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J F Soechting

Publications and source records attributed to J F Soechting.

At least 37 records · Page 2Linked to original sources
PubMed1995

On the form of the internal model for reaching.

We investigated, by using simulations, possible mechanisms responsible for the errors in the direction of arm movements exhibited by deafferented patients. Two aspects of altered feedforward control were evaluated: the inability to sense initial conditions and the degradation of an internal model. A simulation which assumed no compensation for variations in initial arm configuration failed to reproduce the characteristic pattern of errors. In contrast, a simulation that assumed random variability in the generation of joint torque resulted in a distribution of handpaths which resembled some aspects of the pattern of errors exhibited by deafferented patients.

Arm↗
PubMed1995

Psychophysical approaches to motor control.

A variety of experimental approaches have recently helped identify the reference frames and coordinate systems that describe the control of eye and limb movements. These descriptions apply at the behavioral level and also, despite the distributed nature of neural processing, to the population responses of different neural structures. Studies on the process of adaptation to altered environments have also provided new insights into the controlled variables for movements: although handpaths can be adapted to extrinsic demands, the adaptation is, in some cases, in an intrinsic frame of reference.

Animals↗
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 learning of novel finger movement sequences.

1. Experienced typists typed phrases containing words in which one isolated letter was typed with one hand, while the remaining letters were typed with the contralateral hand. 2. The translational and rotational motion of the fingers and wrist of the right hand were obtained optoelectronically from the location of reflective markers placed on the fingers. 3. Midway through the experiment, the key corresponding to the isolated letter was physically switched with another key on the keyboard, and subjects typed the letter in its new location (for 140 trials). The letter "n," typed with the right index finger, was either switched with letters normally typed with the same finger (u), with a different finger but same hand (o), with the same finger of the left hand (v), or with a different finger of the left hand (w). 4. When the words were typed normally, the interkey intervals were relatively short, and the onset of movement of the right hand began before the preceding keypress with the left hand. Thus the movement of the two hands overlapped. Furthermore, the movement to the isolated key was highly stereotypical, with little trial-to-trial variability. 5. After the transposition of keys, there were prolongations in the interkey intervals, with the largest delay occurring directly before the typing of the transposed key. Switches between homologous fingers (involving mirror movements) delayed the onset of keypresses to a lesser extent than did other switches. With practice, these delays were reduced but never reached the control level. 6. After the keyswitch, the onset of movement to the isolated key did not occur on average until after the last keypress with the contralateral hand, except when the switch involved the use of homologous fingers. In the latter case, overlapping movement of the two hands was maintained. Thus the learning of a series of discrete movements does not necessarily require that each movement segment be performed sequentially. 7. After the transposition of keys, the movement pattern and time course to a given key were similar to the movement patterns for that key observed during control trials in all conditions. Thus the learning of a series of movements may involve the use of previously learned movements under new conditions. 8. The results suggest that typing movements may be organized at several levels, including the individual keystroke and word level.

Adult↗
PubMed1993

Non-uniform temporal scaling of hand and finger kinematics during typing.

We examined the manner in which the keystroke kinematics of the hand and the fingers varied with the mean rate of typing by trained typists. We used words and phrases in which only one letter was typed with the right hand and all of the remaining letters were typed using the left hand. We varied the typing rate over a threefold range (intervals between keypresses ranging from 150 ms to 500 ms) with the aid of a metronome. The results from four subjects, and three letters (n, u, and o) were analyzed. We did not find a simple scaling that could account for variations in the velocity profiles with typing rate. For some subjects and some letters, the velocities were independent of typing rate. In other instances, the kinematics did depend on typing rate, but to a much greater extent prior to the time of keypress than afterward. Sometimes the velocity profiles of all of the fingers and of the hand changed in a similar manner as the interval between keypresses was varied. In other instances only the focal movement of the hand and the finger used to press the key depended on the interval, whereas the motions of the other fingers did not. We suggest that the consistencies in the velocity profiles which we observed may simplify the problem of arranging a temporally ordered sequence of goal-directed movements.

Fingers↗
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↗
PubMed1992

Synergistic finger movements in a skilled motor task.

When skilled typists strike one key, typically all of the fingers of one hand are in motion simultaneously. We studied the extent to which the motion of the individual fingers was similar. Subjects were asked to type lists of words, each word designed so that only one key would be pressed by a finger of one hand, the remaining letters being typed with the other hand. Changes in the lengths (flexion-extension) and orientation (abduction-adduction) of each finger were measured and the similarity of the motion of pairs of fingers was assessed by computing correlation coefficients. For each pair of fingers, the correlation coefficients were broadly distributed, but in most instances the mean was significantly greater than zero. Adjacent fingers showed a higher degree of correlation than did non-adjacent fingers. When one of the fingers was actually used to press the key, the degree of correlation decreased substantially. The results demonstrate that in this skilled motor task, the fingers usually tend to be moved together, but they can be moved independently when the task so requires.

Fingers↗
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

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↗
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↗
PubMed1990

Parcellation of sensorimotor transformations for arm movements.

Pointing to a visual target in 3-dimensional space requires a neural transformation from a visually derived representation of target location to an appropriate pattern of activity in arm muscles. Previous results suggested that 1 step in this process involves a transformation from a representation of target location to a representation of intended arm orientation, and that the neural implementation of this transformation involves a linear approximation to the mathematically exact, nonlinear solution. These results led to the hypothesis that the transformation is parceled into 2 separate channels. In 1 channel a representation of target azimuth is transformed into a representation of arm yaw angles, while in the other channel representations of target distance and target elevation are transformed into a representation of arm elevation angles. The present experiments tested this hypothesis by measuring the errors made by human subjects as they pointed to various parameters of the remembered location of a target in space. The results show that subjects can use the 2 hypothesized channels separately. For example, subjects can accurately point to the target's azimuth while ignoring the target's elevation and distance. The results also show that subjects are unable to point to the target's elevation while ignoring the target's distance, consistent with the hypothesis that information about target elevation and target distance is tied together in the same channel. The parcellation demonstrated in this study is compared to reports of parceled sensorimotor transformation in other vertebrate species.

Arm↗
PubMed1989

An assessment of the existence of muscle synergies during load perturbations and intentional movements of the human arm.

A cross-correlation analysis was performed on EMG activities in elbow and shoulder flexors evoked by force perturbations acting in different directions on the forearm and during intentionally generated movements with the purpose of characterizing the temporal relationships between patterns of activation of different muscles. Qualitatively it was found that the shape of the cross-correlation function differed from one experimental condition to the next. A principal component analysis permitted a quantitative assessment of this point. In general it was found that two principal components could account for the data. Furthermore when the cross-correlograms are represented in principal component space, there was no clustering of the data points. Several possible definitions of 'muscle synergies' are discussed from the perspective of this finding. It is concluded that the most restrictive definition is incompatible with the data. Less restrictive definitions, while compatible with the data, do not lead to a simplification of the control problem.

Arm↗