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PubMed1996

Limits on phonetic integration in duplex perception.

The telling fact about duplex perception is that listeners integrate into a unitary phonetic percept signals that are coherent from a phonetic point of view, even though the signals are, on purely auditory grounds, separate sources. Here we explore the limits on the integration of a sinusoidal consonant cue (the F3 transition for [da] vs. [ga]) with the resonances of the remainder of the syllable. Perceiving duplexly, listeners hear the whistle of the sinusoid, but also the [da] and [ga] for which the sinusoid provides the critical information. In the first experiment, phonetic integration was significantly reduced, but not to zero, by a precursor that extended the transition cue forward in time so that it started 50 msec before the cue. The effect was the same above and below the duplexity threshold (the intensity of sinusoid in the combined pattern at which the whistle was just barely audible). In the second experiment, integration was reduced once again by the precursor, and also, but only below the duplexity threshold, by harmonics of the cues that were simultaneous with it. The third experiment showed that the simultaneous harmonics reduced phonetic integration only by serving as distractors while also permitting the conclusion that the precursor produced its effects by making the cue part of a coherent and competing auditory pattern, and so "capturing" it. The fourth experiment supported this interpretation by showing that for some subjects the amount of capture was reduced when the capturing tone was itself captured by being made part of a tonal complex. The results support the assumption that the independent phonetic system will integrate across disparate sources according to the cohesive power of that system as measured against the evidence for separate sources.

Adult↗
PubMed1989

Effect of speaking rate on the perceptual structure of a phonetic category.

When listeners process temporal properties of speech that convey information about the phonetic segments of the language, they do so in a rate-dependent manner. This is seen as a shift in the location of the phonetic category boundary along a temporal continuum toward longer values of the acoustic property in question, as speech is slowed. In a series of experiments, we found that the adjustment for rate is not confined to the region of the category boundary, but extends throughout the phonetic category. Specifically, a change in rate modified the range of stimuli identified as members of a phonetic category, as well as which stimuli were overtly judged to be good exemplars of the category. These findings suggest that the listener's adjustment for speaking rate entails a comprehensive perceptual remapping between acoustic signal and phonetic structure.

Adult↗
PubMed1975

Auditory and phonetic levels of processing in speech perception: neurophysiological and information-processing analyses.

Two new experimental operations were used to distinguish between auditory and phonetic levels of processing in speech perception: the first based on reaction time data in speeded classification tasks with synthetic speech stimuli, and the second based on average evoked potentials recorded concurrently in the same tasks. Each of four experiments compared the processing of two different dimensions of the same synthetic consonant-vowel syllables. When a phonetic dimensions was compared to an auditory dimension, different patterns of results were obtained in both the reaction time and evoked potential data. No such differences were obtained for isolated acoustic components of the phonetic dimension or for two purely auditory dimensions. Together with other recent evidence, the present results constitute additional converging operations on the distinction between auditory and phonetic processes in speech perception and on the idea that phonetic processing involves mechanisms that are lateralized in one cerebral hemisphere.

Acoustic Stimulation↗
PubMed1994

The role of lexical status on the phonetic categorization of speech in aphasia.

Recent results with normal subjects have shown that the locus of the phonetic boundary of a speech continuum may change as a function of the word/nonword status of the endpoint stimuli. This so-called lexical effect in phonetic categorization has been used as evidence for the role of top-down processing in speech perception. This study investigated whether aphasic patients show a similar influence of lexical status on phonetic categorization. Two test continua were created varying in voice-onset time: in one continuum, the two endpoint stimuli were word/nonword, i.e., "duke"--"tuke," and in the other continuum, they were nonword/word, i.e., "doot"--"toot." Twelve aphasic patients were tested including 6 Broca's aphasics and 6 Wernicke/Conduction aphasics. The subject's task was to determine whether the first sound of the stimulus was a "d" or "t." Broca's aphasics showed a large lexical effect, with the magnitude of the effect being greater than that for normals. These results suggest that the Broca's aphasics place a heavier reliance on a heuristic strategy than on the perceptual information embedded in the test stimuli in making a phonetic categorization. In contrast, Wernicke/Conduction aphasics did not show a lexical effect, suggesting that these patients are less likely than either normals or Broca's aphasics to use heuristic strategies in lexical processing. The overall results are considered in relation to current views on language-processing deficits in aphasia.

