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PubMed2005

Temporal relationship between action and visual outcome modulates brain activation: an fMRI study.

Monitoring the visual outcome of our actions is critical to our visuo-motor behavior. To investigate the neural basis of monitoring visual change produced by self-movement, we examined the temporal relationship between manual depression of a button and visual feedback on activation of the brain. Six neurologically normal subjects participated in 3 experiments (synchronous, delayed, and visual [control]). Magnetic resonance (MR) images of their brains were acquired during the experiments using a scanner operating at 3T. In the synchronous experiment, subjects pressed a button at self-paced intervals and received synchronous visual stimuli in response. In the delayed experiment, visual stimuli were presented with a delay after subjects pressed a button at self-paced intervals. In the control experiment (visual experiment), subjects did not press the button, but viewed visual stimuli generated by a computer at random intervals. In the synchronous experiment, activation in the cerebellum and right parietal lobe was stronger than in the delayed experiment, whereas activation in the primary visual cortex was weaker than in the delayed and visual experiments. These results suggest that visual outcomes produced synchronously with action are processed in the cerebellum and the parietal area for the organization of optimal motor behavior, rather than in the primary visual area that is known to process the visual properties of external objects. The cerebellar signal related to visuo-motor contingency may modulate the cortical processing of visual input that is synchronous with action.

Adult↗

PubMed2002

Effects of body lean and visual information on the equilibrium maintenance during stance.

Maintenance of equilibrium was tested in conditions when humans assume different leaning postures during upright standing. Subjects ( n=11) stood in 13 different body postures specified by visual center of pressure (COP) targets within their base of support (BOS). Different types of visual information were tested: continuous presentation of visual target, no vision after target presentation, and with simultaneous visual feedback of the COP. The following variables were used to describe the equilibrium maintenance: the mean of the COP position, the area of the ellipse covering the COP sway, and the resultant median frequency of the power spectral density of the COP displacement. The variability of the COP displacement, quantified by the COP area variable, increased when subjects occupied leaning postures, irrespective of the kind of visual information provided. This variability also increased when vision was removed in relation to when vision was present. Without vision, drifts in the COP data were observed which were larger for COP targets farther away from the neutral position. When COP feedback was given in addition to the visual target, the postural control system did not control stance better than in the condition with only visual information. These results indicate that the visual information is used by the postural control system at both short and long time scales.

Adult↗

PubMed2004

Visual and motor constraints on trajectory planning in pointing movements.

The aim of the present study was to show that planning and controlling the trajectory of a pointing movement is influenced not solely by physical constraints but also by visual constraints. Subjects were required to point towards different targets located at 20 degrees , 40 degrees , 60 degrees and 80 degrees of eccentricity. Movements were either constrained (i.e. two-dimensional movements) or unconstrained (i.e. three-dimensional movements). Furthermore, movements were carried out either under a direct or a remote visual control (use of a video system). Results revealed that trajectories of constrained movements were nearly straight whatever the eccentricity of the target and the type of visual control. A different pattern was revealed for unconstrained movements. Indeed, under direct vision the trajectory curvature increased as the eccentricity augmented, whereas under indirect vision, trajectories remained nearly straight whatever the eccentricity of the target. Thus, movements controlled through a remote visual feedback appear to be planned in extrinsic space as constrained movements.

Adolescent↗

PubMed1998

A visual environment for the manipulation and integration of JAVA beans.

MOTIVATION: Visual programming has the potential to allow non-programmers to redesign and rebuild applications to suit their individual needs. We have built such a visual programming environment, which allows non-programmers to interrogate and combine software components graphically to form new applications. As the needs of the biological community grow, so too will the need for more powerful and easy to use software tools. Intelligent visual programming environments will allow users to design and develop applications easily, so that they can concentrate on the application they wish to build rather than how it is to be done. RESULTS: The environment can read in JAVA Beans, and present relevant information about the beans to the user. The user can then graphically specify how they would like information to flow between the beans by performing simple docking operations. Unnecessary complexities associated with such visual design have been removed by providing intelligent docking of components and visual feedback. With such mechanisms, the complexities of building new applications are reduced. When the biologist has finished the visual construction, the design system is able to generate the new application automatically. The system has been designed specifically to meet the needs of the biological community, and a range of 'BioBeans' are being developed. These include beans for visualization (sequence displays and data visualizers), analysis (feature recognition, error detection) and communication (database access, URL retrieval, DDE communication). AVAILABILITY: Freely available. CONTACT: boyle@synomics.com

Computational Biology↗

PubMed1969

Operant conditioning of cortical unit activity.

