Covariation of cochlear implant users' perception and production of vowel contrasts and their identification by listeners with normal hearing.

This study investigates covariation of perception and production of vowel contrasts in speakers who use cochlear implants and identification of those contrasts by listeners with normal hearing. Formant measures were made of seven vowel pairs whose members are neighboring in acoustic space. The vowels were produced in carrier phrases by 8 postlingually deafened adults, before and after they received their cochlear implants (CI). Improvements in a speaker's production and perception of a given vowel contrast and normally hearing listeners' identification of that contrast in masking noise tended to occur together. Specifically, speakers who produced vowel pairs with reduced contrast in the pre-CI condition (measured by separation in the acoustic vowel space) and who showed improvement in their perception of these contrasts post-CI (measured with a phoneme identification test) were found to have enhanced production contrasts post-CI in many cases. These enhanced production contrasts were associated, in turn, with enhanced masked word recognition, as measured from responses of a group of 10 normally hearing listeners. The results support the view that restoring self-hearing allows a speaker to adjust articulatory routines to ensure sufficient perceptual contrast for listeners.

Changes in speech intelligibility of postlingually deaf adults after cochlear implantation.

OBJECTIVE: This study examines changes in the intelligibility of CVC words spoken by postlingually deafened adults after they have had 6 to 12 mo of experience with a cochlear implant. The hypothesis guiding the research is that the intelligibility of these speakers will improve after extended use of a cochlear implant. The paper also describes changes in CVC word intelligibility analyzed by phoneme class and by features. DESIGN: The speech of eight postlingually deaf adults was recorded before activation of the speech processors of their cochlear implants and at 6 mo and 1 yr after activation. Seventeen listeners with no known impairment of hearing completed a word identification task while listening to each implant user's speech in noise. The percent information transmitted by the speakers in their pre- and postactivation recordings was measured for 11 English consonants and eight vowels separately. RESULTS: An overall improvement in word intelligibility was observed: seven of the eight speakers showed improvement in vowel intelligibility and six speakers showed improvement in consonant intelligibility. However, the intelligibility of specific consonant and vowel features varied greatly across speakers. CONCLUSIONS: Extended use of a cochlear implant by postlingually deafened adults tends to enhance their intelligibility.

Articulatory tradeoffs reduce acoustic variability during American English /r/ production.

The American English phoneme /r/ has long been associated with large amounts of articulatory variability during production. This paper investigates the hypothesis that the articulatory variations used by a speaker to produce /r/ in different contexts exhibit systematic tradeoffs, or articulatory trading relations, that act to maintain a relatively stable acoustic signal despite the large variations in vocal tract shape. Acoustic and articulatory recordings were collected from seven speakers producing /r/ in five phonetic contexts. For every speaker, the different articulator configurations used to produce /r/ in the different phonetic contexts showed systematic tradeoffs, as evidenced by significant correlations between the positions of transducers mounted on the tongue. Analysis of acoustic and articulatory variabilities revealed that these tradeoffs act to reduce acoustic variability, thus allowing relatively large contextual variations in vocal tract shape for /r/ without seriously degrading the primary acoustic cue. Furthermore, some subjects appeared to use completely different articulatory gestures to produce /r/ in different phonetic contexts. When viewed in light of current models of speech movement control, these results appear to favor models that utilize an acoustic or auditory target for each phoneme over models that utilize a vocal tract shape target for each phoneme.

Psychometric equivalence of recorded spondaic words as test items.

In the determination of the speech-reception threshold (SRT), spondaic words are assumed to be homogeneous with respect to intelligibility; and the assumption of equal intelligibility requires that the words be comparable for all signal levels. Previous attempts to assess the equal intelligibility assumption using word thresholds as the sole criterion are not an adequate basis for specifying the equality of intelligibility. In the present study, the recorded spondaic words (Tillman recording) were analyzed in an attempt to create a more homogeneous set of spondaic words for future laboratory work. To achieve this goal, the data reported by Young, Dudley, and Gunter (1982) and data collected in our laboratory were fitted to a logistic function (psychometric function) from which a 50% point (threshold) and slope were obtained. To specify their acoustical parameters, the recorded spondaic words were digitized and the RMS level and duration of each syllable and word were calculated. None of the RMS or duration measures were correlated with word thresholds, so no attempt was made to equate level or duration. On the other hand, when the threshold of each word was adjusted to equal the mean threshold of the set (n = 36), the dispersion among word thresholds and slopes was greatly reduced. Further, we recommend that small sets of "equally intelligible" spondaic words not be used for clinical testing because set size is a strong factor in determining threshold for spondees (Meyer & Bilger, 1997; Punch & Howard, 1985).

