OBJECTIVES:(1) To determine if consonant-vowel-consonant (CVC) syllables [Hillenbrand J, Getty L, Clark M, Wheeler K. Acoustic characteristics of American English vowels. J Acoust Soc Am 1995;97:3099-3111] could be used to evoke cortical far field response patterns in humans,(2) to characterize the effects of cochlear implant-simulated channel number on the perception and physiological detection of these same CVC stimuli, and (3) to define the relationship between perception and the morphology of the physiological responses evoked by these speech stimuli. METHODS: Ten normal hearing monolingual English speaking adults were tested. Unprocessed CVC naturally spoken syllables, containing medial vowels, as well as processed versions (2, 4, 8, 12, and 16 spectral channels) were used for behavioral and physiological testing. RESULTS:(1) CVC stimuli evoked a series of overlapping P1-N1-P2 cortical responses.(2) Amplitude of P1-N1-P2 responses increased as neural conduction time (latency) decreased with increases in the number of spectral channels. Perception of the CVC stimuli improved with increasing number of spectral channels.(3) Coinciding changes in P1-N1-P2 morphology did not significantly correlate with changes in perception. CONCLUSIONS: P1-N1-P2 responses can be recorded using CVC syllables and there is an effect of channel number on the latency and amplitude of these responses, as well as on vowel identification. However, the physiological detection of the acoustic changes does not fully account for the perceptual performance of these same syllables. SIGNIFICANCE: These results provide evidence that it is possible to use vocoded CVC stimuli to learn more about the physiological detection of acoustic changes contained within speech syllables, as well as to explore brain-behavior relationships.

Information transfer analysis [G. A. Miller and P. E. Nicely, J. Acoust. Soc. Am. 27, 338-352 (1955)] is a tool used to measure the extent to which speech features are transmitted to a listener, e.g., duration or formant frequencies for vowels; voicing, place and manner of articulation for consonants. An information transfer of 100% occurs when no confusions arise between phonemes belonging to different feature categories, e.g., between voiced and voiceless consonants. Conversely, an information transfer of 0% occurs when performance is purely random. As asserted by Miller and Nicely, the maximum-likelihood estimate for information transfer is biased to overestimate its true value when the number of stimulus presentations is small. This small-sample bias is examined here for three cases: a model of random performance with pseudorandom data, a data set drawn from Miller and Nicely, and reported data from three studies of speech perception by hearing impaired listeners. The amount of overestimation can be substantial, depending on the number of samples, the size of the confusion matrix analyzed, as well as the manner in which data are partitioned therein.

The aim of this pilot study was to identify the most common speech sound confusions of 5 Norwegian cochlear implanted post-lingually deafened adults. We played recorded nonwords, aCa, iCi and bVb, to our informants, asked them to repeat what they heard, recorded their repetitions and transcribed these phonetically. We arranged the collected data in confusion matrices to find the most common and most uncommon speech sound confusions. We found that the voiced and unvoiced consonants are seldom confused. We also found that there was a higher rate of consonant confusion for the iCi words than for the aCa words. The most frequent confusion was [[image omitted]] perceived as [[image omitted]],[[image omitted]] perceived as [[image omitted]] and [[image omitted]] perceived as [[image omitted]]. For the consonants, manner of articulation was rarely confused, but place of articulation was often confused. An exception from this was the confusion of [l] and [n], which differs only in manner of articulation. The latter is in accordance with reports we get from clinicians. We postulate that this is caused by the speech processing of the cochlear implant. We found less confusion of the vowels, which can be explained by the fact that vowels have much higher energy and longer duration than most of the consonants. The most frequent confusion was [[image omitted]] perceived as [[image omitted]] and [[image omitted]] perceived as [[image omitted]].[[image omitted]],[[image omitted]] and [[image omitted]] were never confused with other vowels.

