The effects of speaker accent and target predictability on perception of mispronunciations.

This study makes use of a listening for mispronunciation task to examine how native English listeners perceive sentences produced by non-native speakers. The effects of target predictability and degree of foreign accent were investigated. Native and non-native speakers produced English sentences containing mispronunciation. Mispronunciations (MPs) were constructed by changing the initial phoneme of target words by a single distinctive feature along the dimensions of voicing, place, or manner. Results showed that listeners (a) were more accurate and faster in detecting MPs produced by native than non-native speakers, (b) were more accurate and faster in detecting MPs in predictable than unpredictable sentences, and (3) were more accurate in detecting MPs produced by non-native speakers with milder accents, as compared to heavier accents. These findings suggest that listening to fairly intelligible but accented speech requires increased processing effort--possibly because of subtle differences in intelligibility and increased variability characteristic of non-native speech.

Perceptual evaluations of spectral and temporal modifications of deaf speech.

The perceptual effect of modifying speech produced by deaf talkers was investigated to discover the changes necessary for disordered speech to be judged normal. Recordings of passages read by three deaf talkers were used as material. For the first two experiments, a three-syllable word was extracted from the deaf talkers' passages and from a similar passage recorded by a hearing talker. Each of the deaf speech samples was paired with the normal speech sample to generate various continua that differed in the spectral and temporal modifications applied to them. Within each continuum, the individual stimuli varied in the shape of the spectrum envelope and were produced by linear interpolation of LPC analysis parameters between the deaf and normal speech end points. Results suggest that correcting the temporal component of deaf speech alone is not enough to make it sound normal. Spectral corrections that approximate about 70% of normal appear to be necessary for the deaf speech samples to be judged normal. A third experiment made use of a 10-syllable segment of speech in which the relative contributions of spectral and temporal adjustments were investigated. The general conclusion of these three experiments is that spectral adjustments are more important to perceptual judgments of normality than temporal adjustments.

Respirator performance ratings for speech intelligibility.

A respirator degrades speech intelligibility and thus interferes with the ability of the wearer to communicate. The magnitude of this degradation is not well-studied and can vary as a function of numerous parameters. This study investigated the performance degradation of speech intelligibility in low-level noise for different speaker-listener distances and message sets (single words or predictable sentences) that occurred while wearing a respirator compared with not wearing a respirator. Thirteen speaker-listener pairs with normal hearing and speech were used. Speaker-listener separation distances were 0.61, 1.22, 1.83, 2.44, 3.05, and 3.66 m (2, 4, 6, 8, 10, and 12 ft) for the respirator condition and 1.22, 2.44, 3.05, 6.1, 9.15, and 12.2 m (4, 8, 10, 20, 30, and 40 ft) for the no-respirator condition. The means of the scores were used to determine the speech performance rating for both the single-word and sentence comprehension tests. The performance rating expresses the percentage of performance that can be expected while wearing a respirator compared with not wearing a respirator. Scores were interpolated linearly at distances at which no data were obtained. As expected, the speech performance rating was higher for the sentence comprehension test than for the single-word comprehension test at each distance. At a distance of 12.2 m, the speech performance rating for the sentence comprehension was 70%. For the single-word comprehension test, the speech performance rating was zero for distances greater than 9.1 m.

Word frequency and age effects in normally developing children's phonological processing.

Eleven kindergarten-age students and 11 second-grade students were asked to perform each of four phonological processing tasks: (a) confrontation naming of object drawings, (b) rapid sequential naming of object drawings and letters, (c) segmentation of words into sounds, and (d) blending sounds to produce words. Response accuracy and, for the picture naming tasks, response latency were measured. In addition, single-word reading ability and silent reading comprehension were evaluated. Results indicated that high-frequency stimuli were named faster and, in one task, more accurately than low-frequency stimuli. Blending sounds to produce high-frequency words was less difficult than blending sounds to produce low-frequency words, but word frequency did not affect sound segmentation performance. Children in second grade generally were faster and more accurate than kindergarten children in naming pictures. They also were able to segment more sounds and correctly blend sounds to produce more target words than kindergarten students. Confrontation naming accuracy, rapid object- and letter-naming latency, and sound segmentation and blending accuracy were intercorrelated and were related to word recognition and to reading comprehension. Serial naming speed was highly related to phonological awareness in kindergarten, whereas confrontation naming accuracy was highly related to phonological awareness in second grade. A limited cognitive resources framework was adopted to interpret these findings.

Auditory duration discrimination in young and elderly listeners with normal hearing.

This study investigated the effects of age on two parameters of auditory temporal processing: auditory duration discrimination and the backward interference of auditory duration discrimination. Young and elderly listeners with normal hearing sensitivity participated. In experiment I, the just-noticeable difference (JND) in duration between a standard 1000-Hz tone of 40 msec and a comparison tone of longer duration was evaluated using a three-interval forced-choice task. In experiment II, the duration discrimination paradigm was presented with a tonal masker following the tonal stimulus at three delay times: 80 msec, 240 msec, and 720 msec. Age effects were observed on the duration discrimination task with interference but not on the initial duration discrimination task without interference. These results suggest that the time required to process the duration characteristics of acoustic stimuli is prolonged in elderly listeners.

