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Biomedical subjects

J R Flanagan

Publications and source records attributed to J R Flanagan.

At least 19 recordsLinked to original sources
PubMed1999

Composition and decomposition of internal models in motor learning under altered kinematic and dynamic environments.

The learning process of reaching movements was examined under novel environments whose kinematic and dynamic properties were altered. We used a kinematic transformation (visuomotor rotation), a dynamic transformation (viscous curl field), and a combination of these transformations. When the subjects learned the combined transformation, reaching errors were smaller if the subject first learned the separate kinematic and dynamic transformations. Reaching errors under the kinematic (but not the dynamic) transformation were smaller if subjects first learned the combined transformation. These results suggest that the brain learns multiple internal models to compensate for each transformation and has some ability to combine and decompose these internal models as called for by the occasion.

Adult↗
PubMed1999

The influence of visual illusions on grasp position.

Visual size illusions have been shown to affect perceived object size but not the aperture of the hand when reaching to those same objects. Thus, vision for perception is said to be dissociated from vision for action. The present study examines the effect of visual-position and visual-shape illusions on both the visually perceived center of an object and the position of a grasp on that object when a balanced lift is required. The results for both experiments show that although the illusions influence both the perceived and the grasped estimates of the center position, the grasp position is more veridical. This partial dissociation is discussed in terms of its implications for streams of visual processing.

Adolescent↗
PubMed1999

Anticipatory grip adjustments are observed in both goal-directed movements and movement tics in an individual with Tourette's syndrome.

We examined grip force adjustments during movements of a hand-held object in a young man (BF) with Tourette's syndrome. We directly compared BF's voluntary up and down movements with tics in the same directions. Movement tics were elicited by cueing BF to move either up or down on a GO signal which appeared after a variable delay. During the delay period, we observed frequent tics which were almost always in the cued movement direction. BF's voluntary movements were well coordinated and featured precise and appropriate anticipatory grip force adjustments such that grip force was modulated in phase with movement-induced fluctuations in load. Precise anticipatory grip force adjustments were also observed in all of BF's movement tics. These results support the hypothesis that tics in Tourette's syndrome are purposeful voluntary movements that are well organized and coordinated.

Adaptation, Physiological↗
PubMed1999

Control of fingertip forces in multidigit manipulation.

Previous studies of control of fingertip forces in skilled manipulation have focused on tasks involving two digits, typically the thumb and index finger. Here we examine control of fingertip actions in a multidigit task in which subjects lifted an object using unimanual and bimanual grasps engaging the tips of the thumb and two fingers. The grasps resembled those used when lifting a cylindrical object from above; the two fingers were some 4.25 cm apart and the thumb was approximately 5.54 cm from either finger. The three-dimensional forces and torques applied by each digit and the digit contact positions were measured along with the position and orientation of the object. The vertical forces applied tangential to the grasp surfaces to lift the object were synchronized across the digits, and the contribution by each digit to the total vertical force reflected intrinsic object properties (geometric relationship between the object's center of mass and the grasped surfaces). Subjects often applied small torques tangential to the grasped surfaces even though the object could have been lifted without such torques. The normal forces generated by each digit increased in parallel with the local tangential load (force and torque), providing an adequate safety margin against slips at each digit. In the present task, the orientations of the force vectors applied by the separate digits were not fully constrained and therefore the motor controller had to choose from a number of possible solutions. Our findings suggest that subjects attempt to minimize (or at least reduce) fingertip forces while at the same time ensure that grasp stability is preserved. Subjects also avoid horizontal tangential forces, even at a small cost in total force. Moreover, there were subtle actions exerted by the digits that included changes in the distribution of vertical forces across digits and slight object tilt. It is not clear to what extent the brain explicitly controlled these actions, but they could serve, for instance, to keep tangential torques small and to compensate for variations in digit contact positions. In conclusion, we have shown that when lifting an object with a three-digit grip, the coordination of fingertip forces, in many respects, matches what has been documented previously for two-digit grasping. At the same time, our study reveals novel aspects of force control that emerge only in multidigit manipulative tasks.

Adult↗
PubMed1999

Control of grasp stability in humans under different frictional conditions during multidigit manipulation.

