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Biomedical subjects

M Flanders

Publications and source records attributed to M Flanders.

At least 19 recordsLinked to original sources
PubMed1995

Moving effortlessly in three dimensions: does Donders' law apply to arm movement?

Donders' law, as applied to the arm, predicts that to every location of the hand in space there corresponds a unique posture of the arm as defined by shoulder and elbow angles. This prediction was tested experimentally by asking human subjects to make pointing movements to a select number of target locations starting from a wide range of initial hand locations. The posture of the arm was measured at the start and end of every movement by means of video cameras. It was found that, in general, the posture of the arm at a given hand location does depend on the starting location of the movement and that, consequently, Donders' law is violated in this experimental condition. Kinematic and kinetic factors that could account for the variations in arm posture were investigated. It proved impossible to predict the final posture of the arm purely from kinematics, based on the initial posture of the arm. One hypothesis was successful in predicting final arm postures, namely that the final posture minimizes the amount of work that must be done to transport the arm from the starting location.

Arm↗
PubMed1994

Errors in kinesthetic transformations for hand apposition.

We investigated the ability of human subjects to duplicate with the left hand the spatial location of the right hand, using only kinesthetic cues. Under this experimental condition, subjects produced large and idiosyncratic errors which varied with the spatial location of the hand. Tactile cues originating from contact of the hand with a rigid surface generally led to a decrease in the variable error. However, even without tactile cues, the variable error was small compared with other tasks in which subjects are required to estimate the spatial location of the hand on the basis of kinesthetic cues. The results suggest that subjects did not derive an estimate of the location of the right hand in extrapersonal space, but rather that they performed the task within intrapersonal space.

Cues↗
PubMed1994

Spatial/temporal characteristics of a motor pattern for reaching.

1. Temporal patterns of electromyographic (EMG) activity were related to the direction of fast reaching movements. Reaches were to 20 targets in the sagittal plane of the human arm. 2. The subtraction of EMG levels recorded during very slow movements to each target allowed this study to focus on the phasic aspects of complex EMGs. 3. General features of the phasic spatial/temporal patterns differed across muscles, even across muscles at the same joint. This indicates that future models of cortical to motoneuronal processing must include nonuniform space-time transformations.

Arm↗
PubMed1994

Muscle activation patterns for reaching: the representation of distance and time.

1. The timing and intensity of phasic muscle activation were related to the distance of reaching movements of the human arm. We dissociated phasic components of muscle activation from complete muscle activation waveforms by subtracting waveforms obtained during very slow movements. 2. We recorded electromyographic (EMG) activity from elbow and/or shoulder muscles as standing subjects reached forward and upward to targets at four distances. Accuracy was deemphasized and no terminal corrections were allowed. In the first part of the experiment subjects were asked to move at their preferred speed. In the second part of the experiment they were asked to move using a range of speeds. 3. In the first part of the experiment subjects moved faster to more distant targets but they also increased movement time as a nearly linear function of target distance. The slope of this function was very similar across subjects. The phasic EMG waveforms for different distances appeared to be similar in shape but of variable duration. EMG time base was quantified using a correlation technique that identified the time base scale factor that best superimposed a given trace with a template. This technique revealed that the slope of the relation between EMG time base and target distance was not the same for all muscles. 4. In the second part of the experiment, where subjects moved to each target at a range of specified speeds, time base scaling was again significantly different for different muscles. The scaling differed most dramatically between anterior deltoid and medial head of triceps. 5. EMG intensity was more strongly related to movement time than to distance. We quantified the correspondence of distance and movement time to phasic EMG intensity using a multiple regression analysis of all distances and speeds, assuming a power relation. Distance exponents were positive and movement time exponents were larger and negative. This implies that movement time is more important than distance in its relation to EMG intensity.

Adult↗
PubMed1994

The role of stereopsis and early postoperative alignment in long-term surgical results of intermittent exotropia.

Despite the presence of good stereopsis, surgically corrected intermittent exotropes may show a gradual outward shift with time. The purpose of this study was to identify early factors that influence the success of corrective surgery. Sixty-seven consecutive patients treated surgically for intermittent exotropia (age range 1.9 to 76 years) constituted our final sample. Sensory status was evaluated with the Titmus stereotest. A successful surgical result was defined as phoria or intermittent tropia of +/- 10 prism dioptres or less for near and distance with maintained or improved stereopsis, 6 months or more after surgery. The average postoperative follow-up period was 3.3 (range 0.5 to 11) years. Good stereopsis (60 seconds of arc or better) was present in only 42% of the patients preoperatively and 61% postoperatively. The overall surgical success rate was 60%. Early overcorrection, defined as an esodeviation present within the first 4 weeks after surgery, caused a significant improvement in the success rate, to 79% (p = 0.03). Poor preoperative stereopsis combined with early overcorrection resulted in a further significant improvement in the surgical success rate, to 92% (p = 0.07). This suggests that poor preoperative stereopsis does not necessarily preclude, and may enhance, long-term alignment stability postoperatively. We suggest that it is peripheral rather than central fusion that keeps the eyes well aligned after surgery and prevents recurrence of the exodeviation.

