Motor mechanisms in speech ontogeny: phylogenetic, neurobiological and linguistic implications.

The rhythmic mandible-generated close-open alternations of the mouth, responsible for the series of consonant-vowel alternations characteristic of babbling and of languages, is receiving increased attention as a possible manifestation of an ontogenetic and phylogenetic 'frame' underlying the serial organization of speech. The supplementary motor area appears important for production of this consonant-vowel frame in adults.

Prosodic correlates of stress in babbling: an acoustical study.

Prelinguistic babbling often seems remarkably speech-like, not because it has recognizable words but because it seems to have adult-like prosody. To quantify this impression, we compared disyllabic sequences from five infants and five adults in terms of the use of frequency, intensity, and duration to mark stress. Significantly larger values for the three acoustic variables were observed on stressed than on unstressed syllables independent of syllable position for both groups. Adults showed the correlates of utterance final syllables--lower f0, lower intensity, and longer duration; infants showed only decrease in intensity. Ratios for stressed to unstressed syllables and participation of the three variables in stress production in individual disyllables were highly similar in both groups. No bias toward the English lexical trochaic stress pattern was observed. We conclude that infants in English environments produce adult-like stress patterns before they produce lexical items, which specify stress. Acoustic and perceptual analyses are used to explore stress marking by prelinguistic infants in an English language environment. Results show that infants employ the three acoustic correlates of stress in individual syllables in a manner largely similar to that of adult speakers, although they do not show second-syllable declination effects or an English language trochaic stress bias.

An embodiment perspective on the acquisition of speech perception.

Understanding the potential relationships between perception and production is crucial to explanation of the nature of early speech acquisition. The 'embodiment' perspective suggests that mental activity in general cannot be understood outside of the context of body activities. Indeed, universal motor factors seem to be more responsible for the distribution of early production preferences regarding consonant place and manner, and use of the vowel space than the often considerable cross-language differences in input available to the perceptual system. However, there is evidence for a perceptual basis to the establishment of a language-appropriate balance of oral-to-nasal output by the beginning of babbling, illustrating the necessary contribution of 'extrinsic' perceptual information to acquisition. In terms of representations, at least one assumption that segmental units underlying either perception or production in early phases of acquisition may be inappropriate. Our work on production has shown that the dominant early organizational structure is a relatively unitary open-close 'frame' produced by mandibular oscillation. Consideration of the role of 'intrinsic' (self-produced) perceptual information suggests that this frame may be an important basis for perceptual as well as production organization.

Deriving speech from nonspeech: a view from ontogeny.

A comparison of babbling and early speech, word patterns of languages, and, in one instance, a protolanguage corpus, reveals three basic movement patterns: (1) a 'Frame' provided by the cycles of mandibular oscillation underlying the basic mouth close-open alternation of speech; this Frame appears in relatively 'pure' form in the tendency for labial consonants to co-occur with central vowels; (2) two other intracyclical consonant-vowel (CV) co-occurrence patterns sharing the alternation: coronal consonants with front vowels and dorsal consonants with back vowels; (3) an intercyclical tendency towards a labial consonant-vowel-coronal consonant (LC) sequence preference for word initiation. The first two patterns were derived from oral movement capabilities which predated speech. The Frame (1) may have evolved from ingestive cyclicities (e.g. chewing). The intracyclical consonant-vowel (CV) co-occurrence patterns involving tongue position constraints common to consonants and vowels (2) may result from the basic biomechanical property of inertia. The third pattern (LC) was a self-organizational result of pressures for interfacing cognition with action - a result which must have numerous analogs in other domains of movement organization.

The motor core of speech: a comparison of serial organization patterns in infants and languages.

