Papers by Jozina De Graaf
Experimental Brain Research, Apr 1, 1991
Information about the direction of the virtual line between two positions in space (directional i... more Information about the direction of the virtual line between two positions in space (directional information) is used in many decision-making and motor tasks. We investigated how accurately directional information is processed by the brain. Subjects performed two types of task. In both tasks they sat at a table. In the first task they had to move their hand slowly and accurately from an initial position 40 cm in front of them to visually presented targets at a distance of 30 cm from the initial position (movement task). We analysed the initial movement direction. In the second task subjects had to position pointers in the direction of the targets as accurately as they could (perceptive task). We found that in the movement task the subjects started the movements to most targets in a direction that deviated consistently from the direction of the straight line between initial position and target position. The maximum deviation ranged from 5-10 ~ for the various subjects. The mean standard deviation was 4 ~. In the perceptive task the subjects positioned the pointer in similarly deviating directions. Furthermore, we found that the maximum deviation in the pointer direction depended on the length of the pointer: the smaller the pointer, the larger the consistent deviations in the pointer direction. The shortest pointer showed deviations comparable to the deviations found in the movement task. These findings suggest that the deviations in the two tasks stem from the same source.
Clinical Neurophysiology, Oct 1, 2001
Objective: To compare the localizations of different neural sources (a) obtained from intracerebr... more Objective: To compare the localizations of different neural sources (a) obtained from intracerebral evoked responses and (b) calculated from surface auditory evoked ®eld responses recorded in the same subjects. Our aim was to evaluate the resolving power of a source localization method currently used in our laboratory, which is based on a recent spatio-temporal algorithm used in magneto-encephalography (MEG). Methods: Auditory evoked responses were studied in 4 patients with medically intractable epilepsy. These responses were recorded from depth electrodes implanted in the auditory cortex for pre-surgical evaluation (stereo-electro-encephalography (SEEG)), as well as from surface captors (for MEG) placed on the scalp after removal of the depth electrodes. Auditory stimuli were clicks and short tone bursts with different frequencies. Results: All middle-latency components (from 13 to 70 ms post-stimulus onset) were recorded and localized (via SEEG) along Heschl's gyrus (HG). MEG reliably localized Pam and P1m in the same area of HG that intracerebral recordings localized them in. No signi®cant delay between SEEG and MEG latencies was observed. Both methods suggest that N1 is generated from different sources in the intermediate and lateral parts of the HG and in the planum temporale (PT). The source of P2 (PT and/or Area 22) remains unclear and was in one case, localized in different regions according to the method used. This latter component may therefore also be generated by different sources. Conclusions: The results suggest that both techniques are useful and may be used together in a complementary fashion. Intracerebral recordings allow the researcher to validate and interpret surface recordings.
Human Movement Science, Dec 1, 1987
In this study the mechanical output (e.g., force, contraction velocity, instantaneous power) abou... more In this study the mechanical output (e.g., force, contraction velocity, instantaneous power) about the ankle was measured during a jump with and without occurrence of transportation of power and pre-stretch potentiation. To examine this, a model of the m. triceps surae was used. Eleven subjects performed a maximal one-legged countermovement jump (CMJ) and a maximal one-legged jump with extended knee (EKJ). Ground reaction forces, cinematographic data and electromyograms of m. triceps surae were recorded. The power output, defined as the product of moment and angular velocity, and work done about the ankle were higher during CMJ (1404 W, 130 J) than during EIU (852 W, 76 J). The peak moments were the same during both jumps. The model of the m. triceps surae showed that the power delivered by m. triceps surae was higher during CMJ than during EKJ, as a result of catapult-action of m. gastrocnemius tendon. The difference in work done is explained, in addition to transportation of energy, by a greater contraction range of m. soleus during CMJ. There is no reason to assume that pre-stretch potentiation plays a role in the difference in mechanical output. The results show that the mechanical output of muscles in complex movements is strongly dependent on the dynamics of the movement, and not only on its contractile capacity.
