Consonant Recognition Performance Research Articles

Effects of Expanding Envelope Fluctuations on Consonant Perception in Hearing-Impaired Listeners.

This study examined the perceptual consequences of three speech enhancement schemes based on multiband nonlinear expansion of temporal envelope fluctuations between 10 and 20 Hz: (a) “idealized” envelope expansion of the speech before the addition of stationary background noise, (b) envelope expansion of the noisy speech, and (c) envelope expansion of only those time-frequency segments of the noisy speech that exhibited signal-to-noise ratios (SNRs) above −10 dB. Linear processing was considered as a reference condition. The performance was evaluated by measuring consonant recognition and consonant confusions in normal-hearing and hearing-impaired listeners using consonant-vowel nonsense syllables presented in background noise. Envelope expansion of the noisy speech showed no significant effect on the overall consonant recognition performance relative to linear processing. In contrast, SNR-based envelope expansion of the noisy speech improved the overall consonant recognition performance equivalent to a 1- to 2-dB improvement in SNR, mainly by improving the recognition of some of the stop consonants. The effect of the SNR-based envelope expansion was similar to the effect of envelope-expanding the clean speech before the addition of noise.

Consonant recognition in noise for bilingual children with simulated hearing loss

The negative impacts of noisy listening environments and hearing loss on speech communication are known to be greater for children and non-native speakers than adult native speakers. Naturally, the synergistic influence of listening environment and hearing loss is expected to be greater for bilingual children than their monolingual or normal-hearing peers, but limited studies have explored this issue. The present study compared the consonant recognition performance of highly fluent school-age Spanish-English bilingual children to that of monolingual English-speaking peers. Stimulus materials were 13 English consonants embedded in three symmetrical vowel-consonant-vowel (VCV) syllables. To control for variability in hearing loss profiles, mild-to-moderate sloping sensorineural hearing loss modeled after Pittman & Stelmachowicz [Ear Hear 24, 198–205 (2003)] was simulated following the method used by Desloge et al. [Trends Amplification 16(1), 19–39 (2012)]. Listeners heard VCVs in quiet and in the background of speech-shaped noise with and without simulated hearing loss. Overall performance and the recognition of individual consonants will be discussed in terms of the influence of language background (bilingual vs. monolingual), listening condition, simulated hearing loss, and vowel context. [Work supported by NIH.].

Electric to acoustic pitch matching: a possible way to improve individual cochlear implant fitting

Poor pitch resolution has been shown to have negative implications for speech and music perception in implanted patients. Surprisingly, works on the subject have not focused much on the impact that the non-correspondence between frequencies allocated to electrodes and perceived frequencies could have on speech and music perception. The aim of the present study is to investigate the correlation between pitch mismatch and speech performance with the implant, and to ascertain the effects of mismatch correction through a mapping function making a personalized frequency reallocation possible. We studied ten postlingually deaf adult patients with detectable bilateral residual hearing, implanted in our Clinic with Cochlear Nucleus devices. In each test session, we asked the patients to find the best match between the pitch elicited by the residual ipsilateral and contralateral pure tones and the pitch elicited by stimulation of electrodes. We also assessed patients' vowel and consonant recognition performance. Finally, in the only implanted patient in our clinic who had bilateral residual hearing and used a Digisonic DX10/C device, which makes manual electrode-by-electrode frequency reallocation possible, we modified electrode-assigned frequency ranges on the basis of the pitch matching test results. We found that in none of the studied patients, the electric-to-acoustic pitch matching corresponds to the theoretical assignment pattern. A very strong correlation was detected between the electric-to-acoustic pitch mismatch and patient's speech performance. In the Digisonic patient, a remarkable improvement in all phoneme recognition scores was obtained 1 month after frequency reallocation. In the light of our results, we propose to assess, whenever possible, any frequency-to-electrode mismatch in all implanted patients, and correct it through mapping programs allowing manual frequency reallocation for the pitch-matched electrodes, and automated allocation of the non-tested electrodes. Cochlear implantation should therefore be proposed when residuals for all frequencies are still present, at least in one ear, so as to allow optimal alignment between allocated and subjectively perceived frequencies.