Comparison of serial organization of infant babbling and early speech with that of 10 languages reveals four movement-related design features reflecting a deep evolutionary heritage: (1) the cyclical consonant-vowel alternation underlying the syllable, a "Frame" for speech consisting of mandibular oscillation, possibly evolving from ingestive cyclicities (e.g., chewing) via visuofacial communicative cyclicities (e.g., lipsmacks); (2) three intracyclical consonant-vowel co-occurrence preferences reflecting basic biomechanical constraints-coronal consonants-front vowels, dorsal consonants-back vowels, and labial consonants-central vowels; (3) a developmental progression from above-chance to below-chance levels of intercyclical consonant repetition; (4) an ease-related labial consonant-vowel-coronal consonant sequence preference for word initiation. These design features presumably result from self-organizational responses to selection pressures, primarily determined by motor factors. No explanation for these design features is available from Universal Grammar, and, except for feature 3, perceptual-motor learning seems to have only a limited causal role in acquisition of any design feature.

On the origin of internal structure of word forms.

This study shows that a corpus of proto-word forms shares four sequential sound patterns with words of modern languages and the first words of infants. Three of the patterns involve intrasyllabic consonant-vowel (CV) co-occurrence: labial (lip) consonants with central vowels, coronal (tongue front) consonants with front vowels, and dorsal (tongue back) consonants with back vowels. The fourth pattern is an intersyllabic preference for initiating words with a labial consonant-vowel-coronal consonant sequence (LC). The CV effects may be primarily biomechanically motivated. The LC effect may be self-organizational, with multivariate causality. The findings support the hypothesis that these four patterns were basic to the origin of words.

Nasalization of vowels in nasal environments in babbling: evidence for frame dominance.

An emerging concept for the characterization of the form of babbling and early speech is 'frame dominance': most of the variance arises from a frame provided by open-close mandibular oscillation. In contrast, the tongue - the most versatile articulator in adults - plays only a minor role in intersegmental and even intersyllabic changes. The contribution of another articulator - the soft palate - to time-domain changes in babbling was evaluated in an acoustic analysis of 433 consonant-vowel-consonant sequences produced by 3 infants. Strong nasal effects on vowels in symmetrical consonantal environment were observed in the form of a lower frequency first formant region in low vowels and a lower frequency second formant region in front vowels. These results, the first of which also occurs in adults, were complemented by perceptual tendencies for transcribers to transcribe more mid vowels relative to low vowels and more central vowels relative to front vowels in nasal environments. Thus the soft palate is like the tongue in making only minor contributions to time-domain changes in babbling, and this is considered to be additional evidence for the frame dominance conception.

The frame/content theory of evolution of speech production.

The species-specific organizational property of speech is a continual mouth open-close alternation, the two phases of which are subject to continual articulatory modulation. The cycle constitutes the syllable, and the open and closed phases are segments-vowels and consonants, respectively. The fact that segmental serial ordering errors in normal adults obey syllable structure constraints suggests that syllabic "frames" and segmental "content" elements are separately controlled in the speech production process. The frames may derive from cycles of mandibular oscillation present in humans from babbling onset, which are responsible for the open-close alternation. These communication-related frames perhaps first evolved when the ingestion-related cyclicities of mandibular oscillation (associated with mastication [chewing] sucking and licking) took on communicative significance as lipsmacks, tonguesmacks, and teeth chatters--displays that are prominent in many nonhuman primates. The new role of Broca's area and its surround in human vocal communication may have derived from its evolutionary history as the main cortical center for the control of ingestive processes. The frame and content components of speech may have subsequently evolved separate realizations within two general purpose primate motor control systems: (1) a motivation-related medial "intrinsic" system, including anterior cingulate cortex and the supplementary motor area, for self-generated behavior, formerly responsible for ancestral vocalization control and now also responsible for frames, and (2) a lateral "extrinsic" system, including Broca's area and surround, and Wernicke's area, specialized for response to external input (and therefore the emergent vocal learning capacity) and more responsible for content.

Production constraints on utterance-final consonant characteristics in babbling.

In order to evaluate hypotheses regarding production constraints on final consonants in babbling, 721 utterance-final consonants produced by 6 infants in consonant-vowel-consonant (CVC) syllables were examined and compared with the preceding consonant in the CVC. Consistent with earlier studies, major patterns were observed for each of the three main consonantal properties--place and manner of articulation and voicing. These patterns included a strong tendency for final consonants to repeat the place of articulation of nonfinal consonants and a tendency for relatively more fricative, nasal and voiceless consonants to occur in final position than in nonfinal position. The high frequency with which final consonants shared place of articulation with the preceding consonant was considered to reflect 'frame dominance' or the tendency of a relatively constant mandibular cycle (the frame) to determine the structure of utterances with very little contribution from other active articulators. The manner and voicing effects were attributed to an overall terminal energy decrease in the vocal production system.

