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PubMed1990

Phoneme discrimination using connectionist networks.

The application of connectionist networks to speech recognition is assessed using a set of eight representative phonetic discrimination problems chose with respect to a theory of phonetics. A connectionist network model called the temporal flow model (TFM) is defined which represents temporal relationships using delay links and permits general patterns of connectivity. It is argued that the model has properties appropriate for time varying signals such as speech. Networks are trained using gradient descent methods of iterative nonlinear optimization to reduce the mean-squared error between the actual and the desired response of the output units. Separate network solutions are demonstrated for all eight phonetic discrimination problems for one male speaker. The network solutions are analyzed carefully and are shown in every case to make use of known acoustic phonetic cues. The network solutions vary in the degree to which they make use of context-dependent cues to achieve phoneme recognition. The network solutions were tested on data not used for training and achieved an average accuracy of 99.5%. It is concluded that acoustic phonetic speech recognition can be accomplished using connectionist networks.

Algorithms↗

PubMed1990

Perception of intraphonemic differences by phoneticians, musicians, and inexperienced listeners.

Several studies have shown that extensive training with synthetic speech sounds can result in substantial improvements in listeners' perception of intraphonemic differences. The purpose of the present study was to investigate the effects of listening experience on the perception of intraphonemic differences in the absence of specific training with the synthetic speech sounds being tested. Phonetically trained listeners, musicians, and untrained listeners were tested on a two-choice identification task, a three-choice identification task, and an ABX discrimination task using a synthetic [bi]-[phi] continuum and a synthetic [wei]-[rei] continuum. The three-choice identification task included the identification of stimuli with an "indefinite" or "ambiguous" quality in addition to clear instances of the opposing phonetic categories. Results included: (1) All three subject groups showed some ability to identify ambiguous stimuli; (2) phonetically trained listeners were better at identifying ambiguous stimuli than musicians and untrained listeners; (3) phonetically trained listeners performed better on the discrimination task than musicians and untrained listeners; (4) musicians and untrained listeners did not differ on any of the listening tasks; and (5) participation by the inexperienced listeners in a 10-week introductory phonetics course did not result in improvements in either the three-choice identification task or the discrimination task.

Adult↗

PubMed1999

Vowel formant discrimination: towards more ordinary listening conditions.

Thresholds for formant frequency discrimination have been established using optimal listening conditions. In normal conversation, the ability to discriminate formant frequency is probably substantially degraded. The purpose of the present study was to change the listening procedures in several substantial ways from optimal towards more ordinary listening conditions, including a higher level of stimulus uncertainty, increased levels of phonetic context, and with the addition of a sentence identification task. Four vowels synthesized from a female talker were presented in isolation, or in the phonetic context of /bVd/ syllables, three-word phrases, or nine-word sentences. In the first experiment, formant resolution was estimated under medium stimulus uncertainty for three levels of phonetic context. Some undesirable training effects were obtained and led to the design of a new protocol for the second experiment to reduce this problem and to manipulate both length of phonetic context and level of difficulty in the simultaneous sentence identification task. Similar results were obtained in both experiments. The effect of phonetic context on formant discrimination is reduced as context lengthens such that no difference was found between vowels embedded in the phrase or sentence contexts. The addition of a challenging sentence identification task to the discrimination task did not degrade performance further and a stable pattern for formant discrimination in sentences emerged. This norm for the resolution of vowel formants under these more ordinary listening conditions was shown to be nearly a constant at 0.28 barks. Analysis of vowel spaces from 16 American English talkers determined that the closest vowels, on average, were 0.56 barks apart, that is, a factor of 2 larger than the norm obtained in these vowel formant discrimination tasks.

Female↗

PubMedDate not supplied

Does babbling sound native? Listener responses to vocalizations produced by Swedish and American 12- and 18-month-olds.

