Travis Wade

Acoustic characteristics of clearly spoken English fricatives

Speakers can adopt a speaking style that allows them to be understood more easily in difficult communication situations, but few studies have examined the acoustic properties of clearly produced consonants in detail. This study attempts to characterize the adaptations in the clear production of American English fricatives in a carefully controlled range of communication situations. Ten female and ten male talkers produced fricatives in vowel-fricative-vowel contexts in both a conversational and a clear style that was elicited by means of simulated recognition errors in feedback received from an interactive computer program. Acoustic measurements were taken for spectral, amplitudinal, and temporal properties known to influence fricative recognition. Results illustrate that (1) there were consistent overall style effects, several of which (consonant duration, spectral peak frequency, and spectral moments) were consistent with previous findings and a few (notably consonant-to-vowel intensity ratio) of which were not; (2) specific acoustic modifications in clear productions of fricatives were influenced by the nature of the recognition errors that prompted the productions and were consistent with efforts to emphasize potentially misperceived contrasts both within the English fricative inventory and based on feedback from the simulated listener; and (3) talkers differed widely in the types and magnitude of all modifications.

Incidental categorization of spectrally complex non-invariant auditory stimuli in a computer game task.

This study examined perceptual learning of spectrally complex nonspeech auditory categories in an interactive multi-modal training paradigm. Participants played a computer game in which they navigated through a three-dimensional space while responding to animated characters encountered along the way. Characters’ appearances in the game correlated with distinctive sound category distributions, exemplars of which repeated each time the characters were encountered. As the game progressed, the speed and difficulty of required tasks increased and characters became harder to identify visually, so quick identification of approaching characters by sound patterns was, although never required or encouraged, of gradually increasing benefit. After 30 min of play, participants performed a categorization task, matching sounds to characters. Despite not being informed of audio-visual correlations, participants exhibited reliable learning of these patterns at posttest. Categorization accuracy was related to several measu...

Effects of Acoustic Variability in the Perceptual Learning of Non-Native-Accented Speech Sounds

This study addressed whether acoustic variability and category overlap in non-native speech contribute to difficulty in its recognition, and more generally whether the benefits of exposure to acoustic variability during categorization training are stable across differences in category confusability. Three experiments considered a set of Spanish-accented English productions. The set was seen to pose learning and recognition difficulty (experiment 1) and was more variable and confusable than a parallel set of native productions (experiment 2). A training study (experiment 3) probed the relative contributions of category central tendency and variability to difficulty in vowel identification using derived inventories in which these dimensions were manipulated based on the results of experiments 1 and 2. Training and test difficulty related straightforwardly to category confusability but not to location in the vowel space. Benefits of high-variability exposure also varied across vowel categories, and seemed to be diminished for highly confusable vowels. Overall, variability was implicated in perception and learning difficulty in ways that warrant further investigation.

Perception of clear fricatives by normal-hearing and simulated hearing-impaired listeners

Speakers may adapt the phonetic details of their productions when they anticipate perceptual difficulty or comprehension failure on the part of a listener. Previous research suggests that a speaking style known as clear speech is more intelligible overall than casual, conversational speech for a variety of listener populations. However, it is unknown whether clear speech improves the intelligibility of fricative consonants specifically, or how its effects on fricative perception might differ depending on listener population. The primary goal of this study was to determine whether clear speech enhances fricative intelligibility for normal-hearing listeners and listeners with simulated impairment. Two experiments measured babble signal-to-noise ratio thresholds for fricative minimal pair distinctions for 14 normal-hearing listeners and 14 listeners with simulated sloping, recruiting impairment. Results indicated that clear speech helped both groups overall. However, for impaired listeners, reliable clear speech intelligibility advantages were not found for non-sibilant pairs. Correlation analyses comparing acoustic and perceptual data indicated that a shift of energy concentration toward higher frequency regions and greater source strength contributed to the clear speech effect for normal-hearing listeners. Correlations between acoustic and perceptual data were less consistent for listeners with simulated impairment, and suggested that lower-frequency information may play a role.

Perceptual effects of preceding nonspeech rate on temporal properties of speech categories

The rate of context speech can influence phonetic perception. This study investigated the bounds of rate dependence by observing the influence of nonspeech precursor rate on speech categorization. Three experiments tested the effects of pure-tone precursor presentation rate on the perception of a [ba]-[wa] series defined by duration-varying formant transitions that shared critical temporal and spectral characteristics with the tones. Results showed small but consistent shifts in the stop-continuant boundary distinguishing [ba] and [wa] syllables as a function of the rate of precursor tones, across various manipulations in the amplitude of the tones. The effect of the tone precursors extended to the entire graded structure of the [w] category, as estimated by category goodness judgments. These results suggest a role for durational contrast in rate-dependent speech categorization.