Cochlear implants are neuroprostheses designed to restore speech perception in case of profound bilateral hearing loss. As speech is fundamentally an audiovisual percept, a deficit in processing auditory information might lead to changes in audiovisual integration of speech comprehension. Using vowel-consonant-vowel stimuli under unimodal, audiovisual congruent and audiovisual incongruent (McGurk) conditions, we tested postlingually deaf cochlear-implanted (CI) users and normally hearing (NH) subjects in order to investigate their audiovisual perceptive strategies. Mode/Place-of-articulation perceptive analysis and information transmission analysis of congruent and incongruent percepts indicated a similar sensory specialization for CI users when compared to NH subjects, with voicing and nasality cues transmitted via audition and place cues principally transmitted via vision. NH as well as CI subjects underwent typical McGurk illusory percepts. However, while normally hearing subjects show a well-balanced bimodal integration of incongruent speech, we demonstrated that cochlear implantees present a bias toward a visual-predominant bimodal integration. Our results are complementary to previous studies showing that CI users maintain a high level of speechreading, even after several years of recovery of auditory speech comprehension. Altogether, our results suggest a cross-modal reorganization of speech comprehension in cochlear-implanted patients that might recruit more strongly than in NH the visual and visuo-auditory brain areas involved in speechreading.

OBJECTIVE:: Scores on consonant-recognition tests are widely used as an index of speech-perception ability in cochlear implant (CI) users. The consonant stimuli in these tests are typically presented in the /alpha/ vowel context, even though consonants in conversational speech occur in many other contexts. For this reason, it would be useful to know whether vowel context has any systematic effect on consonant recognition in this population. The purpose of the present study was to compare consonant recognition for the /alpha, i/, and /u/ vowel contexts for consonants presented in both initial (Cv) and medial (vCv) positions. DESIGN:: Twenty adult CI users with one of three different implanted devices underwent consonant-confusion testing. Twelve stimulus conditions that differed according to vowel context (/alpha, i, u/), consonant position (Cv, vCv), and talker gender (male, female) were assessed in each subject. RESULTS:: Mean percent-correct consonant-recognition scores were slightly (5 to 8%) higher for the /alpha/ and /u/ vowel contexts than for the /i/ vowel context for both initial and medial consonants. This general pattern was observed for both male and female talkers, for subjects with better and poorer average consonant-recognition performance, and for subjects using low, medium, and high stimulation rates in their speech processors. In contrast to the mean data, many individual subjects demonstrated large effects of vowel context. For 10 of 20 subjects, consonant-recognition scores varied by 15% or more across vowel contexts in one or more stimulus conditions. Similar to the mean data, these differences generally reflected better performance for the /alpha/ and /u/ vowel contexts than for the /i/ vowel context. An analysis of consonant features showed that overall performance was best for the voicing feature, followed by the manner and place features, and that the place feature showed the strongest effect of vowel context. Vowel-context effects were strongest for the six consonants /d, j, n, k, m/, and /l/. For three of these consonants (/j, n, k/), the back vowels /alpha/ and /u/ produced substantially (30 to 35%) higher mean scores than the front vowel /i/. For each of the remaining three consonants, a unique pattern was observed in which a different single vowel produced substantially higher scores than the others. Several additional consonants (/s, g, w, b/, and /d/) showed strong context effects in either the initial consonant or medial consonant position. Overall, voiceless stop, nasal, and glide-liquid consonants showed the strongest effects of vowel context, whereas the voiceless fricative and voiceless affricate consonants were least affected. Consistent with the feature analysis, a qualitative assessment of phoneme errors for the six key consonants indicated that vowel-context effects stem primarily from changes in the number of place-of-articulation errors made in each context. CONCLUSIONS:: Vowel context has small but significant effects on consonant-recognition scores for the "average" CI listener, with the back vowels /alpha/ and /u/ producing better performance than the front vowel /i/. In contrast to the average results, however, the effects of vowel context are sizable in some individual subjects. This suggests that it may be beneficial to assess consonant recognition using two vowels, such as /alpha/ and /i/, which produce better and poorer performance, respectively. The present results underscore previous findings that poor transmission of spectral speech cues limits consonant-recognition performance in CI users. Spectral cue transmission may be hindered not only by poor spectral resolution in these listeners but also by the brief duration and dynamic nature of consonant place-of-articulation cues.

Cochlear implants provide users with limited spectral and temporal information. In this study, the amount of spectral and temporal information was systematically varied through simulations of cochlear implant processors using a noise-excited vocoder. Spectral information was controlled by varying the number of channels between 1 and 16, and temporal information was controlled by varying the lowpass cutoff frequencies of the envelope extractors from 1 to 512 Hz. Consonants and vowels processed using those conditions were presented to seven normal-hearing native-English-speaking listeners for identification. The results demonstrated that both spectral and temporal cues were important for consonant and vowel recognition with the spectral cues having a greater effect than the temporal cues for the ranges of numbers of channels and lowpass cutoff frequencies tested. The lowpass cutoff for asymptotic performance in consonant and vowel recognition was 16 and 4 Hz, respectively. The number of channels at which performance plateaued for consonants and vowels was 8 and 12, respectively. Within the above-mentioned ranges of lowpass cutoff frequency and number of channels, the temporal and spectral cues showed a tradeoff for phoneme recognition. Information transfer analyses showed different relative contributions of spectral and temporal cues in the perception of various phonetic/acoustic features.

