Visuo-motor synchronization in children of 7-8 years old

The group of 22 children of 7-8 years old and the group of 17 adults participated in the experiment in which they were asked to synchronize their movements (pressing a button) with an isochronous sequence of visual stimuli. The period of the sequence was varied between 500 to 2000 ms with the 300 ms step. Two successive phases of visuo-motor synchronization were studied: the synchronization phase and the initiation phase which corresponds to the process of transition between reacting to a visual stimulus and the stable synchronization. The initiation phase was characterized by the shape and duration of the asynchrony time course (relaxation curve). The statistical properties of asynchrony were analyzed in the framework of the phase correction of the central timer. It is shown that (1) the range of successful visuo-motor synchronization is narrower in children of 7-8 than in adults and it spans from 600-700 ms to approx. 1700 Mc; (2) The initiation phase lasts about the same time in children of 7-8 and adults and typical shapes of individual relaxation curves are similar in both adults and children. (3) Although the statistical properties of asynchrony are comparable in children and adults, the mechanism of phase correction of the central timer operates with a lower value of the correction gain factor in children than in adults. In children, the phase correction process is also characterized by a substantially higher level of the central and motor noise which leads to a higher asynchrony variability and more frequent and longer lasting synchronization losses.     

Visuomotor synchronization: Analysis of the initiation and stable synchronization phases

The initiation phase of visuomotor synchronization and the phase of stable synchronization were studied in an experiment where eight adult subjects synchronized their motor responses with an isochronous sequence of visual stimuli. The period of the sequence varied in a wide range (from 500 to 2200 ms). Analysis of the statistical characteristics of synchronization errors (asynchronies) showed that the phase of stable visuomotor synchronization fit the model of current phase correction of a central timer; as in the case of audiomotor synchronization, the variability of the intervals of the central timer and the phase correction coefficient increased with increasing period of the stimulus sequence. The initiation phase of visuomotor synchronization was characterized by a considerable inter-and intraindividual variability of the form (exponential, linear, or step) and duration (from one to ten responses) of the transition from reacting to a sensory signal to synchronization. The shape and duration of the transitional region depend on the phase correction coefficient and the possibility of using an estimate of the sequence period stored in memory. The obtained data indicate that the initiation stage is not automatic throughout the studied range of periods of the visual stimulus sequence; in particular, working memory plays a substantial role in its organization.     

Directed corticocortical functional connectivity at the early stages of serial learning in adults and seven- to eight-year-old children

Serial learning at its earlier stages, presumably involving the working memory, was studied in adults and seven- to eight-year-old children during the reproduction of a sequence of discrete movements following the order specified by a sequence of visual stimuli. In both age groups, the learning curves (latent time vs. trial number) were qualitatively similar in shape. The overall shape of the learning curve depended on the relative proportion of the fast vs. slow phases of latent time reduction. Comparison of the corticocortical functional connectivity patterns in the prestimulus period in the sequence reproduction task vs. the simple visuomotor reaction task showed a general tendency of an increase in the influence of postcentral cortical areas accompanied by the reduced influence of prefrontal and central cortical areas. In particular, it was typical of adults to show an increase in the directed influence of temporo-parieto-occipital (TPO) cortical areas, while the children also showed an increase in the directed influence of the parietal cortex. Comparison of the subgroups with different shapes of learning curves in the prestimulus period has shown the difference in their patterns of directed functional connectivity. The results are discussed with a special emphasis on the role of the working memory retaining the internal representations of sequences being learned.     

