Age-related differences in movement control: adjusting submovement structure to optimize performance

Manipulation of a fragile object by elderly individuals

We investigated strategies of healthy elderly participants (74-84 years old) during prehension and transport of an object with varying degrees of fragility. Fragility was specified as the maximal normal force that the object could withstand without collapsing. Specifically, kinetic and kinematic variables as well as and force covariation indices were quantified and compared to those shown by young healthy persons (19-28 years old). We tested three hypotheses related to age-related changes in two safety margins (slip safety margin and crush safety margin) and indices of force covariation. Compared to young controls, elderly individuals exhibited a decrease in object acceleration and an increase in movement time, an increase in grip force production, a decrease in the correlation between grip and load forces, an overall decrease in indices of multi-digit synergies, and lower safety margin indices computed with respect to both dropping and crushing the object. Elderly participants preferred to be at a relatively lower risk of crushing the object even if this led to a higher risk of dropping it. Both groups showed an increase in the index of synergy stabilizing total normal force produced by the four fingers with increased fragility of the object. Age-related changes are viewed as a direct result of physiological changes due to aging, not adaptation to object fragility. Such changes in overall characteristics of prehension likely reflect diminished synergic control by the central nervous system of finger forces with aging. The findings corroborate an earlier hypothesis on an age-related shift from synergic to element-based control.

Age-related changes in optimality and motor variability: an example of multifinger redundant tasks

We used two methods, analytical inverse optimization (ANIO) and uncontrolled manifold (UCM) analysis of synergies, to explore age-related changes in finger coordination during accurate force and moment of force production tasks. The two methods address two aspects of the control of redundant systems: Finding an optimal solution (an optimal sharing pattern) and using variable solutions across trials (covarying finger forces) that are equally able to solve the task. Young and elderly subjects produced accurate combinations of total force and moment by pressing with the four fingers of the dominant hand on individual force sensors. In session-1, single trials covered a broad range of force-moment combinations. Principal component (PC) analysis showed that the first two PCs explained about 90% and 75% of finger force variance for the young and elderly groups, respectively. The magnitudes of the loading coefficients in the PCs suggested that the young subjects used mechanical advantage to produce moment while elderly subjects did not (confirmed by analysis of moments produced by individual digits). A co-contraction index was computed reflecting the magnitude of moment produced by fingers acting against the required direction of the total moment. This index was significantly higher in the young group. The ANIO approach yielded a quadratic cost function with linear terms. In the elderly group, the contribution of the forces produced by the middle and ring fingers to the cost function value was much smaller than in the young group. The angle between the plane of experimental observations and the plane of optimal solutions (D-angle), was very small (about 1.5°) in the young group and significantly larger (about 5°) in the elderly group. In session-2, four force-moment combinations were used with multiple trials at each. Covariation among finger forces (multifinger synergies) stabilizing total force, total moment, and both was seen in both groups with larger synergy indices in the young group. Multiple regression analysis has shown that, at higher force magnitudes, the synergy indices defined with the UCM method were significantly related to the percent of variance accounted by the first two PCs and to the D-angle computed using the ANIO method. We interpret the results as pointing at a transition with age from synergic control to element-based control (back-to-elements hypothesis). Optimization and analysis of synergies are complementary approaches that focus on two aspects of multidigit coordination, sharing and covariation, respectively.

Ability-Based Design

Current approaches to accessible computing share a common goal of making technology accessible to users with disabilities. Perhaps because of this goal, they may also share a tendency to centralize disability rather than ability. We present a refinement to these approaches called ability-based design that consists of focusing on ability throughout the design process in an effort to create systems that leverage the full range of human potential. Just as user-centered design shifted the focus of interactive system design from systems to users, ability-based design attempts to shift the focus of accessible design from disability to ability. Although prior approaches to accessible computing may consider users’ abilities to some extent, ability-based design makes ability its central focus. We offer seven ability-based design principles and describe the projects that inspired their formulation. We also present a research agenda for ability-based design.