OBJECTIVE: The objective of this study was to measure the performance of persons with cochlear implants on a test of environmental-sound reception. DESIGN: The reception of environmental sounds was studied using a test employing closed sets of 10 sounds in each of four different settings (General Home, Kitchen, Office, and Outside). The participants in the study were 11 subjects with cochlear implants. Identification testing was conducted under each of the four closed sets of stimuli using a one-interval, 10-alternative, forced-choice procedure. The data were summarized in terms of overall percent correct identification scores and information transfer (IT) in bits. Confusion patterns were described using a hierarchical-clustering analysis. In addition, individual performance on the environmental-sound task was related to the ability to recognize isolated words through the cochlear implant alone. RESULTS: Levels of performance were similar across the four stimulus sets. Mean scores across subjects ranged from 45.3% correct (and IT of 1.5 bits) to 93.8% correct (and IT of 3.1 bits). Performance on the environmental-sound identification test was roughly related to NU-6 word recognition ability. Specifically, those subjects with word scores greater than 34% correct performed at levels of 80 to 94% on environmental-sound recognition, whereas subjects with word scores less than 34% had greater difficulty on the task. Results of the hierarchical clustering analysis, conducted on two groups of subjects (a high-performing [HP] group and a low-performing [LP] group), indicated that confusions were confined to three or four specific stimuli for the HP subjects and that larger clusters of confused stimuli were observed in the data of the LP group. Signals with distinct temporal-envelope characteristics were easily perceived by all subjects, and confused items tended to share similar overall durations and temporal envelopes. CONCLUSIONS: Temporal-envelope cues appear to play a large role in the identification of environmental sounds through cochlear implants. The finer distinctions made by the HP group compared with the LP group may be related to a better ability both to resolve temporal differences and to use gross spectral cues. These findings are qualitatively consistent with patterns of confusions observed in the reception of speech segments through cochlear implants.

A user-friendly and versatile research platform for use in auditory experiments, referred to as APEX (Application for PsychoElectrical eXperiments), is described. The platform takes care of automatic stimulus presentation and collection of the subject's responses. Acoustical auditory, as well as electrical auditory experiments with CI recipients can be conducted. The platform currently supports LAURA, Nucleus CI22 and Nucleus CI24 cochlear implants. The graphical user interface for the subjects has been extended to allow for testing very young children, by embedding the psychophysical procedures in a computer game. The research platform is available free of charge.

The pitch of stimuli was studied under conditions where place-of-excitation was held constant, and where pitch was therefore derived from "purely temporal" cues. In experiment 1, the acoustical and electrical pulse trains consisted of pulses whose amplitudes alternated between a high and a low value, and whose interpulse intervals alternated between 4 and 6 ms. The attenuated pulses occurred after the 4-ms intervals in condition A, and after the 6-ms intervals in condition B. For both normal-hearing subjects and cochlear implantees, the period of an isochronous pulse train equal in pitch to this "4-6" stimulus increased from near 6 ms at the smallest modulation depth to nearly 10 ms at the largest depth. Additionally, the modulated pulse trains in condition A were perceived as being lower in pitch than those in condition B. Data are interpreted in terms of increased refractoriness in condition A, where the larger pulses are more closely followed by the smaller ones than in condition B. Consistent with this conclusion, the A-B difference was reduced at longer interpulse intervals. These findings provide a measure of supra-threshold effects of refractoriness on pitch perception, and increase our understanding of coding of temporal information in cochlear implant speech processing schemes.

