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PubMed2001

Oculomotor function in the rhesus monkey after deafferentation of the extraocular muscles.

The function of extraocular muscle proprioception in the control of eye movements remains uncertain. In this study, we examined the effect of bilateral proprioceptive deafferentation of the extraocular muscles on eye movements in two rhesus monkeys. Before and after deafferentation, we analyzed baseline ocular alignment, saccades, pursuit, and vestibular eye movements. We also examined visually mediated adaptation of ocular alignment, saccades, and pursuit. Deafferentation of the eye muscles did not affect baseline ocular motor control, either acutely or over a 5-week period of study. Furthermore, visually mediated adaptation of the eye movement subtypes was also unaffected by deafferentation. These results suggest that ocular proprioception in primates is not used in the immediate, on-line control of eye movements and does not interact with visual cues in the adaptive modification of ocular motor function. We conclude that the efferent command (efference copy) provides sufficient information about eye kinematics to the brain for accurate eye movement control in normal monkeys, and that this information is modified by visual feedback independently of proprioception. We hypothesize that proprioception may be used to calibrate the efference copy during development and in response to perturbations by signaling potential mismatches between eye movement information derived from the efferent command and the actual motion of the eye transduced by the proprioceptive organs.

Adaptation, Physiological↗

PubMed2000

The role of proprioception and attention in a visuomotor adaptation task.

The role of proprioception in the control and adaptation of visuomotor relationships is still unclear. We have studied a deafferented subject, IW, and control subjects in a task in which they used single joint elbow extension to move to a visual target, with visual feedback of the terminal position provided by a cursor displayed in the plane of their movements. We report the differences in movement accuracy between the deafferented subject and controls in the normal task and when challenged with a cognitive load, counting backwards. All subjects were less accurate when counting; this was a small effect for the controls (<10% change) but much greater for the deafferented subject (>60% change). We also examined changes in movement kinematics when the instructed amplitude was altered via a changed gain between final arm position and presentation of the feedback cursor. The deafferented subject maintained temporal movement parameters stable and altered amplitude by scaling force (i.e. changed peak velocity), whereas the controls scaled both movement velocity and duration. Finally, we compared the subjects' adaptation of movement amplitude after a period of exposure to the changed visuomotor gain. The deafferented subject was able to adapt, but his adaptation was severely impaired by the counting task. These results suggest that proprioception is not an absolute requirement for adaptation to occur. Instead, proprioception has a more subtle role to play in the adjustment to visuomotor perturbations. It has an important role in the control of reaching movements, while in the absence of proprioception, attention appears necessary to monitor movements.

Adaptation, Physiological↗

PubMed2003

EMG power spectra of cervical muscles in lateral flexion and comparison with sagittal and oblique plane activities.

The purpose of this study was to calculate electromyographic (EMG) power spectra of the sternocleidomastoid (SCM), the splenius capitis (SPL) and the trapezius (TRP) muscles from both sides of the body in bilateral lateral flexion and compare them with the EMG spectral characteristics of the same muscles in the sagittal and oblique planes recorded from the same subjects in the same experimental session but reported elsewhere in the literature. Forty normal and healthy young adults (21 males, 19 females) volunteered for the study. The subjects were prepared and positioned appropriately to exert linearly ramping isometric exertion aided by visual feedback against a rigid and load cell instrumental device. Exertions were carried out in a random order. The maximal voluntary contraction was reached within a 5-s test period. The torque and EMG from the SCM, SPL and TRP muscles were sampled bilaterally at a rate of 1 kHz. The EMG data were subjected to fast Fourier transform analysis. During lateral flexion, the torque generated by females was significantly lower than males ( P<0.01) and represented at 75% of male torque. Contrary to flexion/extension and oblique plane activities, the ipsilateral SCM was most active with highest power and up to four dominant frequencies demonstrating four distinct peaks. The bandwidth of this muscle progressively increased with the grade of contraction up to 400 Hz, similar to flexion/extension with median frequency (MF) spread between 21 and 109 Hz for males and 78 and 99 Hz for females. The ipsilateral SPL was the second most active muscle, which maintained a narrow bandwidth (200 Hz) and one dominant frequency, rising in power with increasing grade of contraction. Flexion and extension caused symmetrical activity bilaterally. The results of MANOVA revealed a significant main effect of gender, activity direction, grade of contraction and individual muscles ( P<0.001). There was a significant interaction between muscle and activity direction ( P<0.001) implying significantly different MF and mean power frequency if the direction of exertion was changed. Male and female subjects responded to direction differently ( P<0.001).