The activity of single neurons in precentral cortex of unanesthetized monkeys (Macaca mulatta) was conditioned by reinforcing high rates of neuronal discharge with delivery of a food pellet. Auditory or visual feedback of unit firing rates was usually provided in addition to food reinforcement. After several training sessions, monkeys could increase the activity of newly isolated cells by 50 to 500 percent above rates before reinforcement.

Action Potentials↗

PubMed2006

Effects of focal hand dystonia on visually guided and internally guided force control.

BACKGROUND: A fundamental feature underlying many movement disorders is increased variability in the motor response. Despite abnormalities of grip force control in people with dystonia, it is not clear whether dystonia is also associated with increased variability in force output and whether force variability in dystonia is affected by the presence or absence of visual feedback. OBJECTIVE: To examine force variability in 16 patients with writer's cramp and 16 matched controls. METHODS: The variability of force output at the wrist under conditions of both vision and no vision was examined. The underlying frequency structure of the force signal was also compared across groups. Participants produced isometric wrist flexion to targets at 25% and 50% of their maximum voluntary contraction strength under conditions of both vision and no vision. RESULTS: Similar levels of force variability were observed in patients with dystonia and controls at the lower force levels, but patients with dystonia were less variable in their force output than controls at the higher force level. This reduction in variability in people with dystonia at 50% maximum voluntary contraction was not affected by vision. Although a similar dominant frequency in force output was observed in people with dystonia and controls, a reduced variability in the group with dystonia at the higher force level was due to reduced power in the 0-4-Hz frequency bin. CONCLUSIONS: The first evidence of a movement disorder with reduced variability is provided. The findings are compatible with a model of dystonia, which includes reduced cortical activation in response to sensory input from the periphery and reduced flexibility in motor output.

Adult↗

PubMed2003

Effect of visual information on step-tracking movements in patients with intention tremor due to multiple sclerosis.

The effect of visual information on step-tracking movements was studied in 18 patients with intention tremor due to multiple sclerosis (MS) and 15 healthy controls. Parricipants performed a slow wrist step-tracking task with stationary targets under five visual feedback conditions. The display of the target and movement cues was selectively withdrawn to examine the effects of visual information on intention tremor and movement accuracy. Results showed that intention tremor was most pronounced when visual display of both target and movement cues was available. Withdrawing visual information of the limb movement reduced tremor more than withdrawing the visual display of the target cues. Both the patient and control group was less accurate when the display of limb movement was occluded. Patients, however, were more dependent on visual information of the limb movement for accurate motor performance than healthy controls. When the visual display of the limb movement was partially occluded between or near to the targets, tremor decreased without deterioration of movement accuracy.

Adult↗

PubMed2002

Optimal control strategies under different feedback schedules: kinematic evidence.

Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, and alternating feedback schedules. Prior knowledge of whether vision would be available had a significant impact on the strategies that participants adopted. When they knew that vision would be available, less time was spent preparing movements before movement initiation. Participants also reached peak deceleration sooner but spent more time after peak deceleration adjusting limb trajectories. Consistent with those findings, analysis of spatial variability at different points in the trajectory indicated that variability increased up to peak deceleration but then decreased from peak deceleration to the end of the movement.

Biomechanical Phenomena↗

PubMed1975

[The effects of feedback signal and model signal on heart rate changes (author's transl)].

An attempt was made to modify heart rate by presenting the Ss: E1-visual feedback and model signals, E2-feedback signals, E3-model signals, or C-no signals as a control group (6 Ss in each group). Model signal was a weak light which flickered at the rate of 20% above or below the pre-stimulus base IBI. All groups were required to either raise or lower HR alternately and E1 group was instructed to synchronize the feedback signal with the model signal. Significant bidirectional HR changes were found in 3 experimental groups and most effective changes were obtained in E1 group. In the second study, extended training to one S with E1 condition resulted in HR increases of 16 bpm and decreases of 9 bpm.