The differences in spectral shape resolution abilities among cochlear implant (CI) listeners, and between CI and normal-hearing (NH) listeners, when listening with the same number of channels (12), was investigated. In addition, the effect of the number of channels on spectral shape resolution was examined. The stimuli were rippled noise signals with various ripple frequency-spacings. An adaptive 41FC procedure was used to determine the threshold for resolvable ripple spacing, which was the spacing at which an interchange in peak and valley positions could be discriminated. The results showed poorer spectral shape resolution in CI compared to NH listeners (average thresholds of approximately 3000 and 400 Hz, respectively), and wide variability among CI listeners (range of approximately 800 to 8000 Hz). There was a significant relationship between spectral shape resolution and vowel recognition. The spectral shape resolution thresholds of NH listeners increased as the number of channels increased from 1 to 16, while the CI listeners showed a performance plateau at 4-6 channels, which is consistent with previous results using speech recognition measures. These results indicate that this test may provide a measure of CI performance which is time efficient and non-linguistic, and therefore, if verified, may provide a useful contribution to the prediction of speech perception in adults and children who use CIs.

In recent years many technical evolutions have been applied in hearing aids. In this paper differences between analog, programmable and fully digital hearing aids, the basic and supplementary functions of a hearing aid, and some important issues and future directions for digital hearing aids will be mentioned.

OBJECTIVE: This study was designed to evaluate threshold estimation procedures for cochlear implantees, both for clinical and research purposes. Precision and testing time of eight procedures were evaluated. These procedures included three variations of two adaptive tasks and two variations of an adjustment procedure. DESIGN: Electrical thresholds were obtained with eight different procedures. For each procedure, one of three tasks was combined with one of four decision strategies. With the adjustment task, current level was adjusted from "inaudible" to "just audible" or from "clearly audible" to "just audible." With the two adaptive tasks (i.e.,"count the number of pulses" and "choose the interval with the pulse"), current level was adjusted during the sequence of trials by subjects' preceding responses according to three decision criteria (Levitt, 1971). Experimental data were collected on both an apical and a basal channel of six Laura cochlear implantees, and test-retest measures were obtained for each procedure, channel and subject. Moreover, total testing time was recorded in each test, to examine the trade-off with precision, and to investigate the feasibility of the procedures in a clinical setting. RESULTS: In general, the "count the pulses" procedures yield higher threshold values than the "choose the interval with the pulse" and adjustment procedures. Precision was not a statistically significant factor, although the test-retest variation was approximately a factor of 2 larger in the adjustment procedures than in the adaptive procedures. Test duration differences were large. Moreover, analyses of the adaptive procedures showed that a stable estimate requires at least six reversals and that the first four reversals should not be taken into account for threshold estimation. CONCLUSIONS: In a clinical setting, where precision and time are important parameters, precise thresholds can be obtained with the adjustment procedure. However, for research purposes, it is advised to use the "choose the interval with the pulse" task together with one of the transformed up-down decision criteria.

The hypothesis of a general (i.e. cross-modal) temporal processing deficit in dyslexia was tested by examining rapid processing in both the auditory and the visual system in the same children with dyslexia. Participants were 10- to 12-year-old dyslexic readers and age-matched normal reading controls. Psychophysical thresholds were estimated for auditory gap and visual double flash detection, using a two-interval, two-alternative forced-choice paradigm. Significant group differences were found for the auditory and the visual test. Furthermore, temporal processing measures were significantly related to word and pseudo-word reading skills. As 70% of the dyslexic readers had significantly higher thresholds than controls for both auditory and visual temporal processing, the evidence tends to support the hypothesis of a general temporal processing deficit in children with dyslexia.

Gap-detection thresholds were determined for different complex patterns of electrical stimulation in four postlingually deafened LAURA cochlear implantees, to examine the nature of within- and across-channel auditory processes in more detail. Gap detectability was examined as a function of stimulus complexity (one, two, or three channels), channel distance within and across multichannel pre- and post-gap markers, stimulus asymmetry, and pulse rate. All markers roved in duration from 200 to 500 ms to ensure that subjects were not using overall stimulus duration as a cue. Gap-detection thresholds for all subjects were short (< 5 ms) when the pre- and post-gap markers stimulated the same single or multiple channels, even when the distance between simultaneously stimulated channels was large (exp. 1). For some subjects, gap detectability was more difficult in the across-channel condition, when the pre- and post-gap markers each stimulated different channels, although performance improved substantially in most subjects after extensive training (exp. 2). Additional tests with random maskers also suggest that neural interaction only affects performance mildly, and that the magnitude of the gap-detection threshold probably depends more on the subject's cognitive (in)ability to attend to the temporal gap than on the temporal acuity of their auditory system. Other stimulus conditions showed a difference in performance related to the order of the markers: gap thresholds were longer when the pre-gap marker stimulated one channel and the post-gap marker stimulated two or more channels, than vice versa (exp. 3). In addition, gap thresholds of three of the subjects increased with decreasing pulse rate from 1250 to 400 pps, a finding which may be related to the rate of the speech processing strategies used by each individual implantee (exp. 4).