Postural asymmetries and language lateralization in humans (Homo sapiens).

Is hemispheric specialization for speech more closely related to left hemisphere specialization for manual skill and sequencing, as is usually supposed, or to control of asymmetries in whole body posture, as recent findings of right-handedness in nonhuman primates suggest? This question can be evaluated in the 10% of humans who have mixed handedness and footedness. Footedness entails postural asymmetry, and persons with mixed limb preferences often prefer the hand ipsilateral to the preferred foot in asymmetrical actions for which whole body postural adjustments are obligatory (e.g., throwing). The dichotic listening test , and indicator of language laterality, was administered to 4 groups of 48 persons with the 4 possible combinations of hand and foot preference. As in 2 past studies, language lateralization was somewhat more strongly related to postural asymmetries than to asymmetries in manual skill and sequencing.

The articulatory basis of babbling.

This article evaluates the "Frames, then Content" hypothesis for speech acquisition, which states that much of the patterning of babbling is a direct result of production of syllabic "Frames" by means of rhythmic mandibular oscillation, with relatively little of the intrasyllabic and intersyllabic "Content" of the syllable-like cycles under mandible-independent control. Analysis was based on a phonetically transcribed corpus of 6,659 utterances of 6 normally developing infants obtained from one-hour weekly audio-recordings over a 4-6 month period. Intrasyllabic predictions were that front vowels would preferentially co-occur with front (alveolar) consonants, back vowels with back (velar) consonants, and central vowels with labial consonants, with the latter effect presumably resulting from mandibular oscillation alone. Intersyllabic predictions were for more variegation in tongue height for vowels than in front-back tongue movement, and for consonant manner changes to predominate over place changes (related primarily to mandibular oscillation). All 30 individual predictions from both hypotheses were confirmed, leading to a conception of the articulatory basis of babbling as "Frame Dominance."

Organization of babbling: a case study.

Speech is probably the most complex serially ordered behavior in living forms. However, no systematic investigation of the organization of speech-related output when it is presumably simplest, namely during the babbling stage, has been attempted. Transcriptions of 423 babbled utterances (1145 syllables) were obtained from one subject 7-12 months of age. Most results could be interpreted in terms of a basic mouth opening-closing alternation, responsible not only for the typical vowel-consonant alternation of babbling, but also for many prominent details including within-utterance variation in vowel height (often stress-related) and in degree of closure for consonants. The results suggest that a "frame" for babbling is provided by mandibular oscillation, perhaps reflected, when operating alone, in the common alternation between labial consonants and central vowels. Variation in the amplitude of this oscillation may be responsible for the within-utterance vowel height and consonant manner variation and much of the perceived stress variation. Further variation is attributed to fronting movements of the tongue, the effects of which often spread beyond single vowels and consonants.

Prolegomena to a theory of the sound pattern of the first spoken language.

Although it would seem fundamental to the understanding of human beings, there has been virtually no attempt, in modern science, to develop a theory regarding the sound pattern of the first language. As a step towards such a theory, I suggest that ontogeny may recapitulate phylogeny. I propose that the pattern of open/close alternation of the mandible underlying the syllable which first appears in infants at the babbling stage is the missing link in the evolution of speech from ancestral primate vocal signals. In addition, I suggest that the conjoint set of sounds and sound patterns favored in babbling and early words, and in the world's languages, constitutes, in effect, the fossil record of true speech, and I provide a tentative enumeration of this set.

Acquisition of correct vowel production: a quantitative case study.