Using statistical decision theory to predict speech intelligibility. III. Effect of audibility on speech recognition sensitivity

The speech recognition sensitivity (SRS) model [H. Müsch and S. Buus, J. Acoust. Soc. Am. 109, 2896-2909 (2001)] is a macroscopic model for predicting speech intelligibility. The present study proposes a modification to the relation between the SRS model's audibility-noise variance and the signal-excitation to noise-excitation ratio (SNRE) in the auditory periphery. The modified relation is derived from data obtained in nine studies that measured normal-hearing listeners' consonant-recognition performance at several levels of speech-spectrum shaped noise. When the audibility-noise variance is directly proportional to the relative power of the noise excitation in the auditory periphery, the SRS model yields good predictions of the data. Four of the nine studies also reported consonant-recognition performance in various filtering conditions. Good predictions of these data were achieved with SRS model parameters that were consistent with the model parameters fitting the speech-in-noise data and with the model parameters used in the original SRS papers.

The intelligibility of speech with "holes" in the spectrum.

The intelligibility of speech having either a single "hole" in various bands or having two "holes" in disjoint or adjacent bands in the spectrum was assessed with normal-hearing listeners. In experiment 1, the effect of spectral "holes" on vowel and consonant recognition was evaluated using speech processed through six frequency bands, and synthesized as a sum of sine waves. Results showed a modest decrease in vowel and consonant recognition performance when a single hole was introduced in the low- and high-frequency regions of the spectrum, respectively. When two spectral holes were introduced, vowel recognition was sensitive to the location of the holes, while consonant recognition remained constant around 70% correct, even when the middle- and high-frequency speech information was missing. The data from experiment 1 were used in experiment 2 to derive frequency-importance functions based on a least-squares approach. The shapes of the frequency-importance functions were found to be different for consonants and vowels in agreement with the notion that different cues are used by listeners to identify consonants and vowels. For vowels, there was unequal weighting across the various channels, while for consonants the frequency-importance function was relatively flat, suggesting that all bands contributed equally to consonant identification.

The effects of compression ratio, signal-to-noise ratio, and level on speech recognition in normal-hearing listeners.

Previous research has demonstrated reduced speech recognition when speech is presented at higher-than-normal levels (e.g., above conversational speech levels), particularly in the presence of speech-shaped background noise. Persons with hearing loss frequently listen to speech-in-noise at these levels through hearing aids, which incorporate multiple-channel, wide dynamic range compression. This study examined the interactive effects of signal-to-noise ratio (SNR), speech presentation level, and compression ratio on consonant recognition in noise. Nine subjects with normal hearing identified CV and VC nonsense syllables in a speech-shaped noise at two SNRs (0 and +6 dB), three presentation levels (65, 80, and 95 dB SPL) and four compression ratios (1:1, 2:1, 4:1, and 6:1). Stimuli were processed through a simulated three-channel, fast-acting, wide dynamic range compression hearing aid. Consonant recognition performance decreased as compression ratio increased and presentation level increased. Interaction effects were noted between SNR and compression ratio, as well as between presentation level and compression ratio. Performance decrements due to increases in compression ratio were larger at the better (+6 dB) SNR and at the lowest (65 dB SPL) presentation level. At higher levels (95 dB SPL), such as those experienced by persons with hearing loss, increasing compression ratio did not significantly affect speech intelligibility.

Place-pitch sensitivity and its relation to consonant recognition by cochlear implant listeners using the MPEAK and SPEAK speech processing strategies