Journal of Biomechanics, 1988
Force-velocity and force-length relations were obtained for the edl of four Wistar rats in order ... more Force-velocity and force-length relations were obtained for the edl of four Wistar rats in order to characterise the contractile properties (CE) of these muscle-tendon complexes. Compliances of the undamped part of the series components (SE) were measured in quick length decreases. Force+xtension relations of SEs were obtained by integration of compliance to force. A muscle model consisting of CE, SE and a visco-elastic element was used to simulate the force output of the muscle tendon complex in response to a changing muscle length I,, as input. This simulated force was compared with the experimental force of the same muscle measured in response to the same I,, as input. Tetanic contractions were used in all experiments. The results show that this muscle model can predict the experimental force within a mean maximal error not larger than approximately 14 "/g of the force amplitude. However the comparison of simulated force with experimental force and a few additional experiments show that the muscles do not have a unique instantaneous force-velocity characteristic. As shown by several other studies, force seems to be influenced by many other variables (time, history etc.) than CE length and velocity.
Kinésithérapie, la Revue, Mar 1, 2023
European Journal of Neuroscience, 2009
Human subjects are able to prepare cognitively to resist an involuntary movement evoked by a supr... more Human subjects are able to prepare cognitively to resist an involuntary movement evoked by a suprathreshold transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1) by anticipatory selective modulation of corticospinal excitability. Uncovering how the sensorimotor cortical network is involved in this process could reveal directly how a prior intention can tune the intrinsic dynamics of M1 before any peripheral intervention. Here, we used combined TMS-EEG to study the cortical integrative processes that are engaged both in the preparation to react to TMS (Resist vs. Assist) and in the subsequent response to it. During the preparatory period, the contingent negative variation (CNV) amplitude was found to be smaller over central electrodes (FC1, C1, Cz) when preparing to resist compared with preparing to assist the evoked movement whereas a-oscillation power was similar in the two conditions. Following TMS, the amplitude of the TMS evoked-N100 component was higher in the Resist than in the Assist condition for some central electrodes (FCz, C1, Cz, CP1, CP3). Moreover, for six out of eight subjects, a single-trial-based analysis revealed a negative correlation between CNV amplitude and N100 amplitude. In conclusion, prior intention can tune the excitability of M1. When subjects prepare to resist a TMS-evoked movement, the anticipatory processes cause a decreased cortical excitability by locally increasing the inhibitory processes.
Annals of Physical and Rehabilitation Medicine, 2018
develop a French version of this questionnaire (PEQ-F) and to assess its psychometric properties.... more develop a French version of this questionnaire (PEQ-F) and to assess its psychometric properties. Material and method International recommendations for translation and cross-cultural validation of questionnaires were followed. Fifty-two subjects (age 53 ± 16, 40 males/12 females, 28/12/12 trans-tibial-gritti-stokes/transfemoral, 21/28/3 ischemic/traumatic/other, years since amputation 10 ± 10) participated. Criterion validity was assessed with the Pearson Correlation Coefficient (PCC) between PEQ-F and other constructs (SF
Annals of Physical and Rehabilitation Medicine, 2018
Annals of Physical and Rehabilitation Medicine, 2014
Neurophysiologie Clinique/Clinical Neurophysiology, 2013
New areas of application for electroencephalography are in braincomputer interfaces, where disabl... more New areas of application for electroencephalography are in braincomputer interfaces, where disabled people might be able to interact with their environment based on measured brain signals. However, conventional electroencephalography is not suitable here. Thus, our aim is to develop novel dry electrodes for home use. We developed various novel EEG electrodes with titanium and polyurethane as base materials and a nanometer sized coatings of titanium-nitride. We present results of the comparison of these electrodes with gold and silver/silver-cloride electrodes. In conclusion, our novel electrodes show equivalent signal quality compared to conventional electrodes and are suitable for home use.