Acoustic characteristics of clearly produced fricatives

Research suggests that speakers can adopt a speaking style that allows them to be understood more easily when confronted with difficult communication situations, but few studies have examined the acoustic properties of clearly produced consonants in detail. This study attempts to characterize the type and magnitude of adaptations in the clear production of English fricatives in a carefully controlled range of communication situations. Ten female and ten male talkers produced nonsense syllables containing the eight English fricatives in VCV contexts, both in a conversational style and in a clear style (elicited by means of feedback consisting of simulated recognition errors received from an interactive computer program). Acoustic measurements were taken for spectral, amplitudinal, and temporal properties known to influence fricative recognition. Results illustrate that (1) there were some consistent overall clear speech effects, several of which (consonant duration, spectral peak location, spectral moments...

Perception of clear English fricatives

Two experiments investigated whether and how clear speech production enhances intelligibility of English fricatives for normal‐hearing listeners and listeners with simulated hearing impairment. Fricative intelligibility in clear and conversational speech was assessed using a database of 8800 VCV ([a]‐fricative‐[a]) stimuli produced by 20 speakers. Babble thresholds were measured for minimal pair distinctions for 14 normal‐hearing listeners and 14 listeners with simulated sloping, recruiting impairment. Clear speech benefited both groups overall; however, for impaired listeners, the clear speech effect held only for sibilant pairs. In a previous acoustic study involving the same stimuli [Maniwa, Jongman, and Wade, J. Acoust. Soc. Am. 119, 3301 (2006)], 14 parameters were measured: spectral peak location, the first four spectral moments, F2 onset transitions, spectral slopes below and above typical peak locations, pitch of adjacent vowels, overall rms amplitude, relative amplitude (frication amplitude relat...

Perception of coarticulated speech with contrastively enhanced spectrotemporal patterns

High‐level contrastive mechanisms cause perception of auditory events to be influenced by spectral and temporal properties of surrounding acoustic context, and may play a role in perceptual compensation for coarticulation in human speech. However, it is unknown whether auditory contrast is incorporated optimally to compensate for different speakers, languages and situations or whether amplification of the processes involved would provide additional benefit, for example, in the perception of hypoarticulated speech, under adverse listening conditions, or in an incompletely acquired language. This study examines effects of artificial contrastive modification of spectrotemporal trajectories on the intelligibility of connected speech in noise by native and non‐native listeners. Adopting methods known to improve automatic classification of speech sounds, we model contrast‐providing context as an averaged estimated vocal tract function (LPC‐derived log area ratio coefficient vector) over a Gaussian‐weighted temp...

Perceptual effects of preceding non‐speech‐rate information on temporal properties of speech categories

The purpose of the study was to determine whether a general mechanism such as durational contrast can explain the apparent rate‐dependent nature of speech perception. Four experiments were performed to test effects of pure tone presentation rate on perception of following speech continua involving duration‐varying formant transitions with which the tones shared critical temporal and spectral properties. Results showed small but consistent shifts in the stop‐continuant boundary distinguishing /ba/ and /wa/ syllables based on the rate of precursor tones similar in duration and frequency to syllable‐initial F1 and F2 transitions, across differences in amplitude of tones and despite variability in their duration. Additionally, the shift was shown to involve the entire graded structure of the [w] category and was not limited to an ambiguous boundary region, affecting goodness judgments on both sides of an estimated best exemplar range. These results are problematic for accounts of rate‐dependent processing tha...

Contrastive backward effects of nonspeech tones on speech perception

Nonspeech stimuli influence phonetic categorization, but effects observed so far have been limited to precursors’ influence on perception of following sounds. However, both preceding and following speech affect phonetic categorization. This asymmetry in nonspeech and speech effects raises questions about whether general auditory processes play a role in context‐dependent speech perception. Here, experiments test whether the asymmetry stems from methodological issues rather than genuine mechanistic limitations. To determine whether backward effects of nonspeech on speech may be achieved when listeners are sufficiently encouraged to incorporate later‐occurring acoustic events, a series of experiments examined perception of CVC words with [da]–[ga] series onsets followed by embedded tones and one of two possible final consonants. When the final consonant was required for word identification, subjects showed clear contrastive effects; more [d]‐initial words were heard with higher‐frequency tones approximating...