Visuomotor synchronization in adults and seven- to eight-year-old children

A group of 22 seven- to eight-year-old children and a group of 17 adults participated in the experiment in which they synchronized their movements (pressing a button) with an isochronous sequence of visual stimuli. The period of the sequence was varied between 500 to 2000 ms at a step of 300 ms. Two consecutive phases of visuomotor synchronization were studied: the initiation phase, which corresponds to the process of transition between responding to a visual stimulus to stable synchronization with them, and the synchronization phase. 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 terms of the phase correction of the central timer. It was shown that (1) the range of successful visuomotor synchronization was narrower in seven- to eight-year-old children than in adults (from 600–700 ms to ∼1700 ms); (2) the initiation phase duration was about the same in seven- to eight-year-old children and adults, and typical shapes of individual relaxation curves were similar in both adults and children; (3) although the statistical properties of asynchrony were comparable in children and adults, the mechanism of phase correction of the central timer operated at a lower correction gain factor in children than in adults. In children, the phase correction process was also characterized by a substantially higher level of the central and motor noise, which leads to higher asynchrony variability and more frequent and longer 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.     

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.     

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.     

Changes in face expression recognition caused by additional visual-spatial load

Changes in face expression recognition and EEG synchronization arising from additional load on working memory were studied in healthy adults. Two types of additional task--semantic and visuospatial--were used to load working memory in an experiment with a visual set, formed to facial stimuli. During perception of new facial stimuli, both these types of additional task caused an increase of erroneous face expression recognitions in the form of assimilative illusions. Alpha-band (8-10 Hz) EEG synchronization analysis revealed that additional memory load causes a decrease of frontal attention system input in set-forming and set-shifting. As for theta-band (4-7 Hz) synchronization, it changed ambiguously at additional memory load--in right fronto-temporal region coherence function decreased; other coherence connections, especially intra-hemispheric and in the left hemisphere, increased. At issue is the crucial role of fronto-thalamic and cortico-hippocampal systems in plasticity of visual sets formed to facial expressions.     

Developmental changes in hierarchical visual stimulus recognition in children aged 5-10 years

Reaction time (RT) and performance accuracy in hierarchical visual stimulus recognition at local and global levels were studied in 95 healthy 5-6, 6-7, 7-8 and 9-10-year-old children and 10 adults. Task performance of all examined subjects, both children and adults, was faster and more accurate during global feature recognition (global advantage effect), with increased RT to incongruent stimuli in local condition (global interference effect). Significant inter-individual differences were found in the youngest group (5-6-year-olds): 7 children from the total number of 37 subjects failed to show the global advantage and global interference effects. Significant progressive shifts in performance accuracy during hierarchical stimulus recognition at both local and global levels were observed in the period between 6-7 and 7-8 years and then between 9-10 years and adulthood. The time course of age-dependent changes in recognition time was different for the global and local features of the hierarchical stimuli: the RT significantly decreased in every successive age group for local feature recognition beginning from 6-7-year-old children, whereas there was no significant difference between 7-8 and 9-10-year-old children in the RT of the recognition of the global feature. In the two younger groups (5-6 and 6-7 years), the stimulus type affected performance in a specific manner: RT increased to both incongruent and neutral stimuli irrespective of the level of the target feature. It was assumed that nonlinear developmental trends in hierarchical stimulus recognition parameters depend on both maturation of visual information processing and development of executive functions, especially those related to selection of relevant signals.     

Spatial synchronization of cortical electrical activity at different stages of visual set in preschool children

Changes in the alpha-rhythm synchronization were revealed at different stages of cognitive visual set in 5- to 7-year-old children. We found a clear-cut correlation of these changes with set plasticity. In children with a plastic set, the EEG synchronization between the frontal and other brain regions substantially increased in the period of set-shifting (the actualization stage). At the set extinction stage, after set-shifting has already taken place, the EEG-synchronization becomes minimal. On the contrary, in children who formed a rigid set, EEG coherence considerably increases at the set extinction stage. This finding suggests that the rigid set still affects the cognitive activity even after (judging from oral reports) the set shift has been completed. The age-related differences in cognitive set formation clearly correlate with the time course of the EEG synchronization between the frontal and other brain regions. We think that the ability to form a plastic visual set depends on the frontal cortex maturation, which occurs at the age of 6-7 years, and its age-related effect on the brain cognitive functions.     

