceptual boundaries between /s/ and /∫/ sounds in various contexts, as modeled by mixed-effects logistic regression. Owing to the spectral contrasts thought to underlie these context effects, CI listeners were predicted to perform poorly, but showed considerable success. Listeners with CIs not only showed sensitivity to auditory cues to gender, they were also able to use visual cues to gender (i.e., faces) as a supplement or proxy for information in the acoustic domain, in a pattern that was not observed for listeners with NH. Spectrally-degraded stimuli heard by listeners with NH generally did not elicit strong context effects, underscoring the limitations of noise vocoders and/or the importance of experience with electric hearing. Visual cues for consonant lip rounding and vowel lip rounding were perceived in a manner consistent with coarticulation and were generally used more heavily by listeners with CIs. Results suggest that listeners with CIs are able to accommodate various sources of acoustic variability either by attending to appropriate acoustic cues or by inferring them via the visual signal.

Effects of speaker variability and noise on Mandarin fricative identification by native and non-native listeners

Speaker variability and noise are two common sources of acoustic variability. The goal of this study was to examine whether these two sources of acoustic variability affected native and non-native perception of Mandarin fricatives to different degrees. Multispeaker Mandarin fricative stimuli were presented to 40 native and 52 non-native listeners in two presentation formats (blocked by speaker and mixed across speakers). The stimuli were also mixed with speech-shaped noise to create five levels of signal-to- noise ratios. The results showed that noise affected non-native identification disproportionately. By contrast, the effect of speaker variability was comparable between the native and non-native listeners. Confusion patterns were interpreted with reference to the results of acoustic analysis, suggesting native and non-native listeners used distinct acoustic cues for fricative identification. It was concluded that not all sources of acoustic variability are treated equally by native and non-native listeners. Whereas noise compromised non-native fricative perception disproportionately, speaker variability did not pose a special challenge to the non-native listeners.

Subglottal pressure, tracheal airflow, and intrinsic laryngeal muscle activity during rat ultrasound vocalization

Vocal production requires complex planning and coordination of respiratory, laryngeal, and vocal tract movements, which are incompletely understood in most mammals. Rats produce a variety of whistles in the ultrasonic range that are of communicative relevance and of importance as a model system, but the sources of acoustic variability were mostly unknown. The goal was to identify sources of fundamental frequency variability. Subglottal pressure, tracheal airflow, and electromyographic (EMG) data from two intrinsic laryngeal muscles were measured during 22-kHz and 50-kHz call production in awake, spontaneously behaving adult male rats. During ultrasound vocalization, subglottal pressure ranged between 0.8 and 1.9 kPa. Pressure differences between call types were not significant. The relation between fundamental frequency and subglottal pressure within call types was inconsistent. Experimental manipulations of subglottal pressure had only small effects on fundamental frequency. Tracheal airflow patterns were also inconsistently associated with frequency. Pressure and flow seem to play a small role in regulation of fundamental frequency. Muscle activity, however, is precisely regulated and very sensitive to alterations, presumably because of effects on resonance properties in the vocal tract. EMG activity of cricothyroid and thyroarytenoid muscle was tonic in calls with slow or no fundamental frequency modulations, like 22-kHz and flat 50-kHz calls. Both muscles showed brief high-amplitude, alternating bursts at rates up to 150 Hz during production of frequency-modulated 50-kHz calls. A differentiated and fine regulation of intrinsic laryngeal muscles is critical for normal ultrasound vocalization. Many features of the laryngeal muscle activation pattern during ultrasound vocalization in rats are shared with other mammals.

Talker variability in lexical access: Evidence from semantic priming.

It is usually assumed that lexical representations are abstract and devoid of detailed information about various sources of acoustic variability. This assumption is evaluated in this study by examining the effect of talker variability on the access to word meaning in a short‐term semantic priming experiment. Prime‐target pairs that were semantically related (e.g., king‐queen) or unrelated (e.g., bell‐queen) were produced by the same talker or different talkers. Two interstimulus intervals (50 and 250 ms) were used between the prime and target to explore the time course of semantic priming. The auditory stimuli were presented to 60 listeners, whose task was to judge whether the target was a word or nonword item in English. It was hypothesized that a change in talker between the prime and target would influence the magnitude of semantic facilitation. Analysis of response accuracy and reaction time showed that the magnitude of semantic priming was attenuated in the different‐talker condition, although the effect was obtained only for targets produced by the female speaker. There were no effects involving different interstimulus intervals. These results provided partial evidence that talker variability is encoded in lexical representations and affects lexical access.

Inferior Frontal Regions Underlie the Perception of Phonetic Category Invariance

The problem of mapping differing sensory stimuli onto a common category is fundamental to human cognition. Listeners perceive stable phonetic categories despite many sources of acoustic variability. What are the neural mechanisms that underlie this perceptual stability? In this functional magnetic resonance imaging study, a short-interval habituation paradigm was used to investigate neural sensitivity to acoustic changes within and between phonetic categories. A region in the left inferior frontal sulcus showed a pattern of activation consistent with phonetic invariance: insensitivity to acoustic changes within a phonetic category and sensitivity to changes between phonetic categories. Left superior temporal regions, in contrast, showed graded sensitivity to both within- and between-category changes. These results suggest that perceptual insensitivity to changes within a phonetic category may arise from decision-related mechanisms in the left prefrontal cortex and add to a growing body of literature suggesting that the inferior prefrontal cortex plays a domain-general role in computing category representations.