In this study speech intelligibility in background noise was evaluated with 10 binaural hearing-aid users for hearing aids with one omnidirectional microphone and a hearing aid with a two-microphone configuration (enabling an omnidirectional as well as a directional mode). Signal-to-noise ratio (SNR) measurements were carried out for three different types of background noise (speech-weighted noise, traffic noise and restaurant noise) and two kinds of speech material (bisyllabic word lists and sentences). The average SNR improvement of the directional microphone configuration relative to the omnidirectional one was 3.4 dB for noise presented from 90 degrees azimuth. This improvement was independent of the specific type of noise and speech material, indicating that one speech-in-noise condition may yield enough relevant information in the evaluation of directional microphones and speech understanding in noise.

The status of speech processing for cochlear implants is reviewed. Points of interest to enhance further speech intelligibility based on improved signal processing, are discussed.

We demonstrate a compact, fiber-pigtailed, 4-by-4 wavelength router in Silicon-on-insulator photonic wires, fabricated using CMOS processing methods. The core is an AWG with a 250GHz channel spacing and 1THz free spectral range, on a 425x155 microm(2) footprint. The insertion loss of the AWG was reduced to 3.5dB by applying a two-step processing technique. The crosstalk is -12dB. The device was pigtailed using vertical fiber couplers and an eight-fiber array connector.

Biosynthesis of the universal terpenoid precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), from three acetyl CoA moieties through mevalonate was studied extensively in the 1950s. For several decades, the mevalonate paradigm reigned supreme and a mevalonate origin was attributed to a growing number of natural products, in many cases erroneously. Besides this biosynthetic pathway, the existence of a second one leading to IPP and DMAPP through 1-deoxy-D-xylulose 5-phosphate and 2C-methyl-D-erythritol 4-phosphate was discovered more recently in plants and some eubacteria. This pathway is widely distributed in the bacterial kingdom including major human pathogens, such as Mycobacterium tuberculosis or Helicobacter pylori and is also essential in the malaria vector Plasmodium falciparum. During the last few years, the genes, enzymes, intermediates and mechanisms of the biosynthetic route have been elucidated by a combination of methods including comparative genomics, enzymology, advanced NMR technology and crystallography. The present crystallographic review of enzymes involved in isoprenoid biosynthesis will be useful for understanding the various catalytic mechanisms and could potentially help for structure-based drug design.

OBJECTIVES: Studies of tinnitus are often conducted on patient populations presenting for treatment. It is, however, difficult to generalise prevalence numbers and aetiological results from these studies to a healthy, elderly population. The first aim of our study was to determine the prevalence of tinnitus in an otologically screened population between 55 and 65 years old. Secondly, both prevalence and the specific characteristics of tinnitus were compared in subjects with either a flat audiogram, a high-frequency gently sloping audiogram or a high-frequency steeply sloping audiogram. METHODS: 1147 subjects (549 males and 598 females) were recruited through population registers and underwent thorough clinical and audiological examinations. Subjects who reported tinnitus in the general questionnaire about medical history and environmental exposure were invited to complete an additional questionnaire on tinnitus history. RESULTS: The prevalence of tinnitus was 19.3% according to the general questionnaire on medical health and environmental exposure and 11.8% according to the additional detailed tinnitus-specific questionnaire. Furthermore, our results indicate that gender has a significant effect (tinnitus is more common in males than in females), as does audiometric configuration (tinnitus is more common in subjects with a high-frequency steeply sloping audiogram than in subjects with a flat audiogram). Both effects were significant in noise-/solvent-exposed subjects, as well as in non-exposed subjects. Finally, comparison of "tinnitus characteristics" in subjects categorised by audiogram configuration revealed significant differences in loudness, pitch, temporal variability and family history of tinnitus.