Effects of hand termination and accuracy requirements on eye-hand coordination in older adults

This study investigated how aging compromises the control of saccades and eye-hand coordination when accuracy constraints and termination requirements of hand movement are altered. Seventeen older adults and seventeen young controls performed two-segment aiming movements. The first segment had two target sizes to alter accuracy constraints. Two-segment eye movements were always made to first and second targets, whereas hand movements were varied across three hand-movement types with different termination requirements: (1) stop both at the first and second targets, (2) stop at the first target and discontinue, and (3) move through the first target and discontinue. Compared to the young adults, the older adults produced hypometric primary saccades and delayed gaze fixation to the first target. The older adults also modified eye movements less depending on the hand termination and accuracy requirements. After pointing completion to the first target, the older adults maintained their gaze fixation to that target for a longer duration than young adults. However, this prolonged gaze fixation was minimized when a hand termination was not required. Conversely, the prolongation of gaze fixation was magnified when the hand termination was required at the first target while the eye movement was continuing to the next target. Thus, older adults have difficulties in concurrent control of inhibiting hand movement and initiating eye movement at a target within a sequence. Taken together, it is suggested that aging reduces the ability to modify eye movements to meet various behavioral constraints imposed on manual aiming tasks.

From Intention to Input: Motor Cognition, Motor Performance, and the Control of Technology

Fundamental knowledge of motor cognition is an important component in a human factors repertoire, and this chapter serves as a guide to the history, theory, and application of motor cognition research.“From intention to input” captures the scope of this chapter in that cognitive theories of motor control, neural control of movement, and the effects of feedback on movement are all discussed. The chapter progresses from an overview and history of motor cognition theories down to the neural basis for movement, then to an application of these theories via the study of specific actions. From there, rooted in the scientist-practitioner paradigm of human factors, the chapter covers applied considerations for designing control tasks and their associated inputs, taking into account individual differences in motor cognition and control and identifying critical issues in designing for input. General, applied guidelines are provided for use with current and future systems that have a motor cognition component.

Toward a psychological science of advanced technology design for older adults

OBJECTIVES

Technology represents advances in knowledge that change the way humans perform tasks. Ideally, technology will make the task easier, more efficient, safer, or perhaps more pleasurable. Unfortunately, new technologies can sometimes make a task more difficult, slower, dangerous, or perhaps more frustrating. Older adults interact with a variety of technologies in the course of their daily activities and thus products should be designed to be used by people of varying ages.

METHODS

In this article, we provide an overview of what psychology has to offer to the design of technology-from understanding what people need, to identifying their preferences for design characteristics, and to defining their capabilities and limitations that will influence technology interactions.

RESULTS

We identify how research in the field of psychology and aging has advanced understanding of technology interactions and how research on technology interactions can inform theories of aging.

DISCUSSION

Design for aging involves understanding the unique capabilities and limitations of older adults; identifying their needs, preferences, and desires for technology in their lives; and involving them in the design process.

Effects of motor practice on cognitive disorders in older adults

The demographics of our societies have changed drastically during the past few decades. The general population is aging rapidly as human life spans continue to expand and more adults are set to mature during the next quarter century. This aging process has numerous implications for the way we live and will have particularly important impacts on health and healthcare. In particular, substantial evidence suggests that cognitive–motor function deteriorates considerably as the result of inactive life style, biological aging, and cognitive impairments. The number of individuals with Alzheimer's disease (AD), an aging-related cognitive disorder, is expected to increase significantly during the next 40 years. The development of mild cognitive impairment (MCI) or AD can exaggerate the functional declines observed in cognitive or motor performance. The functional declines affect an array of social, cognitive, mental, physical, and motor activities in our daily lives. However, recent studies suggest that cognitive, physical, motor practice, or skill learning can improve motor speed, smoothness, and accuracy in both MCI and AD patients and their age-matched healthy peers. From theoretical and practical perspectives, this paper addresses several critical aspects of motor deficits and the kinematical characteristics of motor skill development in MCI and AD populations. Empirical data will be presented relative to the sensory–motor functions of MCI and AD, the motor skill acquisition, exercise rehabilitation in older adults with memory loss, as well as the implications for therapies. Finally, this review concludes with thoughts and suggestions for future research in these areas.