Adult↗

PubMed1996

Identification of static and dynamic postural instability following traumatic brain injury.

OBJECTIVE: Quantitative evaluation of static and dynamic aspects of postural instability as a long-term consequence of traumatic brain injury (TBI). DESIGN: Experimental two-group design. SETTING: Outpatient rehabilitation department. PATIENTS AND OTHER PARTICIPANTS: From a consecutive sample of TBI patients at least 6 months after trauma, 20 subjects were selected who complained of reduced gross motor skills but showed no sensorimotor impairments in a standard neurological examination (11 men, 9 women; mean age 36.2 +/- 10.7 years). Thirteen patients had sustained mild, 2 moderate, and 5 severe TBI. Twenty healthy controls were matched for age and gender. INTERVENTION: None. MAIN OUTCOME MEASURES: A dual-plate force platform recorded the amplitude and velocity of the center-of-pressure fluctuations in the anteroposterior (AP) and lateral (LAT) sway directions during quiet standing. Also, the speed and fluency of weight shifting using visual feedback was registered. Both balance tasks were combined with an arithmetic task, whereas quiet standing was also tested with visual deprivation. RESULTS: Compared to controls, TBI patients showed an increase of over 50% in AP and LAT sway, and a weight-shifting speed 20% lower. Dual-task interference was never significant. Visual deprivation was most detrimental for the TBI patients, particularly for LAT sway control. CONCLUSION: A long-term overall reduction in both static and dynamic control of posture can be present after TBI, even in patients without clear neurological deficits. Force-plate recordings can identify such (latent) balance problems. Visual deprivation during quiet standing appears a simple, sensitive test for postural instability related to sensory integration deficits.

Adolescent↗

PubMed1999

Event-related desynchronization related to the anticipation of a stimulus providing knowledge of results.

In the present paper, event-related desynchronization (ERD) in the alpha and beta frequency bands is quantified in order to investigate the processes related to the anticipation of a knowledge of results (KR) stimulus. In a time estimation task, 10 subjects were instructed to press a button 4 s after the presentation of an auditory stimulus. Two seconds after the response they received auditory or visual feedback on the timing of their response. Preceding the button press, a centrally maximal ERD is found. Preceding the visual KR stimulus, an ERD is present that has an occipital maximum. Contrary to expectation, preceding the auditory KR stimulus there are no signs of a modality-specific ERD. Results are related to a thalamo-cortical gating model which predicts a correspondence between negative slow potentials and ERD during motor preparation and stimulus anticipation.

Adult↗

PubMed1983

Effects of feedback stimulation training and cyclical electrical stimulation on knee extension in hemiparetic patients.

Positional feedback stimulation training and cyclical electrical stimulation were used in combination as a treatment for facilitating knee extension in hemiparetic patients. Forty adult hemiparetic patients who demonstrated minimal active control of their quadriceps femoris muscles were randomly assigned to control or study groups. The control patients received a program of physical therapy, and the study patients received the positional feedback stimulation training in addition to their therapy program. The stimulation training provided the patient with immediate auditory and visual feedback of his changing joint angle while he voluntarily extended his knee. When the patient reached a near maximal extension effort, electrical stimulation of the quadriceps femoris muscle was automatically triggered, completing the patient's available range of motion in extension. The stimulation training was supplemented with two hours of cyclical electrical stimulation daily. At the end of four weeks, analysis revealed a statistically significant increase in knee extension torque and active synergistic range of motion in the study group. No change was noted in their ability to extend their knees using isolated quadriceps femoris muscle control. This study suggests that positional feedback stimulation training is effective when used to augment a facilitation program for improving knee extension control in hemiparetic patients.

Adult↗

PubMed1998

Orienting gaze shifts during muscimol inactivation of caudal fastigial nucleus in the cat. II. Dynamics and eye-head coupling.

