Recording Sessions Research Articles

Exploring production-perception relationships in normal hearing and cochlear implant adults: A lip-tube perturbation study

It has been claimed that auditory feedback mechanisms enable monitoring and calibration of feedforward commands in speech production. Therefore, lack of auditory feedback may interfere with adequate compensation strategies in perturbed situations. This study investigates the effect of hearing status and a lip tube perturbation on vowel production. Eleven normal-hearing controls, and seventeen cochlear implant (CI) users (7 prelingually, 10 postlingually) were recorded during the production of the vowel /u/. Acoustic analyses were conducted with and without a 15-mm-diam tube inserted between the lips. Recording sessions were also made before and after the perturbation, with and without auditory feedback. Deaf participants’ auditory feedback was provided by the CI and interrupted by switching off their implant devices. Separate analyses were conducted on the first (F1), the second formant (F2), and the fundamental frequency (F0). Results revealed a main effect of group and an interaction between condition and hearing status. Together, results suggest that auditory feedback plays an important role in speech compensation.

Time-lapse electrical recordings of single neurons from the mouse neocortex

The ability of the brain to adapt to environmental demands implies that neurons can change throughout life. The extent to which single neurons actually change remains largely unstudied, however. To evaluate how functional properties of single neurons change over time, we devised a way to perform in vivo time-lapse electrophysiological recordings from the exact same neuron. We monitored the contralateral and ipsilateral sensory-evoked spiking activity of individual L2/3 neurons from the somatosensory cortex of mice. At the end of the first recording session, we electroporated the neuron with a DNA plasmid to drive GFP expression. Then, 2 wk later, we visually guided a recording electrode in vivo to the GFP-expressing neuron for the second time. We found that contralateral and ipsilateral evoked responses (i.e., probability to respond, latency, and preference), and spontaneous activity of individual L2/3 pyramidal neurons are stable under control conditions, but that this stability could be rapidly disrupted. Contralateral whisker deprivation induced robust changes in sensory-evoked response profiles of single neurons. Our experiments provide a framework for studying the stability and plasticity of single neurons over long time scales using electrophysiology.

Influence of local objects on hippocampal representations: Landmark vectors and memory

The hippocampus is thought to represent nonspatial information in the context of spatial information. An animal can derive both spatial information as well as nonspatial information from the objects (landmarks) it encounters as it moves around in an environment. In this article, correlates of both object-derived spatial as well as nonspatial information in the hippocampus of rats foraging in the presence of objects are demonstrated. A new form of CA1 place cells, called landmark-vector cells, that encode spatial locations as a vector relationship to local landmarks is described. Such landmark vector relationships can be dynamically encoded. Of the 26 CA1 neurons that developed new fields in the course of a day's recording sessions, in eight cases, the new fields were located at a similar distance and direction from a landmark as the initial field was located relative to a different landmark. In addition, object-location memory in the hippocampus is also described. When objects were removed from an environment or moved to new locations, a small number of neurons in CA1 and CA3 increased firing at the locations where the objects used to be. In some neurons, this increase occurred only in one location, indicating object + place conjunctive memory; in other neurons, the increase in firing was seen at multiple locations where an object used to be. Taken together, these results demonstrate that the spatially restricted firing of hippocampal neurons encode multiple types of information regarding the relationship between an animal's location and the location of objects in its environment.

Inducing Gamma Oscillations and Precise Spike Synchrony by Operant Conditioning via Brain-Machine Interface

Neural oscillations in the low-gamma range (30-50 Hz) have been implicated in neuronal synchrony, computation, behavior, and cognition. Abnormal low-gamma activity, hypothesized to reflect impaired synchronization, has been evidenced in several brain disorders. Thus, understanding the relations between gamma oscillations, neuronal synchrony and behavior is a major research challenge. We used a brain-machine interface (BMI) to train monkeys to specifically increase low-gamma power in selected sites of motor cortex to move a cursor and obtain a reward. The monkeys learned to robustly generate oscillatory gamma waves, which were accompanied by a dramatic increase of spiking synchrony of highly precise spatiotemporal patterns. The findings link volitional control of LFP oscillations, neuronal synchrony, and the behavioral outcome. Subjects' ability to directly modulate specific patterns of neuronal synchrony provides a powerful approach for understanding neuronal processing in relation to behavior and for the use of BMIs in a clinical setting.