Exploring Methods to Improve Pen-Based Menu Selection for Younger and Older Adults

Tablet PCs are gaining popularity, but many individuals still struggle with pen-based interaction. In a previous baseline study, we examined the types of difficulties younger and older adults encounter when using pen-based input. The research reported in this article seeks to address one of these errors, namely, missing just below. This error occurs in a menu selection task when a user’s selection pattern is downwardly shifted, such that the top edge of the menu item below the target is selected relatively often, while the corresponding top edge of the target itself is seldom selected. We developed two approaches for addressing missing just below errors: reassigning selections along the top edge and deactivating them. In a laboratory evaluation, only the deactivated edge approach showed promise overall. Further analysis of our data revealed that individual differences played a large role in our results and identified a new source of selection difficulty. Specifically, we observed two error-prone groups of users: the low hitters, who, like participants in the baseline study, made missing just below errors, and the high hitters, who, in contrast, had difficulty with errors on the item above. All but one of the older participants fell into one of these error-prone groups, reinforcing that older users do need better support for selecting menu items with a pen. Preliminary analysis of the performance data suggests both of our approaches were beneficial for the low hitters, but that additional techniques are needed to meet the needs of the high hitters and to address the challenge of supporting both groups in a single interface.

Using Direct and Indirect Input Devices: Attention Demands and Age-Related Differences

Researchers have suggested that attention is a key moderating variable predicting performance with an input device [e.g., Greenstein & Arnaut, 1988] without directly assessing the attention demands of devices We hypothesized that the attentional demands of input devices would be intricately linked to whether the device matched the input requirements of the on-screen task. Further, matching task and device should be more important for attentionally reduced groups, such as older adults. Younger and older adults used either a direct (touch screen) or indirect (rotary encoder) input device to perform matched or mismatched input tasks under a spectrum of attention allocation conditions. Input devices required attention - more so for older adults, especially in a mismatch situation. In addition, task performance was influenced by the mach between task demands and input device characteristics. Though both groups benefited from a match between input device and task input requirements, older adults benefited more and this benefit increased as less attention was available. We offer an a priori method to choose an input device for a task by considering the overlap between device attributes and input requirements. These data have implications for design decisions concerning input device selection across age groups and task contexts.

Origins of submovements in movements of elderly adults

Background

Slowness is a well-recognized feature of movements in aging. One of the possible reasons for slowness suggested by previous research is production of corrective submovements that compensate for shortened primary submovement to the target. Here, we re-examine this traditional interpretation and argue that the majority of submovements in older adults may be a consequence rather than the cause of slowness.

Methods

Pointing movements in young and older adults were recorded. Conditions for submovement emergence were manipulated by using small and large targets and three movement modes: discrete (required stopping on the target), reciprocal (required reversal on the target), and passing (required crossing the target and stopping after that). Movements were parsed into a primary and secondary submovement based on zero-crossings of velocity (type 1 submovements), acceleration (type 2 submovements), and jerk (type 3 submovements). In the passing mode, secondary submovements were analyzed only after crossing the target to exclude that they were accuracy adjustments.

Results

Consistent with previous research, the primary submovement was shortened and total secondary submovement incidence was increased in older adults. However, comparisons across conditions suggested that many submovements were non-corrective in both groups. Type 1 submovements were non-corrective because they were more frequent for large than small targets. They predominantly emerged due to arm stabilization and energy dissipation during motion termination in the discrete and passing mode. Although type 2 and 3 submovements were more frequent for small than large targets, this trend was also observed in the passing mode, suggesting that many of these submovements were non-corrective. Rather, they could have been velocity fluctuations associated predominantly with low speed of movements to small targets.

Conclusion

The results question the traditional interpretation of frequent submovements in older adults as corrective adjustments. Rather, the increased incidence of submovements in older adults is directly related to low movement speed observed in aging, whereas the relationship between submovement incidence and target size is a result of speed-accuracy trade-off. Aging-related declines in muscular control that may contribute to the disproportional increases in submovement incidence during slow movements of older adults are discussed.

Alzheimer's disease and mild cognitive impairment deteriorate fine movement control

Sensory-motor dysfunctions are often associated with Alzheimer's disease (AD) or mild cognitive impairment (MCI). This study suggests that deterioration in fine motor control and coordination characterizes sensory-motor deficiencies of AD and MCI. Nine patients with a clinical diagnosis of probable AD, 9 amnestic MCI subjects and 10 cognitively normal controls performed four types of handwriting movement on a digitizer. Movement time and smoothness were analyzed between the groups and across the movement patterns. Kinematic profiles were also compared among the groups. AD and MCI patients demonstrated slower, less smooth, less coordinated, and less consistent handwriting movements than their healthy counterparts. The theoretical relevance and practical implications of fine motor tasks, such as these movements involved in handwriting, are discussed relative to the deteriorated sensory-motor system of AD and MCI patients.