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).     

Cortical slow negative potentials during eye fixation and preparing of visually triggered saccades in a man

In 10 right-handed healthy subjects EEGs preceding saccades with mean latent periods were selectively averaged. Two standard schemes of visual stimulation were used: with immediate presentation of a peripheral target stimuli after the central fixation stimulus (a single step paradigm) and with the interval between the stimuli in 200 ms (GAP paradigm). Two waves of slow premotor negativity (early PMN1 and late PMN2) that appeared 930 +/- 79 and 609 +/- 82 ms, respectively, prior to a saccade onset were observed. The PMN2 was followed by the negative potentials N-3, N-2, and N-1 (saccadic initiation potential). It was found that in GAP stimulation condition the PMN1 was less pronounces and N-1 was increased as compared to the single step. These findings suggest that disengage of attention from the central point during the GAP period clears the saccadic system for decision making and initiation of a saccade. Under such conditions, the expectation of a visual target does not require a high level of nonspecific activation and motor attention.     

Positive potentials of the human brain at different stages of preparation of a visually triggered saccade

The EEG of 10 right-handed subjects preceding saccades with mean values of latent periods were selected and averaged. Two standard paradigms of presentation of visual stimuli (central fixation stimulus-peripheral target succession): with a 200-ms inerstimulus interval (GAP) and successive single step (SS). During the period of central fixation, two kinds of positive potentials were observed: fast potentials of "inermediate" positivity (IP) developing 600-400 ms prior to saccade onset and fast potentials of "leading" positivity (LP), which immediately preceded the offset of the central fixation stimulus. Peak latency of the LP potentials was 300 ms prior to saccade onset in the SS paradigm and 400 ms in the GAP paradigm. These potentials were predominantly recorded in the frontal and frontosagittal cortical areas. Decrease in the latency by 30-50 ms in the GAP paradigm was associated with more pronounced positive potentials during the fixation period and absence of the initiation potential P-1' (or decrease in its amplitude). The obtained evidence suggest that the fast positive presaccadic potentials are of a complex nature related to attention, anticipation, motor preparation, decision making, saccadic initiation, and backward afferentation.     

Developmental changes of BOLD signal correlations with global human EEG power and synchronization during working memory

In humans, theta band (5-7 Hz) power typically increases when performing cognitively demanding working memory (WM) tasks, and simultaneous EEG-fMRI recordings have revealed an inverse relationship between theta power and the BOLD (blood oxygen level dependent) signal in the default mode network during WM. However, synchronization also plays a fundamental role in cognitive processing, and the level of theta and higher frequency band synchronization is modulated during WM. Yet, little is known about the link between BOLD, EEG power, and EEG synchronization during WM, and how these measures develop with human brain maturation or relate to behavioral changes. We examined EEG-BOLD signal correlations from 18 young adults and 15 school-aged children for age-dependent effects during a load-modulated Sternberg WM task. Frontal load (in-)dependent EEG theta power was significantly enhanced in children compared to adults, while adults showed stronger fMRI load effects. Children demonstrated a stronger negative correlation between global theta power and the BOLD signal in the default mode network relative to adults. Therefore, we conclude that theta power mediates the suppression of a task-irrelevant network. We further conclude that children suppress this network even more than adults, probably from an increased level of task-preparedness to compensate for not fully mature cognitive functions, reflected in lower response accuracy and increased reaction time. In contrast to power, correlations between instantaneous theta global field synchronization and the BOLD signal were exclusively positive in both age groups but only significant in adults in the frontal-parietal and posterior cingulate cortices. Furthermore, theta synchronization was weaker in children and was--in contrast to EEG power--positively correlated with response accuracy in both age groups. In summary we conclude that theta EEG-BOLD signal correlations differ between spectral power and synchronization and that these opposite correlations with different distributions undergo similar and significant neuronal developments with brain maturation.     

