Emergent Control of Manual and Vocal-Motor Activity in Relation to the Development of Speech

Babbling typically precedes, resembles, and conceivably facilitates development of speech, and yet there is no accepted neurobiological characterization of babbling. Here we report a study of infants′ developing control of vocal behavior in relation to manual activity performed under differing conditions of audibility. We hypothesized that babbling is associated with the onset of left-lateralized motor control, as expressed in repetitive right-handed activity, and that audibility facilitates such activity, Sixty-one normally developing infants were seen before (N = 21) or at various intervals following (N = 40) the onset of babbling. In experimental trials, audible or inaudible rattles were placed in left or right hands equally often. Analysis of manual activity revealed little shaking movement in the youngest and vocally least differentiated infants, and a sharp increase in shaking in slightly older infants who had recently begun to babble. Surprisingly, audibility only marginally enhanced shaking activity. A dextral bias was evident in the shaking of infants who had recently begun to babble, but not in younger or older infants. These and other findings suggest that the left cerebral hemisphere may be disproportionately involved in the production of repetitive vocal-motor activity as occurs in babbling.     

Associations between gross motor and communicative development in at-risk infants

Infants’ advances in locomotion relate to advances in communicative development. However, little is known about these relations in infants at risk for delays in these domains and whether they may extend to earlier achievements in gross motor development in infancy. We examined whether advances in sitting and prone locomotion are related to communicative development in infants who have an older sibling with autism spectrum disorder (ASD) and are at risk for motor and communication delays (heightened-risk; HR). We conducted a longitudinal study with 37 HR infants who did not receive an ASD diagnosis at 36 months. Infants were observed monthly between the ages of 5 and 14 months. We assessed gross motor development using the Alberta Infant Motor Scales (AIMS) and recorded ages of onset of verbal and nonverbal communicative behaviors. Results indicated increased presence of early gross motor delay from 5 to 10 months. In addition, there were positive relations between sitting and gesture and babble onset and between prone development and gesture onset. Thus, links between gross motor development and communication extend to at-risk development and provide a starting point for future research on potential cascading consequences of motor advances on communication development.     

Contingent auditory feedback of arm movement facilitates reaching behavior in infancy

The purpose of this study was to investigate the influence of contingent auditory feedback on the development of infant reaching. Eleven full-term infants were observed biweekly from the age of 10 weeks to 16 weeks, and their arm kinematics were recorded. Auditory feedback that was contingent on arm kinematics was provided in the form of: (a) the mother's voice; and (b) musical tones. Results showed that providing auditory feedback (mother's voice or musical tones): (i) increased the amplitude of exploratory arm movements before the onset of reaching; and (ii) increased the number of reaches at the onset of reaching. These results show that infants are able to use contingent auditory feedback to explore the relevant possibilities for action that are subsequently shaped into goal-directed movements.     

Some perceptual properties of consonants in multitalker babble

This study investigated whether consonant phonetic features or consonant acoustic properties more appropriately describe perceptual confusions among speech stimuli in multitalker babble backgrounds. Ten normal-hearing subjects identified 19 consonants, each paired with /a/, 1–19 and lui in a CV format. The stimuli were presented in quiet and in three levels of babble. Multidimensional scaling analyses of the confusion data retrieved stimulus dimensions corresponding to consonant acoustic parameters. The acoustic dimensions identified were: periodicity/burst onset, friction duration, consonant-vowel ratio, second formant transition slope, and first formant transition onset. These findings are comparable to previous reports of acoustic effects observed in white-noise conditions, and support the theory that acoustic characteristics are the relevant perceptual properties of speech in noise conditions. Perceptual effects of vowel context and level of the babble also were observed. These condition effects contrast with those previously reported for white-noise interference, and are attributed to direct masking of the low-frequency acoustic cues in the nonsense syllables by the low-frequency spectrum of the babble.     