Origins of submovements during pointing movements

Submovements that are frequently observed in the final portion of pointing movements have traditionally been viewed as pointing accuracy adjustments. Here we re-examine this long-lasting interpretation by developing evidence that many of submovements may be non-corrective fluctuations arising from various sources of motor output variability. In particular, non-corrective submovements may emerge during motion termination and during motion of low speed. The contribution of these factors and the factor of accuracy regulation in submovement production is investigated here by manipulating movement mode (discrete, reciprocal, and passing) and target size (small and large). The three modes provided different temporal combinations of accuracy regulation and motion termination, thus allowing us to disentangle submovements associated with each factor. The target size manipulations further emphasized the role of accuracy regulation and provided variations in movement speed. Gross and fine submovements were distinguished based on the degree of perturbation of smooth motion. It was found that gross submovements were predominantly related to motion termination and not to pointing accuracy regulation. Although fine submovements were more frequent during movements to small than to large targets, other results show that they may also be not corrective submovements but rather motion fluctuations attributed to decreases in movement speed accompanying decreases in target size. Together, the findings challenge the traditional interpretation, suggesting that the majority of submovements are fluctuations emerging from mechanical and neural sources of motion variability. The implications of the findings for the mechanisms responsible for accurate target achievement are discussed.

Assessing design features of virtual keyboards for text entry

OBJECTIVE

The present research examined design of a virtual keyboard for text entry with a rotary controller, emphasizing users who differ in age and system experience.

BACKGROUND

Existing research has minimally addressed usage frequency, age, and the effects of display shape and letter arrangement on movement and visual search components of text entry tasks. The present research was conducted to close these gaps.

METHOD

Two experiments were completed to examine younger (18-28 years) and older (60-75 years) adults' movement and visual search capabilities using four keyboard shapes and three keyboard arrangements. In a third experiment examining combined effects on shape design, 32 younger (18-28 years) and 32 older (60-75 years) adults entered words on the two best shapes from the first experiments.

RESULTS

For the movement task, movement time was lowest for shapes with higher shape-controller compatibility. For the visual search task, search time and accuracy were best on the alphabetic arrangement. In the combined task, shape did not significantly influence performance at different levels of practice. Transfers, however, suggested that the shape with salient visual features elicited a text entry strategy for older adults that may promote more consistent performance under occasional usage.

CONCLUSION

The studies together demonstrate that keyboard shape is important for efficient performance. Shape-controller compatibility facilitated performance in both age groups. Salient features facilitate performance, especially for older adults. In nearly all cases alphabetic arrangement yielded the best performance.

APPLICATION

Recommendations are provided for virtual keyboard design for different usage frequencies, contexts, and users.

Movement structure in young and elderly adults during goal-directed movements of the left and right arm

Elderly adults often exhibit performance deficits during goal-directed movements of the dominant arm compared with young adults. Recent studies involving hemispheric lateralization have provided evidence that the dominant and non-dominant hemisphere-arm systems are specialized for controlling different movement parameters and that hemispheric specialization may be reduced during normal aging. The purpose was to examine age-related differences in the movement structure for the dominant (right) and non-dominant (left) during goal-directed movements. Young and elderly adults performed 72 aiming movements as fast and as accurately as possible to visual targets with both arms. The findings suggest that previous research utilizing the dominant arm can be generalized to the non-dominant arm because performance was similar for the two arms. However, as expected, the elderly adults showed shorter relative primary submovement lengths and longer relative primary submovement durations, reaction times, movement durations, and normalized jerk scores compared to the young adults.

Goal Crossing with Mice and Trackballs for People with Motor Impairments

Prior research shows that people with motor impairments face considerable challenges when using conventional mice and trackballs. One challenge is positioning the mouse cursor within confined target areas; another is executing a precise click without slipping. These problems can make mouse pointing in graphical user interfaces very difficult for some people. This article explores goal crossing as an alternative strategy for more accessible target acquisition. In goal crossing, targets are boundaries that are simply crossed by the mouse cursor. Thus, goal crossing avoids the two aforementioned problems. To date, however, researchers have not examined the feasibility of goal crossing for people with motor difficulties. We therefore present a study comparing area pointing and goal crossing. Our performance results indicate that although Fitts' throughput for able-bodied users is higher for area pointing than for goal crossing (4.72 vs. 3.61 bits/s), the opposite is true for users with motor impairments (2.34 vs. 2.88 bits/s). However, error rates are higher for goal crossing than for area pointing under a strict definition of crossing errors (6.23% vs. 1.94%). We also present path analyses and an examination of submovement velocity, acceleration, and jerk (the change in acceleration over time). These results show marked differences between crossing and pointing and almost categorically favor crossing. An important finding is that crossing reduces jerk for both participant groups, indicating more fluid, stable motion. To help realize the potential of goal crossing for computer access, we offer design concepts for crossing widgets that address the occlusion problem, which occurs when one crossing goal obscures another in persistent mouse-cursor interfaces. This work provides the motivation and initial steps for further exploration of goal crossing on the desktop, and may help researchers and designers to radically reshape user interfaces to provide accessible goal crossing, thereby lowering barriers to access.