Accommodation, Ocular↗
PubMed1993

Parallel, interdependent channels for location and orientation in sensorimotor transformations for reaching and grasping.

1. Subjects were presented with a cylinder, whose orientation with respect to the vertical and location in space varied from trial to trial. They grasped a similar cylinder in their hands and were instructed to align the grasped cylinder with the target cylinder. In some experiments the task was performed from memory, and subjects attempted to reproduce both location and orientation of the cylinder. In others, they attempted to reproduce only its orientation, either from memory or while the cylinder was in view. 2. Multivariate linear regression analysis was used to determine persistent and variable errors in performance. This analysis related the subjects' performance (reproduced orientation) to target parameters (location and orientation). 3. We have interpreted the experimental results starting from the assumption that there are two parallel neural processes underlying reaching and grasping: one relating proximal arm motion to target location and the other relating distal hand motion to target orientation. 4. Variable errors did not vary with task conditions, even when subjects were asked to dissociate target orientation from target location by matching target orientation with the arm at the side, irrespective of the location of the target. This finding suggests that the neural transformations involving target location and target orientation are performed in parallel. 5. Persistent errors did vary with task condition. The subjects made the largest errors in matching target orientation when the target was in view, but they were asked to match its orientation at a location that differed from that of the target. These errors depended mostly on the elevation of the target and on its slant (inclination relative to the vertical). They were related to the posture of the arm in a manner that suggested that matching orientation is influenced by both extrinsic (spatial) and intrinsic (arm posture) parameters. 6. The fact that persistent errors depend on target location and on arm posture as well as on target orientation implies that the neural transformation from target orientation to hand orientation is not independent of the transformation dealing with target location.

Attention↗
PubMed1993

Effectiveness of botulinum toxin in the treatment of spasmodic torticollis.

Thirty-two patients with spasmodic torticollis were assessed quantitatively for posture deformity, tremor and range of neck movement, and qualitatively for pain and global subjective disability. All patients were then treated with intramuscular botulinum toxin injections into appropriate neck muscles. Fifty-three treatments were administered using dosages of toxin in the range of 50-100 U per muscle. The maximum dose administered at a single sitting was 280 U. The progress of the patients was assessed during an 18-month period. Seventy-five percent of patients showed documented improvement in both subjective and objective parameters and were considered treatment successes. Pain improved in 65%, posture in 65%, tremor in 50% and range in 46%. The side effects that occurred were transient and included fatigue, dysphagia, neck weakness, hoarseness and local pain. This study demonstrates that treatment with botulinum toxin is of significant benefit for the majority of patients with spasmodic torticollis.

Adult↗
PubMed1993

Botulinum toxin: preferred treatment for hemifacial spasm.

This paper retrospectively analyses the clinical data of 65 consecutive cases of hemifacial spasm. A benign etiology was clinically evident in the majority of cases. Neuroradiologic investigation ruled out serious intracranial pathology in atypical cases. Trials of oral medication in 26 patients were consistently unsuccessful. Fifty-one patients had repeated lid and facial muscle injections of botulinum toxin during a period of 8 years. The mean duration of effective relief from spasm following an initial treatment was 18.9 weeks. This effect did not diminish with repeated injections.

Adult↗
PubMed1992

Two components of muscle activation: scaling with the speed of arm movement.

1. The temporal waveform of muscle activity was related to the speed of arm movement. Speed was expressed in terms of the duration of a fixed amplitude movement or the "movement time." 2. Human subjects moved their arms to targets in three-dimensional space. The right arm started at a standard initial position and moved directly to the target in a single stroke. The targets were placed in various directions in a vertical plane. The arm movements consisted of shoulder and elbow rotations. 3. Subjects were required to vary the speed of their movements. In most of the experiments, trials with different movement times were randomly ordered. One of the experiments also included randomly interspersed static trials, in which the subject held the arm still at the initial posture, the final posture, or halfway between the two extremes. 4. Electromyographic (EMG) activity was recorded from several superficial elbow and/or shoulder muscles. The time base of rectified EMG records was normalized for movement time such that records from movements with various speeds were compressed to align the ending times of the movements. 5. A principal component (PC) analysis revealed that the compressed EMG waveforms could be described by a summation of PC1 and PC2 waveforms; each individual EMG waveform was approximated by a weighted sum of these two components. 6. The PC1 weighting coefficients scaled down in a monotonic relationship with movement time such that the fastest movement corresponded to a large positive weighting coefficient and the slowest movement corresponded to a small positive weighting coefficient. The PC2 weighting coefficients exhibited a similar monotonic scaling, but the values ranged from positive to negative. Further analysis demonstrated that these two components can be mathematically transformed into a tonic waveform with a constant mathematically transformed into a tonic waveform with a constant weighting coefficient and a phasic waveform with positive weighting coefficients that scale down with movement time. 7. The amplitude scaling of EMG records cannot be described by a single component, but instead requires a summation of two separate components. The tonic component may correspond to the force element needed to counteract gravity, because the magnitude of this element does not scale with movement speed. The phasic component may correspond to the force element that scales quadratically to produce a linear increase in velocity.