Fatty acid amide hydrolase (FAAH), a membrane-anchored enzyme responsible for the termination of endocannabinoid signalling, is an attractive target for treating conditions such as pain and anxiety. Inhibitors of the enzyme, optimized using rodent FAAH, are known but their pharmacology and medicinal chemistry properties on the human FAAH are missing. Therefore recombinant human enzyme would represent a powerful tool to evaluate new drug candidates. However, the production of high amounts of enzyme is hampered by the known refractiveness of FAAH to overexpression. Here, we report the successful overexpression of rat and human FAAH as a fusion to the E. coli maltose-binding protein, retaining catalytic properties of native FAAH. Several known FAAH inhibitors were tested and differences in their potencies toward the human and rat FAAH were found, underscoring the importance of using a human FAAH in the development of inhibitors.

The multiband product rule, also known as band-independence, is a basic assumption of articulation index and its extension, the speech intelligibility index. Previously Fletcher showed its validity for a balanced mix of 20% consonant-vowel (CV), 20% vowel-consonant (VC), and 60% consonant-vowel-consonant (CVC) sounds. This study repeats Miller and Nicely's version of the hi-/lo-pass experiment with minor changes to study band-independence for the 16 Miller-Nicely consonants. The cut-off frequencies are chosen such that the basilar membrane is evenly divided into 12 segments from 250 to 8000 Hz with the high-pass and low-pass filters sharing the same six cut-off frequencies in the middle. Results show that the multiband product rule is statistically valid for consonants on average. It also applies to subgroups of consonants, such as stops and fricatives, which are characterized by a flat distribution of speech cues along the frequency. It fails for individual consonants.

There is significant variability in the benefit provided by cochlear implants to severely deafened individuals. The reasons why some subjects exhibit low speech recognition scores are unknown; however, underlying physiological or psychophysical factors may be involved. Certain phenomena, such as indiscriminable electrodes and nonmonotonic pitch rankings, might hint at limitations in the ability of individual channels in the cochlear implant and/or sensorineural pathway to convey speech information. In this paper, four approaches for analyzing the results of a simple listening test using speech stimuli are investigated for the purpose of targeting channels of concern in order for follow-on psychophysical experiments to correctly identify channels performing in an "impaired" or anomalous manner. Listening tests were first conducted with normal-hearing subjects and acoustic models simulating channel-specific anomalies. Results indicate that these proposed analyses perform significantly better than chance in providing information about the location of anomalous channels. Vowel and consonant confusion matrices from six cochlear implant subjects were also analyzed to test the robustness of the proposed analyses to variability intrinsic to cochlear implant data. The current study suggests that confusion matrix analyses have the potential to expedite the identification of impaired channels by providing preliminary information prior to exhaustive psychophysical testing.

OBJECTIVE:: To evaluate Mandarin-speaking cochlear implant patients' understanding of telephone speech. DESIGN:: Telephone speech was simulated by band-limiting broadband speech stimuli (300-3200 Hz) and adding Gaussian noise (35 dB signal-to-noise ratio). Recognition of multitalker vowels, consonants, voice gender, and Chinese tones was measured for both simulated telephone speech and broadband speech in fifteen Mandarin-speaking cochlear implant patients. RESULTS:: Results showed no significant difference in Chinese tone recognition scores between broadband and telephone speech. However, mean recognition scores for vowels, consonants and voice gender were significantly lower with telephone speech. The effect of the limited telephone bandwidth on speech recognition was highly variable among subjects. Some subjects were more sensitive to high-frequency speech cues, resulting in a significant drop in performance with band-limited telephone speech, while other subjects were less sensitive to high-frequency speech cues, resulting in similar performance between broadband and band-limited telephone speech. CONCLUSIONS:: These results suggest that the limited bandwidth negatively affects cochlear implant patients' understanding of telephone speech. Because the effect of band-limited speech was highly variable among subjects, the results also suggest that the contribution of high frequency information to speech recognition may vary significantly among cochlear implant patients. For patients who receive little benefit from high-frequency speech cues, speech processor adjustments may be necessary to access the additional cues provided in broadband speech.