The Model Human Processor and the older adult: parameter estimation and validation within a mobile phone task

The authors estimate weighted mean values for nine information processing parameters for older adults using the Card, Moran, and Newell (1983) Model Human Processor model. The authors validate a subset of these parameters by modeling two mobile phone tasks using two different phones and comparing model predictions to a sample of younger (N = 20; M-sub(age) = 20) and older (N = 20; M-sub(age) = 69) adults. Older adult models fit keystroke-level performance at the aggregate grain of analysis extremely well (R = 0.99) and produced equivalent fits to previously validated younger adult models. Critical path analyses highlighted points of poor design as a function of cognitive workload, hardware/software design, and user characteristics. The findings demonstrate that estimated older adult information processing parameters are valid for modeling purposes, can help designers understand age-related performance using existing interfaces, and may support the development of age-sensitive technologies.

Age-related differences in corrected and inhibited pointing movements

It has been widely reported that aging is accompanied by a decline in motor skill performance and in particular, it has been shown that older subjects take longer to adapt their ongoing reach in response to a target location shift. In the present experiment, we investigated the influence of aging on the ability to perform trajectory corrections in response to a target jump, but also assessed inhibition by asking a younger and an older group of participants to either adapt or stop their ongoing movement in response to a target location change. Results showed that although older subjects took longer to initiate, execute, correct and inhibit an ongoing reach, they performed both tasks with the same level of accuracy as the younger sample. Moreover, the slowing was also observed when older subjects were asked to point to stationary targets. Our findings thus indicate that aging does not specifically influence the ability to perform or inhibit fast online corrections to target location changes, but rather produces a general slowing and increased variability of movement planning, initiation and execution to both perturbed and stationary targets. For the first time, we demonstrate that aging is not accompanied by a decrease in the inhibition of motor control.

Control of laparoscopic instrument motion in an inanimate bench model: implications for the training and the evaluation of technical skills

Computer-assisted analysis of wrist movement has recently emerged as an objective laparoscopic performance evaluation method. The first purpose of this study was to assess the differences in motion characteristics between the tip of the instrument and the wrist. The second purpose was to describe the control strategies used to move laparoscopic instruments. During a bead transfer task, motions of a laparoscopic needle driver's tip, heel, and the participants' wrist were monitored. Results showed that large amplitude movements were best described by movements of the wrist, and small amplitude movements were evidenced by motions of the instrument tip. Thus, for describing expertise, and for evaluation and feedback, motion of the tip of the laparoscopic instrument should be quantified, in addition to motion of the wrist. The motions of the instrument were controlled by utilizing the flexibility of the skin of the laparoscopic trainer in addition to using the fulcrum, and sliding through the trocar. In order to increase fidelity, virtual reality trainers should simulate the flexibility of the real structures around the insertion of the instrument.

Notebook input devices put to the age test: the usability of trackpoint and touchpad for middle-aged adults

In two experiments, the usability of input devices integrated into computer notebooks was under study. The most common input devices, touchpad (experiment 1) and trackpoint (experiment 2) were examined. So far, the evaluation of mobile input devices has been restricted to younger users. However, due to ongoing demographic change, the main target group of mobile devices will be older users. Therefore, the present study focused on ageing effects. A total of 14 middle-aged (40-65 years) and 20 younger (20-32 years) users were compared regarding speed and accuracy of cursor control in a point-click and a point-drag-drop task. Moreover, the effects of training were addressed by examining the performance increase over time. In total, 640 trials per task and input device were executed. The results show that ageing is a central factor to be considered in input device design. Middle-aged users were significantly slower than younger users when executing the different tasks. Over time, a significant training effect was observed for both devices and both age groups, although the benefit of training was greater for the middle-aged group. Generally, the touchpad performance was higher than the trackpoint performance in both age groups, but the age-related performance decrements were less distinct when using the touchpad.

