Nancy S. McGarr

The cricothyroid muscle in voicing control

Initiation and maintenance of vibrations of the vocal folds require suitable conditions of adduction, longitudinal tension, and transglottal airflow. Thus manipulation of adduction/abduction, stiffening/slackening, or degree of transglottal flow may, in principle, be used to determine the voicing status of a speech segment. This study explores the control of voicing and voicelessness in speech with particular reference to the role of changes in the longitudinal tension of the vocal folds, as indicated by cricothyroid (CT) muscle activity. Electromyographic recordings were made from the CT muscle in two speakers of American English and one speaker of Dutch. The linguistic material consisted of reiterant speech made up of CV syllables where the consonants were voiced and voiceless stops, fricatives, and affricates. Comparison of CT activity associated with the voiced and voiceless consonants indicated a higher level for the voiceless consonants than for their voiced cognates. Measurements of the fundamental frequency (F0) at the beginning of a vowel following the consonant show the common pattern of higher F0 after voiceless consonants. For one subject, there was no difference in cricothyroid activity for voiced and voiceless affricates; in this case, the consonant‐induced variations in the F0 of the following vowel were also less robust. Consideration of timing relationships between the EMG curves for voiced and voiceless consonants suggests that the differences most likely reflect control of vocal‐fold tension for maintenance or suppression of phonatory vibrations. The same mechanism also seems to contribute to the well‐known difference in F0 at the beginning of vowels following voiced and voiceless consonants.

Laryngeal vibrations: A comparison between high‐speed filming and glottographic techniques

This study was designed to compare information on laryngeal vibrations obtained by high-speed filming, photoglottography (PGG), and electroglottography (ECG). Simultaneous glottographic signals and high-speed films were obtained from two subjects producing steady phonation. Measurements of glottal width were made at three points along the glottis in the anterior--posterior dimension and aligned with the other records. Results indicate that PGG and film measurements give essentially the same information for peak glottal opening and glottal closure. The EGG signal appears to reliably indicate vocal-fold contact. Together, PGG and EGG may provide much of the information obtained from high-speed filming as well as potentially detect horizontal phase differences during opening and closing.

Speech Production Characteristics of the Hearing Impaired

Publisher Summary This chapter discusses speech production characteristics of the hearing impaired. It focuses on language skills only in those instances where there is no clear-cut separation between language and speech. One of the most devastating effects of congenital hearing loss is that normal development of speech is often disrupted. Production of non-articulatory aspects or suprasegmentals also contributes to the overall patterns of speech production in the hearing impaired. Perhaps of all the speech production errors characteristic of the severely and profoundly hearing impaired, the area that has received the greatest attention is that involving the articulation of consonants, vowels, and diphthongs. The chapter also discusses characteristics such as timing, intonation, and stress assignments of non-articulatory patterns in the speech of severely and profoundly hearing-impaired speakers. The majority of information available on the speech of hard-of-hearing children involves analyses of articulatory skills. Although profoundly hearing-impaired children produce more segmental errors than hard-of-hearing children, the relative proportion of errors for each error type is similar for both groups of children.

The effect of context on the intelligibility of hearing and deaf children's speech.

This study examines the effect of redundancy of information on the intelligibility of hearing and deaf childrens speech. Listeners, including those experienced and inexperienced with respect to the speech of the deaf, heard two kinds of stimuli: (1) test words in sentences that varied in the amount of redundant information available, and (2) test words excised from these sentences and presented to the listeners as isolated words. For both groups of children, test words heard in sentences were perceived correctly more often than the same words heard in isolation. However, the effect of redundant information on intelligibility was opposite to that reported for adults (Lieberman, 1963). That is, in the speech of both hearing and deaf children, the scores for test words segmented from sentences with high redundancy were greater than scores for test words segmented from sentences with low redundancy. This suggests that children are not using the same production strategies as adults to assist listeners. The data also do not support the hypothesis that experienced listeners to deaf speech achieve higher intelligibility scores than inexperienced listeners by simply making better use of context.

Pitch deviancy and intelligibility of deaf speech

The relationship between pitch deviancy and other aspects of speech production that affect intelligibiliyy of deaf speech was investigated. The speech skills assessed included the following: ratings of pitch deviancy, ratings of overall intelligibility, production of the prosodic features--stress, intonation, and pause, and production of phonemes. Children who could not sustain phonation had speech that was consistently judged unintelligible. This group of children also had pure tone averages greater than 90 dB. For the remaining children, the relationship among pitch deviancy, intelligibility, and hearing level was variable. The highest intercorrelations were among prosodic feature production, phoneme production, and intelligibility.