Previous studies of infants' babbling have reported contradictory results as to the extent and timing of discernible phonetic influences of the ambient language. In the present experiment, five experienced phoneticians were asked to listen for ambient language effects on vocalizations produced by American and Swedish 12- and 18-month-olds (with 8 children in each language and age group), and to motivate their decisions in terms of word or phonetic cue perception. Group results indicated that listeners did not perceive effects of ambient language on pure babbles for either of the two age groups, whereas a clear effect appeared in both age groups given a more liberal definition of babbling. This is taken to suggest that results of ambient language listening tests may depend crucially on judgments of vocalizations' word status. As compared to the group trends, listener responses to individual children's vocalizations did not indicate that a majority of either 12- or 18-monthers were sufficiently native-sounding to be reliably identified on the basis of ambient language. A closer analysis of listeners' use of phonetic cues indicated that one single phonetic property, the grave tonal word accent, was discerned by most listeners in vocalizations produced by the Swedish 18-monthers; this property was also discerned by one listener in vocalizations produced by Swedish 12-monthers. This result is consistent with the generally held belief in the primacy of tonal features in phonetic acquisition, and with experimental evidence indicating that Swedish mothers tend to enhance word accent contours in baby talk. In the final section of the paper, the results are discussed with a view to reconcile competing theories of babbling development, notably the 'babbling drift' and the 'independence' hypotheses.

Child Development↗

PubMed1991

A trial of piracetam in two subgroups of students with dyslexia enrolled in summer tutoring.

Sixty children with dyslexia (41 boys, 19 girls; ages 9 to 13) were enrolled in a 10-week summer tutoring program that emphasized word-building skills. They were randomly and blindly assigned to receive either placebo or piracetam, a purportedly memory-enhancing drug that has been reported to facilitate reading skill acquisition. The children were subtyped as "dysphonetic" or "phonetic" on the basis of scores from tests of phonological sensitivity and phoneme-grapheme correspondence skills. Of the 53 children who completed the program, 37 were classified as dysphonetic and 16 as phonetic. The phonetic group improved significantly more in word-recognition ability than the dysphonetic group. Overall, the children on medication did not improve more than the nonmedicated ones in any aspect of reading. The phonetic subgroup on piracetam gained more in word recognition than any subgroup but did not improve significantly more than the phonetic subgroup on placebo. Results are discussed in relation to findings from previous studies of piracetam in children with dyslexia.

Adolescent↗

PubMed2000

Speech perception without hearing.

In this study of visual phonetic speech perception without accompanying auditory speech stimuli, adults with normal hearing (NH; n = 96) and with severely to profoundly impaired hearing (IH; n = 72) identified consonant-vowel (CV) nonsense syllables and words in isolation and in sentences. The measures of phonetic perception were the proportion of phonemes correct and the proportion of transmitted feature information for CVs, the proportion of phonemes correct for words, and the proportion of phonemes correct and the amount of phoneme substitution entropy for sentences. The results demonstrated greater sensitivity to phonetic information in the IH group. Transmitted feature information was related to isolated word scores for the IH group, but not for the NH group. Phoneme errors in sentences were more systematic in the IH than in the NH group. Individual differences in phonetic perception for CVs were more highly associated with word and sentence performance for the IH than for the NH group. The results suggest that the necessity to perceive speech without hearing can be associated with enhanced visual phonetic perception in some individuals.

Adolescent↗

PubMed2002

Learning to recognize talkers from natural, sinewave, and reversed speech samples.

In 5 experiments, the authors investigated how listeners learn to recognize unfamiliar talkers and how experience with specific utterances generalizes to novel instances. Listeners were trained over several days to identify 10 talkers from natural, sinewave, or reversed speech sentences. The sinewave signals preserved phonetic and some suprasegmental properties while eliminating natural vocal quality. In contrast, the reversed speech signals preserved vocal quality while distorting temporally based phonetic properties. The training results indicate that listeners learned to identify talkers even from acoustic signals lacking natural vocal quality. Generalization performance varied across the different signals and depended on the salience of phonetic information. The results suggest similarities in the phonetic attributes underlying talker recognition and phonetic perception.

Female↗

PubMed1998

Event-related brain potentials elicited during phonological processing differentiate subgroups of reading disabled adolescents.