Age-related specificity of the processing of visual information in the system of working memory

In adults and seven- to eight-year-old children, event-related potentials (ERPs) were analyzed during quiet observation and detailed paired comparison of visual stimuli. In both age groups, we showed the differences in the initial stages (component N1) of sensory analysis in these situations. In adults, an increase in the negativity during the initial stages of analysis was observed in the caudal and central areas of the cortex during presentation of standard and test stimuli. In the frontal areas of the cortex, an increase in the negative potential was observed only in ERPs induced by the test stimulus. In children, an increase in the negativity at the initial phases of analysis of stimuli in the situation of working memory, as compared to quiet observation, was confined to the caudal areas of the cortex. Differential curves that characterize analysis of standard and test stimuli showed age-related differences in the initial and late phases of information processing under the conditions of working memory. In adults, the differential curves that characterize analysis of the standard stimulus were represented by negative phases, and the curves related to the test stimulus, by positive phases. In children, late phases of analysis of the standard and test stimuli had smaller differences as compared to adults: the late positive wave was predominant in the responses to both standard and test stimulus in the caudal areas of the cortex. In the frontal areas, there was no considerable increase in the amplitude of the late positive wave in response to the test stimulus. This fact, together with the absence of enhancement of initial negativity in the frontal areas, which reflects analysis of the test stimulus, indicates that the prefrontal cortex plays a smaller role in the comparison of the memory trace with the current information in seven- to eight-year-old children. The data obtained suggest that the central executive of working memory is not sufficiently mature in children aged seven to eight years.     

Functional organization of the brain in the period of preparation for recognizing fragmented images in seven- to eight-year-old children and adults

Functional connectivity between the prefrontal cortex and the temporal and temporo-parieto-occipital cortices in the process of preparing for the recognition of fragmented images were analyzed in adults (n = 26) and seven- to eight-year-old children (n = 20).The evaluations of the imaginary part of the complex-valued coherency for the EEG alpha-rhythm (Jα) were used as an index for the strength of cortico-cortical interactions. The Jα value was analyzed in the following three experimental conditions corresponding to different stages of readiness for visual recognition: (1) nonspecific attention holding in the period preceding a warning stimulus (S1); (2) focused attention in the interval preceding a not-yet-recognized target stimulus (S2) and (3) pretuning preceding a recognized stimulus (S3). Adult subjects tended towards a growing level of functional connectivity in α-rhythm in progressing from attention holding to focused attention preceding the emergence of a target stimulus, but children, on the contrary, demonstrated a decreasing trend. Comparing the Jα values in the subgroups of adults and children who showed the highest recognition scores in the solution of cognitive tasks helped reveal age-specific patterns in the rearrangements of cortico-cortical functional connectivity in α-rhythm in the left and right hemispheres at different stages of readiness for recognizing incomplete images. In adults, the maximal Jα values were found in the left hemisphere in the interval preceding the recognition of a target image. At this stage of pretuning, the Jα values at the leads in the left hemisphere in adults significantly exceeded those in children. The Jα values for the right hemisphere in adults were maximal during focused prestimulus attention when the image was not yet recognized and these values were significantly higher than in children under the same experimental conditions. Children showed maximal Jα values in both hemispheres during nonspecific attention. The specifics of functional connectivity observed between the prefrontal, temporal and temporo-parieto-occipital cortices in seven- to eight-year-old children during functional pretuning to the recognition of fragmented images are considered to reflect the relative immaturity of neurophysiological mechanisms underlying the voluntary attention and working memory in children of this age group.     

Specificity of recognition of fragmented images in seven- to eight-year-old children: Analysis of event-related potentials

The topography and parameters of event-related potentials (ERPs) recorded during the presentation of incomplete images with different fragmentation were analyzed in seven- to eight-year-old children. The degree and mode of the involvement of different cortical zones at different stages of analysis and processing of fragmented images were determined. It was found in children that the prefrontal cortical areas were involved in the recognition of incomplete images in the same way as in adults. Age-related differences manifested themselves in a lower intensity of the slow positive complex in children, reflecting the decision-making and information retention processes required for the preparation of an answer.     