Arm↗
PubMed1992

Kinematics of typing: parallel control of the two hands.

1. Experienced touch typists were asked to type words in which only a single letter was typed by one hand, while the remaining letters were typed with the other hand. 2. Translational and rotational motion of each finger was computed optoelectronically from the location of reflective markers. Translational and rotational motion of both wrists was also computed from the locations of these markers. 3. Typically, when a subject typed a single letter, all of the fingers of the hand were in motion, as was the wrist. For each letter, this overall kinematic pattern of finger and wrist motion was highly repeatable. Thus the keystroke kinematics formed a repeatable signature for a particular letter typed by a particular subject. 4. During the keystroke the other hand was also in motion, typing the preceding and succeeding letters. During this period the motion of the two wrists and the motions of corresponding fingers of both hands was uncorrelated. 5. Because the keystroke kinematics are highly repeatable and independent of the movement of the contralateral hand, each keystroke represents a fundamental element of the typing movement. Thus these results provide a basis for determining the processes whereby sequences of keystrokes are assembled to type words.

Biomechanical Phenomena↗
PubMed1992

Organization of sequential typing movements.

1. Experienced touch typists were asked to type words that contained only one or two letters typed by one of the two hands. When a word contained a pair of letters typed by one hand, the letters could be consecutive, or there could be one, two, or three intervening letters typed with the other hand. 2. We studied cases in which pairs of letters were either identical, different but typed with the same finger, or typed with two different fingers on the same hand. 3. Translational and rotational motion of the fingers and wrist was computed optoelectronically from the location of reflective markers on the hands. Finger and wrist motion recorded when subjects typed pairs of letters was compared with the motion recorded when the subject typed either letter in isolation. 4. When the subject typed the same letter consecutively, or separated by intervening letters, the second keystroke began only after the first key had been pressed. The same result was obtained when the second letter was not identical but was typed with the same finger. Up to the time of the first keypress, the initial keystroke kinematics were identical to those for that letter typed in isolation. 5. When the second letter in a pair was typed with the use of a different finger, the initial focal movement (wrist and finger striking the key) was unaffected up to the time of initial keypress. However, the second finger could begin to move toward the second key shortly before the initial keypress, and therefore the corollary movements normally involved in the initial keystroke were affected. 6. These results indicate that typing movements are executed primarily in a serial fashion, letter by letter. There can be some overlap between consecutive keystrokes only if they are executed with different fingers. 7. Words in which two letters typed with one hand were separated by three letters typed with the other hand provided subjects the opportunity to initiate the second keystroke at a range of times after the first keypress. 8. When the second letter differed from the first, subjects always returned to the home position after the first keypress and initiated the second keystroke with a normal latency. However, when the second letter was the same as the first letter, subjects sometimes suppressed the return to the home position after the first keystroke and maintained their finger poised over the key. 9. Thus keystrokes of one hand are best described as being executed sequentially. However, the findings presented here also indicate that movement planning encompasses strings of letters.

Biomechanical Phenomena↗
PubMed1991

Mucolipidosis type IV: clinical manifestations and natural history.

The clinical manifestations and psychomotor development of five patients with mucolipidosis IV (MLIV) from three Ashkenazi-Jewish families are reported. The presenting symptoms were hypotonia, developmental delay, corneal clouding, and puffy eyelids. Four of the patients had convergent strabismus and none progressed beyond a developmental age of 15 months. One patient died of aspiration at 17 years while the oldest patient entered puberty at 20 years, developed a coarse face at 30 years, and is now 32 years old. Histopathological studies in four patients showed storage changes characteristic of MLIV.

Adolescent↗
PubMed1991

Temporal patterns of muscle activation for arm movements in three-dimensional space.