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.     

Is High Temporal Resolution Achievable for Paediatric Cardiac Acquisitions during Several Heart Beats? Illustration with Cardiac Phase Contrast Cine-MRI

Background

During paediatric cardiac Cine-MRI, data acquired during cycles of different lengths must be combined. Most of the time, Feinstein’s model is used to project multiple cardiac cycles of variable lengths into a mean cycle.

Objective

To assess the effect of Feinstein projection on temporal resolution of Cine-MRI.

Methods

1/The temporal errors during Feinstein’s projection were computed in 306 cardiac cycles fully characterized by tissue Doppler imaging with 6-phase analysis (from a population of 7 children and young adults). 2/The effects of these temporal errors on tissue velocities were assessed by simulating typical tissue phase mapping acquisitions and reconstructions. 3/Myocardial velocities curves, extracted from high-resolution phase-contrast cine images, were compared for the 6 volunteers with lowest and highest heart rate variability, within a population of 36 young adults.

Results

1/The mean of temporal misalignments was 30 ms over the cardiac cycle but reached 60 ms during early diastole. 2/During phase contrast MRI simulation, early diastole velocity peaks were diminished by 6.1 cm/s leading to virtual disappearance of isovolumic relaxation peaks. 3/The smoothing and erasing of isovolumic relaxation peaks was confirmed on tissue phase mapping velocity curves, between subjects with low and high heart rate variability (p = 0.05).

Conclusions

Feinstein cardiac model creates temporal misalignments that impair high temporal resolution phase contrast cine imaging when beat-to-beat heart rate is changing.     

Development of working memory brain organization in young schoolchildren

In children of 7-8 and 9-10 years old, the ERP components were studied by comparing two non-verbalized visuo-spatial stimuli shown in succession with 1.5-1.8 s interstimulus interval. We found the age-related differences in the specific way (and the extent to which) the cortical areas were involved into the processes of the reference stimulus (the first stimulus in the pair) encoding and into the process of comparing the memory trace against the test stimulus. In both age groups, the sensory-specific N1 ERP component in the visual cortices had larger amplitude during working memory than during free observation. Age-related differences in the processing of the sensory-specific parameters of a stimulus are most pronounced in ERP to the test stimulus: in children of 9-10, the amplitude of N1 component increased significantly in all caudal leads following the earlier increase in P1 component in the inferior temporal and occipital areas. In the children of that age, unlike children of 7-8, the early involvement of ventro-lateral prefrontal cortex becomes apparent. In that area an increase of positivity confined to 100-200 ms post-stimulus is observed. Substantial inter-group differences are observed in the late ERP components that are related to cognitive operations. In children of 7-8, presenting both reference and test stimuli causes a significant increase in the amplitude of late positive complex (LPC) in caudal leads with maximal increase being observed in parietal areas at 300-800 ms post-stimulus. In children of 9-10, one can see some adult-like features of the late ERP components during different stages of the working memory process: in fronto-central areas N400 component increases in response to the reference stimulus, whereas LPC increases in response to the test stimulus. The data reported in this work show that the almost mature functional organization of working memory is already in place at the age of 9-10. However, the extent of the prefrontal cortex (especially its dorsal areas) involvement does not yet match the level of maturity.     

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.     

Modulation of backward pattern masking by focal visual attention

The effect of focal visual attention on backward pattern masking was investigated using an orientation discrimination task. The results show that attention reduces primarily the effect of interruption masking, the later component of pattern masking, which occurs when the delay between the target and mask onset is about 50-150 ms. The strongest spatial cueing effect, i.e. the strongest reduction of the orientation discrimination threshold due to focal attention, was observed at intermediate (approximately 100 ms) target-to-mask stimulus onset asynchrony (SOA). There was a weak effect of cueing at shorter SOAs, and no or a very weak attentional effect was present at longer target-to-mask SOAs, where the pattern masking effect is absent. The dynamics of attentional modulation of backward pattern masking correlates closely with the dynamics of the attentional modulation of neuronal responses in the early visual cortex.     