Surface EMG force modeling with joint angle based calibration

In this paper, a calibration method to compensate for changes in SEMG amplitude with joint angle is introduced. Calibration factors were derived from constant amplitude surface electromyogram (SEMG) recordings from the biceps brachii (during elbow flexion) and the triceps brachii (during elbow extension) across seven elbow joint angles. SEMG data were then recorded from the elbow flexors (biceps brachii and brachioradialis) and extensors (triceps brachii) during isometric, constant force flexion and extension contractions at the same joint angles. The resulting force at the wrist was measured. The fast orthogonal search method was used to find a mapping between the system inputs – estimated SEMG amplitudes and joint angle – and the system output – measured force, for both calibrated and non-calibrated SEMG data. Models developed with calibrated data yielded a statistically significant improvement in force estimation compared to models developed with non-calibrated data, suggesting that the calibration method can compensate for changes in the SEMG–force relationship with changing joint angle. It was also found that the number of non-linear, joint angle-dependent terms used in the SEMG–force model was reduced with calibration. Additionally, initial inter-session analysis performed for four subjects suggests that calibration values can be used for subsequent recording sessions, and different output force levels.

Test/retest repeatability of effect contralateral acoustic stimulation on the magnitudes of distortion product ototacoustic emissions

Contralateral inhibition of distortion product otoacoustic emissions (DPOAE) has become an important tool to assess the functioning of the medial olivocochlear efferents in humans. However, before this measurement can be applied clinically, the test/retest repeatability needs to be established. Therefore, the current study aimed at evaluating intra- and intersession test/retest repeatability of contralateral inhibition of DPOAE at 2f(1) -f(2) . Prospective Test/Retest Reliability Study. Contralateral inhibition of DPOAE magnitudes were measured in the right ear of 24 adult male participants. To assess the intrasession repeatability, measurements were repeated without altering the position of the DPOAE probe (single-probe-fit). To assess intersession reliability, measurements were repeated on 8 different days (multiple-probe-fit). Repeatability of inhibition of DPOAE magnitudes was evaluated by Cronbach's alpha, interclass correlations, standard error of measurement, and its 95% confidence interval and smallest detectable difference. DPOAE magnitudes were highly stable and repeatable across different recording sessions. However, test/retest reliability coefficients of DPOAE inhibition magnitudes were less than satisfactory for all the frequencies, in both single-probe-fit and multiple-probe-fit modes. Results of the present study showed that contralateral inhibition magnitudes of DPOAEs varied considerably, even though DPOAEs magnitudes remained essentially the same across different recording sessions. As reliability is an essential aspect of any clinical procedure, it is suggested that at present contralateral inhibition of DPOAEs should not be used clinically to evaluate the medial efferent system. Laryngoscope, 2012.