We have shown in the companion paper that muscimol injection in the caudal part of the fastigial nucleus (cFN) consistently leads to dysmetria of visually triggered gaze shifts that depends on movement direction. Based on the observations of a constant error and misdirected movements toward the inactivated side, we have proposed that the cFN contributes to the specification of the goal of the impending ipsiversive gaze shift. To test this hypothesis and also to better define the nature of the hypometria that affects contraversive gaze shifts, we report in this paper on various aspects of movement dynamics and of eye/head coordination patterns. Unilateral muscimol injection in cFN leads to a slight modification in the dynamics of both ipsiversive and contraversive gaze shifts (average velocity decrease = 55 degrees/s). This slowing in gaze displacements results from changes in both eye and head. In some experiments, a larger gaze velocity decrease is observed for ipsiversive gaze shifts as compared with contraversive ones, and this change is restricted to the deceleration phase. For two particular experiments testing the effect of visual feedback, we have observed a dramatic decrease in the velocity of ipsiversive gaze shifts after the animal had received visual information about its inaccurate gaze responses; but virtually no change in hypermetria was noted. These observations suggest that there is no obvious causal relationship between changes in dynamics and in accuracy of gaze shifts after muscimol injection in the cFN. Eye and head both contribute to the dysmetria of gaze. Indeed, muscimol injection leads to parallel changes in amplitude of both ocular and cephalic components. As a global result, the relative contribution of eye and head to the amplitude of ipsiversive gaze shifts remains statistically indistinguishable from that of control responses, and a small (1.6 degrees) increase in the head contribution to contraversive gaze shifts is found. The delay between eye and head movement onsets is increased by 7.3 +/- 7.4 ms for contraversive and decreased by 8.3 +/- 10.1 ms for ipsiversive gaze shifts, corresponding respectively to an increased or decreased lead time of head movement initiation. The modest changes in gaze dynamics, the absence of a link between eventual dynamics changes and dysmetria, and a similar pattern of eye-head coordination to that of control responses, altogether are compatible with the hypothesis that the hypermetria of ipsiversive gaze shifts results from an impaired specification of the metrics of the impending gaze shift. Regarding contraversive gaze shifts, the weak changes in head contribution do not seem to reflect a pathological coordination between eye and head but would rather result from the tonic deviations of gaze and head toward the inactivated side. Hence, our data suggest that the hypometria of contraversive gaze shifts also might result largely from an alteration of processes that specify the goal rather than the on-going trajectory, of saccadic gaze shifts.

Analysis of Variance↗

PubMed2005

A clinical interactive technique for MR-CT image registration for target delineation of intracranial tumors.

Replacement of current CT-based, three-dimensional (3D) treatment planning systems by newer versions capable of automated multi-modality image registration may be economically prohibitive for most radiation oncology clinics. We present a low-cost technique for MR-CT image registration on a "first generation" CT-based, 3D treatment planning system for intracranial tumors. The technique begins with fabrication of a standard treatment mask. A second truncated mask, the "minimask," is then made, using the standard mask as a mold. Two orthogonal leveling vials glued onto the minimask detect angular deviations in pitch and roll. Preservation of yaw is verified by referencing a line marked according to the CT laser on the craniocaudal axis. The treatment mask immobilizes the patient's head for CT. The minimask reproduces this CT-based angular treatment position, which is then maintained by taping the appropriately positioned head to the MR head coil for MR scanning. All CT and MR images, in DICOM 3.0 format, are entered into the treatment planning system via a computer network. Interactive registration of MR to CT images is controlled by real-time visual feedback on the computer monitor. Translational misalignments at the target are eliminated or minimized by iterative use of qualitative visual inspection. In this study, rotational errors were measured in a retrospective series of 20 consecutive patients who had undergone CT-MR image registration using this technique. Anatomic structures defined the three CT orthogonal axes from which angular errors on MR image were measured. Translational errors at the target isocenter were within pixel size, as judged by visual inspection. Clinical setup using the minimask resulted in overall average angular deviation of 3 degrees +/-2 degrees (mean +/- SD) and translational deviation within the edges of the target volume of typically less than 2 mm. The accuracy of this registration technique for target delineation of intracranial tumors is compatible with practice guidelines. This method, then, provides a cost-effective means to register MR and CT images for target delineation of intracranial tumors.