Adult↗

PubMed2003

The force-velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions.

In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force-velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. Seven subjects performed submaximal voluntary lengthening, shortening(at angular, velocities of +5, -5, +15, -15 and +30, and -30 degrees s(-1)) and isometric plantar flexor efforts against an ankle torque motor. Angle-specific (90 degrees ) measures of plantar flexor torque plus surface and intramuscular electromyography from soleus, medial gastrocnemius and tibialis anterior were made. The level of activation (30% of maximal voluntary isometric effort) was maintained by providing direct visual feedback of the soleus electromyogram to the subject. In an attempt to isolate the contribution of soleus to the resultant plantar flexion torque, activation of the synergist and antagonist muscles were minimised by: (1) flexing the knee of the test limb, thereby minimising the activation of gastrocnemius, and (2) applying an anaesthetic block to the common peroneal nerve to eliminate activation of the primary antagonist muscle, tibialis anterior and the synergist muscles, peroneus longus and peroneus brevis. Plantar flexion torque decreased significantly ( P<0.05) after blocking the common peroneal nerve which was likely due to abolishing activation of the peroneal muscles which are synergists for plantar flexion. When normalised to the corresponding isometric value, the force-velocity relationship between pre- and post-block conditions was not different. In both conditions, plantar flexion torques during shortening actions were significantly less than the isometric torque and decreased at faster velocities. During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).

Adult↗

PubMed2004

Integrated characterization of the human chemoreflex system controlling ventilation, using an equilibrium diagram.

The chemoreflex system controlling ventilation consists of two subsystems, i.e., the central controller (controlling element), and peripheral plant (controlled element). We developed an integral framework to quantitatively characterize individual ventilatory regulation by experimental determination of an equilibrium diagram using a modified metabolic hyperbola and the CO2 response curve. In 13 healthy males, the steady-state arterial CO2 pressure (P(a)CO2) and minute ventilation (V(E)) were measured. To characterize the central controller, we changed fraction of inspired CO2 (0, 3.5, 5 and 6% CO2 in 80% oxygen with nitrogen balance) and measured the P(a)CO2-V(E) relation. To characterize the peripheral plant, we altered V(E) by hyper- or hypoventilation using a visual feedback method, which made it possible to control both tidal volume and breathing frequency, and measured the VE-P(a)CO2 relation. The intersection between the two relationship lines gives the operating point. The relationship between P(a)CO2 and V(E) for the central controller was reasonably linear in each subject (r2 = 0.808-0.995). The peripheral plant approximated a modified metabolic hyperbolic curve (r = 0.962-0.996). The operating points of the system estimated from the two relationship lines were in good agreement with those measured under the closed-loop condition. The gain of the central controller was 1.9 (1.0) l min(-1) mmHg(-1) and that of the peripheral plant was 3.0 (0.5) mmHg l(-1) min(-1). The total loop gain, the product of the two gains, was 5.3 (2.5). We conclude that human ventilatory regulation by the respiratory chemoreflex system can be quantitatively characterized using an equilibrium diagram. This framework should be useful for understanding the mechanisms responsible for abnormal ventilation under various pathophysiological conditions.

Adult↗

PubMed2004

Repeated maximal eccentric actions causes long-lasting disturbances in movement control.