The ontogeny of the neurophysiological mechanisms of stereognosis: An EEG study

Age-related characteristics of the systemic organization of intra- and interhemispheric interactions during a stereognostic task (tactile shape recognition with the right or left hand) were studied in adults and children aged five to six, seven to eight, and nine to ten years. A combined pattern of cortical interactions was found in adults. It was expressed in a considerable enhancement of relationships between cortical bioelectric potentials compared to the baseline accompanied by a substantial increase in the intensity of the systemic interactions between anterior and posterior cortical areas. This pattern was revealed by both coherence and cross-correlation analyses of the electroencephalogram (EEG). In the EEGs of children, the enhancement of interhemispheric relationships was observed at an age as early as five to six years and was the highest in seven- to eight-year-old children, whereas the increase in the cross-correlation of cortical bioelectric potentials in the frontal—occipital direction developed gradually, approaching the definitive level typical of adults by the age of nine to ten years. The results suggest that the central mechanisms of stereognosis, a function important for manual and occupational activities, gradually develop during postnatal ontogeny. Heterochronic involvement of intra- and interhemispheric interactions in the performance of stereognostic task may be related to gradual, heterochronic myelination of commissural and associative pathways.     

Development of a function to recognize angry facial expressions in 5- to 11-year-old children

In 5- to 6-, 7- to 8-, and 10- to 11-year-old children, age-related features of the effects of former experience on the recognition of emotional facial expressions were found using a cognitive set model. In five- to six-year-old children, an inert set to an angry facial expression was formed and expressed during testing as a large number of erroneous recognition of facial expressions of the perseverative type (assimilative) illusions. Set plasticity was increased in seven- to eight-year-old children and the number of assimilative illusions decreased. In 10- to 11-year-old children, the cognitive set was similar to adults in terms of its plasticity and a ratio of assimilative and contrast illusions. Changes in the spatial synchronization of electrical potentials in the ??- and ??-frequency bands were observed in all age groups, mainly during set formation. In all age groups, we observed a correlation between the bioelectrical data and the effects of former experience on the recognition of facial expression. Based on the data on the coherence of the potentials of the ??- and ??-ranges we propose age-related changes in the involvement of the cortico-hippocampal and fronto-thalamic functional systems of integration of brain activity in organizing the sets to emotionally negative facial expressions.     

Neurophysiological mechanisms of recognition fragmented images by five- to six-year-old children

Behavioral indices and event-related potentials (ERP) were analyzed in five- to six-year-old children who were shown a set of previously unseen fragmented drawings of familiar images. These children recognized less fragmented images than seven- to eight-year-old children. At the age of five to six years, there was no increase in N350–400 prefrontal negativity and slow positive complex, which is characteristic of mature recognition that involves executive control. Comparison of ERP for recognized vs. unrecognized stimuli revealed a significant increase in the P300 and N400 amplitudes in the right occipital area. Note that, in children of this age, there were no significant differences between reactions to recognized and unrecognized images in the lateral extrastriate cortex (T₅/T₆), which is the key structure for recognition of familiar images via integration of their sensory features. Our data suggest that in five- to six-year-old children recognition of fragmented images has specific features determined by immaturity of the executive control and insufficient involvement of the ventral visual system.     

Long-Range Correlation in Synchronization and Syncopation Tapping: A Linear Phase Correction Model

We propose in this paper a model for accounting for the increase in long-range correlations observed in asynchrony series in syncopation tapping, as compared with synchronization tapping. Our model is an extension of the linear phase correction model for synchronization tapping. We suppose that the timekeeper represents a fractal source in the system, and that a process of estimation of the half-period of the metronome, obeying a random-walk dynamics, combines with the linear phase correction process. Comparing experimental and simulated series, we show that our model allows accounting for the experimentally observed pattern of serial dependence. This model complete previous modeling solutions proposed for self-paced and synchronization tapping, for a unifying framework of event-based timing.     