Brain Neoplasms↗

PubMed1977

Significance of different feedbacks for the transient processes of the discharges of single motor units during step-like voluntary movements.

Studies are made of the transient processes of the discharges of single tonic low-threshold and phasic high-threshold motor units (MUs) during step-like voluntary movements performed in case of visual feedback by the result of the movement and in case of artificial auditory feedback by the sound of the MU impulses, as well as in cases of absence of exteroceptive feedback. The studies comprise isometric and isotonic flexion and extension in the elbow joint, the MUs studied being from m. biceps brachii. The previously observed differences of the transient processes in tonic and phasic MUs are found to exist not only during movements taking place under visual control but also under other conditions studied. Under conditions of articicial auditory feedback the subjects may or may not use this feedback for control of the motor response.

Adult↗

PubMed2005

Independence between the amount and structure of variability at low force levels.

The purpose of the current experiment was to investigate the amount (standard deviation (S.D.) and coefficient of variation (CV)) and structure (approximate entropy (ApEn)) of force variability at very low force levels. Participants produced isometric force output of index finger abduction at five levels (0.4, 0.8, 1.0, 2.0, and 4.0 N) with high and low visual feedback gain. The findings showed that: subjects scaled their force output to the targets; S.D. increased non-linearly with force level and decreased with visual gain; and CV decreased with force level as well as visual gain. ApEn of the force output did not change as a function of force level, although the high gain increased ApEn in contrast to low gain. It is proposed that the recruitment of additional motor units at very low force levels does not significantly alter the structure of the force output, although it does increase the magnitude of force and its amount of variability. Overall, the findings provide evidence that the amount and structure of motor variability can be influenced by separate control processes at low force levels.

Adult↗

PubMed2004

The role of sight of the hand in the development of prehension in childhood.

In two studies, children between 5 and 10 years of age were asked to reach to grasp an object without sight of the hand during the movement. The oldest children and adults were faster when they could see the hand and increased maximum grip aperture when they could not see the hand. The 10-year-olds were less able to integrate grasp and lift than adults when they could see their hands. Children aged 5 and 6 showed no increase in movement time when they could not see the hand and did not adapt maximum grip aperture to lack of sight. These effects remained when children were encouraged to reach for and lift the target as quickly as possible. The results indicate that younger children did not give preference to vision in the control of prehension, while older children used visual feedback to improve efficiency. Dependence on sight of the hand for the control of prehension does not simply decrease with age, but it may be integrated into an anticipatory control strategy where it contributes to the efficiency of control.

Child↗

PubMed2006

Modeling sensorimotor learning with linear dynamical systems.

Recent studies have employed simple linear dynamical systems to model trial-by-trial dynamics in various sensorimotor learning tasks. Here we explore the theoretical and practical considerations that arise when employing the general class of linear dynamical systems (LDS) as a model for sensorimotor learning. In this framework, the state of the system is a set of parameters that define the current sensorimotor transformation-the function that maps sensory inputs to motor outputs. The class of LDS models provides a first-order approximation for any Markovian (state-dependent) learning rule that specifies the changes in the sensorimotor transformation that result from sensory feedback on each movement. We show that modeling the trial-by-trial dynamics of learning provides a substantially enhanced picture of the process of adaptation compared to measurements of the steady state of adaptation derived from more traditional blocked-exposure experiments. Specifically, these models can be used to quantify sensory and performance biases, the extent to which learned changes in the sensorimotor transformation decay over time, and the portion of motor variability due to either learning or performance variability. We show that previous attempts to fit such models with linear regression have not generally yielded consistent parameter estimates. Instead, we present an expectation-maximization algorithm for fitting LDS models to experimental data and describe the difficulties inherent in estimating the parameters associated with feedback-driven learning. Finally, we demonstrate the application of these methods in a simple sensorimotor learning experiment: adaptation to shifted visual feedback during reaching.

Algorithms↗