This study examined acute and long-lasting effects of fatigue and muscle damage on fast and accurate elbow flexion and extension target movements (TM) with eight male students. An isokinetic machine was used to perform 100 maximal eccentric and concentric elbow flexions at 4-week intervals. Movement range was 40-170 degrees in eccentric exercise (ECCE) and 170-40 degrees in concentric exercise (CONE), with an angular velocity of 2 rad s(-1). TM was performed in sitting position with the right forearm fixed to lever arm above protractor. Subjects performed TM in horizontal plane (amplitude 60 degrees ) by visual feedback of movement from a television monitor. Surface EMG was recorded from the biceps brachii and triceps brachii muscles. TM measurements and serum creatine kinase (CK) determinations were conducted before, after, 0.5 h, 2 days, and 7 days after both exercises. Blood lactate was taken before, after, and 0.5 h after the exercises. Both ECCE and CONE led to a large decline in maximal voluntary contractions, but the recovery was slower after ECCE when it remained incomplete even until day 7 post-exercise. Lactate increased (P < 0.001) similarly after both exercises. Delayed-onset muscle soreness peaked on day 2 and CK peaked on day 7 after ECCE. Exhaustive eccentric exercise of agonistic muscles impaired the flexion TM performance, and had a long-duration modulation effect on the triphasic EMG activity pattern of flexion and extension TM. In the acute phase, the observed changes in performance and in the EMG patterns are suggested to be related to metabolic changes via III and IV muscle afferents. The delayed recovery, on the other hand, may be related to problems in the proprioceptive feedback caused by muscle damage.

Adaptation, Physiological↗

PubMed2000

Tension regulation during lengthening and shortening actions of the human soleus muscle.

In the present study we investigated tension regulation in the human soleus (SOL) muscle during controlled lengthening and shortening actions. Eleven subjects performed plantar flexor efforts on an ankle torque motor through 30 degrees of ankle displacement (75 degrees -105 degrees internal ankle angle) at lengthening and shortening velocities of 5, 15 and 30 degrees. S(-1). To isolate the SOL from the remainder of the triceps surae, the subject's knee was flexed to 60 degrees during all trials. Voluntary plantar flexor efforts were performed under two test conditions: (1) maximal voluntary activation (MVA) of the SOL, and (2) constant submaximal voluntary activation (SVA) of the SOL. SVA trials were performed with direct visual feedback of the SOL electromyogram (EMG) at a level resulting in a torque output of 30% of isometric maximum. Angle-specific (90 degrees ankle angle) torque and EMG of the SOL, medial gastrocnemius (MG) and tibialis anterior (TA) were recorded. In seven subjects from the initial group, the test protocol was repeated under submaximal percutaneous electrical activation (SEA) of SOL (to 30% isometric maximal effort). Lengthening torques were significantly greater than shortening torques in all test conditions. Lengthening torques in MVA and SVA were independent of velocity and remained at the isometric level, whereas SEA torques were greater than isometric torques and increased at higher lengthening velocities. Shortening torques were lower than the isometric level for all conditions. However, whereas SVA and SEA torques decreased at higher velocities of shortening, MVA torques were independent of velocity. These results indicate velocity- and activation-type-specific tension regulation in the human SOL muscle.

Adult↗

PubMed2001

Effect of step and ramp static contractions on the median frequency of electromyograms of back muscles in humans.

The purpose of this study was to compare the electromyogram median frequency (MF) values from two contraction modes (ramp vs step) at different force levels of eight back muscles. A group of 20 healthy male subjects stood in a dynamometer with the trunk in a vertical position and performed trunk extension contractions using the displayed L5/S1 extension moment as visual feedback. The electromyogram (EMG) signals from four pairs of back muscles were collected at 4,096 Hz using active surface electrodes during two 7 s static ramp contractions ranging from 0% to 100% of the maximal voluntary contraction (MVC) and two 5 s static step contractions performed at five forces (10%, 20%, 40%, 60% and 80% MVC). The root mean square (RMS) and MF of the EMG signals corresponding to 250 ms windows were computed at each force level for both contraction modes. The RMS from the ramp contractions were significantly higher than from the step contractions in six muscles. The corresponding MF showed a significant (alpha = 0.05) contraction mode x force interaction in four muscles. A significant contraction mode main effect was obtained in four muscles having higher MF during step than during ramp contractions. These differences were more obvious (10-15 Hz) and more frequent at the lower (10%, 20% and 40% MVC) forces. It was suggested that mechanisms not related to motor unit recruitment might influence MF in contraction modes. These unknown mechanisms contaminate any possible relationship between the MF measurements and muscle composition.