Two related studies investigated the relationship between place-pitch sensitivity and consonant recognition in cochlear implant listeners using the Nucleus MPEAK and SPEAK speech processing strategies. Average place-pitch sensitivity across the electrode array was evaluated as a function of electrode separation, using a psychophysical electrode pitch-ranking task. Consonant recognition was assessed by analyzing error matrices obtained with a standard consonant confusion procedure to obtain relative transmitted information (RTI) measures for three features: stimulus (RTI stim), envelope (RTI env[plc]), and place-of-articulation (RTI plc[env]). The first experiment evaluated consonant recognition performance with MPEAK and SPEAK in the same subjects. Subjects were experienced users of the MPEAK strategy who used the SPEAK strategy on a daily basis for one month and were tested with both processors. It was hypothesized that subjects with good place-pitch sensitivity would demonstrate better consonant place-cue perception with SPEAK than with MPEAK, by virtue of their ability to make use of SPEAK's enhanced representation of spectral speech cues. Surprisingly, all but one subject demonstrated poor consonant place-cue performance with both MPEAK and SPEAK even though most subjects demonstrated good or excellent place-pitch sensitivity. Consistent with this, no systematic relationship between place-pitch sensitivity and consonant place-cue performance was observed. Subjects' poor place-cue perception with SPEAK was subsequently attributed to the relatively short period of experience that they were given with the SPEAK strategy. The second study reexamined the relationship between place-pitch sensitivity and consonant recognition in a group of experienced SPEAK users. For these subjects, a positive relationship was observed between place-pitch sensitivity and consonant place-cue performance, supporting the hypothesis that good place-pitch sensitivity facilitates subjects' use of spectral cues to consonant identity. A strong, linear relationship was also observed between measures of envelope- and place-cue extraction, with place-cue performance increasing as a constant proportion (approximately 0.8) of envelope-cue performance. To the extent that the envelope-cue measure reflects subjects' abilities to resolve amplitude fluctuations in the speech envelope, this finding suggests that both envelope- and place-cue perception depend strongly on subjects' envelope-processing abilities. Related to this, the data suggest that good place-cue perception depends both on envelope-processing abilities and place-pitch sensitivity, and that either factor may limit place-cue perception in a given cochlear implant listener. Data from both experiments indicate that subjects with small electric dynamic ranges (< 8 dB for 125-Hz, 205-microsecond/ph pulse trains) are more likely to demonstrate poor electrode pitch-ranking skills and poor consonant recognition performance than subjects with larger electric dynamic ranges.

Attentional effects of variability in phonetic context

Understanding how listeners cope with variability in the acoustic patterns of phonetic categories is a basic theoretical problem. Our previous research has suggested that talker and speaking rate variation slows phoneme recognition and increases cognitive load whereas amplitude variation does not. The present study examines the effect of varying phonetic context. Previous research has shown that varying phonetic context slows phoneme recognition. Using the same method as in our previous studies, we also found recognition slows when there is variation in phonetic context. In a second study, cognitive load was manipulated using a number recall task with lists varying in length. Consonant recognition performance was measured with a constant vowel context and when vowel context varied. Both conditions were tested with a low cognitive load and a high cognitive load. Our previous experiments demonstrated that talker and rate variability interact with cognitive load to slow phonetic recognition. The results of the present study will be compared with the results of prior work on talker and rate variabilty. The implications of these findings for the role of attention in theories of speech perception will be discussed.

Evaluating the articulation index for auditory‐visual consonant recognition

The ANSI standard for calculating the articulation index [ANSI S3.5‐1969 (R1986)] includes a procedure for estimating the effects of visual cues on speech intelligibility. This procedure assumes that listening conditions with the same auditory articulation index (AIA) will have the same auditory‐visual AI (AIAV) regardless of the spectral composition of the signal. In contrast, other studies have suggested that the redundancy between A and V speech cues might be a better predictor of AV performance than either the AIA or the overall (e.g., percent correct) auditory recognition score. In the present study, the ANSI procedure is evaluated by measuring A, V, and AV consonant recognition under a variety of different signal‐to‐noise and bandpass‐filtered speech conditions. The results indicate that auditory conditions having the same AIA do not necessarily result in the same AIAV, and that low‐frequency bands of speech tend to provide more benefit to speechreading than high‐frequency bands of speech. Analyses of the auditory error patterns produced by the different filter conditions showed a strong negative correlation between the degree of A and V redundancy and the AV benefit obtained. These data indicate that the ANSI procedure is inadequate for predicting AV consonant recognition performance under conditions of severe spectral shaping. [Work supported by NIH Grant No. DC00792.]

Evaluating the articulation index for auditory-visual consonant recognition.