Visual and auditory rhyme judgment tasks were administered to adolescent dyslexics and normal readers while event-related brain potentials were recorded. Reading disabled subjects were split into two groups based on a median split of scores on a visual non-word decoding test. The better decoders were called Phonetics and the poorer decoders were referred to as Dysphonetics. Single syllable, real word stimuli were used, and both rhyming and non-rhyming targets had a 50% chance for matching orthography. In the visual paradigm the normal readers exhibited a left frontal CNV before targets, a large reduction in frontal N400 for matching orthography (orthographic priming), and a large reduction in parietal N400 for rhyming targets (phonological priming). Dysphonetics had an intact CNV and orthographic priming, but the group's phonological priming was very reduced. Phonetics showed both orthographic and phonological priming but had a marked reduction in their CNV. In the auditory task, controls showed a left parietal N400 priming effect for rhyming targets. Dysphonetics showed a similar bilateral effect. The Phonetics did not show a normal priming effect, but produced evidence for priming at a longer latency. Additionally, the Phonetic group responded more slowly than either of the other two groups, who responded with similar latencies. These results support the separation of the reading disabled into a group that has difficulty translating orthography into phonology, and a group that is slower functioning and has reduced capacity in preparing for a response.

Adolescent↗

PubMed2005

Frequency and category factors in the reduction and assimilation of function words: EPG and acoustic measures.

Many studies have observed phonetic and phonological differences between function words and content words. However, as many of the most commonly cited function words are also very high in frequency, it is unclear whether these differences are the result of syntactic category or word frequency. This study attempts to determine whether syntactically defined function words are indeed phonologically and phonetically reduced or assimilated when word frequency is balanced. Three experiments were designed to distinguish the relative contributions of the factors of category and frequency on phonetic and phonological reduction and assimilation. Overall results suggest that syntactic category and word frequency interact with phonetic and phonological processes in a more complex way than previously believed. Experiment 1 measured final t/d dropping, a reduction process, using electropalatography (EPG). Experiment 2 examined vowel reduction using acoustic measures. In Experiment 3, palatalization, an assimilation process, was examined using EPG. Results showed that t/d dropping responds to the factor of syntactic category, whereas palatalization is affected by word frequency; vowel reduction responded to both factors, with a dominant syntactic category effect and a secondary within-category frequency effect. The implications of these findings for models of lexical representation and theories of language acquisition are discussed.

Electromyography↗

PubMed2005

Foveal splitting causes differential processing of Chinese orthography in the male and female brain.

Chinese characters contain separate phonetic and semantic radicals. A dominant character type exists in which the semantic radical is on the left and the phonetic radical on the right; an opposite, minority structure also exists, with the semantic radical on the right and the phonetic radical on the left. We show that, when asked to pronounce isolated tokens of these two character types, males responded significantly faster when the phonetic information was on the right, whereas females showed a non-significant tendency in the opposite direction. Recent research on foveal structure and reading suggests that the two halves of a centrally fixated character are initially processed in different hemispheres. The male brain typically relies more on the left hemisphere for phonological processing compared with the female brain, causing this gender difference to emerge. This interaction is predicted by an implemented computational model. This study supports the existence of a gender difference in phonological processing, and shows that the effects of foveal splitting in reading extend far enough into word recognition to interact with the gender of the reader in a naturalistic reading task.

Adult↗

PubMed2005

The acquisition of allophonic rules: statistical learning with linguistic constraints.

Phonological rules relate surface phonetic word forms to abstract underlying forms that are stored in the lexicon. Infants must thus acquire these rules in order to infer the abstract representation of words. We implement a statistical learning algorithm for the acquisition of one type of rule, namely allophony, which introduces context-sensitive phonetic variants of phonemes. This algorithm is based on the observation that different realizations of a single phoneme typically do not appear in the same contexts (ideally, they have complementary distributions). In particular, it measures the discrepancies in context probabilities for each pair of phonetic segments. In Experiment 1, we test the algorithm's performances on a pseudo-language and show that it is robust to statistical noise due to sampling and coding errors, and to non-systematic rule application. In Experiment 2, we show that a natural corpus of semiphonetically transcribed child-directed speech in French presents a very large number of near-complementary distributions that do not correspond to existing allophonic rules. These spurious allophonic rules can be eliminated by a linguistically motivated filtering mechanism based on a phonetic representation of segments. We discuss the role of a priori linguistic knowledge in the statistical learning of phonology.

Humans↗

PubMed1997

Neural dynamics of variable-rate speech categorization.