Evidence for dissociation between the perceptual and visuomotor systems in humans

When a visual stimulus is continuously moved behind a small stationary window, the window appears displaced in the direction of motion of the stimulus. In this study we showed that the magnitude of this illusion is dependent on (i) whether a perceptual or visuomotor task is used for judging the location of the window (ii) the directional signature of the stimulus, and (iii) whether or not there is a significant delay between the end of the visual presentation and the initiation of the localization measure. Our stimulus was a drifting sinusoidal grating windowed in space by a stationary, two-dimensional, Gaussian envelope (sigma=1 cycle of sinusoid). Localization measures were made following either a short (200 ms) or long (4.2 s) post-stimulus delay. The visuomotor localization error was up to three times greater than the perceptual error for a short delay. However, the visuomotor and perceptual localization measures were similar for a long delay. Our results provide evidence in support of the hypothesis that separate cortical pathways exist for visual perception and visually guided action and that delayed actions rely on stored perceptual information.     

Adaptive Visual Re-Weighting in Children’s Postural Control

This study investigated how children’s postural control adapts to changes in the visual environment and whether they use previous experience to adjust postural responses to following expositions. Four-, eight-, and twelve-year-old children (10 in each group) and 10 young adults stood upright inside of a moving room during eight trials each lasting one-minute. In the first trial, the room was stationary. In the following seven trials, the room oscillated at 0.2 Hz, amplitude of 0.5 cm, with the exception of the fifth trial, in which the room oscillated with amplitude of 3.2 cm. Body sway responses of young adults and older children down-weighted more to the increased visual stimulus amplitude when compared to younger children. In addition, four- and eight-year-old children quickly up-weighted body responses to visual stimulus in the subsequent two trials after the high amplitude trial. Sway variability decreased with age and was greatest during the high-amplitude trial. These results indicate that four year olds have already developed the adaptive capability to quickly down-weight visual influences. However, the increased gain values and residual variability observed for the younger children suggest that they have not fully calibrated their adaptive response to that of the young adults tested. Moreover, younger children do not carry over their previous experience from the sensorial environment to adapt to future changes.     

Development of mechanisms of recognition of fragmented images differing in the degree of fragmentation in children of preschool and primary school ages

Recognition of fragmented images with an increasing number of fragments was studied in children of three age groups (five to six, seven to eight, and nine to ten years of age) to compare the behavioral and neurophysiological parameters of recognition in these groups. The most pronounced changes in effectiveness of recognition were observed when the five- to six-year-old and seven- to eight-year-old children were compared. In the former, recognition was not accompanied by any significant changes in the event-related potentials of the prefrontal cortex or by an increase in N250?C400 (Ncl) in the extrastriate cortex (though it is an important characteristic of the process). However, the amplitude of the N170?C200 component, which reflects analysis and encoding of sensory features, did increase at the age of five to six years. Immaturity of the prefrontal cortex is manifested in a deficiency of the control: these children respond hastily and make numerous mistakes. In seven- to eight-year-old children, recognition is accompanied by an increase in the amplitude of the N100 and N250 components in the prefrontal cortex, whereas the amplitude of the Ncl component increases in the extrastriate cortex. The error rate and recognition threshold are significantly lower in these children than at the age of five to six years. The role of prefrontal cortex is the most pronounced at the age of nine to ten years, which is manifested in the Ncl amplitude and the later phases corresponding to the cognitive recognition. Our results demonstrate qualitative differences in the mechanisms of recognition in children of the preschool and primary school age. At the age of five to six years, recognition is a result of integration of the sensory signs. Beginning from the age of seven to eight years, the prefrontal cortex plays an important role in recognition of the fragmentary images; this brain region is responsible for a search of possible analogues in memory and identification of an object.     