To whom the play signal is directed: a study of headshaking in black-handed spider monkeys (Ateles geoffroyi)

Spider monkeys shake their heads so as to facilitate amicable social contact. This occurs frequently during vigorous play fighting, and so is common during the juvenile period. Occasionally, juvenile spider monkeys use headshakes during nonsocial locomotor play. In this study, head shaking in early infancy and in adulthood was studied in a captive troop of spider monkeys, with a total of 8 infants studied from shortly after birth to just before weaning. Three hypotheses to account for these nonsocial headshakes were tested. The play as the experience of the unexpected hypothesis was found wanting because nonsocial headshakes were most common in early infancy, before the onset of the juvenile peak in play. The immature misdirection of signals hypothesis was also found wanting because the headshakes were correctly directed at other monkeys, but not at inanimate objects that were grabbed and mouthed. Both also failed to predict the occurrence of the observed nonsocial headshakes in adults. The hypothesis best supported by the data is that, under some situations, headshakes are self-directed to promote action when confronting contexts of uncertainty.     

Three- to eight-month-old infants' catching under monocular and binocular vision

We report a cross-sectional and a longitudinal experiment that examined developmental changes in the relative contribution of monocular and binocular variables in the guidance of interceptive arm movements. Three- to eight-month-old infants were observed while presented with differently sized balls that approached frontally with a constant velocity under both monocular and binocular viewing conditions. Movement onset indicated that with age infants increasingly came to rely on binocular variables in controlling the timing of the interceptive arm movements. That is, from 7 to 8 months of age movement onset was independent from object size under binocular but not under monocular viewing. In contrast, binocular viewing enhanced the spatial accuracy of the interceptive arm movements at all ages. We concluded that attunement to binocular information is a key process in infants' gaining adaptive control of goal-directed arm movements. However, interceptive arm movements entail the formation of multiple on-line couplings between optic and movement variables, each of which appears to develop at its own pace.     

The formation of rhythmic categories and metric priming

Two experiments on categorical rhythm perception are reported, the object of which was to investigate how listeners perceive discrete rhythmic categories while listening to rhythms performed on a continuous time scale. This is studied by considering the space of all temporal patterns (all possible rhythms made up of three intervals) and how they, in perception, are partitioned into categories, ie where the boundaries of these categories are located. This process of categorisation is formalised as the mapping from the continuous space of a series of time intervals to a discrete, symbolic domain of integer-ratio sequences. The methodological framework uses concepts from mathematics and psychology (eg convexity and entropy) that allow precise characterisations of the empirical results. In the first experiment, twenty-nine participants performed an identification task with 66 rhythmic stimuli (a systematic sampling of the performance space). The results show that listeners do not just perceive the time intervals between onsets of sounds as placed in a homogeneous continuum. Instead, they can reliably identify rhythmic categories, as a chronotopic time clumping map reveals. In a second experiment, the effect of metric priming was studied by presenting the same stimuli but preceded with a duple or triple metre subdivision. It is shown that presenting patterns in the context of a metre has a large effect on rhythmic categorisation: the presence of a specific musical metre primes the perception of specific rhythmic patterns.     

Development of Infant Action Systems and Exploratory Activity: A Tribute to Edward S. Reed

I use Edward S. Reed's work on action systems as a framework to discuss an ecological approach to the development of infant action. I use illustrations from infant action to argue that during development, infants make use of the intrinsic dynamics of their spontaneous motor activity, under a variety of task constraints, to create a small set of action systems. The paper focuses on dynamical systems that generate oscillations as the basis for observable rhythmic behaviors during infancy, such as rocking, shaking the arms, and babbling. Data are presented to illustrate the development of action systems for crawling, object manipulation, and speech. Particular underlying dynamical systems, under different task constraints, may transform body effectors into task-specific action systems: The leg becomes a "kicker," the arm holding a rattle becomes a "shaker," and the vocal tract a "talker."     