Tongue surface displacement during bilabial stops.

The goals of this study were to characterize tongue surface displacement during production of bilabial stops and to refine current estimates of vocal-tract wall impedance using direct measurements of displacement in the vocal tract during closure. In addition, evidence was obtained to test the competing claims of passive and active enlargement of the vocal tract during voicing. Tongue displacement was measured and tongue compliance was estimated in four subjects during production of /aba/ and /apa/. All subjects showed more tongue displacement during /aba/ than during /apa/, even though peak intraoral pressure is lower for /aba/. In consequence, compliance estimates were much higher for /aba/, ranging from 5.1 to 8.5 x 10(-5) cm3/dyn. Compliance values for /apa/ ranged from 0.8 to 2.3 x 10(-5) cm3/dyn for the tongue body, and 0.52 x 10(-5) for the single tongue tip point that was measured. From combined analyses of tongue displacement and intraoral pressure waveforms for one subject, it was concluded that smaller tongue displacements for /p/ than for /b/ may be due to active stiffening of the tongue during /p/, or to intentional relaxation of tongue muscles during /b/ (in conjunction with active tongue displacement during /b/).

Acoustic and articulatory measures of sibilant production with and without auditory feedback from a cochlear implant.

The articulator positions of a subject with a cochlear implant were measured with an electromagnetic midsagittal articulometer (EMMA) system with and without auditory feedback available to the subject via his implant. Acoustic analysis of sibilant productions included specific measures of their spectral properties as well as the F3 formant amplitude. More general postural characteristics of the utterances, such as speech rate and sound level, were measured as well. Because of the mechanical and aerodynamic interdependence of the articulators, the postural variables must be considered before attributing speech improvement to the selective correction of a phonemic target with the use of auditory feedback. The tongue blade position was related to the shape and central tendency of the /integral of/ spectra; however, changes in the spectral contrast between /s/ and /integral of/ were not related to changes in the more general postural variables of rate and sound level. These findings suggest that the cochlear implant is providing this subject with important auditory cues that he can use to monitor his speech and maintain the phonemic contrast between /s/ and /integral of/.

A preliminary study of the effects of cochlear implants on the production of sibilants.

The potential influence of auditory information in the production of /s/ and /integral of/ was explored for postlingually deafened adults with four-channel Ineraid cochlear implants. Analyses of the spectra of the sibilant sounds were compared for speech obtained prior to implant activation, after early implant use and after 6 months of use. In addition, the output of the Ineraid device (measured at each of the four electrodes) was analyzed with pre- and postactivation speech samples to explore whether the speech production changes were potentially audible to the cochlear-implant user. Results indicated that subjects who showed abnormally low or incorrect contrast between /s/ and /integral of/ preactivation, and who received significant auditory benefit from their implants were able to increase the distinctiveness of their productions of the two speech sounds.

Trading relations between tongue-body raising and lip rounding in production of the vowel /u/: a pilot "motor equivalence" study.

Articulatory and acoustic data were used to explore the following hypothesis for the vowel /u/: The objective of articulatory movements is an acoustic goal; varying and reciprocal contributions of different articulators may help to constrain acoustic variation in achieving the goal. Previous articulatory studies of similar hypotheses, expressed entirely in articulatory terms, have been confounded by interdependencies of the variables being studied (e.g., lip and mandible displacements). One case in which this problem may be minimized is that of lip rounding and tongue-body raising (formation of a velo-palatal constriction) for the vowel /u/. Lip rounding and tongue-body raising should have similar acoustic effects for /u/, mainly to lower F2. In multiple repetitions, reciprocal contributions of lip rounding and tongue-body raising could help limit F2 variability for /u/; thus this experiment looked for complementary covariation (negative correlations) in measures of these two parameters. An electro-magnetic midsagittal articulometer (EMMA) was used to track movements of midsagittal points on the tongue body, upper and lower lips, and mandible for large numbers of repetitions of utterances containing /u/. (Interpretation of the data was aided by results from area-function-to-formant modeling.) Three of four subjects showed weak negative correlations, tentatively supporting the hypothesis; a fourth showed the opposite pattern: positive correlations of lip rounding and tongue raising. The results are discussed with respect to ideas about motor equivalence, the nature of speech motor programming, and potential improvements to the paradigm.