Fronto-Central Theta Oscillations Are Related to Oscillations in Saccadic Response Times (SRT): An EEG and Behavioral Data Analysis

The phase reset hypothesis states that the phase of an ongoing neural oscillation, reflecting periodic fluctuations in neural activity between states of high and low excitability, can be shifted by the occurrence of a sensory stimulus so that the phase value become highly constant across trials (Schroeder et al., 2008). From EEG/MEG studies it has been hypothesized that coupled oscillatory activity in primary sensory cortices regulates multi sensory processing (Senkowski et al. 2008). We follow up on a study in which evidence of phase reset was found using a purely behavioral paradigm by including also EEG measures. In this paradigm, presentation of an auditory accessory stimulus was followed by a visual target with a stimulus-onset asynchrony (SOA) across a range from 0 to 404 ms in steps of 4 ms. This fine-grained stimulus presentation allowed us to do a spectral analysis on the mean SRT as a function of the SOA, which revealed distinct peak spectral components within a frequency range of 6 to 11 Hz with a modus of 7 Hz. The EEG analysis showed that the auditory stimulus caused a phase reset in 7-Hz brain oscillations in a widespread set of channels. Moreover, there was a significant difference in the average phase at which the visual target stimulus appeared between slow and fast SRT trials. This effect was evident in three different analyses, and occurred primarily in frontal and central electrodes.     

Realigning Thunder and Lightning: Temporal Adaptation to Spatiotemporally Distant Events

The brain is able to realign asynchronous signals that approximately coincide in both space and time. Given that many experience-based links between visual and auditory stimuli are established in the absence of spatiotemporal proximity, we investigated whether or not temporal realignment arises in these conditions. Participants received a 3-min exposure to visual and auditory stimuli that were separated by 706 ms and appeared either from the same (Experiment 1) or from different spatial positions (Experiment 2). A simultaneity judgment task (SJ) was administered right afterwards. Temporal realignment between vision and audition was observed, in both Experiment 1 and 2, when comparing the participants’ SJs after this exposure phase with those obtained after a baseline exposure to audiovisual synchrony. However, this effect was present only when the visual stimuli preceded the auditory stimuli during the exposure to asynchrony. A similar pattern of results (temporal realignment after exposure to visual-leading asynchrony but not after exposure to auditory-leading asynchrony) was obtained using temporal order judgments (TOJs) instead of SJs (Experiment 3). Taken together, these results suggest that temporal recalibration still occurs for visual and auditory stimuli that fall clearly outside the so-called temporal window for multisensory integration and appear from different spatial positions. This temporal realignment may be modulated by long-term experience with the kind of asynchrony (vision-leading) that we most frequently encounter in the outside world (e.g., while perceiving distant events).     

Indicators of functional maturity of cerebral hemispheres in first-year primary school students from the risk groups for early dysontogeny

Electrophysiological and psychophysiological studies were performed in a group of seven- to eight-year-old children, who had been born and lived in Arkhangelsk, with various risk factors of early dysontogeny. Analysis of the data demonstrated that “disturbing” factors affected maturation of the neuronal apparatus of the cerebral cortex. In children from risk groups, the immaturity of cortical rhythmogenesis was expressed in the inconsistency with the functional loads of the main rhythm at rest and of the α rhythm response. Depending on the risk factors of early dysontogeny, the examined children were divided into groups differing in the phenomena of functional immaturity of the cerebral cortex and in psychophysiological functions. An injury at birth to a child and a combination of numerous risk factors of early dysontogeny has the most negative effect on the functional maturity of the rhythmogenic structures of cerebral cortex.     

The Importance of Synchrony and Temporal Order of Visual and Tactile Input for Illusory Limb Ownership Experiences – An fMRI Study Applying Virtual Reality