Adult↗
PubMed1999

The influence of neighborhood density on phonetic categorization in aphasia.

The present study examined the contribution of lexically based sources of information to acoustic-phonetic processing in fluent and nonfluent aphasic subjects and age-matched normals. To this end, two phonetic identification experiments were conducted which required subjects to label syllable-initial bilabial stop consonants varying along a VOT continuum as either /b/ or /p/. Factors that were controlled included the lexical status (word/nonword) and neighborhood density values corresponding to the two possible syllable interpretations in each set of stimuli. Findings indicated that all subject groups were influenced by both lexical status and neighborhood density in making phonetic categorizations. Results are discussed with respect to theories of acoustic-phonetic perception and lexical access in normal and aphasic populations.

Adult↗
PubMedDate not supplied

On the internal structure of phonetic categories: a progress report.

There is growing evidence that phonetic categories have a rich internal structure, with category members varying systematically in category goodness. Our recent findings on this issue, which are summarized in this paper, underscore the existence and robustness of this structure and indicate further that the mapping between acoustic signal and internal category structure is complex: just as in the case of category boundaries, the best exemplars of a given category are highly dependent on acoustic-phonetic context and are specified by multiple properties of the speech signal. These findings suggest that the listener's representation of phonetic form preserves not only categorical information, but also fine-grained information about the detailed acoustic-phonetic characteristics of the language.

Attention↗
PubMed2005

Process dissociation of sight vocabulary and phonetic decoding in reading: a new perspective on surface and phonological dyslexias.

Recent research on developmental dyslexia has suggested a phonological core deficit hypothesis (e.g., Manis, Seidenberg, Doi, McBride-Chang, & Peterson, 1996; Stanovich, Siegel, & Gottardo, 1997) whereby pure cases of developmental phonological dyslexia (dysfunctional phonetic decoding processing but normal sight vocabulary processing) can exist, but pure cases of developmental surface dyslexia (dysfunctional sight vocabulary processing but normal phonetic decoding processing) should not. By applying Jacoby's (1991) and Lindsay and Jacoby's (1994) process dissociation procedure to the reading of regular and exception words, we present a method that serves to estimate readers' reliance on sight vocabulary and phonetic decoding during real word recognition. These reliance estimates are then used in Castles and Coltheart's (1993) regression-based approach to identify normal readers and developmental dyslexics. This new method: (1) allows one to explore normal reading acquisition and both the delay and deviance accounts of developmental dyslexia, (2) provides an alternative to matching dyslexics to both chronological-age and reading-age control groups, and (3) uses only real words. We present evidence that pure cases of developmental surface dyslexia can be obtained with both Castles and Coltheart's measure as well as our own, and that developmental surface dyslexia is not simply a delayed reading deficit. The theoretical importance and utility of estimates of reliance on sight vocabulary and phonetic decoding is discussed.

Child↗
PubMed1989

Lexical effects on the phonetic categorization of speech: the role of acoustic structure.

This study examines the extent to which acoustic parameters contribute to lexical effects on the phonetic categorization of speech. Experiment 1 was designed to replicate previous findings. Two test continua were created varying in voice onset time. Results of both identification and reaction time (RT) range data showed an effect of lexical status at the phonetic boundary, but only in the slowest RT ranges, suggesting that lexical effects on phonetic categorization are postperceptual. Experiment 2 explored whether the lexical effect would emerge when the stimulus continua more nearly approximated the parameter values of natural speech. Both identification and RT range data indicated that the lexical effect disappeared. These results suggest that without attention to the acoustic structure of the stimuli, the role of top-down processing in phonetic categorization may be overemphasized.