Functional near‐infrared spectroscopy for the assessment of overt reading

Functional near-infrared spectroscopy (fNIRS) has become increasingly established as a promising technique for monitoring functional brain activity. To our knowledge, no study has yet used fNIRS to investigate overt reading of irregular words and nonwords with a full coverage of the cerebral regions involved in reading processes. The aim of our study was to design and validate a protocol using fNIRS for the assessment of overt reading. Twelve healthy French-speaking adults underwent one session of fNIRS recording while performing an overt reading of 13 blocks of irregular words and nonwords. Reading blocks were separated by baseline periods during which participants were instructed to fixate a cross. Sources (n = 55) and detectors (n = 16) were placed bilaterally over frontal, temporal, parietal, and occipital regions. Two wavelengths were used: 690 nm, more sensitive to deoxyhemoglobin (HbR) concentration changes, and 830 nm, more sensitive to oxyhemoglobin (HbO) concentration changes. For all participants, total hemoglobin (HbT) concentrations (HbO + HbR) were significantly higher than baseline for both irregular word and nonword reading in the inferior frontal gyri, the middle and superior temporal gyri, and the occipital cortices bilaterally. In the temporal gyri, although the difference was not significant, [HbT] values were higher in the left hemisphere. In the bilateral inferior frontal gyri, higher [HbT] values were found in nonword than in irregular word reading. This activation could be related to the grapheme-to-phoneme conversion characterizing the phonological pathway of reading. Our findings confirm that fNIRS is an appropriate technique to assess the neural correlates of overt reading.

Differential representation of auditory categories between cell classes in primate auditory cortex

A comprehensive understanding of the neural mechanisms of cognitive function requires an understanding of how neural representations are transformed across different scales of neural organization: from within local microcircuits to across different brain areas. However, the neural transformations within the local microcircuits are poorly understood. Particularly, the role that two main cell classes of neurons in cortical microcircuits (i.e. pyramidal neurons and interneurons) have in auditory behaviour and cognition remains unknown. In this study, we tested the hypothesis that pyramidal cells and interneurons in the auditory cortex play a differential role in auditory categorization. To test this hypothesis, we recorded single-unit activity from the auditory cortex of rhesus monkeys while they categorized speech sounds. Based on the spike-waveform shape, a neuron was classified as either a narrow-spiking putative interneuron or a broad-spiking putative pyramidal neuron. We found that putative interneurons and pyramidal neurons in the auditory cortex differentially coded category information: interneurons were more selective for auditory categories than pyramidal neurons. These differences between cell classes may be an essential property of the neural computations underlying auditory categorization within the microcircuitry of the auditory cortex.

The Augmented String Quartet: Experiments and Gesture Following

We present interdisciplinary research undertaken for the development of an ‘augmented’ string quartet. Hardware and software components were especially designed to enable mixed acoustic/electronic music where bow gestures drive digital sound processes. Precisely, inertial motion sensors and a bow force sensor were added to each musician's bow, and dedicated modules allowed forthe wireless data transmission to an on-line gesture analysis system. Prior to the performance, a research phase was performed to evaluate qualitatively the variability of the gesture data. Recording sessions of both gesture and audio data were carried out with a professional string quartet. The music material included a set of prototypical musical phrases containing various bowing styles and playing techniques as well as a complete music composition. The analysis of the recorded sessions allowed us to compare the consistency within and between players. While a given player was found to be generally consistent, the comparison between players revealed significant gesture idiosyncrasies. These results helped us to adapt a real-time gesture analysis system called the gesture follower. This tool was successful to automatically synchronize the live performance with electronic sound transformation in two concerts. A quantitative assessment is reported on a specific section of the piece, illustrating the accuracy and the types of errors encountered.

Accuracy of landmark identification on postero-anterior cephalograms

ObjectivesThe aim of this study was to examine accuracy in landmark identification on digital postero-anterior cephalograms, (PAC) assessing the intra-observer and the inter-observer repeatability in determining these landmarks. Materials and methodsTwenty postero-anterior digital cephalometric radiographs were randomly selected from data files of patients aged between 11 to 15 years and were used in this study. Thirty-four commonly used PAC landmarks were included in this investigation and each observer performed the determination of all landmarks on every PAC cephalograms twice (T1 and T2). Mean positions located by the three observers in the first recording session both on the x and y axes, were calculated and defined as the “best estimate” for every landmarks. Systematic differences between the two records at T1 and T2 of the same observer were evaluated using the paired t-test with P<0.05. In order to test the hypothesis of equal mean of the vectors of differences to the “best estimate” for the three raters, a one-way ANOVA test was performed. ResultsMost landmarks showed a good reproducibility between the two recording sessions, except for some landmarks located in the zygomatic arch, mandible and dentition. As regards inter-observer reliability, there were statistically significant differences (P<0.05) in both x and y axis. ConclusionsEach landmark has its own margin of error and there is a clear difference in the localization accuracy between the x and y coordinates. Since condylar points (CDr-CDl), coronoid points (CORr-CORl) and mental foramen points (MFr-MFl) showed to have a questionable localization accuracy, PAC cannot be strictly recommended for accurate evaluation of any asymmetry. Some dental landmarks seem to be poorly reproducible; therefore the usefulness of postero-anterior cephalometric analysis to evaluate dental discrepancies or maxillo-mandibular molar relationship is questioned.