Electromagnetic midsagittal articulometer systems for transducing speech articulatory movements.

This paper describes two electromagnetic midsagittal articulometer (EMMA) systems that were developed for transducing articulatory movements during speech production. Alternating magnetic fields are generated by transmitter coils that are mounted in an assembly that fits on the head of a speaker. The fields induce alternating voltages in a number of small transducer coils that are attached to articulators in the midline plane, inside and outside the vocal tract. The transducers are connected by fine lead wires to receiver electronics whose output voltages are processed to yield measures of transducer locations as a function of time. Measurement error can arise with this method, because as the articulators move and change shape, the transducers can undergo a varying amount of rotational misalignment with respect to the transmitter axes; both systems are designed to correct for transducer misalignment. For this purpose, one system uses two transmitters and biaxial transducers; the other uses three transmitters and single-axis transducers. The systems have been compared with one another in terms of their performance, human subjects compatibility, and ease of use. Both systems can produce useful midsagittal-plane data on articular movement, and each one has a specific set of advantages and limitations. (Two commercially available systems are also described briefly for comparison purposes). If appropriate experimental controls are used, the three-transmitter system is preferable for practical reasons.

Temporal measures of anticipatory labial coarticulation for the vowel/u/: within- and cross-subject variability.

The timing of upper lip protrusion movements and accompanying acoustic events was examined for multiple repetitions of word pairs such as "lee coot" and "leaked coot" by four speakers of American English. The duration of the intervocalic consonant string was manipulated by using various combinations of /s/, /t/, /k/, /h/, and /#/. Pairwise comparisons were made of consonant string duration (acoustic /i/ offset to acoustic /u/ onset) with durations of: protrusion movement beginning to acoustic /u/ onset, maximum acceleration of the movement to acoustic /u/ onset, and acoustic /u/ onset to movement end. There were some consonant-specific protrusion effects, primarily on the movement beginning event for /s/. Inferences from measures of the maximum acceleration and movement end events for the non-/s/ subset suggested the simultaneous and variable expression of three competing constraints: (1) end the protrusion movement during the voiced part of the /u/; (2) use a preferred movement duration; and (3) begin the /u/-related protrusion movement when permitted by relaxation of the perceptually motivated constraint that the preceding /i/ be unrounded. The subjects differed in the degree of expression of each constraint, but the results generally indicate that anticipatory coarticulation of lip protrusion is influenced both by acoustic-phonetic context dependencies and dynamical properties of movements. Because of the extensive variation in the data and the small number of subjects, these ideas are tentative; additional work is needed to explore them further.

Genetic implications of gender differences in the prevalence of spontaneous otoacoustic emissions.

Spontaneous otoacoustic emissions (SOAEs), which occur in about 40% of normal-hearing humans, do not have a firm explanation in auditory theory nor are their distributional properties well understood. To enhance our understanding of SOAEs, we have pooled data from three reports (Hammel, 1983; Strickland, Burns, & Tubis, 1985; Zurek, 1981) to assemble a large enough sample to assess the relevant hypotheses about the effects of ear and gender on their presence. The results, based on loglinear analyses of the pooled sample of 131 normal-hearing subjects, indicated that (a) the prevalence of SOAEs for female subjects [P(S/F) = .533] was significantly higher than that for male subjects [P(S/M) = .268]; (b) the percentage of right ears with SOAEs (36.6%) was significantly greater than that of left ears (25.2%); and (c) right and left ears were not independent with respect to the presence of SOAEs. These results can be explained by assuming that the (a) tendency to exhibit emissions is inherited, perhaps as a sex-linked trait and (b) ears are asymmetric with respect to the anatomical anomalies of the apical portion of the organ of Corti that may precipitate SOAEs.

Correlations between various measures of head size and auditory brainstem response latencies.