Control of grasp stability under different frictional conditions has primarily been studied in manipulatory tasks involving two digits only. Recently we found that many of the principles for control of forces originally demonstrated for two-digit grasping also apply to various three-digit grasps. Here we examine the control of grasp stability in a multidigit task in which subjects used the tips of the thumb, index, and middle finger to lift an object. The grasp resembled those used when lifting a cylindrical object from above. The digits either all contacted the same surface material or one of the digits contacted a surface material that was more, or less, slippery than that contacted by the other two digits. The three-dimensional forces and torques applied by each digit and the contact positions were measured along with the position and orientation of the object. The distribution of forces among the digits strongly reflected constraints imposed by the geometric relationship between the object's center of mass and the contact surfaces. On top of this distribution, we observed changes in force coordination related to changes in the combination of surface materials. When all digits contacted the same surface material, the ratio between the normal force and tangential load (F(n):L ratio) was similar across digits and scaled to provide an adequate safety margin against slip. With different contact surfaces subjects adapted the F(n):L ratios at the individual digits to the local friction with only small influences by the friction at the other two digits. They accomplished this by scaling the normal forces similarly at all digits and changing the distribution of load among the digits. The surface combination did not, however, influence digit position, tangential torque, or object tilting systematically. The change in load distribution, rather, resulted from interplay between these factors, and the nature of this interplay varied between trials. That is, subjects achieved grasp stability with various combinations of fingertip actions and appeared to exploit the many degrees of freedom offered by the multidigit grasp. The results extend previous findings based on two-digit tasks to multidigit tasks by showing that subjects adjust fingertip forces at each digit to the local friction. Moreover, our findings suggest that subjects adapted the load distribution to the current frictional condition by regulating the normal forces to allow slips to occur early in the lift task, prior to object lift-off.

Adult↗
PubMed1999

Randomized study of online vaccine reminders in adult primary care.

Online immunization reminders were implemented in an adult medicine setting in which all immunization history, vaccine ordering and charting were required online. Physicians were randomized to one of two arms in a cross-over design. Each arm was shown online recommendations for vaccines indicated by nationally accepted guidelines either during the first or during the second part of the study period. The main purpose of the study was to assess the impact of reminders on correct decisions related to prescribing vaccines. Online reminders had the following impact on physician behavior: 1) Physicians used the application almost 3 times as often when shown reminders. 2) Physicians in the reminder group were 27% less likely to order a vaccine in the reminder group (P- value 0.0005). 3) Compliance with guidelines was improved significantly for Tetanus and for Hepatitis B in several analyses. No such effects were found for Pneumoccocal, Measles, or Influenza vaccines.

Adult↗
PubMed1999

Tracking vaccine compliance in a primary care setting: online history, reminders, order entry, and charting.

In a new primary care setting with three medical disciplines participating, a vaccine history and order entry system was implemented along with other online documentation systems as the primary documentation tools for the clinic. Reminders were generated based upon a set of algorithms consistent with 1998 nationally accepted vaccine guidelines. Vaccine compliance data were analyzed for the entire population cared for in this setting for a 6 month period. Rates of compliance with national recommendations for eight key vaccine groups were calculated based on the online data. Trends in the rates of compliance, interpreted within limitations, showed statistically and clinically significant improvements. The immunization application accomplished several goals: accurate history and patient-specific recommendations, online ordering of vaccines or serum products, online charting of administration that, in turn, automatically maintained the vaccine history.

Adolescent↗
PubMed1998

The reaching movements of patients with Parkinson's disease under self-determined maximal speed and visually cued conditions.

Two-dimensional kinematic analysis was performed of the reaching movements that six subjects with Parkinson's disease and six healthy subjects produced under self-determined maximal speed and visually cued conditions. Subjects were required to reach as fast as possible to grasp a ball (i) that was fixed stationary in the centre of a designated contact zone on an inclined ramp (self-determined maximal speed condition), or (ii) that rolled rapidly from left to right down the incline and into the contact zone (visually cued condition). Parkinson's disease subjects displayed bradykinesia when performing maximal speed reaches to the stationary ball, but not when they reached for the moving ball. In response to the external driving stimulus of the moving ball, Parkinson's disease subjects showed the ability to exceed their self-determined maximal speed of reaching and still maintain a movement accuracy that was comparable to that of healthy subjects. Thus, the bradykinesia of Parkinson's disease subjects did not seem to be the result of a basic deficit in their force production capacity or to be a compensatory mechanism for poor movement accuracy. Instead, bradykinesia appeared to result from the inability of Parkinson's disease subjects to maximize their movement speed when required to internally drive their motor output. The occasional failure of Parkinson's disease subjects to successfully grasp the moving ball suggested errors of coincident anticipation and impairments in grasp performance rather than limitations in the speed or accuracy of their reaches. These results are discussed in relation to the notion that the motor circuits of the basal ganglia play an important role in the modulation of internally regulated movements.

Aged↗
PubMed1997

The role of internal models in motion planning and control: evidence from grip force adjustments during movements of hand-held loads.