In the so-called rubber hand illusion, synchronous visuotactile stimulation of a visible rubber hand together with one''s own hidden hand elicits ownership experiences for the artificial limb. Recently, advanced virtual reality setups were developed to induce a virtual hand illusion (VHI). Here, we present functional imaging data from a sample of 25 healthy participants using a new device to induce the VHI in the environment of a magnetic resonance imaging (MRI) system. In order to evaluate the neuronal robustness of the illusion, we varied the degree of synchrony between visual and tactile events in five steps: in two conditions, the tactile stimulation was applied prior to visual stimulation (asynchrony of −300 ms or −600 ms), whereas in another two conditions, the tactile stimulation was applied after visual stimulation (asynchrony of +300 ms or +600 ms). In the fifth condition, tactile and visual stimulation was applied synchronously. On a subjective level, the VHI was successfully induced by synchronous visuotactile stimulation. Asynchronies between visual and tactile input of ±300 ms did not significantly diminish the vividness of illusion, whereas asynchronies of ±600 ms did. The temporal order of visual and tactile stimulation had no effect on VHI vividness. Conjunction analyses of functional MRI data across all conditions revealed significant activation in bilateral ventral premotor cortex (PMv). Further characteristic activation patterns included bilateral activity in the motion-sensitive medial superior temporal area as well as in the bilateral Rolandic operculum, suggesting their involvement in the processing of bodily awareness through the integration of visual and tactile events. A comparison of the VHI-inducing conditions with asynchronous control conditions of ±600 ms yielded significant PMv activity only contralateral to the stimulation site. These results underline the temporal limits of the induction of limb ownership related to multisensory body-related input.     

Influence of the initial autonomic tone on the state of hemodynamics of primary schoolchildren

The functional state of the cardiovascular system and its reaction to local isometric exercise in seven- and eight-year-old children was studied with consideration for the initial tone of the autonomic nervous system. Using the methods of variational pulsometry and tetrapolar thoracic rheography, it was established that children with predominant sympathetic influences on the heart rate (67?56.55% of the total number of those examined) had increased stroke and minute blood volumes against the background of relative tachycardia, compared with normo- and vagotonics. In sympathotonic boys, the leading component in the mechanism of urgent adaptation of the cardiovascular system to static exercise is spastic reactions of the vascular bed, which allow this contingent of schoolchildren to be identified as a group of children at high risk of autonomic dystonia with the hypertensive vascular syndrome.     

Brain Mechanisms of Voluntary Regulation of Activity during Acquisition of the Skill of Writing in Seven- to Eight-Year-Old Children

With the aim of studying the formation of brain mechanisms of voluntary activity regulation in junior schoolchildren and the role of these mechanisms in the acquisition of the skill of writing, a complex neuropsychological investigation was carried out. In the EEG of children with learning problems and a deficit of voluntary activity regulation (VAR), signs of the functional immaturity of the fronto–thalamic regulatory system (FTS) were found. Comparative neuropsychological analysis revealed a specific impairment of the VAR in these children in the form of pronounced impulsiveness, instability of a program, problems in switching over from one program to another, and self-control difficulties. It is concluded that the functional maturation of the FTS is a mechanism of VAR development. It is shown that the VAR deficiency in children with FTS immaturity is combined with a delay in the development of semantic and mediating speech functions. It was found that the features of the development of the higher mental functions in seven- to eight-year-old children with FTS immaturity specifically affect both the semantic and graphic aspects of writing acquisition.     

No,There Is No 150 ms Lead of Visual Speech on Auditory Speech,but a Range of Audiovisual Asynchronies Varying from Small Audio Lead to Large Audio Lag

An increasing number of neuroscience papers capitalize on the assumption published in this journal that visual speech would be typically 150 ms ahead of auditory speech. It happens that the estimation of audiovisual asynchrony in the reference paper is valid only in very specific cases, for isolated consonant-vowel syllables or at the beginning of a speech utterance, in what we call “preparatory gestures”. However, when syllables are chained in sequences, as they are typically in most parts of a natural speech utterance, asynchrony should be defined in a different way. This is what we call “comodulatory gestures” providing auditory and visual events more or less in synchrony. We provide audiovisual data on sequences of plosive-vowel syllables (pa, ta, ka, ba, da, ga, ma, na) showing that audiovisual synchrony is actually rather precise, varying between 20 ms audio lead and 70 ms audio lag. We show how more complex speech material should result in a range typically varying between 40 ms audio lead and 200 ms audio lag, and we discuss how this natural coordination is reflected in the so-called temporal integration window for audiovisual speech perception. Finally we present a toy model of auditory and audiovisual predictive coding, showing that visual lead is actually not necessary for visual prediction.