Identification of vowels in “vowelless” syllables by 3-year-olds

The ability of 3-year-old children to perceive the identity of vowels in full-vowel and silentcenter, consonant-vowel-consonant (CVC) syllables was investigated using a two-alternative pointing procedure. Silence replaced the middle 10%, 35%, 65%, or 90% of the steady-state formants of synthetic “bad” and “bud” syllables. Identification of the two full-vowel syllables was 87% correct, whereas performance for the silent-center syllables was somewhat lower (72%, 70%, 67%, and 66% correct for the 10%, 35%, 65%, and 90% deletion stimuli, respectively). The performance of individual children fell into two subgroups: (1) those who performed like adults by maintaining correct vowel identification for all of the silent-center syllables, and (2) those who identified the full-vowel syllables correctly but performed at chance for all of the silent-center syllables. Three additional experiments showed that none of the children performed poorly when noise replaced the gap in the silent-center syllables. These results demonstrate that many 3-year-olds can identify vowels correctly in CVC syllables in the absence of the full spectral properties of steady-state formants.     

The relation between discriminability and memory for vowels,consonants, and silent-center vowels

People remember lists of vowel-contrasting syllables better than lists that vary only in stop consonant identity. Most views suggest that this difference is due to the structure of immediate memory and the greater discriminability of vowels compared with consonants. In all of these views, there is a presumed systematic relationship between discriminability and recall so that the more discriminable an item, the better that item should be recalled. The 11 experiments reported here measured the relative discriminability of and compared serial recall for (1) intact syllables that varied only in the medial vowel, (2) intact syllables that varied only in the initial consonant, and (3) syllables with the center vowel replaced by silence (so-called silent-center vowels). When item discriminability, as measured by identification, was equated for consonant-contrasting and silent-center lists, serial recall performance was also equal. However, even when the vowels were less discriminable than the consonants or silentcenter vowels, serial recall performance for the vowels was still better. These results are problematic for theories based on acoustic discriminability but can be explained parsimoniously by Nairne’s (1990) feature model.     

Perception of dynamic information for vowels in syllable onsets and offsets.

It has been demonstrated using the "silent-center" (SC) syllable paradigm that there is sufficient information in syllable onsets and offsets, taken together, to support accurate identification of vowels spoken in both citation-form syllables and syllables spoken in sentence context. Using edited natural speech stimuli, the present study examined the identification of American English vowels when increasing amounts of syllable onsets alone or syllable offsets alone were presented in their original sentence context. The stimuli were /d/-vowel-/d/ syllables spoken in a short carrier sentence by a male speaker. Listeners attempted to identify the vowels in experimental conditions that differed in the number of pitch periods presented and whether the pitch periods were from syllable onsets or syllable offsets. In general, syllable onsets were more informative than syllable offsets, although neither onsets nor offsets alone specified vowel identity as well as onsets and offsets together (SC syllables). Vowels differed widely in ease of identification; the diphthongized long vowels /e/, /ae/, /o/ were especially difficult to identify from syllable offsets. Identification of vowels as "front" or "back" was accurate, even from short samples of the syllable; however, vowel "height" was quite difficult to determine, again, especially from syllable offsets. The results emphasize the perceptual importance of time-varying acoustic parameters, which are the direct consequence of the articulatory dynamics involved in producing syllables.     

Developmental differences in short-lived auditory memory for various classes of speech sounds

Spoken serial recall by second-grade children of aurally presented lists of digits, synthetic stop consonants, and synthetic vowels showed a significant suffix effect (selective debilitation of recall at the final position under the stimulus suffix condition) only for the lists of digits and not for either consonants or vowels. Making the synthetic syllables more distinctive by simultaneously covarying the consonant and vowel failed to produce a suffix effect under a strict scoring criterion which required both consonant and vowel to be recalled correctly; however, when subjects were given credit for partially correct answers the suffix effect emerged. Adults given the redundant consonant-vowel syllables showed a significant suffix effect with the strict scoring criterion. However, when consonants and vowels varied orthogonally, the adults' performance showed the suffix effect only under the lenient scoring criterion. An argument is made for equivalence of basic memorial processing between children and adults, the difference being in the number of features needed to disambiguate the target items and in the ability to integrate these features to exploit interstimulus redundancy.     