The effect of distinct mental strategies on classification performance for brain–computer interfaces

Motor imagery is the task most commonly used to induce changes in electroencephalographic (EEG) signals for mental imagery-based brain computer interfacing (BCI). In this study, we investigated EEG patterns that were induced by seven different mental tasks (i.e. mental rotation, word association, auditory imagery, mental subtraction, spatial navigation, imagery of familiar faces and motor imagery) and evaluated the binary classification performance. The aim was to provide a broad range of reliable and user-appropriate tasks to make individual optimization of BCI control strategies possible. Nine users participated in four sessions of multi-channel EEG recordings. Mental tasks resulting most frequently in good binary classification performance include mental subtraction, word association, motor imagery and mental rotation. Our results indicate that a combination of ‘brain-teasers’ – tasks that require problem specific mental work (e.g. mental subtraction, word association) – and dynamic imagery tasks (e.g. motor imagery) result in highly distinguishable brain patterns that lead to an increased performance.

Spatial extent of the local field potential in macaque area LIP

Event Abstract Back to Event Spatial extent of the local field potential in macaque area LIP Elsie Premereur1 and Peter Janssen1* 1 KULeuven, Belgium The spatial extent of gamma oscillations in the local field potential (LFP) is heavily debated at present. To address this issue we recorded multi-unit activity (MUA) and LFPs in the Lateral Intraparietal area (LIP) with a multi-electrode probe with 16 contact points spaced 150 microns apart (total distance covered: 2.25 mm). The recording cylinder was positioned in an oblique angel to allow recordings orthogonal to the lateral bank of the intraparietal sulcus. We positioned the probe so that all electrodes were located in the cortex of the lateral bank. Spike rate and LFP-activity were recorded while the monkey was performing a memory guided saccade task towards ten different positions in the contralateral visual field. We recorded activity in 14 grid positions, during 40 recording sessions. We found that only the MUA and high-gamma (80-170 Hz) power were significantly affected by target position. Furthermore, for every recording session, we determined the electrode which showed the highest visual spike rate response across target positions (0-320 ms after target onset), which we termed the primary electrode. We then calculated the MUA and LFP responses for this condition on neighboring electrodes and determined the distance from the primary electrode where the response fell below 50% of the response at the primary electrode. Consistent with previous studies we found that the visual MUA response was highly localized within 200 micron around the primary electrode: the MUA response fell below 50% of the primary electrode response at an average distance of 213 micron. The high-gamma response was also significantly affected by distance from the primary electrode but fell to 50% of the primary electrode response at an average distance of 1650 micron (where no MUA response was present), indicating that even the high-gamma oscillations are shared over a much larger distance across the cortical thickness. The medium gamma (50-80 Hz), low gamma (25-50 Hz), beta (12-25 Hz) and alpha (8-12 Hz) power never fell below 50% of the primary electrode response along the probe shaft. These results show that target-selective MUA responses in area LIP are highly localized, whereas LFP-responses, even in the high, medium and low gamma band, extend over a much larger region of cortex, sometimes even across the entire cortical thickness. Acknowledgements ERC-StG 260607, FWO, GOA, PFV, IUAP Keywords: multielectrode arrays, Macaca mulatta, Lateral Intraprietal Area (LIP), Saccades, local field potential (LFP) Conference: Belgian Brain Council, Liège, Belgium, 27 Oct - 27 Oct, 2012. Presentation Type: Poster Presentation Topic: Other basic/clinical neurosciences topic Citation: Premereur E and Janssen P (2012). Spatial extent of the local field potential in macaque area LIP. Conference Abstract: Belgian Brain Council. doi: 10.3389/conf.fnhum.2012.210.00072 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Aug 2012; Published Online: 12 Sep 2012. * Correspondence: Prof. Peter Janssen, KULeuven, Leuven, Belgium, Peter.Janssen@med.kuleuven.be Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Elsie Premereur Peter Janssen Google Elsie Premereur Peter Janssen Google Scholar Elsie Premereur Peter Janssen PubMed Elsie Premereur Peter Janssen Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The Role of Prominence and Position in the Acquisition of Codas in the Speech of Hearing-impaired Children