We investigated the issue of whether or not the CNS makes use of an internal model of the motor apparatus in planning and controlling arm movements. In particular, we tested the ability of subjects to predict different hand-held loads by examining grip force adjustments used to stabilize the load in the hand during arm movements. Subjects grasped a manipulandum using a precision grip with the tips of the thumb and index finger on either side. The grip force (normal to the contact surfaces) and the load force (tangential to the surfaces) were measured, along with the trajectory of the hand. The manipulandum was attached to two servo-controlled linear motors used to create inertial and viscous loads as well as a composite load, including inertial, viscous, and elastic components. The form of the hand trajectory was independent of load for some subjects but varied systematically across load conditions in others. Nevertheless, under all load conditions and in all subjects, grip force was modulated in parallel with, and thus anticipated, fluctuations in load force despite the marked variation in the form of the load function. This indicates that the CNS is able to predict the load force and the kinematics of hand movement on which the load depends. We suggest this prediction is based on an internal model of the motor apparatus and external load and is used to determine the grip forces required to stabilize the load.

Adaptation, Physiological↗
PubMed1997

Anticipatory postural adjustments in stance and grip.

The reactive forces and torques associated with moving a hand-held object between two points are potentially destabilising, both for the object's position in the hand and for body posture. Previous work has demonstrated that there are increases in grip force ahead of arm motion that contribute to object stability in the hand. Other studies have shown that early postural adjustments in the legs and trunk minimise the potential perturbing effects on body posture of rapid voluntary arm movement. This paper documents the concurrent evolution of grip force and postural adjustments in anticipation of dynamic and static loads. Subjects held a manipulandum in precision grasp between thumb and index finger and pulled or pushed either a dynamic or a fixed load horizontally towards or away from the body (the grasp axis was orthogonal to the line of the load force). A force plate measured ground reaction torques, and force transducers in the manipulandum measured the load (tangential) and grip (normal) forces acting on the thumb and finger. In all conditions, increases in grip force and ground reaction torque preceded any detectable rise in load force. Rates of change of grip force and ground reaction torque were correlated, even after partialling out a common dependence on load force rate. Moreover, grip force and ground reaction torque rates at the onset of load force were correlated. These results imply the operation of motor planning processes that include anticipation of the dynamic consequences of voluntary action.

Adult↗
PubMed1997

Tangential torque effects on the control of grip forces when holding objects with a precision grip.

When we manipulate small objects, our fingertips are generally subjected to tangential torques about the axis normal to the grasp surface in addition to linear forces tangential to the grasp surface. Tangential torques can arise because the normal force is distributed across the contact area rather than focused at a point. We investigated the effects of tangential torques and tangential forces on the minimum normal forces required to prevent slips (slip force) and on the normal forces actually employed by subjects to hold an object in a stationary position with the use of the tips of the index finger and thumb. By changing the location of the object's center of gravity in relation to the grasp surface, various levels of tangential torque (0-50 N x mm) were created while the subject counteracted object rotation. Tangential force (0-3.4 N) was varied by changing the weight of the object. The flat grasp surfaces were covered with rayon, suede, or sandpaper, providing differences in friction in relation to the skin. Under zero tangential force, both the employed normal force and the slip force increased in proportion to tangential torque with a slope that reflected the current frictional condition. Likewise, with pure tangential force, these forces increased in proportion to tangential force. The effects of combined tangential torques and tangential forces on the slip force were primarily additive, but there was a significant interaction of these variables. Specifically, the increase in slip force for a given increment in torque decreases as a function of tangential force. A mathematical model was developed that successfully predicted slip force from tangential torque, tangential force, and an estimate of coefficient of static friction in the digit-surface interface. The effects of combined tangential torques and forces on the employed normal force showed the same pattern as the effects on the slip force. The safety margin against frictional slips, measured as the difference between the employed normal force and the slip force, was relatively small and constant across all tangential force and torque levels except at small torques (< 10 N x mm). There was no difference in safety margin between the digits. In conclusion, tangential torque strongly influences the normal force required for grasp stability. When controlling normal force, people take into account, in a precise fashion, the slip force reflecting both tangential force and tangential torque and their interaction as well as the current frictional condition in the object-digit interface.

Adult↗
PubMed1997

Effects of surface texture and grip force on the discrimination of hand-held loads.

In this paper, we report the results from two experiments in which subjects were required to discriminate horizontal load forces applied to a manipulandum held with a precision grip. The roughness (and hence friction) of the grip surfaces and required grip force were manipulated. In the first experiment, subjects were instructed to judge the load while maintaining hand position and not letting the manipulandum slip. It was found that performance was influenced by surface texture; a given load was judged to be greater when the surface texture was smooth than when it was rough. This result is consistent with a previous study based on lifting objects and indicates that the effect of surface texture applies to loads in general and not just to gravitational loads (i.e., weight). To test whether the load acting on a smooth object is judged to be greater because the grip force required to prevent it from slipping is larger, a second experiment was carried out. Subjects used a visual feedback display to maintain the same grip force for smooth and rough manipulandum surfaces. In this case, there was no effect of surface texture on load perception. These results provide evidence that perceived load depends on the grip force used to resist the load. The implications of these results in terms of central and peripheral factors underlying load discrimination are considered.