Perception of dynamic information for vowels in syllable onsets and offsets

It has been demonstrated using the “silent-center” (SC) syllable paradigm that there is sufficient information in syllable onsets and offsets,taken together, to support accurate identification of vowels spoken in both citation-form syllables and syllables spoken in sentence context. Using edited natural speech stimuli, the present study examined the identification of American English vowels when increasing amounts of syllable onsetsalone or syllable offsetsalone were presented in their original sentence context. The stimuli were /d/-vowel-/d/ syllables spoken in a short carrier sentence by a male speaker. Listeners attempted to identify the vowels in experimental conditions that differed in the number of pitch periods presented and whether the pitch periods were from syllable onsets or syllable off-sets. In general, syllable onsets were more informative than syllable offsets, although neither onsets nor offsets alone specified vowel identity as well as onsets and offsets together (SC syllables). Vowels differed widely in ease of identification; the diphthongized long vowels /e/, /ae/, /o/ were especially difficult to identify from syllable offsets. Identification of vowels as “front” or “back” was accurate, even from short samples of the syllable; however, vowel "height" was quite difficult to determine, again, especially from syllable offsets. The results emphasize the perceptual importance of time-varying acoustic parameters, which are the direct consequence of the articulatory dynamics involved in producing syllables.     

Impairment of auditory perception and language comprehension in dysphasia

Men with chronic focal brain wounds were examined for their ability to discriminate complex tones, synthesized steady-state vowels, and synthesized consonant—vowel syllables. Subjects with left hemisphere damage, but not right hemisphere damage, were impaired in their ability to respond correctly to rapidly changing acoustic stimuli, regardless of whether stimuli were verbal or nonverbal. The degree of impairment in auditory processing correlated highly with the degree of language comprehension impairment. The pattern of impairment of the group with left hemisphere damage on these perceptual tests was similar to that found in children with developmental language disorders.     

Nonword repetition stimuli for Vietnamese-speaking children

Nonword repetition (NWR) has been a widely used measure of language-learning ability in children with and without language disorders. Although NWR tasks have been created for a variety of languages, minimal attention has been given to Asian tonal languages. This study introduces a new set of NWR stimuli for Vietnamese. The stimuli include 20 items ranging in length from one to four syllables. The items consist of dialect-neutral phonemes in consonant–vowel (CV) and CVC sequences that follow the phonotactic constraints of the language. They were rated high on wordlikeness and have comparable position segments and biphone probabilities across stimulus lengths. We validated the stimuli with a sample of 59 typically developing Vietnamese–English bilingual children, ages 5 to 8. The stimuli exhibited the expected age and length effects commonly found in NWR tasks: Older children performed better on the task than younger children, and longer items were more difficult to repeat than shorter items. We also compared different scoring systems in order to examine the individual phoneme types (consonants, vowels, and tones) and composite scores (proportions of phonemes correct, with and without tone). The study demonstrates careful construction and validation of the stimuli, and future directions are discussed.     

Zebra finches and Dutch adults exhibit the same cue weighting bias in vowel perception

Vocal tract resonances, called formants, are the most important parameters in human speech production and perception. They encode linguistic meaning and have been shown to be perceived by a wide range of species. Songbirds are also sensitive to different formant patterns in human speech. They can categorize words differing only in their vowels based on the formant patterns independent of speaker identity in a way comparable to humans. These results indicate that speech perception mechanisms are more similar between songbirds and humans than realized before. One of the major questions regarding formant perception concerns the weighting of different formants in the speech signal (“acoustic cue weighting”) and whether this process is unique to humans. Using an operant Go/NoGo design, we trained zebra finches to discriminate syllables, whose vowels differed in their first three formants. When subsequently tested with novel vowels, similar in either their first formant or their second and third formants to the familiar vowels, similarity in the higher formants was weighted much more strongly than similarity in the lower formant. Thus, zebra finches indeed exhibit a cue weighting bias. Interestingly, we also found that Dutch speakers when tested with the same paradigm exhibit the same cue weighting bias. This, together with earlier findings, supports the hypothesis that human speech evolution might have exploited general properties of the vertebrate auditory system.     