Adequacy of the ANSI standard for calculating the articulation index (AI) [ANSI S3.5-1969 (R1986)] was evaluated by measuring auditory (A), visual (V), and auditory-visual (AV) consonant recognition under a variety of bandpass-filtered speech conditions. Contrary to ANSI predictions, filter conditions having the same auditory AI did not necessarily result in the same auditory-visual AI. Low-frequency bands of speech tended to provide more benefit to AV consonant recognition than high-frequency bands. Analyses of the auditory error patterns produced by the different filter conditions showed a strong negative correlation between the degree of A and V redundancy and the amount of benefit obtained when A and V cues were combined. These data indicate that the ANSI auditory-visual AI procedure is inadequate for predicting AV consonant recognition performance under conditions of severe spectral shaping.

Relationship between consonant recognition and subjective ratings of hearing aids

The relationships between consonant recognition performance and subjective ratings (using continuous discourse and nonsense syllables as stimuli) of speech understanding, listening comfort, quality, noise interference and overall liking were examined in quiet and in noise using hearing-impaired subjects and seven different hearing aids. Correlations among the subjective scales varied depending on test conditions and test stimuli. Scores on the speech understanding and overall liking scales correlated moderately with scores on a consonant-recognition test presented in noise and when syllables were used as the materials for judgments. The overall liking scale (for a hearing aid) correlated with all other subjective scales and consonant recognition performance. However, the relative contribution of each subjective scale to overall liking varied depending on test conditions and test materials.

Hidden Markov models for Spanish stops

In this work, the design and evaluation of the recognition performance of hidden Markov models (HMM) for the intervocalic Spanish stops are described. The proposed HMMs were context dependent in order to account for coarticulatory effects. Continuous probability density functions were used for the output vectors, which included spectral dynamic parameters. Initial model parameter estimates were obtained by means of an ad hoc segmentation procedure for careful modeling of spectral transitions. The speech database consisted of a total of 2592 productions of the Spanish stops/p, t, k, b, d, g/ in intervocalic position with the vowels /a, i, u/ in all combinations. The speech data were produced by two male Argentine speakers. As a step to evaluate the recognition performance with running speech, three different consonants were produced embedded in VCVCVCV nonsense utterances. Results were obtained from variations of the basic models that consisted of a comparative study of the recognition performance under different degrees of context dependence, and the alternative use of spectral transition parameters. In the best condition the average consonant recognition performance, obtained in a speaker‐dependent manner, was 96.61% and 96.53% for each speaker. The errors were concentrated mainly in the voiced stops, with almost perfect recognition obtained for the unvoiced stops.

Consonant recognition in quiet as a function of aging among normal hearing subjects.

Consonant recognition in quiet using the Nonsense Syllable Test (NST) [Resnick et al., J. Acoust. Soc. Am. Suppl. 1 58, S114 (1975)] was investigated in 62 normal hearing subjects 20 to 65 years of age at their most comfortable listening levels (MCLs) and at 8 dB above and below MCL. Although overall consonant recognition performance was high (as expected for normal listeners), the effects of age decade, relative presentation level, and NST subsets were all significant, as was the interaction of age X level. The interactions of age X NST subset, and age X subset X level were nonsignificant. These findings suggest that consonant recognition decreases with normal aging, particularly below MCL. However, the relative perceptual difficulty of the seven subtests is the same across age groups. Confusion matrices were similar across levels and age groups. Percent information transmitted for several consonant features was calculated from the confusion matrices. Older subjects showed decrements in performance primarily for the features recognized relatively less accurately by the younger subjects. The results suggest that normal hearing older individuals listening in quiet have decreased consonant recognition ability, but that their confusions are similar to those of younger persons.

Some effects of training on speech recognition by hearing-impaired adults.

The purpose of this research was to determine some of the effects of consonant recognition training on the speech recognition performance of hearing-impaired adults. Two groups of ten subjects each received seven hours of either auditory or visual consonant recognition training, in addition to a standard two-week, group-oriented, inpatient aural rehabilitation program. A third group of fifteen subjects received the standard two-week program, but no supplementary individual consonant recognition training. An audiovisual sentence recognition test, as well as tests of auditory and visual consonant recognition, were administered both before and following training. Subjects in all three groups significantly increased in their audiovisual sentence recognition performance, but subjects receiving the individual consonant recognition training improved significantly more than subjects receiving only the standard two-week program. A significant increase in consonant recognition performance was observed in the two groups receiving the auditory or visual consonant recognition training. The data are discussed from varying statistical and clinical perspectives.