Little is known about the patterns of muscle activation that subserve arm movement in three-dimensional space. In this study, activation patterns of seven arm muscles were related to the spatial direction of human arm movement. Twenty movement directions defined two orthogonal vertical planes in space. The arm movements were moderately paced; each movement lasted approximately 500 msec. New techniques of EMG analysis were developed to describe the temporal pattern of muscle activation. For each muscle, a principal component analysis revealed a common phasic and tonic waveform for all directions of movement, within one plane. A temporal shifting procedure based on best covariance values revealed activation delays associated with different movement directions. The results show a consistent pattern of temporal shifting of the common waveform for movements in different directions. Coupled with past results showing that activation amplitude is a function of the cosine angle of movement or force direction, the present results suggest a relatively simple control strategy for mechanically complex arm movements: neural circuits produce a common phasic and tonic activation waveform that is scaled in amplitude and delayed in time, depending on the desired movement direction.

Arm↗
PubMed1991

A coordinate system for the synthesis of visual and kinesthetic information.

The results of this study suggest that information derived from kinesthetic inputs alone is not normally used to generate an estimate of the location of the hand in extrapersonal space. This finding provides support for the interpretation of previous results suggesting that a representation of a visual target in extrapersonal space must be transformed into a kinesthetic reference frame before the parameters of a targeted arm movement can be computed (Soechting and Flanders, 1989b). We asked subjects to use a pointer to indicate the spatial location of their hand following an unseen passive displacement. We found that subjects had large errors in the locations that they chose and that there was a large degree of variability for repeated trials with the same hand location. The errors were a result neither of using the pointer to indicate a spatial locus nor of an inability to make use of kinesthetic information. Instead, the errors resulted from an inability of subjects to synthesize an estimate of the hand's spatial location from only kinesthetic cues. We also asked subjects to use the pointer to indicate the location of their hand following a passive displacement when they had visual information about the passive displacement. In this case, we found that subjects performed better than when they had only kinesthetic information, but not as well as when they had only visual information about target location. This finding suggests that kinesthetic information about target location affects the processing of visual information.

Arm↗
PubMed1991

Treatment of blepharospasm and hemifacial spasm with botulinum A toxin: a Canadian multicentre study.

Botulinum A exotoxin was recently approved for use in Canada. We describe the efficacy of botulinum toxin in the management of 235 patients with blepharospasm (mean age 64.3 years) and 130 patients with hemifacial spasm (mean age 60.4 years) treated at three Canadian ophthalmologic centres between 1984 and 1989. A total of 98% of the patients with blepharospasm and 100% of the patients with hemifacial spasm had significant relief of their symptoms; however, 11% of the former and 2% of the latter did not respond to the usual starting concentrations of the drug and needed stronger dosages for relief. The duration of relief varied widely in both groups. Up to 7% of patients had ineffective treatments but responded to subsequent injections. Analysis of variance and linear trend statistics showed that there were no changes in the mean duration of relief over the first several treatments for individual patients in either group. Side effects were transient and included ptosis, exposure keratitis, epiphora and strabismus.

Adult↗
PubMed1990

Arm muscle activation for static forces in three-dimensional space.

1. Muscle activity was related to the direction of a static force at the human wrist. For each muscle the force direction of maximal activity and the directional tuning characteristics were determined. 2. Electromyographic (EMG) activity was recorded from nine superficial elbow and/or shoulder muscles while subjects held the right arm stationary in one of six postures. The direction of the force at the wrist was varied in two orthogonal planes. In each experiment a cable was attached to the subject's wrist, and a constant force magnitude was applied in various directions with the use of a pulley system. 3. The relationship between the averaged EMG level and the force direction was described for each muscle, in each posture, and in each plane. The EMG data were fit with a nonlinear, multiple cosine function, which allowed the identification of one, two, or sometimes three separate cosine peaks. 4. Two-cosine functions often provided the best fit to the EMG data. All nine muscles were best fit with a two-cosine function in at least two of the six postures. Four of the muscles had a second peak of activity in more than one-half of the experimental situations. The second peak was often in a direction that was nearly opposite the direction of the first peak and represented a negative contribution to the total force produced at the wrist ("coactivation"). We suggest that multimodal directional tuning results from the convergence of multiple sources of descending signals onto motoneurons. 5. The mechanical actions of nine elbow and/or shoulder muscles were estimated with the use of published data from a cadaver study by Wood and co-workers. Postural changes in the mechanical actions of muscles were substantial. A 45 degrees rotation of the shoulder, for example, might cause a 30-50 degrees change in the direction of force at the wrist that could be produced by the contraction of a given muscle. The magnitude of these postural changes suggests that arm position is an important determinate of EMG patterns. 6. Postural changes in the direction of maximal EMG activity usually paralleled the postural changes in mechanical pulling direction. Postural changes in EMG amplitudes usually covaried with postural changes in mechanical advantage. 7. The posterior deltoid (PD) was an exception to the general rule of covariation of mechanical actions and EMG activities. Instead of reflecting the muscle's mechanical action, the EMG activity of the PD closely resembled the EMG activity of the medial deltoid (MD).(ABSTRACT TRUNCATED AT 400 WORDS)

Arm↗