Control of Rapid Arm Movements When Target Position Is Altered During Saccadic Suppression

This experiment examined whether rapid arm movements can be corrected in response to a change in target position that occurs just prior to movement onset, during saccadic suppression of displacement. Because the threshold of retinal input reaches its highest magnitude at that time, displacement of the visual target of a saccade is not perceived. Subjects (N = 6) were instructed to perform very rapid arm movements toward visual targets located 16, 20, and 24 degrees from midline (on average, movement time was 208 ms). On some trials the 20 degrees target was displaced 4 degrees either to the right or to the left during saccadic suppression. For double-step trials, arm movements did not deviate from their original trajectory. Movement endpoints and movement structure (i.e., velocity-and acceleration-time profiles) were similar whether or not target displacements occurred, showing the failure of proprioceptive signals or internal feedback loops to correct the arm trajectory. Following this movement, terminal spatially oriented movements corrected the direction of the initial movement (as compared with the single-step control trials) when the target eccentricity decreased by 4 degrees. Subjects were unaware of these spatial corrections. Therefore, spatial corrections of hand position were driven by the goal level of the task, which was updated by oculomotor corrective responses when a target shift occurred.     

Auditory processing of brain-damaged adults under competitive listening conditions

Right CVAs, mild left CVAs, and non-brain-damaged adults received the Token Test under three conditions: quiet, white noise, and speech babble. Left CVAs performed most poorly of all groups in all conditions experiencing difficulty with subtests III, IV, and V. Right CVAs were inferior to controls on each of these three subtests in the speech babble condition only. Thus, right CVA difficulty with both memory and syntactic tasks was demonstrated in speech babble. These results are explained by the hypothesis that both hemispheres are necessary to process auditory information under complex listening conditions. Total brain capacity of right CVA patients may be overloaded if either memory load or linguistic complexity is increased in the presence of certain types of listening competition.     

Synergistic influences of sensory and central stimuli on non-voluntary rhythmic arm movements

In recent years, neuromodulation of the cervical spinal circuitry has become an area of interest for investigating rhythmogenesis of the human spinal cord and interaction between cervical and lumbosacral circuitries, given the involvement of rhythmic arm muscle activity in many locomotor tasks. We have previously shown that arm muscle vibrostimulation can elicit non-voluntary upper limb oscillations in unloading body conditions. Here we investigated the excitability of the cervical spinal circuitry by applying different peripheral and central stimuli in healthy humans. The rationale for applying combined stimuli is that the efficiency of only one stimulus is generally limited. We found that low-intensity electrical stimulation of the superficial arm median nerve can evoke rhythmic arm movements. Furthermore, the movements were enhanced by additional peripheral stimuli (e.g., arm muscle vibration, head turns or passive rhythmic leg movements). Finally, low-frequency transcranial magnetic stimulation of the motor cortex significantly facilitated rhythmogenesis. The findings are discussed in the general framework of a brain-spinal interface for developing adaptive central pattern generator-modulating therapies.     

Wrist and arm movements of varying difficulties

Although a great deal of experimental attention has been directed at understanding Fitts' law, only a limited number of experiments have attempted to determine if performance differs across effectors for a given movement difficulty. In three experiments reciprocal wrist and arm movements were compared at IDs of 1.5, 3, 4.5 and 6. When absolute movement requirements and visual display were constant, participants' movement times and response characteristics for the arm and wrist were remarkably similar (Experiment 1). However, when amplitude for wrist movements was reduced to 8° and the gain (4×) for the visual display increased participants' movement time, defined on the basis of kinematic markers (movement onset − movement termination), was increasingly shorter relative to arm movements as movement difficulty was increased (Experiment 2). Experiment 3 where the arm was tested at 32° and 8° with the 8° movements provided the same gain (4×) that was used for the 8° wrist movements in Experiment 2, no advantage was observed for the arm at the shorter amplitude. The results are interpreted in terms of the advantages afforded by the increased gain of the visual display, which permitted the wrist, but not the arm, to more effectively preplan and/or correct ongoing movements to achieve the required accuracy demands. It was also noted that while the wrist was more effective during the actual movement production this was accompanied by an offsetting increase in dwell time which presumably is utilized to dissipate the forces accrued during movement production and plan the subsequent movement segment.     