This paper presents the results of a closed-set recognition task for 64 consonant-vowel sounds (16 C X 4 V, spoken by 18 talkers) in speech-weighted noise (-22,-20,-16,-10,-2 [dB]) and in quiet. The confusion matrices were generated using responses of a homogeneous set of ten listeners and the confusions were analyzed using a graphical method. In speech-weighted noise the consonants separate into three sets: a low-scoring set C1 (/f/,/theta/,/v/,/d/,/b/,/m/), a high-scoring set C2 (/t/,/s/,/z/,/S/,/Z/) and set C3 (/n/,/p/,/g/,/k/,/d/) with intermediate scores. The perceptual consonant groups are C1:{/f/-/theta/,/b/-/v/-/d/,/theta/-/d/}, C2:{/s/-/z/,/S/-/Z/}, and C3:/m/-/n/, while the perceptual vowel groups are /a/-/ae/ and /epsilon/-/iota/. The exponential articulation index (AI) model for consonant score works for 12 of the 16 consonants, using a refined expression of the AI. Finally, a comparison with past work shows that white noise masks the consonants more uniformly than speech-weighted noise, and shows that the AI, because it can account for the differences in noise spectra, is a better measure than the wideband signal-to-noise ratio for modeling and comparing the scores with different noise maskers.

Previous studies in normal-hearing and cochlear-implant subjects have shown high levels of speech recognition with primarily temporal envelope cues. The present study used principal component analysis (PCA) to extract important features in temporal envelopes and then constructed a 3-layer feedforward artificial neural network to study their role in vowel recognition. Twelve vowels by 30 speakers in a /hVd/ context served as the test material. Temporal envelopes from 1 to 8 spectral bands were extracted and subjected to PCA with 15 principle components. Similar to previous perceptual data, the present study showed that 63% correct vowel recognition was achieved with only 4-band envelope cues. The principle components responsible for this high level of vowel recognition included phonemic transition cues and steady-state amplitude cues. The present result can be applied to the development of novel algorithms to improve performance for automatic speech recognition and auditory prosthetic devices.

OBJECTIVE:: Scores on consonant-recognition tests are widely used as an index of speech-perception ability in cochlear implant (CI) users. The consonant stimuli in these tests are typically presented in the /alpha/ vowel context, even though consonants in conversational speech occur in many other contexts. For this reason, it would be useful to know whether vowel context has any systematic effect on consonant recognition in this population. The purpose of the present study was to compare consonant recognition for the /alpha, i/, and /u/ vowel contexts for consonants presented in both initial (Cv) and medial (vCv) positions. DESIGN:: Twenty adult CI users with one of three different implanted devices underwent consonant-confusion testing. Twelve stimulus conditions that differed according to vowel context (/alpha, i, u/), consonant position (Cv, vCv), and talker gender (male, female) were assessed in each subject. RESULTS:: Mean percent-correct consonant-recognition scores were slightly (5 to 8%) higher for the /alpha/ and /u/ vowel contexts than for the /i/ vowel context for both initial and medial consonants. This general pattern was observed for both male and female talkers, for subjects with better and poorer average consonant-recognition performance, and for subjects using low, medium, and high stimulation rates in their speech processors. In contrast to the mean data, many individual subjects demonstrated large effects of vowel context. For 10 of 20 subjects, consonant-recognition scores varied by 15% or more across vowel contexts in one or more stimulus conditions. Similar to the mean data, these differences generally reflected better performance for the /alpha/ and /u/ vowel contexts than for the /i/ vowel context. An analysis of consonant features showed that overall performance was best for the voicing feature, followed by the manner and place features, and that the place feature showed the strongest effect of vowel context. Vowel-context effects were strongest for the six consonants /d, j, n, k, m/, and /l/. For three of these consonants (/j, n, k/), the back vowels /alpha/ and /u/ produced substantially (30 to 35%) higher mean scores than the front vowel /i/. For each of the remaining three consonants, a unique pattern was observed in which a different single vowel produced substantially higher scores than the others. Several additional consonants (/s, g, w, b/, and /d/) showed strong context effects in either the initial consonant or medial consonant position. Overall, voiceless stop, nasal, and glide-liquid consonants showed the strongest effects of vowel context, whereas the voiceless fricative and voiceless affricate consonants were least affected. Consistent with the feature analysis, a qualitative assessment of phoneme errors for the six key consonants indicated that vowel-context effects stem primarily from changes in the number of place-of-articulation errors made in each context. CONCLUSIONS:: Vowel context has small but significant effects on consonant-recognition scores for the "average" CI listener, with the back vowels /alpha/ and /u/ producing better performance than the front vowel /i/. In contrast to the average results, however, the effects of vowel context are sizable in some individual subjects. This suggests that it may be beneficial to assess consonant recognition using two vowels, such as /alpha/ and /i/, which produce better and poorer performance, respectively. The present results underscore previous findings that poor transmission of spectral speech cues limits consonant-recognition performance in CI users. Spectral cue transmission may be hindered not only by poor spectral resolution in these listeners but also by the brief duration and dynamic nature of consonant place-of-articulation cues.