The paper describes the developmental phases in the acquisition of codas in the speech of Hebrew-acquiring hearing-impaired children, with reference to prosodic properties—the prominence (stress) and the position of the syllable hosting the coda. The participants were 10 hearing-impaired children using cochlear implant or conventional hearing aid device, ranging in age from 1;5 to 3;5 years old in their first recording session. Data collection continued until each child completed the acquisition of codas. A prosodic analysis of the phases of coda acquisition reveals a similarity between hearing impaired children and typically developing hearing children acquiring Hebrew, as well as other languages. The results suggest that the position of the syllable in the word (final, penultimate, antepenultimate) plays a major role in the development of codas, whereas stress has no significant effect.

Study of biomechanical overload in urban gardeners of Barcelona: application of analytical models for risk exposure evaluation in annual working cycle

Occupational musculoskeletal disorders in the upper limbs and its consequences on the impact and prevalence in the work force are subject of many investigations in almost all the production fields. However, the exposure to this kind of risk factor on urban gardeners has not been well studied so far. The kind of plant varieties used in the parks, the tools that they use, as much as the necessary actions for the maintenance of the park, have an impact on the biomechanical overload of the upper limbs. Additionally, the analysis of the exposure to the biomechanical overload on upper limbs in gardening work is a complex task, mainly because it is an activity highly variable and of annual cycle. For this reason an analytical model for risk exposure evaluation is necessary. During this research the work activity of 29 gardeners in 3 urban parks of Barcelona has been analyzed. Each park has a specific acting plan, in relation with the quantity and the typology of vegetal species, its classification and the season of the year. Work and observation and video recording sessions on-site were conducted. The video-graphic registration was done on workers without any prior musculoskeletal disorder and with a minimum labour experience of 5 years. Moreover, the analysis of saturation time, considered as the relation of the repetitive working hours in reference with the hours of effective work was done. Using the registered tasks on video, the biomechanical overload on upper limbs applying the OCRA Checklist method was analyzed. A methodological procedure to analyze the risk exposure in annual working cycle has been proposed. The results that we got allow us to get information that can help in the assignment of the tasks and in the training of staff, as well as in the recommendations of the urban landscape's design. All these aspects have the goal to decrease the risk to develop work-related musculoskeletal disorders.

The effects of notch filtering on electrically evoked myoelectric signals and associated motor unit index estimates