Analysis and modeling of time-variant amplitude–frequency couplings of and between oscillations of EEG bursts

Low-frequency (0.5-2.5 Hz) and individually defined high-frequency (7-11 or 8-12 Hz; 11-15 or 14-18 Hz) oscillatory components of the electroencephalogram (EEG) burst activity derived from thiopental-induced burst-suppression patterns (BSP) were investigated in seven sedated patients (17-26 years old) with severe head injury. The predominant high-frequency burst oscillations (>7 Hz) were detected for each patient by means of time-variant amplitude spectrum analysis. Thereafter, the instantaneous envelope (IE) and the instantaneous frequency (IF) were computed for these low- and high-frequency bands to quantify amplitude-frequency dependencies (envelope-envelope, envelope-frequency, and frequency-frequency correlations). Time-variant phase-locking, phase synchronization, and quadratic phase couplings are associated with the observed amplitude-frequency characteristics. Additionally, these time-variant analyses were carried out for modeled burst patterns. Coupled Duffing oscillators were adapted to each EEG burst and by means of these models data-based burst simulations were generated. Results are: (1) strong envelope-envelope correlations (IE courses) can be demonstrated; (2) it can be shown that a rise of the IE is associated with an increase of the IF (only for the frequency bands 0.5-2.5 and 7-11 or 8-12 Hz); (3) the rise characteristics of all individually averaged envelope-frequency courses (IE-IF) are strongly correlated; (4) for the 7-11 or 8-12 Hz oscillation these associations are weaker and the variation between the time courses of the patients is higher; (5) for both frequency ranges a quantitative amplitude-frequency dependency can be shown because higher IE peak maxima are accompanied by stronger IF changes; (6) the time range of significant phase-locking within the 7-11 or 8-12 Hz frequency bands and of the strongest quadratic phase couplings (between 0.5-2.5 and 7-11 or 8-12 Hz) is between 0 and 1,000 ms; (7) all phase coupling characteristics of the modeled bursts accord well with the corresponding characteristics of the measured EEG burst data. All amplitude-frequency dependencies and phase locking/coupling properties described here are known from and can be discussed using coupled Duffing oscillators which are characterized by autoresonance properties.     

When is now? Perception of simultaneity.

We address the following question: Is there a difference (D) between the amount of time for auditory and visual stimuli to be perceived? On each of 1000 trials, observers were presented with a light-sound pair, separated by a stimulus onset asynchrony (SOA) between -250 ms (sound first) and +250 ms. Observers indicated if the light-sound pair came on simultaneously by pressing one of two (yes or no) keys. The SOA most likely to yield affirmative responses was defined as the point of subjective simultaneity (PSS). PSS values were between -21 ms (i.e. sound 21 ms before light) and +150 ms. Evidence is presented that each PSS is observer specific. In a second experiment, each observer was tested using two observer-stimulus distances. The resultant PSS values are highly correlated (r = 0.954, p = 0.003), suggesting that each observer''s PSS is stable. PSS values were significantly affected by observer-stimulus distance, suggesting that observers do not take account of changes in distance on the resultant difference in arrival times of light and sound. The difference RTd in simple reaction time to single visual and auditory stimuli was also estimated; no evidence that RTd is observer specific or stable was found. The implications of these findings for the perception of multisensory stimuli are discussed.     

Timers in Early Development of Sea Urchin Embryos

To elucidate the timing mechanisms in the early development of sea urchin embryos, we measured the times of initiation of the first four cleavages, of ciliary movement, of primary mesenchyme cell ingression, and of gastrulation at four temperatures ranging from 11 to 20°C. The times of cleavage and of initiation of ciliary movement showed similar temperature dependency, indicating that these events may be controlled by a common timer (the first timer). Although batches of eggs often showed variation in the period between fertilization and the first cleavage, their subsequent cleavages were more regular. This indicates that the first timer may not start at fertilization. The ingression of mesenchyme cells and the onset of gastrulation showed similar temperature dependency that was higher than that of other events, suggesting the existence of a second timer. Temperature shift experiments indicate that the second timer starts at the mid-blastula (the 8–9th cleavage) stage when divisions of blastomeres become asynchronous.     

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.