Adult↗
PubMed1980

Some effects of acoustic attributes of speech on the processing of phonetic feature information.

How do acoustic attributes of the speech signal contribute to feature-processing interactions that occur in phonetic classification? In a series of five experiments addressed to this question, listeners performed speeded classification tasks that explicitly required a phonetic decision for each response. Stimuli were natural consonant-vowel syllables differing by multiple phonetic features, although classification responses were based on a single target feature. In control tasks, no variations in nontarget features occurred, whereas in orthogonal tasks nonrelevant feature variations occurred but had to be ignored. Comparison of classification times demonstrated that feature information may either be processed separately as independent cues for each feature or as a single integral segment that jointly specifies several features. The observed form on processing depended on the acoustic manifestations of feature variation in the signal. Stop-consonant place of articulation and voicing cues, conveyed independently by the pattern and excitation source of the initial formant transitions, may be processed separately. However, information for consonant place of articulation and vowel quality, features that interactively affect the shape of initial formant transitions, are processed as an integral segment. Articulatory correlates of each type of processing are discussed in terms of the distinction between source features that vary discretely in speech production and resonance features that can change smoothly and continuously. Implications for perceptual models that include initial segmentation of an input utterance into a phonetic feature representation are also considered.

Female↗
PubMed2006

The effects of distributional learning on rats' sensitivity to phonetic information.

During the first year of life, infants show decreased sensitivity to phonetic differences not used in their native language and increased sensitivity to the differences that are used. It has been shown that this change in speech perception is a function of the distributional properties of the input. The present study explores whether the mechanism responsible for the developmental changes regarding the organization of phonetic categories is a general mechanism shared with other animals. The results demonstrate that the distributional exposure to a phonetic continuum affects the subsequent discrimination of these phonemes in rats, indicating that the ability to use distributional cues to change the phonetic category structure extends beyond humans.

Animals↗
PubMed2002

Articulatory control of vowel length for contiguous jaw cycles: the effects of speaking rate and phonetic context.

The current study examined contiguous cycles of jaw movement in order to determine if select suprasegmental manipulations operate globally across the entire utterance, while phonetic changes are more locally administered. Specifically, articulatory kinematics were examined to determine if intra- and inter-articulatory spatial and temporal organization across manipulations of speaking rate was maintained for both jaw cycles while differing between the two cycles for phonetic changes (i.e., in coda composition) specific to the second jaw cycle. Five normal speakers repeated the syllables /paep/, /paeps/, and /paepst/, embedded in the carrier phrase, "Now say again," using slow, normal, and fast speaking rates. Measures were made of the magnitude of jaw opening peak velocity and time to peak velocity, as well as of coarticulatory overlap and interarticulator timing, for the first jaw cycle (jaw lowering for /eI/ in "say" to the first /p/) and the second jaw cycle (jaw lowering for /ae/ to the second /p/). The current data indicate that, for intra-articulatory kinematics, the manipulation of phonetic context resulted in localized adjustments, whereas the manipulation of speaking rate was applied globally across the utterance. Conversely, for inter-articulatory kinematics, the upper lip-jaw synergy was reconfigured across the utterance for manipulations of speaking rate, whereas this synergy was maintained for localized manipulations in phonetic context. Results are discussed with respect to motor strategies being flexibly implemented as a result of contextual variation and speech rate.

Adult↗
PubMed1990

Taxonomies in biology, phonetics, phonology, and speech motor control.

This article begins with a review explaining the different purposes of biological taxonomies. Taxonomic units are often dependent on the purpose for which the taxonomy has been constructed. Biological taxonomies provide an analogy that we use to emphasize some of the distinctions among the units of phonetic transcription systems, competence phonologies, and performance phonologies. The units of both phonology and phonetic transcription are considered as possible units of the speech motor system, and some of the difficulties of this assumption are explained. Although phonemic units, like units of phonetic transcription, are useful for many purposes, it is not theoretically necessary to use units derived as part of competence phonologies in systems attempting to explain phonological performance or speech motor performance. In this regard, we challenge the concept of coarticulation, because it is based on assumptions about the role of phonological or phonetic units in speech motor control. We offer an integrated perspective that has implications for research in speech motor control and deficits of the speech motor system. We see speech motor deficits as distinct from, yet possibly interacting with, phonological deficits.