Equine Veterinary Journal, 2014
Reasons for performing study: The relationship between the biomechanical horse-rider interaction ... more Reasons for performing study: The relationship between the biomechanical horse-rider interaction and endurance race performance requires further investigation. Objectives: To characterise, both quantitatively and qualitatively, elite and advanced horse-rider dyads on the basis of the biomechanical horse-rider interaction during endurance races. Study design: Five elite and 5 advanced horse-rider dyads were recorded during CEI*/CEI** endurance races using 2 synchronised triaxial accelerometers each placed close to horse and rider centres of mass. Methods: For each horse-rider dyad, analyses focused on the vertical displacements of horse and rider per stride. This allowed quantification of the proportional use of each gait and riding technique per loop. The quality of the biomechanical horse-rider interaction was examined through the relative phases (RP) of their respective vertical displacement minima. Instantaneous speed and rider heart rates were recorded using a global positioning system device/heart rate monitor. Results: All dyads predominantly used 2 riding techniques per gait. The 2-point trot proportion was limited in both groups (11%). Throughout the race, the advanced horse-rider dyads showed a global stability in speed, in the proportion of 4 combinations of gait and riding techniques and in mean RP. However, the elite horse-rider dyads initially had higher mean RP values (P<0.01), and from mid-race to the end an increasing proportion of sitting canter, with associated increases in racing speed (P<0.001) and in mean heart rate (P<0.01). Intradyad RP variability in 2-point canter increased in both groups (P<0.01). Conclusions: Accelerometers are a valuable tool to follow the quantitative and qualitative trends of the biomechanical horse-rider interaction during international endurance races. The overall results emphasise the influence of the level of expertise on the adopted gait and riding techniques, thus influencing the racing speed. It remains to be established whether fatigue and/or strategy underlie our observations.
IEEE Transactions on Medical Robotics and Bionics
Voluntary phantom movements are systematically associated with muscle contractions in the residua... more Voluntary phantom movements are systematically associated with muscle contractions in the residual limb. These latter are specific to the type of movement and can be classified by pattern recognition algorithms. However, phantom mobility generates fatigue that could impact classification metrics. This study explored whether daily phantom movement training at home with no other feedback than inherent somatosensory information can impact the classification success rate. Kinematics and muscle activity were compared between before and after a two-mo 1 nth home training in six major upper limb amputees. Surface EMG patterns were classified to quantify a potential change in the features space with training. Our results showed that this type of training induces faster, smoother, and richer phantom mobility. However, classification metrics did not change with training. When including the new types of movements achievable after training, accuracy did not decrease, indicating that muscle activation patterns associated with these movements were sufficiently different not to interfere with the already existing movement classes. Thus, although phantom training with only somatosensory feedback increases the overall phantom movement capacity, it does not increase the classification success rate. Yet, it is possible that paired with other forms of feedback, phantom training could improve this success rate.
2017 International Conference on Rehabilitation Robotics (ICORR), 2017
An arm amputation is extremely invalidating since many of our daily tasks require bi-manual and p... more An arm amputation is extremely invalidating since many of our daily tasks require bi-manual and precise control of hand movements. Perfect hand prostheses should therefore offer a natural, intuitive and cognitively simple control over their numerous biomimetic active degrees of freedom. While efficient polydigital prostheses are commercially available, their control remains complex to master and offers limited possibilities, especially for high amputation levels. In this pilot study, we demonstrate the possibility for upper-arm amputees to intuitively control a polydigital hand prosthesis by using surface myoelectric activities of residual limb muscles (sEMG) associated with phantom limb movements, even if these residual arm muscles on which the phantom activity is measured were not naturally associated with hand movements before amputation. Using pattern recognition methods, three arm amputees were able, without training, to initiate 5-8 movements of a robotic hand (including individual finger movements) by simply mobilizing their phantom limb while the robotic hand was mimicking the action in real time. This innovative control approach could offer to numerous upper-limb amputees an access to recent biomimetic prostheses with multiple controllable joints, without requiring surgery or complex training; and might deeply change the way the phantom limb is apprehended by both patients and clinicians.
IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, Jan 4, 2016
Decoding finger and hand movements from sEMG electrodes placed on the forearm of transradial ampu... more Decoding finger and hand movements from sEMG electrodes placed on the forearm of transradial amputees has been commonly studied by many research groups. A few recent studies have shown an interesting phenomenon: simple correlations between distal phantom finger, hand and wrist voluntary movements and muscle activity in the residual upper arm in transhumeral amputees, i.e., of muscle groups that, prior to amputation, had no physical effect on the concerned hand and wrist joints. In this study, we are going further into the exploration of this phenomenon by setting up an evaluation study of phantom finger, hand, wrist and elbow (if present) movement classification based on the analysis of surface electromyographic (sEMG) signals measured by multiple electrodes placed on the residual upper arm of 5 transhumeral amputees with a controllable phantom limb who did not undergo any reinnervation surgery. We showed that with a state-of-the-art classification architecture, it is possible to co...
Neuroscience, Jan 10, 2015
After limb amputation, patients often wake up with a vivid perception of the presence of the miss... more After limb amputation, patients often wake up with a vivid perception of the presence of the missing limb, called "phantom limb". Phantom limbs have mostly been studied with respect to pain sensation. But patients can experience many other phantom sensations, including voluntary movements. The goal of the present study was to quantify phantom movement kinematics and relate these to intact limb kinematics and to the time elapsed since amputation. Six upper arm and two forearm amputees with various delays since amputation (6months to 32years) performed phantom finger, hand and wrist movements at self-chosen comfortable velocities. The kinematics of the phantom movements was indirectly obtained via the intact limb that synchronously mimicked the phantom limb movements, using a Cyberglove® for measuring finger movements and an inertial measurement unit for wrist movements. Results show that the execution of phantom movements is perceived as "natural" but effortful. T...
Vision Research, 1994
Subjects performed a three-dot alignment in the frontoparallel plane. We found systematic deviati... more Subjects performed a three-dot alignment in the frontoparallel plane. We found systematic deviations in alignment, especially for diagonally oriented stimuli. The biases did not depend on the angular size of the stimuli which was varied between 0.8 and 20 deg. We put forward a tentative explanation based on saccade trajectories. Extending the task to judgements of the straightness of virtual lines consisting of a varying number of dots showed that the biases decrease gradually when the number of dots increases. This suggests that there are two different and competing mechanisms to judge the straightness of virtual lines. Perceptual straightness Direction estimation Scale invariance Perceptu*motor interaction Human I
Experimental Brain Research, 1999
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Experimental Brain Research, 1994
In a previous study we found that the initial direction of slow, goal-directed arm movements devi... more In a previous study we found that the initial direction of slow, goal-directed arm movements deviates consistently from the direction of the actual straight line between the starting position and the target position. We now investigate whether these deviations are caused by imperfections or peculiarities in the processing of vision-related spatial information, such as retinal information, and eye-and head-position information. This could lead to incorrect localization of the target relative to the starting position. Subjects were seated in front of a horizontal surface and had to move their arm slowly and accurately in the direction of target positions. We varied the amount of vision-related spatial information. In experiment 1, subjects were presented with visual targets and could see their moving arm. In experiment 2, the subjects were again presented with visual targets, but now they could not see their moving arm. In experiment 3, the subjects were blindfolded and had to move their arm towards tactile targets. In all three experiments we found comparable consistent deviations in the initial movement direction. We also instructed congenitally and early-blind subjects to move their arm towards tactile targets. Their performance showed deviations congruous with those found in the
Une amputation a comme consequence la privation soudaine d'entrees sensorielles au niveau du ... more Une amputation a comme consequence la privation soudaine d'entrees sensorielles au niveau du systeme nerveux central ainsi que la perte de cibles musculaires pour les fibres efferentes. Le systeme nerveux central, avec sa grande capacite d'adaptation, reagit a cette privation par une reorganisation anatomique et fonctionnel a differentes echelles de temps. Ce papier resume les reorganisations fonctionnelles au niveau des aires sensorimotrices primaires suite a une amputation d'un membre. Ensuite, nous abordons les mecanismes sous-jacents au membre fantome avec l'accent sur sa mobilite, peu connue mais repandue. Nous finissons avec l'interet que peut avoir la mobilite du membre fantome pour la readaptation de patients amputes du membre superieur.
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Papers by Jozina De Graaf