Adult↗

PubMed2006

Tests of models for saccade-vergence interaction using novel stimulus conditions.

During natural activities, two types of eye movements - saccades and vergence - are used in concert to point the fovea of each eye at features of interest. Some electrophysiological studies support the concept of independent neurobiological substrates for saccades and vergence, namely saccadic and vergence burst neurons. Discerning the interaction of these two components is complicated by the near-synchronous occurrence of saccadic and vergence components. However, by positioning the far target below the near target, it is possible to induce responses in which the peak velocity of the vertical saccadic component precedes the peak velocity of the horizontal vergence component by approximately 75 ms. When saccade-vergence responses are temporally dissociated in this way, the vergence velocity waveform changes, becoming less skewed. We excluded the possibility that such change in skewing was due to visual feedback by showing that similar behavior occurred in darkness. We then tested a saccade-related vergence burst neuron (SVBN) model proposed by Zee et al. in J Neurophysiol 68:1624-1641 (1992), in which omnipause neurons remove inhibition from both saccadic and vergence burst neurons. The technique of parameter estimation was used to calculate optimal values for responses from human subjects in which saccadic and convergence components of response were either nearly synchronized or temporally dissociated. Although the SVBN model could account for convergence waveforms when saccadic and vergence components were nearly synchronized, it could not when the components were temporally dissociated. We modified the model so that the saccadic pulse changed the parameter values of the convergence burst units if both components were synchronized. The modified model accounted for velocity waveforms of both synchronous and dissociated convergence movements. We conclude that both the saccadic pulse and omnipause neuron inhibition influence the generation of vergence movements when they are made synchronously with saccades.

Action Potentials↗

PubMed1999

The effect of a second-generation 3D endoscope on the laparoscopic precision of novices and experienced surgeons.

BACKGROUND: Endoscopic surgeons rely on visual feedback to control their movements but lack stereopsis, an important depth cue. Previous three-dimensional (3D) systems alternated images on a two-dimensional (2D) screen, which was uncomfortable for surgeons. A second-generation 3D system provides continuous stereoscopic images on a monitor suspended at arm's length. We studied its effect on the laparoscopic precision of novices and experienced surgeons. METHODS: Experienced laparoscopic surgeons (n = 12) and novices (n = 16) performed a total of 672 tasks in 2D, 3D, and under direct vision. Precision was assessed using the Imperial College Surgical Assessment Device (ICSAD), which generates objective scores of performance by analyzing the movements of surgical instruments. RESULTS: We found that 2D endoscopic vision impaired performance by 35-100% when compared with direct vision, whereas 3D reduced this endoscopic handicap by 41-53% in novices and experienced surgeons (p < 0.03). No side effects were reported with the new 3D system. Even in 2D, novices performed better with an image at arm's length (p < 0. 03). CONCLUSIONS: Second-generation 3D significantly improved the laparoscopic precision of novices and experienced surgeons, without the side effects reported from previous systems. This technology is expected to improve the ease and safety of laparoscopic surgery.

Adolescent↗

PubMed2002

Recovery of postural stability following conscious sedation with midazolam in the elderly.