An interactive face-to-face setting is used to study natural infant directed speech (IDS) compared to adult directed speech (ADS). With distinctive vowel quantity and vowel quality, Norwegian IDS was used in a natural quasi-experimental design. Six Norwegian mothers were recorded over a period of 6 months alone with their infants and in an adult conversation. Vowel duration and spectral attributes of the vowels /a:/,/i:/ and /u:/, and their short counterparts /a//i/ and /u/ were analysed. Repeated measures analyses show that effects of vowel quantity did not differ between ADS and IDS, and for back vowel qualities, the vowel space was shifted upwards in IDS compared to ADS suggesting that fronted articulations in natural IDS may visually enhance speech to infants.

Cochlear implants provide users with limited spectral and temporal information. In this study, the amount of spectral and temporal information was systematically varied through simulations of cochlear implant processors using a noise-excited vocoder. Spectral information was controlled by varying the number of channels between 1 and 16, and temporal information was controlled by varying the lowpass cutoff frequencies of the envelope extractors from 1 to 512 Hz. Consonants and vowels processed using those conditions were presented to seven normal-hearing native-English-speaking listeners for identification. The results demonstrated that both spectral and temporal cues were important for consonant and vowel recognition with the spectral cues having a greater effect than the temporal cues for the ranges of numbers of channels and lowpass cutoff frequencies tested. The lowpass cutoff for asymptotic performance in consonant and vowel recognition was 16 and 4 Hz, respectively. The number of channels at which performance plateaued for consonants and vowels was 8 and 12, respectively. Within the above-mentioned ranges of lowpass cutoff frequency and number of channels, the temporal and spectral cues showed a tradeoff for phoneme recognition. Information transfer analyses showed different relative contributions of spectral and temporal cues in the perception of various phonetic/acoustic features.

This study presents 2 experiments investigating whether listeners with cochlear hearing loss (hearing impaired; HI) and listeners with normal hearing (NH) show differential susceptibility to masking in double-vowel identification. Experiment 1 addressed how double-vowel perception changes as a function of differences in fundamental frequency (deltaF0) of 0 and 2 semitones and the relative amplitudes of the constituent vowels (target-to-masker ratios:-10,-5, 0, 5, 10 dB). When deltaF0 is 0 semitones, listeners in the HI group often perceive the presence of only 1 vowel, whereas listeners in the NH group generally perceive the presence of 2 vowels. In both groups, deltaF0 benefits target-vowel identification, with the greatest benefit occurring when the target-to-masker ratio is -10 dB. When identification rates of specific vowels (in d') were rank ordered, different patterns of vowel dominance were found between the NH and HI groups. In Experiment 2, the effects of deltaF0 (0 to 4 semitones) were compared for monaural and dichotic presentation of double vowels. Both groups show significant dichotic benefit. In addition, individual listeners in the HI group showed trends toward greater dichotic benefit. In both experiments, identification of competing vowels was significantly worse in HI listeners. The results of this study support the idea that increased susceptibility to masking is a primary factor underlying the degraded double-vowel perception in listeners with hearing loss.

The effect of the filter bank on fundamental frequency (F0) discrimination was examined in four Nucleus CI24 cochlear implant subjects for synthetic stylized vowel-like stimuli. The four tested filter banks differed in cutoff frequencies, amount of overlap between filters, and shape of the filters. To assess the effects of temporal pitch cues on F0 discrimination, temporal fluctuations were removed above 10 Hz in one condition and above 200 Hz in another. Results indicate that F0 discrimination based upon place pitch cues is possible, but just-noticeable differences exceed 1 octave or more depending on the filter bank used. Increasing the frequency resolution in the F0 range improves the F0 discrimination based upon place pitch cues. The results of F0 discrimination based upon place pitch agree with a model that compares the centroids of the electrical excitation pattern. The addition of temporal fluctuations up to 200 Hz significantly improves F0 discrimination. Just-noticeable differences using both place and temporal pitch cues range from 6% to 60%. Filter banks that do not resolve the higher harmonics provided the best temporal pitch cues, because temporal pitch cues are clearest when the fluctuation on all channels is at F0 and preferably in phase.