What is the neural representation of a speech code as it evolves in time? A neural model simulates data concerning segregation and integration of phonetic percepts. Hearing two phonetically related stops in a VC-CV pair (V = vowel; C = consonant) requires 150 ms more closure time than hearing two phonetically different stops in a VC1-C2V pair. Closure time also varies with long-term stimulus rate. The model simulates rate-dependent category boundaries that emerge from feedback interactions between a working memory for short-term storage of phonetic items and a list categorization network for grouping sequences of items. The conscious speech code is a resonant wave. It emerges after bottom-up signals from the working memory select list chunks which read out top-down expectations that amplify and focus attention on consistent working memory items. In VC1-C2V pairs, resonance is reset by mismatch of C2 with the C1 expectation. In VC-CV pairs, resonance prolongs a repeated C.

Computer Simulation↗

PubMed1983

Perceptual organization of speech sounds by infants.

An operant head-turn procedure was used to test whether 6-month-old infants recognize the auditory similarity of speech sounds sharing a value on a phonetic-feature dimension. One group of infants was reinforced for head turns when a change occurred from a series of repeating background stimuli containing nasal consonants [( m, n, eta]) to repetitions from a category of syllables containing voiced stop consonants [( b, d, g]), or to a change from stops to nasals. The stimuli were naturally produced by both male and female talkers. The performance of infants in this "phonetic" group was compared to that of infants in a "nonphonetic" control group. Using the same procedures, these infants were reinforced for head turns to a group of phonetically unrelated speech sounds. Results indicated that the performance of infants in the group trained on phonetically related speech sounds was far superior to that of infants in the nonphonetic control group. These findings suggest that prelinguistic infants can perceptually organize speech sounds on the basis of auditory properties related to feature similarity.

Child Language↗

PubMed2000

Some acoustic characteristics in the voices of 6- to 10-year-old children and adults: a comparative sex and developmental perspective.

This study is a follow-up investigation of some of the acoustic characteristics reported for a group of twenty 6-, 8- and 10-year-old children's voices (Whiteside SP, Hodgson C. Log Phon Vocol 1999; 24: 6-13) and compares the data of these children with data from a group of nine adults. The acoustic characteristics for both the children and the adults were examined as a function of age and sex. Fundamental frequency (F0) and the standard deviation (SD) of F0 were investigated for the entire duration of a phrase-final vowel. In addition, the first three formant frequencies of the midpoints for the phrase-final vowel were also investigated, with reference to phonetic context. All acoustic parameters were investigated by examining the age, sex and context-determined differences. Results indicated significant age differences for all acoustic parameters investigated, which were characterized by a general decrease in the frequency values of parameters with increasing age. In addition, significant sex differences were found for all parameters, with the females generally having higher formant frequency values than their male peers across all ages. Significant phonetic context differences were only found for the second formant frequency, with formant values being highest for the context "jar" and lowest for the context "bar". No significant interactions were found for age-by-context, sex-by-context or age-by-sex-context comparisons. Relative formant frequency differences were also examined using Fant's Kn factor, by considering sex-, age- and context-linked patterns. The data also provided some evidence for parallel developmental patterns in the different phonetic contexts of a phrase-final vowel. Furthermore, the results showed that there was some evidence of all three types of the aforementioned patterns in addition to phonetic context-determined changes in K2 factor values. The results reported here, therefore, provide further evidence for age- and sex-linked differences in the patterns of development and maturation of the vocal apparatus.

Adult↗

PubMed1997

Electrophysiological correlates of categorical phoneme perception in adults.

Event-related potentials, recorded through a 128-electrode net, were used to study phonemic processing in the human auditory system. Within a stream of identical syllables, acoustic deviants were introduced that either crossed a phonetic boundary or remained within the same category. Two phonetic boundaries were explored, one present and the other absent in the subjects' native language. A large mismatch negativity was induced by native phonetic deviants, but not by non-native or within-category deviants. We suggest that a language-specific phonemic code has a separate neural representation in sensory memory and can serve as the basis for auditory mismatch detection. The subjects' inability to discriminate non-native phonetic contrasts does not seem related to a late attentional filter, but rather to a genuine loss of auditory discrimination abilities.

Adult↗

PubMed1995

Comparison of two multichannel tactile devices as supplements to speechreading in a postlingually deafened adult.