Humans↗
PubMed1996

Phonetic profiles of toddlers with specific expressive language impairment (SLI-E).

Spontaneous language samples of 30 24-month-old toddlers diagnosed with Specific Expressive Language Impairment (SLI-E) were compared with samples produced by an age-matched group of 30 typically developing toddlers. Vocalization patterns, phonetic inventories, and syllable formation patterns were compared. Toddlers with SLI-E vocalized significantly less often than their typically developing peers, had proportionately smaller consonantal and vowel inventories, and used a more restricted and less mature array of syllable shapes. Although the mean incidence of phoneme usage varied significantly in all comparisons, profiles of consonant usage were similar between the two groups for initial phoneme usage, but considerably different for final consonant closure. Such patterns of vocal and phonetic behavior confirm earlier reports of phonetic delay in SLI-E, and suggest that nongrammatical factors contribute to the development of expressive language deficits in toddlers. We further propose a bidirectional model for the expressive deficits in SLI-E, in which the child's limited phonetic capacity interacts with propensities in caretaker interaction to further reduce opportunities for expressive language learning and practice.

Child, Preschool↗
PubMedDate not supplied

PET studies of phonetic processing of speech: review, replication, and reanalysis.

Positron emission tomography was used to investigate cerebral blood flow (CBF) changes associated with the processing of speech. In a first experiment, normal right-handed volunteers were scanned under two conditions that required phonetic processing (discrimination of final consonants and phoneme monitoring), and one baseline condition of passive listening. Analysis was carried out by paired-image subtraction, with MRI overlay for anatomical localization. Comparison of each phonetic condition with the baseline condition revealed increased CBF in the left frontal lobe, close to the border between Broca's area and the motor cortex, and in a left parietal region. A second experiment showed that this area was not activated by a semantic judgement task. Reanalysis of data from an earlier study, in which various baseline conditions were used, confirmed that this region of left frontal cortex is consistently involved in phonetic tasks. The findings support a model whereby articulatory processes involving a portion of Broca's area are important when phonetic segments must be extracted and manipulated, whereas left posterior temporal cortex is involved in perceptual analysis of speech.

Brain↗
PubMed2001

Challenging the notion of innate phonetic boundaries.

Numerous studies of infants' speech perception abilities have demonstrated that these young listeners have access to acoustic detail in the speech signal. Because these studies have used stimuli that could be described in terms of adult-defined phonetic categories, authors have concluded that infants innately recognize stimuli as members of these categories, as adults do. In fact, the predominant, current view of speech perception holds that infants are born with sensitivities for the universal set of phonetic boundaries, and that those boundaries supported by the ambient language are maintained, while those not supported by the ambient language dissolve. In this study, discrimination abilities of 46 infants and 75 3-year-olds were measured for several phonetic contrasts occurring in their native language, using natural and synthetic speech. The proportion of children who were able to discriminate any given contrast varied across contrasts, and no one contrast was discriminated by anything close to all of the children. While these results did not differ from those reported by others, the interpretation here is that we should reconsider the notion of innate phonetic categories and/or boundaries. Moreover, success rates did not differ for natural and synthetic speech, and so a minor conclusion was that children are not adversely affected by the use of synthetic stimuli in speech experiments.

Child, Preschool↗
PubMed2004

Acoustic-phonetic correlates of talker intelligibility for adults and children.