BackgroundNotch filtering is the most commonly used technique for suppression of power line and harmonic interference that often contaminate surface electromyogram (EMG) signals. Notch filters are routinely included in EMG recording instrumentation, and are used very often during clinical recording sessions. The objective of this study was to quantitatively assess the effects of notch filtering on electrically evoked myoelectric signals and on the related motor unit index measurements.MethodsThe study was primarily based on an experimental comparison of M wave recordings and index estimates of motor unit number and size, with the notch filter function of the EMG machine (Sierra Wave EMG system, Cadwell Lab Inc, Kennewick, WA, USA) turned on and off, respectively. The comparison was implemented in the first dorsal interosseous (FDI) muscle from the dominant hand of 15 neurologically intact subjects and bilaterally in 15 hemiparetic stroke subjects.ResultsOn average, for intact subjects, the maximum M wave amplitude and the motor unit number index (MUNIX) estimate were reduced by approximately 22% and 18%, respectively, with application of the built-in notch filter function in the EMG machine. This trend held true when examining the paretic and contralateral muscles of the stroke subjects. With the notch filter on vs. off, across stroke subjects, we observed a significant decrease in both maximum M wave amplitude and MUNIX values in the paretic muscles, as compared with the contralateral muscles. However, similar reduction ratios were obtained for both maximum M wave amplitude and MUNIX estimate. Across muscles of both intact and stroke subjects, it was observed that notch filtering does not have significant effects on motor unit size index (MUSIX) estimate. No significant difference was found in MUSIX values between the paretic and contralateral muscles of the stroke subjects.ConclusionsThe notch filter function built in the EMG machine may significantly reduce the M wave amplitude and the MUNIX measurement. However, the notch filtering does not jeopardize the evaluation of the reduction ratio in maximum M wave amplitude and MUNIX estimate of the paretic muscles of stroke subjects when compared with the contralateral muscles.

Evaluation of sublingual microcirculatory blood flow in the critically ill

The microcirculation regulates the supply of oxygen and nutrients to tissues. The sublingual region is frequently used as a window to microcirculation in critically ill patients. Numerous studies have reported impaired sublingual microcirculatory flow. We hypothesized that the quality of sidestream dark field imaging (SDF) recordings could be systematically analyzed to justify the monitoring of sublingual microcirculation in interventional studies or in clinical practice. The sublingual microcirculation in critically ill patients with septic shock, open heart surgery, or alcoholic pancreatitis, and healthy subjects was recorded with a hand held SDF device by one trained investigator in observational setting. A total of 82 video recording sessions were performed and 240 video clips eligible for quality assessment were identified. Quality assessment was performed offline by two investigators independently and blinded for the origin of the video file. Of the 240 clips, pressure artifact was detected in 86 (36%), major blood in 5 (2.1%), major saliva in 21 (8.8%) and extreme brightness causing loss of visible capillaries in 16 (6.7%) clips. The dominating vessel architecture was multiple size vessels in 228 (95%) and repeating capillary loop motif in 12 (5.0%). The mean (± SD) relative size reduction during stabilization was -6.9% (± 4.7%). Excellent technical quality was detected in 74 of 240 (30.8%) recordings. Our findings highlight the need of a comprehensive training period and reporting of data quality before findings with SDF imaging can be accepted as surrogate end points in interventional studies or as guidance in clinical practice.

Fractal and nonlinear changes in the long-term baseline fluctuations of fetal heart rate

The interpretation of heart rate patterns obtained by fetal monitoring relies on the definition of a baseline, which is considered as the running average heart rate in the absence of external stimuli during periods of fetal rest. We present a study along gestation of the baseline's fluctuations, in relation to fractal and nonlinear properties, to assess these fluctuations according with time-varying attracting levels introduced by maturing regulatory mechanisms. A low-risk pregnancy was studied weekly from the 17th to 38th week of gestation during long-term recording sessions at night (>6h). Fetal averaged pulse rate samples and corresponding baseline series were obtained from raw abdominal ECG ambulatory data. The fractal properties of these series were evaluated by applying detrended fluctuation analysis. The baseline series were also explored to evaluate nonlinear properties and time ordering by applying the scaling magnitude and sign analyses. Our main findings are that the baseline shows fractal and even nonlinear anticorrelated fluctuations. This condition was specially the case before mid-gestation, as revealed by α values near to unit, yet becoming significantly more complex after 30 weeks of gestation as indicated by α(mag) values >0.5. The structured (i.e. not random) fluctuations and particular nonlinear changes that we found thus suggest that the baseline provides on itself information concerning the functional integration of cardiac regulatory mechanisms.