Temporal changes in word revisions by children and adults.

A study was conducted to investigate the temporal changes that occur when a speaker attempts to revise words for a listener. Specifically, the study was designed to examine whether adults and children modify the timing of vowel and consonant production in response to listener miscomprehension. Four adults and sixteen 5-year-old boys and girls served as subjects. They were asked to repeat words that differed in voicing of initial and final stop consonants (back, pack, cab, cap), and to respond to either specific revision requests focused on initial or final sound segments, or to a general revision request. The speech waveform was used to measure the following: Voice Onset Time, vowel duration, final closure duration, and total word duration. Results revealed that children and adults made segmental changes in duration while preserving total word length in revised speech. The effect was a decrease in vowel duration and an increase in final closure duration for revised responses, regardless of the source of miscomprehension. These durational changes result in an apparent enhancement of the final consonantal portion of the misperceived word. All linguistic distinctions in voicing were maintained in the revised words. There were no major differences between adults and children in the type of revision responses produced.

Lesion locations associated with speech perception deficits following penetrating head injury.

Speech discrimination and identification tasks assessing voicing and place distinctions were given to 16 unilaterally brain injured subjects free of aphasic or dysarthric symptoms 12-15 yr post head injury. Seven subjects did not demonstrate any difficulty with these speech tasks, while five left- and four right-brain-injured subjects showed moderate difficulties. These difficulties were more pronounced on the discrimination than on the identification tasks. Analysis of CT scans demonstrated that the lesion locations most clearly associated with the speech discrimination deficits were upper levels of the white matter subjacent to cortical regions in either hemisphere.

Incidence of left-handed writing in a college population with reference to family patterns of hand preference.

Hand preference data were obtained for 1816 university students, 4793 siblings and 3632 parents. Results support the following conclusions. (1) There is currently a 13.8% incidence of left handedness among young adults, representing a dramatic increase over past generations. (2) Left and right-handed respondents do not differ in terms of familial sinistrality. (3) Mother's left-handedness is associated with an increase in the incidence of sinistrality for sons and daughters, while father's left handedness is related only to sons.

Recognition of vowels from information in fricatives: perceptual evidence of fricative-vowel coarticulation.

Four studies investigated the perceptual effects of spectral variations in fricatives produced in different vowel contexts. The alveolar and palatal fricatives, [s, z, integral of, 3], were produced by two talkers in the context of the vowels [a, i, u], generating 12 fricative-vowel combinations. A computer-controlled editing procedure was used to excise fricative segments of 150-ms duration, as measured back from vowel onset. These excised segments were used as test stimuli in the four experiments. In the first experiment, fricative identification was highly accurate, especially for segments produced in the [a] context. The results of the subsequent three vowel identification experiments, revealed that the high vowels [i] and [u] were identified 60%--80% of the time in all fricative contexts, with the exception of [i] produced in the context of [integral of]. In contrast, identification scores for [a] were close to chance in all fricative contexts. Acoustic analyses of the stimuli revealed that the fricative segments with high vowel identification scores exhibited clear evidence of spectral changes associated with the vowels, while those segments with the highest fricative identification scores exhibited spectra most similar to fricatives produced in isolation. These results, in combination with more extensive acoustic analyses [S. D. Soli, J. Acoust. Soc. Am. 70, 976--984 (1981)] are discussed in terms of variations in the articulatory compatibility of tongue movements required to produce fricative-vowel sequences.

Acoustical and perceptual characteristics of speech produced with an electronic artificial larynx.

Five normal-speaking adult males were taught to produce speech using an electrolarynx. Speech phoneme intelligibility was measured in a closed-set word discrimination test and through phonetic transcriptions of the spoken materials. Mean percentages of correct identification for the five talkers were 90% and 57% for the word-identification test and phonetic transcription, respectively. An analysis of perceptual confusions revealed that errors were most frequently associated with the voicing feature and that few manner or place of articulation errors occurred. Over the range of variables observed, the intensity of both the speech and the noise radiating directly from the electrolarynx, the spectrum of the radiated noise and speaking rate were not found to be determinants of intelligibility.

Anatomical study of cerebral asymmetry in the temporal lobe of humans, chimpanzees, and rhesus monkeys.

It is generally accepted that anatomical asymmetries in the temporal lobe language region of humans are associated with the asymmetrical representation of language function in the left hemisphere. Comparative measurements were taken of the length of the left and right Sylvian fissures of human, chimpanzee, and rhesus monkey brains. Measurements confirmed the findings of other studies that the human Sylvian fissure is longer on the left than on the right. The chimpanzee brains had a similar asymmetry but to a lesser degree than the human brains. The rhesus brains, however, showed no significant differences between left and right fissure lengths.