There have been relatively few studies of the course of acquisition of correct vowel production. The present study suggests this gives an illusory impression that vowels are acquired easily and are of little theoretical interest. Despite a relatively precocious rate of vocabulary acquisition over the period from 14 to 20 months, the subject studied produced less than 60% of her vowels correctly according to evidence from phonetic transcriptions. A complex pattern of vowel preferences and errors was only partially related to typical prespeech babbling preferences, but was strongly related to word structure variables (monosyllabic vs. disyllabic) including stress patterns of disyllabic words, as reflected in patterns of relative frequencies of vowels in stressed and unstressed syllables. Consonant-vowel interdependence was observed, in both the favoring of high front vowels in the environment of alveolar consonants, and a reciprocal relation between vowel reduplication and consonant reduplication in disyllabic words.

Functional precursors to language and its lateralization.

An adequate account of language evolution must reconcile the propositions that language is unique but has precursors. The paper of Bellman and Goldberg and that of Tzeng and Wang each neglects one of these propositions. We suggest that the uniqueness of language lies primarily in its dualistic structure which has a frame-content mode of organization: at the phonological level, consonant and vowel elements are inserted into syllabic frames; and at the morphological level, stem forms of content words are inserted into syntactic frames. We suggest that the morphological level evolved from the phonological level and that the frame-content mode of organization in phonology had a precursor in the form of bimanual coordination in which the nonpreferred (frame) hand holds an object operated on by the preferred hand (content). It is argued that lateralization of cortical function evolved first for bimanual coordination, then for language. Old World monkey hand preferences may be consistent with both the putative left-hemisphere specialization for bimanual coordination and the human right-hemisphere specialization for spatial functions.

Cricothyroid activity and control of voicing in Hindi stops and affricates.

Simultaneous recordings of voice and cricothyroid activity during speech gestures by one speaker of Hindi were made. The experimental utterances consisted of monosyllabic and bisyllabic meaningful and nonsense words containing in prestressed initial and medial and poststressed final positions the voiced and unvoiced stops and affricates from both the aspirated and unaspirated categories. All of the words were embedded in the carrier sentence 'baba - ap bolrye'. The results show markedly higher levels of cricothyroid activity for the unvoiced stops and affricates than for their voiced cognates. This cricothyroid activity appears to facilitate voicelessness through increased fold tension during unvoiced stops and affricates and thus contributes to the execution of voicing distinction in voiced and unvoiced stops and affricates. Fundamental frequency data obtained on precisely the utterances reported in this paper also seem to fit the hypothesis that unvoiced stops and affricates have higher fold tension than voiced stops and affricates.

Mechanical properties of single motor units in speech musculature.

Electromyograms were recorded from three subjects during steady, low-rate discharge of single motor units of anterior belly of digastric, accompanying maintenance of isometric tension. The overall tension developed in muscles subserving mandibular depression was recorded from a force tansducer situated inferior to the mandibular symphysis. The force transducer output from the 90 ms period immediately following each of the several hundred discharges of a motor unit was averaged to obtain a characteristic tension curve for the contractile response (twitch) of that unit. Peak twitch tensions and time taken to develop peak tension (contraction time) were recorded for 27 motor units. The obtained median twitch tension of 0.26 g and contraction time of 29 ms were compared with values obtained for units in other human muscles and in animal muscles. As expected from the size principle, later recruited units possessed higher twitch tensions. Contrary to some statements of the size principle, contraction times were not shorter in later recruited units. Data on muscles elevating the mandible were also evaluated.

Motor unit correlates of stress: preliminary observations.

Motor unit activity was measured during 20 repetitions of [aepae] and 20 repetitions of [aepaé] with emphatic stress placed on the second syllable. A definite pattern of recruitment and discharge reorganization was observed during stressed productions characterized by (1) an increase in motor unit discharge rate, (2) recruitment of additional motor units, (3) a reduction in time intervals separating successively activated motor units, (4) an earlier onset of mandibular lowering for the open vowel in relation to initiation of motor unit activity, (5) fewer discharges of a given motor unit per utterance, and (6) sharply reduced variability in recruitment intervals. The shortened and highly stable latencies between motor unit events and motor unit-articulator events point to a more carefully orchestrated motor program for heavily stressed productions as a more forceful attainment of target specification is carried out.