Obstruent production by hearing‐impaired speakers: Interarticulator timing and acoustics

This study examines the organization of laryngeal control and interarticulator timing in the production of obstruents and obstruent clusters by three severely-profoundly deaf adults. Glottal activity was monitored by transillumination; temporal patterns of oral articulation (lips and tongue-palate) were recorded using an electrical transconductance technique. For each of the deaf speakers, an inappropriate abduction gesture was often found between words, a pattern never observed for hearing speakers. At the same time, the deaf speakers differed from each other with respect to types of errors, variability, and interarticulator coordination. For the most intelligible speaker, the timing of glottal opening with respect to oral articulation was most like that observed for normals. The second deaf speaker often failed to observe voicing contrasts with respect to glottal opening. This subject was nevertheless consistent in producing most plosives without a glottal opening, and all fricatives with an opening gesture. For the third deaf speaker, the pattern of errors was more complex and included both missing and inappropriate glottal opening gestures.

Perception of stress contrasts by the hearing impaired

Waveform manipulation and LPC resynthesis techniques were used to develop test stimuli in which the F0, amplitude, and durational cues for first versus second syllable stress were systematically and independently controlled. Both normal and exaggerated stress contrasts were represented in the test corpus. Twenty severely to profoundly hearing‐impaired students served as subjects for a perceptual experiment and were asked to indicate whether the stress was on the first or second syllable of each two‐syllable test item (data were also collected on a group of normal hearing controls). Results revealed that the hearing‐impaired listeners were able to correctly identify the stressed syllable only for stimuli in which the amplitude cue was available. That is, they scored below chance on stimuli in which the durational and/or F0 cues were present but where the amplitude cue had been neutralized. Exaggerating the amplitude cue for stress resulted in higher identification scores. Exaggerating F0 and/or durational ...

Jaw kinematics in hearing‐impaired speakers

This study examines jaw movements as a function of vowel height and stress in real‐word phrases produced by three hearing‐impaired speakers and a hearing control. Movements of the lips and jaw were recorded using an optical tracking system. Measures included duration, displacement, and peak velocity of movement. There were statistically significant main effects for vowel height in nearly all movement records for both the hearing‐impaired and the hearing speakers. However, the related measures for stress had no significant effects for the subjects. The hearing speaker distinguished stressed and unstressed segments by maintaining the jaw in a lowered position for a longer period in the stressed vowels. With few exceptions, kinematic values for the hearing and the hearing‐impaired speakers were comparable. These results thus suggest that some characteristics of speech production are not adversely affected by congenital and profound hearing loss. [Work supported by NIH.]

Electromyographic and kinematic measures of articulatory coordination in a deaf speaker

Variability in production and disruption of interarticulator timing is reported for a deaf speaker. Acoustic, electromyographic, and movement records were obtained from a deaf subject and a hearing control, producing multiple repetitions of nonsense syllables (e.g., ə bib ɑ b) with stress on either V1 or V2. Electromyographic recordings were obtained from genioglossus, geniohyoid, and anterior belly of digastricus. Temporal patterns of lip closure were recorded using an electrical conductance technique. Infrared LEDs were attached to the jaw and monitored using a modified SELSPOT optical tracking system. Tokens were sorted into perceptually correct versus error patterns according to listener judgments, and formant frequency measures obtained. The deaf speaker differed from the normal control in several ways. She was unable to consistently execute changes in stress across different syllables and did not differentiate high versus low vowels in either genioglossus or relative jaw position. Timing of geniohyo...

Vowels and final consonant production by adults with Down’s syndrome

Speech production studies have suggested a typical voice quality as well as vowel and consonant errors in speakers with Down’s syndrome. In this study, the production of bVt or bVd words produced by ten adults with Down’s syndrome and age and gender matched controls was examined for influence of final consonant voicing status. Acoustic measures of vowel duration and consonant voicing were made. Listener judgments were also obtained. Contrasts between vowels pairs were maintained by most subjects, e.g., duration for tense vowels was greater than for lax, although duration for the test subjects productions was greater overall than for the controls. Similarly, consonant voicing contrasts were maintained, e.g., vowel duration preceding voiced consonants was longer than for voiceless, but again overall duration was longer for the Down’s syndrome adults than the controls. The results of the acoustic analyses suggest that while the test subjects demonstrate knowledge for producing final voicing contrasts, aspect...