Identification of vowels in “vowelless” syllables

Traditionally, it has been held that the primary information for vowel identification is provided by formant frequencies in the quasi-steady-state portion of the spoken syllable. Recent search has advanced an alternative view that emphasizes the role of temporal factors and dynamic (time-varying) spectral information in determining the perception of vowels. Nine vowels spoken in /b/ + vowel + /b/ syllables were recorded. The syllables were modified electronically in several ways to suppress various sources of spectral and durational information. Two vowel-perception experiments were performed, testing subjects’ ability to identify vowels in these modified syllables. Results of both experiments revealed the importance of dynamic spectral information at syllable onset and offset (in its proper temporal relation) in permitting vowel identification. On the other hand, steady-state spectral information, deprived of its durational variation, was a poor basis for identification. Results constitute a challenge to traditional accounts of vowel perception and point toward important sources of dynamic information.     

Minimal spectral contrast of formant peaks for vowel recognition as a function of spectral slope

In four experiments we investigated whether listeners can locate the formants of vowels not only from peaks, but also from spectral “shoulders”—features that give rise to zero crossings in the third, but not the first, differential of the excitation pattern—as hypothesized by Assmann and Summerfield (1989). Stimuli were steady-state approximations to the vowels [a, i, з, u, ?] created by summing the first 45 harmonics of a fundamental of 100 Hz. Thirty-nine harmonics had equal amplitudes; the other 6 formed three pairs that were raised in level to define three “formants.” An adaptive psychophysical procedure determined the minimal difference in level between the 6 harmonics and the remaining 39 at which the vowels were identifiably different from one another. These thresholds were measured through simulated communication channels, giving overall slopes to the excitation patterns of the five vowels that ranged from ?1 dB/erb to +2 dB/erb. Excitation patterns of the threshold stimuli were computed, and the locations of formants were estimated from zero crossings in the first and third differentials. With the more steeply sloping communication channels, some formants of some vowels were represented as shoulders rather than peaks, confirming the predictions of Assmann and Summerfield’s models. We discuss the limitations of the excitation pattern model and the related issue of whether the location of formants can be computed from spectral shoulders in auditory analysis.     

Identification of consonants and vowels presented to left and right ears

The results of earlier studies by several authors suggest that speech and nonspeech auditory patterns are processed primarily in different places in the brain and perhaps by different modes. The question arises in studies of speech perception whether all phonetic elements or all features of phonetic elements are processed in the same way. The technique of dichotic presentation was used to examine this question.

The present study compared identifications of dichotically presented pairs of synthetic CV syllables and pairs of steady-state vowels. The results show a significant right-ear advantage for CV syllables but not for steady-state vowels. Evidence for analysis by feature in the perception of consonants is discussed.     

Single formant contrast in vowel identification

Subjects rated ambiguous steady-state vowels from a continuum with respect to the categories/i/ and /I/ (Experiment 1) or/ε/ and/ae/ (Experiment 2). Each target was preceded, .35 sec earlier, by one of the following precursors: (1) one endpoint from the target continuum, (2) the other endpoint, (3) the isolated first formant (F1) from (1), (4) the isolated F1 from (2), or (5), a hissing noise. Although (3) and (4) did not sound like they came from the target continuum, they produced reliable contrast in both experiments. In the /i/-/I/ experiment, contrast was as powerful from single formants as from the full vowels. These results suggest a sensory, rather than a judgmental, basis for the vowel contrast effects obtained.     

Differential vowel duration associated with children's word-final fricative deletion.