Adolescent↗
PubMed1997

Clinical communication among health providers and systems using Web tools.

Three needs have driven the development of a Web front end to our legacy system. 1) A Web Intranet is needed to provide service for the quantity and diversity of platforms within our health care system. 2) Information transfer in our system is required in more than one format: in viewer-friendly, HTML format and in a database-friendly, down-loadable format. 3) The system encounters the need to electronically exchange information with providers that are not employees of our health care enterprise. This presents a problem with the authentication aspect of security for which we have devised a system to allow the carefully-monitored exchange of records with care providers who are "strangers" to our system.

Communication↗
PubMed1996

Evolution of a legacy system to a Web patient record server: leveraging investment while opening the system.

A layered system is under development to enhance our legacy system as a backend in a WEB-enabled system. Each layer of the system has defined functionality, leverages the investment in the layer below, and follows the strategy of reducing support requirements for workstations. The mainframe system provides administrative integration of sub-systems, security, and the central data repository for most information. The second layer is a graphical user interface (GUI) to the system for Windows platforms. Support needs are limited by relying chiefly on X-terminals and application servers. The "Intranet" layer is a WEB Server building upon the second layer gateways to provide platform-independent access to selected information and images. The fourth layer, under evaluation, will extend access to the central data repository for Internet users of web browsers that support private-key/public-key encryption.

Computer Communication Networks↗
PubMed1995

The stability of precision grip forces during cyclic arm movements with a hand-held load.

In this paper we examine the coordination of grip force and load during brisk cyclic arm movements with a hand-held object under a range of conditions. We show that, regardless of the surface texture of the object or movement frequency, grip force is modulated in parallel with load. Thus, the tight coupling between grip force and load observed in short-duration tasks such as lifting or point-to-point movements is also seen in longer-duration cyclic movements. Moreover, the gain of the relation between grip force and load remains essentially constant over time. Across conditions, we find a dissociation between the gain of the relation between grip force and load and the grip force offset. With a more slippery surface texture both the gain and offset increase, whereas increases in frequency lead to an increase in the offset but a decrease in gain. This suggests that these two parameters are under independent high-level control. We also observe that when subjects were instructed to maintain a high-baseline grip force during the movement, grip force was still modulated with load even though an increase in grip was not necessary to prevent slip. This suggests that there is an obligatory coupling between grip force and load. This coupling might be subserved by low-level mechanisms not under high-level control.

Adult↗
PubMed1995

Trajectory adaptation to a nonlinear visuomotor transformation: evidence of motion planning in visually perceived space.

1. Although reaching movements are characterized by hand paths that tend to follow roughly straight lines in Cartesian space, a fundamental issue is whether this reflects constraints associated with perception or movement production. 2. To address this issue, we examined two-joint planar reaching movements in which we manipulated the mapping between actual and visually perceived motion. In particular, we used a nonlinear transformation such that straight line hand paths in Cartesian space would result in curved paths in perceived space and vice versa. 3. Under these conditions, subjects learned to make straight line paths in perceived space even though the paths of the hand in Cartesian space were markedly curved. In contrast, when the motion was perceived in Cartesian space (i.e., in the absence of a nonlinear distortion), straight line hand paths were observed. 4. These findings suggest that visually guided reaching movements are planned in a perceptual frame of reference. Reaching movements in the horizontal plane are adapted so as to produce straight lines in visually perceived space.

Adaptation, Physiological↗
PubMed1995

Effects of surface texture on weight perception when lifting objects with a precision grip.

In this paper, we show that, when lifting an object using a precision grip with the distal pads of the thumb and index finger at its sides, the perceived weight depends on the object's surface texture. The smoother the surface texture, the greater the perceived weight. We suggest that a smoother object is judged to be heavier because the grip force, normal to the surface, required to prevent it from slipping is greater. The possibility of there being an influence of surface texture per se is excluded by a second experiment that employed a variant of the precision grip in which the thumb supports the weight of the object from underneath. With the grip oriented in this way, there is no need to match grip force to surface texture and, under these conditions, there is no effect of surface texture on weight perception. In the first two experiments, the test and comparison weights were lifted successively by the same hand. In a third experiment, the effect of surface texture was replicated for sequential lifts made with separate hands. Thus, the effect is not restricted to comparisons made with the same hand.

Adolescent↗