OBJECTIVE: The purpose of this study was to conduct a single-subject comparison of the effectiveness of two multichannel vibrotactile devices that encode different classes of speech information. One device, the Portapitch, is designed to convey fundamental frequency (F0) and its variation over time. The other, the TACTAID 7, is designed to convey the first two formant frequencies (F1 and F2) and their variation over time. DESIGN: The subject, a postlingually deafened adult, underwent an intensive 17-wk training and testing protocol with the Portapitch and then completed a similar 17-wk protocol with the TACTAID 7. Performance measures were obtained on phonetic-contrast perception by speechreading alone, tactile device alone, and speechreading plus tactile device, and on open-set word and sentence recognition by speechreading alone and speechreading plus tactile device. RESULTS: On phonetic-contrast testing, the subject demonstrated some ability to perceive voicing, stress, and intonation contrasts using the Portapitch, but gave little evidence of phonetic-contrast perception with the TACTAID 7. On open-set word recognition testing, no significant improvements were seen with either device. On open-set sentence recognition testing, the subject showed a significant 9 percentage point enhancement effect using the Portapitch; the mean 5 percentage point enhancement effect provided by the TACTAID 7 was not statistically significant. CONCLUSIONS: A small advantage was seen in favor of the tactile display of F0 relative to the tactile display of formant frequency information on both phonetic-contrast testing and open-set sentence recognition. The difference, however, was of questionable significance and could have been confounded with an order effect. Nevertheless, the subject's preference was for the tactile formant frequency display.

Adult↗

PubMed2001

Vowel formant discrimination II: Effects of stimulus uncertainty, consonantal context, and training.

This study is one in a series that has examined factors contributing to vowel perception in everyday listening. Four experimental variables have been manipulated to examine systematical differences between optimal laboratory testing conditions and those characterizing everyday listening. These include length of phonetic context, level of stimulus uncertainty, linguistic meaning, and amount of subject training. The present study investigated the effects of stimulus uncertainty from minimal to high uncertainty in two phonetic contexts, /V/ or /bVd/, when listeners had either little or extensive training. Thresholds for discriminating a small change in a formant for synthetic female vowels /I,E,ae,a,inverted v,o/ were obtained using adaptive tracking procedures. Experiment I optimized extensive training for five listeners by beginning under minimal uncertainty (only one formant tested per block) and then increasing uncertainty from 8-to-16-to-22 formants per block. Effects of higher uncertainty were less than expected; performance only decreased by about 30%. Thresholds for CVCs were 25% poorer than for isolated vowels. A previous study using similar stimuli [Kewley-Port and Zheng. J. Acoust. Soc. Am. 106, 2945-2958 (1999)] determined that the ability to discriminate formants was degraded by longer phonetic context. A comparison of those results with the present ones indicates that longer phonetic context degrades formant frequency discrimination more than higher levels of stimulus uncertainty. In experiment 2, performance in the 22-formant condition was tracked over 1 h for 37 typical listeners without formal laboratory training. Performance for typical listeners was initially about 230% worse than for trained listeners. Individual listeners' performance ranged widely with some listeners occasionally achieving performance similar to that of the trained listeners in just one hour.

Adult↗

PubMed2005

Prosodic strengthening and featural enhancement: evidence from acoustic and articulatory realizations of /a,i/ in English.

In this study the effects of accent and prosodic boundaries on the production of English vowels (/a,i/), by concurrently examining acoustic vowel formants and articulatory maxima of the tongue, jaw, and lips obtained with EMA (Electromagnetic Articulography) are investigated. The results demonstrate that prosodic strengthening (due to accent and/or prosodic boundaries) has differential effects depending on the source of prominence (in accented syllables versus at edges of prosodic domains; domain initially versus domain finally). The results are interpreted in terms of how the prosodic strengthening is related to phonetic realization of vowel features. For example, when accented, /i/ was fronter in both acoustic and articulatory vowel spaces (enhancing [-back]), accompanied by an increase in both lip and jaw openings (enhancing sonority). By contrast, at edges of prosodic domains (especially domain-finally), /i/ was not necessarily fronter, but higher (enhancing [+high]), accompanied by an increase only in the lip (not jaw) opening. This suggests that the two aspects of prosodic structure (accent versus boundary) are differentiated by distinct phonetic patterns. Further, it implies that prosodic strengthening, though manifested in fine-grained phonetic details, is not simply a low-level phonetic event but a complex linguistic phenomenon, closely linked to the enhancement of phonological features and positional strength that may license phonological contrasts.

Adult↗