This study assessed whether 3 children, 5 to 6 years old, who deleted word-final fricatives preserve the voicing contrast for those fricatives by producing dif ferential duration of the preceding vowel. The children's CV syllable productions were compared to their CV(C) syllable productions in which the final consonant was intended but actually deleted. Analysis indicated that all 3 children exhibited significantly longer vowel duration, in CV syllables than in CV(C) syllables. This differential duration of the preceding vowel was shown in both isolation and carrier phrase conditions. Of the 3 children 2 preserved the voicing contrast by showing significantly longer vowels preceding voiced consonants as compared to voiceless consonants. One child did this in both isolation and carrier phrase conditions and the other child did this in isolation only. All 3 children manipulated vowel duration to signify the linguis tic contrast, therefore these findings support a linguistic perspective of speech development which focuses on the acquisition and knowledge of the linguistic rules of the language. In addition, the large amount of variability in vowel duration for CV and CV(C) syllables and the marked variability in performance across children support a biological view of a developing vocal tract undergoing structural and physiological changes.     

Perception of place-of-articulation information in natural speech by monkeys versus humans

Four monkeys and 6 humans representing five different native languages were compared in the ability to categorize natural CV tokens of /b/ versus /d/ produced by 4 talkers of American English (2 male, 2 female) in four vowel contexts (/i, e, a, u/). A two-choice "left/right" procedure was used in which both percentage correct and response time data were compared between species. Both measures indicated striking context effects for monkeys, in that they performed better for the back vowels /a/ and /u/ than for the front vowels /i/ and /e/. Humans showed no context effects for the percentage correct measure, but their response times showed an enhancement for the /i/ vowel, in contrast with monkeys. Results suggest that monkey perception of place of articulation is more dependent than human perception on the direction of the F2 onset transitions of syllables, since back-vowel F2s differentiate /b/ and /d/ more distinctively. Although monkeys do not provide an accurate model of the adult human in place perception, they may be able to model the preverbal human infant before it learns a more speech-specific strategy of place information extraction.     

Effect of consonant/vowel letter organisation on the syllable counting task: evidence from English

Recent studies in alphabetic writing systems have investigated whether the status of letters as consonants or vowels influences the perception and processing of written words. Here, we examined to what extent the organisation of consonants and vowels within words affects performance in a syllable counting task in English. Participants were asked to judge the number of syllables in written words that were matched for the number of spoken syllables but comprised either 1 orthographic vowel cluster less than the number of syllables (hiatus words, e.g., triumph) or as many vowel clusters as syllables (e.g., pudding). In 3 experiments, we found that readers were slower and less accurate on hiatus than control words, even when phonological complexity (Experiment 1), number of reduced vowels (Experiment 2), and number of letters (Experiment 3) were taken into account. Interestingly, for words with or without the same number of vowel clusters and syllables, participants’ errors were more likely to underestimate the number of syllables than to overestimate it. Results are discussed in a cross-linguistic perspective.     

Seating position and length of utterance of preschoolers with cerebral palsy

This study investigated the effects of semireclining and upright positions on production of utterances of increasing length by 10 physically typical preschoolers and 10 children with cerebral palsy. Sentences of 3, 7, and 10 syllables were imitated on one breath using the Respitrace to gather kinematic data of chest wall use. Analysis indicated that the reclining position led to 83% productions on one breath, while 95% could be produced on one breath in the upright position. During the longer 7- and 10-syllable utterances, children with cerebral palsy successfully imitated 48% and 18% of these utterances, while the control group performed 83% and 35% correctly for the 7- and 10-syllable tasks, respectively.     

Auditory and phonetic processes in speech perception: Evidence from a dichotic study

The distinction between auditory and phonetic processes in speech perception was used in the design and analysis of an experiment. Earlier studies had shown that dichotically presented stop consonants are more often identified correctly when they share place of production (e.g., /ba-pa/) or voicing (e.g., /ba-da/) than when neither feature is shared (e.g., /ba-ta/). The present experiment was intended to determine whether the effect has an auditory or a phonetic basis. Increments in performance due to feature-sharing were compared for synthetic stop-vowel syllables in which formant transitions were the sole cues to place of production under two experimental conditions: (1) when the vowel was the same for both syllables in a dichotic pair, as in our earlier studies, and (2) when the vowels differed. Since the increment in performance due to sharing place was not diminished when vowels differed (i.e., when formant transitions did not coincide), it was concluded that the effect has a phonetic rather than an auditory basis. Right ear advantages were also measured and were found to interact with both place of production and vowel conditions. Taken together, the two sets of results suggest that inhibition of the ipsilateral signal in the perception of dichotically presented speech occurs during phonetic analysis.     