This study investigated acoustic-phonetic correlates of intelligibility for adult and child talkers, and whether the relative intelligibility of different talkers was dependent on listener characteristics. In experiment 1, word intelligibility was measured for 45 talkers (18 women, 15 men, 6 boys, 6 girls) from a homogeneous accent group. The material consisted of 124 words familiar to 7-year-olds that adequately covered all frequent consonant confusions; stimuli were presented to 135 adult and child listeners in low-level background noise. Seven-to-eight-year-old listeners made significantly more errors than 12-year-olds or adults, but the relative intelligibility of individual talkers was highly consistent across groups. In experiment 2, listener ratings on a number of voice dimensions were obtained for the adults talkers identified in experiment 1 as having the highest and lowest intelligibility. Intelligibility was significantly correlated with subjective dimensions reflecting articulation, voice dynamics, and general quality. Finally, in experiment 3, measures of fundamental frequency, long-term average spectrum, word duration, consonant-vowel intensity ratio, and vowel space size were obtained for all talkers. Overall, word intelligibility was significantly correlated with the total energy in the 1- to 3-kHz region and word duration; these measures predicted 61% of the variability in intelligibility. The fact that the relative intelligibility of individual talkers was remarkably consistent across listener age groups suggests that the acoustic-phonetic characteristics of a talker's utterance are the primary factor in determining talker intelligibility. Although some acoustic-phonetic correlates of intelligibility were identified, variability in the profiles of the "best" talkers suggests that high intelligibility can be achieved through a combination of different acoustic-phonetic characteristics.

Adolescent↗
PubMed1983

Enhanced discriminability at the phonetic boundaries for the place feature in macaques.

Discrimination of speech-sound pairs drawn from a computer-generated continuum in which syllables varied along the place of articulation phonetic feature (/b,d,g/) was tested with macaques. The acoustic feature that was varied along the two-formant 15-step continuum was the starting frequency of the second-formant transition. Discrimination of stimulus pairs separated by two steps was tested along the entire continuum in a same-different task. Results demonstrated that peaks in the discrimination functions occur for macaques at the "phonetic boundaries" which separate the /b-d/ and /d-g/ categories for human listeners. The data support two conclusions. First, although current theoretical accounts of place perception by human adults suggest that isolated second-formant transitions are "secondary" cues, learned by association with primary cues, the animal data are more compatible with the notion that second-formant transitions are sufficient to allow the appropriate partitioning of a place continuum in the absence of associative pairing with other more complex cues. Second, we discuss two potential roles played by audition in the evolution of the acoustics of language. One is that audition provided a set of "natural psychophysical boundaries," based on rather simple acoustic properties, which guided the selection of the phonetic repertoire but did not solely determine it; the other is that audition provided a set of rules for the formation of "natural classes" of sound and that phonetic units met those criteria. The data provided in this experiment provide support for the former. Experiments that could more clearly differentiate the two hypotheses are described.

Adult↗
PubMed1990

A new version of duplex perception: evidence for phonetic and nonphonetic fusion.

In a series of experiments, a variant of duplex perception was investigated. In its original form, duplex perception is created by presenting an isolated transition to one ear and the remainder of the syllable, the standard base, to the other ear. Listeners hear a chirp at the ear receiving the isolated transition, and a full syllable at the ear receiving the base. The new version of duplex perception was created by presenting a third-formant transition in isolation to one ear and the same transition electronically mixed with the base to the other ear; the modified base now has all the information necessary for syllabic perception. With the new procedure, listeners reported hearing a chirp centered in the middle of their head and a syllable in the ear presented the modified base that was clearer than that produced by the isolated transition and standard base. They could also reliably choose the patterns that contained the additional transition in the base when attending to either the phonetic or nonphonetic sides of the duplex percept. In addition, when the fundamental frequency, onset time, and intensity of the isolated third-formant transition were varied relative to the base, the phonetic and nonphonetic (lateralization) percepts were differentially affected, although not always reliably. In general, nonphonetic fusion was more affected by large differences in these variables than was phonetic fusion. However, when two isolated third-formant transitions were presented dichotically, fusion and the resulting central location of the chirp failed markedly with relatively small differences in each variable. The results were discussed in terms of the role of fusion in the new version of duplex perception and the nature of the information that undergoes both phonetic and nonphonetic fusion.

Adult↗