PURPOSE: To investigate the differences in recovery of postural stability, after obtaining similar intravenous sedation levels with midazolam, in elderly and younger patients undergoing dental surgery. METHODS: We studied 15 elderly patients (>65 years) and 15 younger patients (<55 years) after intravenous sedation. Midazolam was carefully titrated over 4-5 min until slow response to verbal commands, ptosis of the eyelid, or slight slurring of speech was obtained. Parameters were postural balance tests and an addition test, as a psychomotor function test. RESULTS: The dose of midazolam in the elderly group (0.045 +/- 0.012 mg.kg(-1)) was 62% of that in the younger group (0.074 +/- 0.026 mg.kg(-1)). In evaluation of the percentile rank of a balance test with a visual feedback system, which contained a dynamic balance element, recovery at 60 min in the elderly group was significantly slower than that in the younger group. However, the recovery times for the balance test and the addition test, at which the significantly changed values were restored to the baseline values, were 120 min and 90 min, respectively, in both groups. CONCLUSION: In the recovery from sedation, elderly patients had more difficulty in acquiring postural adjustment during movement than in maintaining a standing posture. If the dose is carefully administered, however, even elderly patients might be able to return home 2 h after midazolam administration, as could the younger patients.

Journal Article↗

PubMed2004

Repositioning accuracy and movement parameters in low back pain subjects and healthy control subjects.

STUDY DESIGN: A control group study with repeated measures. OBJECTIVE: To compare trunk repositioning parameters in chronic low back pain (LBP) and healthy subjects. SUMMARY AND BACKGROUND DATA: Recent evidence suggests that chronic LBP patients exhibit deficits in trunk proprioception and motor control. Trunk repositioning and the various spatio-temporal parameters related to it can be used to evaluate sensori-motor control and movement strategies. METHODS: Fifteen control subjects and 16 chronic LBP subjects participated in this study. Subjects were required to reproduce different trunk position in flexion (15 degrees, 30 degrees and 60 degrees) and extension (15 degrees). In the learning phase preceding each condition, visual feedback was provided. Following these learning trials, subjects were asked to perform ten consecutive trials without any feedback. Movement time, movement time variability and peak velocity were obtained and a temporal symmetry ratio was calculated. Peak angular position variability and absolute error in peak angular position were also calculated to evaluate spatial accuracy. RESULTS: Two subgroups of LBP patients were identified. One subgroup of LBP subjects demonstrated longer movement time and smaller peak velocities and symmetry ratios than normal subjects. No group difference was observed for peak angular position variability and absolute error in peak angular position. CONCLUSION: Chronic LBP patients, when given a sufficient learning period, were able to reproduce trunk position with a spatial accuracy similar to control subjects. Some LBP subjects, however, showed modifications of movement time, peak velocity and acceleration parameters. We propose that the presence of persistent chronic pain could induce an alteration or an adaptation in the motor responses of chronic LBP subjects.

Adult↗

PubMed2006

Perceptual adaptation to spectrally shifted vowels: training with nonlexical labels.

Although normal-hearing (NH) and cochlear implant (CI) listeners are able to adapt to spectrally shifted speech to some degree, auditory training has been shown to provide more complete and/or accelerated adaptation. However, it is unclear whether listeners use auditory and visual feedback to improve discrimination of speech stimuli, or to learn the identity of speech stimuli. The present study investigated the effects of training with lexical and nonlexical labels on NH listeners' perceptual adaptation to spectrally degraded and spectrally shifted vowels. An eight-channel sine wave vocoder was used to simulate CI speech processing. Two degrees of spectral shift (moderate and severe shift) were studied with three training paradigms, including training with lexical labels (i.e., "hayed," "had," "who'd," etc.), training with nonlexical labels (i.e., randomly assigned letters "f," "b," "g," etc.), and repeated testing with lexical labels (i.e., "test-only" paradigm without feedback). All training and testing was conducted over 5 consecutive days, with two to four training exercises per day. Results showed that with the test-only paradigm, lexically labeled vowel recognition significantly improved for moderately shifted vowels; however, there was no significant improvement for severely shifted vowels. Training with nonlexical labels significantly improved the recognition of nonlexically labeled vowels for both shift conditions; however, this improvement failed to generalize to lexically labeled vowel recognition with severely shifted vowels. Training with lexical labels significantly improved lexically labeled vowel recognition with severely shifted vowels. These results suggest that storage and retrieval of speech patterns in the central nervous system is somewhat robust to tonotopic distortion and spectral degradation. Although training with nonlexical labels may improve discrimination of spectrally distorted peripheral patterns, lexically meaningful feedback is needed to identify these peripheral patterns. The results also suggest that training with lexically meaningful feedback may be beneficial to CI users, especially patients with shallow electrode insertion depths.