Maturational and situational determinants of reaching at its onset

At 3 months of age, reaching behavior was measured in a group of 10 girls and 10 boys born at term. The assessments were carried out on the average 2 days after reaching onset. Reaching kinematics was measured in both supine and reclined positions. Girls reached more than boys, had straighter reaching trajectories and movements of shorter durations as well as fewer movement units. The reclined position gave rise to straighter trajectories in both girls and boys. Several anthropometric parameters were measured. Girls had less length and volume of the forearm than boys but similar upper arm volumes. There was a weak relation between kinematic and anthropometric variables.     

Does a rhythmic context have an effect on perceptual weights in auditory intensity processing?

The effects of a rhythmic context on auditory intensity processing were studied. Experiment 1 tested the hypothesis that the involuntary temporal direction of attention by a rhythmic context sequence influences the temporal weighting of loudness. Perceptual weight analysis was used to measure the attention directed to individual temporal portions of a longer stimulus by estimating the importance of individual temporal segments for global loudness judgements. A rhythmic context resulted in a sharper temporal weighting profile, but the expected rhythmic pattern of weights was not observed. In Experiment 2, the accuracy for detecting a peak in the temporal loudness profile of a level-fluctuating noise was measured for the level increment presented at expected and unexpected times. The rhythmic context again caused a more pronounced temporal weighting profile. However, the accuracy was neither significantly increased for expected target segment positions nor decreased for unexpected target segment positions, relative to the condition without a rhythmic context sequence.     

Laughter: A signal of ceased alarm toward a perceived incongruity between life and stiffness

Main aim of this study is to determine what causes humor, and secondarily, to find out why rhythmic laughter is its expression. In this review, we have analyzed the characteristics of humor and laughter, their effects on health and social behavior, and their correlations with several areas of the brain. Then, we have described the features of laughter, its rhythmic shape and its correlations with other rhythmic human behaviors. We have noticed that the most plausible theory for humor is that of incongruity/resolution, where a) an incongruous event or object provokes a sense of wonder, and b) it is followed by something that reassures the bystanders about its innocuity; but c) not all incongruities provoke humor, but just those that introduce something stiff and stereotyped into a vital and fluid event. What this study adds to what is known, is that not all incongruities produce humor, but only those between a living process and any stereotipy or stiffness we find in it. Laughter is the stigmatization of this unnatural incongruity, through its loud and rhythmic shape, as a sort of signal of ceased alert after the shock induced by what seems hazardous to the fluidity of life.     

The effects of dual-tasking on arm muscle responses in young and older adults

This study examined whether dual-tasking affects an individual’s ability to generate arm muscle responses following a loss of balance. Nineteen young and 16 older adults recovered their balance in response to a surface translation. This balance task was either completed on its own or while counting backwards by 2’s (easy counting difficulty) or 7’s (hard counting difficulty). With increasing counting difficulty, less attentional resources were assumed to be available for balance recovery. The ability to generate arm muscle responses was quantified through the measurement of electromyographic (EMG) onset latencies and amplitudes from three arm muscles. Results indicated that the attentional requirements of the counting task did not greatly affect EMG onset latencies or amplitudes for both young and older adults. Even when an effect was observed, the magnitude of change was small (e.g., ∼3 ms earlier EMG onset and ∼2.0%MVC smaller EMG amplitude during the dual- compared to the single-task conditions). Thus, the generation of arm muscle responses do not appear to require a significant amount of attentional resources and the decreased ability to cope with cognitive interference with ageing is unlikely to explain why older adults have difficulty in generating arm responses following a loss of balance.     