The literature is mixed concerning the degree to which between-subject variance in the latencies of the auditory brainstem response (ABR) relates to differences in the length of the auditory pathway. Most investigations have used one of several measures of head size to indirectly index brain size and neural pathway length. While some studies have found a positive correlation between head size and the latencies of the ABR, others have reported little or no relationship. We hypothesized that the differences between studies result from differences in the head dimensions measured, the precision of measurement technique, and issues of sampling. We therefore decided to use the International 10-20 system of electrode placement to provide reproducible skull benchmarks on which to base head size measures, to obtain measures of head size via two procedures, and to control external variables that might influence the ABR. The results show that head size has a moderate positive influence on the latencies of the ABR given precise head size measures.

Auditory brain-stem responses in children with previous otitis media.

The auditory brain-stem responses (ABRs) of 18 children who received tympanostomy tubes due to well-documented history of otitis media with effusion (OME) were compared with a matched control group with little or no history of effusion. The subjects in the OME group had significantly longer ABR latencies for waves III and V, with the most compelling delay for wave III and the III-I interwave interval. Although wave I prolongation in the OME group was not significant, the possible contribution of a peripheral effect on the latencies of waves III and V was investigated. The typical gender effect for the ABR latencies was unaltered in the OME group, and there was no group by gender interaction. We suggest that although the data support increased ABR latencies for children with a history of OME, they do not establish a causal relationship.

Recovery from OME-related phonologic delay following tube placement.

Subjects with documented histories of frequent or persistent otitis media with effusion (OME) who were judged to be below age level phonologically prior to placement of pressure equalization (PE) tubes were reassessed at 4-month intervals. Group A (n = 22) subjects caught up with their peers by the age of 4 years; Group B (n = 14) subjects' progress was delayed and phonologic intervention was advised. At initial testing the two groups were found to differ significantly in scores on postvocalic singleton obstruent omission, velar deviation, and stridency deletion. Elapsed time between initial diagnosis of OME and beginning of the first remission of 6 months or more also differed significantly, as did scores on the first phonologic reassessment. Subject scores on initial phonologic adequacy, retest adequacy, and elapsed time from diagnosis to remission appropriately classified all but 2 subjects by group. A formula is provided that appears to make early prediction of eventual need for phonologic intervention a practical possibility.

A modified speech tracking procedure as a communicative performance measure.

A modified speech tracking procedure was investigated to determine the effects of controlling connected discourse materials and of specific prompting techniques on tracking rate and subjects' responses. In addition, comprehension was tested after subjects completed the tracking task. Two experiments were conducted with normally hearing subjects, one in which subjects tracked in an auditory plus noise condition and the second in which they tracked in a visual-alone condition. The results of these two experiments showed significant differences between tracking rates for controlled versus uncontrolled materials for both modalities, with higher tracking rates observed for the controlled materials. The use of specific prompting techniques reduced intertester variability in both modalities. Further, results indicated that comprehension ability and tracking skill are not perfectly related.

Effects of external stimuli on spontaneous otoacoustic emissions.

The behavior of spontaneous otoacoustic emissions (SOAEs) is affected by external stimuli. A series of experiments was conducted with 25 normal-hearing subjects to explore multiple and bilateral SOAEs, frequency and amplitude drift of SOAEs, suppression functions and existence regions for distortion products generated by the interaction of SOAEs and external tones.

Normal adult performance on a temporally modified staggered spondaic word task.

Competing syllables in the Staggered Spondaic Work (SSW) test exhibit considerable variation in alignment. These alignment variations have shown discrepant effects on selected subject populations. Since Berlin et al. (1973) found that dichotic presentation of temporally off-set CV syllables may result in improved intelligibility of the trailing syllable, the same lag effect would be expected to influence performance on a staggered spondaic word identification task. The purpose of this study was to examine the effect of temporal alignment of competing syllables in a staggered spondaic word identification task. Forty-eight adults having no prior experience with or knowledge of the SSW test and no history of speech, language, hearing or reading disorders participated in the study. Each subject was administered two recorded versions of the SSW test. One recording contained items as presented on the commercially available test. The second recording contained SSW test items in which competing monosyllables were temporally aligned. Results revealed no significant difference in performance between the two alignment conditions. In addition, no significant ear effect was demonstrated. Variables which may influence subject performance are described.