Adaptation, Physiological↗

PubMed2001

Semiautomatic segmentation of the cochlea using real-time volume rendering and regional adaptive snake modeling.

The human cochlea in the inner ear is the organ of hearing. Segmentation is a prerequisite step for 3-dimensional modeling and analysis of the cochlea. It may have uses in the clinical practice of otolaryngology and neuroradiology, as well as for cochlear implant research. In this report, an interactive, semiautomatic, coarse-to-fine segmentation approach is developed on a personal computer with a real-time volume rendering board. In the coarse segmentation, parameters, including the intensity range and the volume of interest, are defined to roughly segment the cochlea through user interaction. In the fine segmentation, a regional adaptive snake model designed as a refining operator separates the cochlea from other anatomic structures. The combination of the image information and expert knowledge enables the deformation of the regional adaptive snake effectively to the cochlear boundary, whereas the real-time volume rendering provides users with direct 3-dimensional visual feedback to modify intermediate parameters and finalize the segmentation. The performance is tested using spiral computed tomography (CT) images of the temporal bone and compared with the seed point region growing with manual modification of the commercial Analyze software. Our method represents an optimal balance between the efficiency of automatic algorithm and the accuracy of manual work.

Cochlea↗

PubMed1989

Color flow duplex screening of infrainguinal grafts combining low- and high-velocity criteria.

The aim of this prospective study was to evaluate the ability of duplex ultrasonography to identify infrainguinal grafts at high risk for failure. The criteria used identified low flow by low peak systolic velocity (less than 45 cm/s) and stenosis by high velocity (greater than 300 cm/s) or by velocity at the stenosis three times the velocity in the adjacent normal graft. A total of 114 patent grafts were scanned and compared with concurrent angiograms. Duplex scanning correctly identified 18 high-risk grafts by low-flow criteria and an additional 21 by stenosis criteria. There was one false-negative finding (sensitivity 98 percent). The velocity ratio of the stenosis to the adjacent graft was useful in estimating the degree of stenosis. Color flow duplex imaging reduced examination time through visual feedback by highlighting the graft and areas of high velocity. These results indicate that color flow duplex scanning, combining low- and high-peak systolic criteria, is a very sensitive screening test in the early detection of failing grafts.

Blood Vessel Prosthesis↗

PubMed1971

Keyboard entry.

Many recent studies of keyboard entry are summarized with particular emphasis on performance data and fundamental questions about the design of keyboards. The role of auditory and visual feedback and physiological measurements are reviewed. Typical speed and error rates are given for several types of situations and operators. Other methods of data entry are considered, as are source documents, ordering of keys, keyboard interlocks, and chord keyboards. These data should be of interest to anyone concerned with the design and use of keyboards or other data entry devices.

Journal Article↗

PubMed1986

Human factors aspects of pointing as an input technique in interactive computer systems.

The use of pointing devices to input to interactive computer systems is increasing. This paper considers the human factors aspects of the use of a range of these devices. A distinction is drawn between direct and indirect devices. A number of aspects of pointing responses are discussed with reference to the experimental evidence: that pointing is non-linguistic, serial, involves gross motor movement and relies on visual feedback. The overall speed and the extent to which it is a natural form of response are also discussed. The paper ends with some conclusions about the suitability of different devices for different tasks.

Journal Article↗

PubMed1991

Behavior therapy for spasmodic torticollis: a case study suggesting a causal role for anxiety.

A 29-year old male with an 8-month history of spasmodic torticollis was treated after three baseline assessments with progressive relaxation, positive practice, and visual feedback. Subjective, behavioral, and physiological (EMG) data indicated that EMG declined across baseline assessments and treatment, while substantial changes in subjective and behavioral data occurred with treatment. Improvement on all dependent measures also was found at a 2-year follow-up. The data are discussed in terms of the non-specific effects of treatment, and the utility and economy of these primarily self-administered procedures.

Adult↗