Transcranial magnetic stimulation and motor plasticity in human lateral cerebellum: dual effect on saccadic adaptation.

The cerebellum is a key area for movement control and sensory-motor plasticity. Its medial part is considered as the exclusive cerebellar center controlling the accuracy and adaptive calibration of saccadic eye movements. However, the contribution of other zones situated in its lateral part is unknown. We addressed this question in healthy adult volunteers by using magnetic resonance imaging (MRI)-guided transcranial magnetic stimulation (TMS). The double-step target paradigm was used to adaptively lengthen or shorten saccades. TMS pulses over the right hemisphere of the cerebellum were delivered at 0, 30, or 60 ms after saccade detection in separate recording sessions. The effects on saccadic adaptation were assessed relative to a fourth session where TMS was applied to Vertex as a control site. First, TMS applied upon saccade detection before the adaptation phase reduced saccade accuracy. Second, TMS applied during the adaptation phase had a dual effect on saccadic plasticity: adaptation after-effects revealed a potentiation of the adaptive lengthening and a depression of the adaptive shortening of saccades. For the first time, we demonstrate that TMS on lateral cerebellum can influence plasticity mechanisms underlying motor performance. These findings also provide the first evidence that the human cerebellar hemispheres are involved in the control of saccade accuracy and in saccadic adaptation, with possibly different neuronal populations concerned in adaptive lengthening and shortening. Overall, these results require a reappraisal of current models of cerebellar contribution to oculomotor plasticity.

Testing the ICA mixing matrix based on inter-subject or inter-session consistency

Independent component analysis (ICA) is increasingly used for analyzing brain imaging data. ICA typically gives a large number of components, many of which may be just random, due to insufficient sample size, violations of the model, or algorithmic problems. Few methods are available for computing the statistical significance (reliability) of the components. We propose to approach this problem by performing ICA separately on a number of subjects, and finding components which are sufficiently consistent (similar) over subjects. Similarity is defined here as the similarity of the mixing coefficients, which usually correspond to spatial patterns in EEG and MEG. The threshold of what is "sufficient" is rigorously defined by a null hypothesis under which the independent components are random orthogonal components in the whitened space. Components which are consistent in different subjects are found by clustering under the constraint that a cluster can only contain one source from each subject, and by constraining the number of the false positives based on the null hypothesis. Instead of different subjects, the method can also be applied on different recording sessions from a single subject. The testing method is particularly applicable to EEG and MEG analysis.

Adaptive tracking of discriminative frequency components in electroencephalograms for a robust brain–computer interface

In an electroencephalogram (EEG)-based brain–computer interface (BCI), motor imagery has been successfully used as a communication strategy. Motor imagery causes detectable amplitude changes in certain frequency bands of EEGs, which are dubbed event-related desynchronization\\synchronization. The frequency components that give effective discrimination between different types of motor imagery are subject specific and identification of these subject-specific discriminative frequency components (DFCs) is important for the accurate classification of motor imagery activities. In this paper, we propose a new method to estimate the DFC using the Fisher criterion and investigate the variability of these DFCs over multiple sessions of EEG recording. Observing the variability of DFC over sessions in the analysis, a new BCI approach called the Adaptively Weighted Spectral-Spatial Patterns (AWSSP) algorithm is proposed. AWSSP tracks the variation in DFC over time adaptively based on the deviation of discriminative weight values of frequency components. The classification performance of the proposed AWSSP is compared with a static BCI approach that employs fixed DFCs. In the offline and online experiments, AWSSP offers better classification performance than the static approach, emphasizing the significance of tracking the variability of DFCs in EEGs for developing robust motor imagery-based BCI systems. A study of the effect of feedback on the variation in DFCs is also performed in online experiments and it is found that the presence of visual feedback results in increased variation in DFCs.