Paradoxical decrease of imitation performance with age in children

Imitation development was studied in a cross-sectional design involving 174 primary-school children (aged 6–10), focusing on the effect of actions' complexity and error analysis to infer the underlying cognitive processes. Participants had to imitate the model's actions as if they were in front of a mirror (‘specularly’). Complexity varied across three levels: movements of a single limb; arm and leg of the same body side; or arm and leg of opposite body sides. While the overall error rate decreased with age, this was not true of all error categories. The rate of ‘side’ errors (using a limb of the wrong body side) paradoxically increased with age (from 9 years). However, with increasing age, the error rate also became less sensitive to the complexity of the action. This pattern is consistent with the hypothesis that older children have the working memory (WM) resources and the body knowledge necessary to imitate ‘anatomically’, which leads to additional side errors. Younger children might be paradoxically free from such interference because their WM and/or body knowledge are insufficient for anatomical imitation. Yet, their limited WM resources would prevent them from successfully managing the conflict between spatial codes involved in complex actions (e.g. moving the left arm and the right leg). We also found evidence that action side and content might be stored in separate short-term memory (STM) systems: increasing the number of sides to be encoded only affected side retrieval, but not content retrieval; symmetrically, increasing the content (number of movements) of the action only affected content retrieval, but not side retrieval. In conclusion, results suggest that anatomical imitation might interfere with specular imitation at age 9 and that STM storages for side and content of actions are separate.     

Joint control strategies and hand trajectories in multijoint pointing movements

The role of timing in the control of multijoint pointing movements was evaluated. Eight subjects performed rapid pointing movements to a variety of target locations. The subject's right arm was strapped to a 2 degrees of freedom manupilandum that permitted shoulder and elbow motion in the horizontal plane. Initial and final position of the hand and magnitude of displacement was varied to determine effects on timing characteristics. Kinematics and kinetics of the shoulder, elbow, and hand were analyzed. The hand paths and velocity profiles observed were consistent with prior reports. Multiple regression analysis of kinematic variables disclosed that timing of joint movement onset was independent of initial and final positions of the hand, but was linearly related to joint displacement: the joint that moved farther started moving first. Using computer simulations to create joint movement onset, times that were different from the observed ones always resulted in hand paths with increased curvatures and loss of the smooth velocity profiles. Secondly, a very stable, linear relationship was observed between peak velocity and displacement at both the elbow and shoulder joints. This relationship was not affected by variations in movement space. We suggest that space-time transformation based on difference in joint displacement is used to regulated timing of joint movement onset. The simulations indicate that this transformation is set to produce smooth velocity profiles. The relationships between timing of movement onset and displacement and between peak velocity and displacement complement each other: by maintaining a linear relationship between velocity and displacement, a linear space time transformation can be used to control timing. Furthermore, these relationships are probably used to simplify coordination between the moving joints.     

语音型噪音对二语者汉语元音声调感知的影响

在安静、语音型噪音、语音调制型噪音三种背景下测量了汉语母语者、汉语中、高水平的韩语母语者感知汉语元音和声调的正确率。安静背景下,三组人的语音感知类似,而在语音型噪音背景下,汉语母语者的感知正确率显著高于中水平二语者。进一步的检验表明中水平二语者在语音型噪音背景下的感知难度较大是由于其受到的语音型噪音中能量掩蔽的影响比母语被试要大,而其受到的信息掩蔽的干扰和另外两组被试相近。     

Co‐occurences of preverbal vocal behavior and motor action in early infancy

This study reports on co‐occurrence of vocal behaviors and motor actions in infants in the prelinguistic stage. Four Japanese infants were studied longitudinally from the age of 6 months to 11 months. For all the infants, a 40 min sample was coded for each monthly period. The vocalizations produced by the infants co‐occurred with their rhythmic actions with high frequency, particularly in the period preceding the onset of canonical babbling. Acoustical analysis was conducted on the vocalizations recorded before and after the period when co‐occurrence took place most frequently. Among the vocalizations recorded in the period when co‐occurrence appeared most frequently, those that co‐occurred with rhythmic action had significantly shorter syllable duration and shorter formant‐frequency transition duration compared with those that did not co‐occur with rhythmic action. The rapid transitions and short syllables were similar to patterns of duration found in mature speech. The acoustic features remained even after co‐occurrence disappeared. These findings suggest that co‐occurrence of rhythmic action and vocal behavior may contribute to the infant’s acquisition of the ability to perform the rapid glottal and articulatory movements that are indispensable for spoken language acquisition.