Coherence masking protection in speech sounds: The role of formant synchrony

Three experiments were performed to examine listeners’ thresholds for identifying stimuli whose spectra were modeled after the vowels /i/ and /ε/, with the differences between these stimuli restricted to the frequency of the first formant. The stimuli were presented in a low-pass masking noise that spectrally overlapped the first formant but not the higher formants. Identification thresholds were lower when the higher formants were present than when they were not, even though the first formant contained the only distinctive information for stimulus identification. This indicates that listeners were more sensitive in identifying the first formant energy through its contribution to the vowel than as an independent percept; this effect is given the namecoherence masking protection. The first experiment showed this effect for synthetic vowels in which the distinctive first formant was supported by a series of harmonics that progressed through the higher formants. In the second two experiments, the harmonics in the first formant region were removed, and the first formant was simulated by a narrow band of noise. This was done so that harmonic relations did not provide a basis for grouping the lower formant with the higher formants; coherence masking protection was still observed. However, when the temporal alignment of the onsets and offsets of the higher and lower formants was disrupted, the effect was eliminated, although the stimuli were still perceived as vowels. These results are interpreted as indicating that general principles of auditory grouping that can exploit regularities in temporal patterns cause acoustic energy belonging to a coherent speech sound to stand out in the auditory scene.     

When do children overestimate their knowledge of unfamiliar targets?

We report four investigations in which 5 to 7 year olds judged whether or not they knew familiar- and unfamiliar-named targets. Under some conditions judgments were made in relation to performance on a relevant task, e.g., children judged whether they knew the picture they had picked from a set was the target. Under other conditions, children judged their state of knowledge not in relation to performance, e.g., they answered "Do you know who (target) is?" Under both types of condition, children nearly always made correct "know" judgments when targets were familiar. Correct "don't know" judgments about unfamiliar targets were relatively common when judgments were not made in relation to performance on a task (average scores 80-90% correct), but were less frequent when knowledge was judged in relation to performance on a task (average scores 40-70% correct). Knowledge judged in relation to performance was overestimated even when children did not choose the picture they thought might be the target before making their judgment, when the pictures were face-down, and when children predicted performance on a task not yet present. It seems that although children can make relatively accurate judgments of their own knowledge states, they tend to overestimate their competence when assessing their knowledge in relation to performance on a task. We discuss why this might be.     

Helping children correctly say "I don't know" to unanswerable questions

Adults ask children questions in a variety of contexts, for example, in the classroom, in the forensic context, or in experimental research. In such situations children will inevitably be asked some questions to which they do not know the answer, because they do not have the required information ("unanswerable" questions). When asked unanswerable questions, it is important that children indicate that they do not have the required information to provide an answer. These 2 studies investigated whether preinterview instructions (Experiment 1) or establishing a memory narrative (Experiment 2) helped children correctly indicate a lack of knowledge to unanswerable questions. In both studies, 6- and 8-year-olds participated in a classroom-based event about which they were subsequently interviewed. Some of the questions were answerable, and some were unanswerable. Results showed that preinterview instructions increased the number of younger children's appropriate "don't know" responses to unanswerable questions, without decreasing correct responses to answerable questions. This suggests that demand characteristics affect children's tendency correctly to say "I don't know." The opportunity to provide a narrative account increased children's appropriate "don't know" responses to unanswerable yes/no questions, and increased the number of younger children's correct responses to answerable questions. This suggests that cognitive factors also contribute to children's tendency correctly to say "I don't know." These results have implications for any context where adults need to obtain information from children through questioning, for example, a health practitioner asking about a medical condition, in classroom discourse, in the investigative interview, and in developmental psychology research.