Practice effects on motor control in healthy seniors and patients with mild cognitive impairment and Alzheimer's disease

This research was designed to test the hypothesis that motor practice can enhance the capabilities of motor control in healthy controls (NC) and patients with a diagnosis of probable Alzheimer's disease (AD) and mild cognitive impairment (MCI), and consequently results in better motor performance. Approximately half of the subjects in the NC (n = 31), AD (n = 28), and MCI (n = 29) either received or did not receive practice on a task of fast and accurate arm movement with a digitizer. Changes in movement time (MT), movement smoothness (jerk), and percentage of primary submovement (PPS) were recorded and compared among the three groups across six blocks of trials (baseline and five training sessions). For all subjects, practice improved motor functions as reflected by faster and smoother motor execution, as well as a greater proportion of programming control. Compared to unaffected matched controls, AD and MCI subjects exhibited a greater reduction in movement jerk due to practice. Movement time and PPS data revealed that motor practice appeared to reduce the use of "on-line" correction adopted by the AD or MCI patients while performing the aiming movements. Evidently, their arm movements were quicker, smoother, and temporally more consistent than their untrained peers. The findings of this study shed light on how MCI and AD may affect motor control mechanisms, and suggest possible therapeutic interventions aimed at improving motor functioning in these impaired individuals.

Efficient control of arm movements in advanced age

The present study addresses the influence of aging on the ability to regulate mechanical effects arising during arm movements due to the multi-joint structure of the arm. Two mechanical factors were considered, interaction torque (IT) and inertial resistance (IR). Regulation of these two factors can be demanding in terms of the timing and magnitude of the required muscle torque (MT), specifically during fast movements. We hypothesized that aging exacerbates the challenge regarding the regulation of these effects with muscular control due to declines in the motor system. This hypothesis was tested by comparing performance of a cyclic line-drawing task in two age groups, young and older adults. Only two joints, the shoulder and elbow, participated in motion. Four orientations of the lines were used to provide variations in the requirements for regulation of IT and IR. Cyclic frequency was manipulated to emphasize the dependence of the mechanical factors on movement speed. Various characteristics of fingertip motion showed that there were no age-related deteriorations in accuracy of line drawing. However, older adults were systematically slower, particularly in the directions of high IR. A detailed analysis of the magnitude of MT and the contribution of this torque to production of net torque at each joint demonstrated that older adults modified joint control and decreased the demands for MT by skillful exploitation of IT in a way specific for each particular line orientation. The results point to a tendency in older adults to decrease the production of muscle force. Nevertheless, older adults also demonstrated an ability to partially compensate for declines in the force production by developing sophisticated strategies of joint control that exploit the multi-joint mechanical structure of the arm. This ability suggests that the internal representation of inter-segmental dynamics and the capability to use it for movement control does not decay with age. The study emphasizes the importance of analysis of joint motion and control characteristics for the investigation of arm movements and for comparison of these movements between different subject populations.

The role of different submovement types during pointing to a target

The present study extends our previous findings in challenging the traditional interpretation of irregularities in the velocity profile of pointing movements as corrective submovements performed to improve accuracy of target achievement. The study is driven by a hypothesis that pointing includes at least two subtasks, accurate target achievement and motion termination, each of which can cause submovements (Dounskaia et al. Exp Brain Res 164:505-516, 2005). To investigate submovements associated with these subtasks, two tasks were performed in the experiment. Task 1 was used to examine the contribution of the two subtasks on submovement production by comparing submovements in discrete movements that include motion termination and in cyclic movements during which motion termination is not performed. Target size manipulations emphasized submovements related to the accuracy subtask. The results confirmed that both subtasks included in pointing cause submovements. Gross types of submovements (types 1 and 2) were associated with motion termination and fine submovements (type 3) with accuracy regulation. Task 2 further investigated sources of the accuracy-associated type 3 submovements by including only cyclic movements performed at two levels of frequency. Most (97.6%) of the submovements in task 2 were of type 3. Submovement incidence was strongly (inversely) associated with cyclic frequency, and it was independent of target size. This result questions the accuracy subtask as a primary source for type 3 submovements, and it raises the possibility that these submovements are an inherent property of low-speed movements. Together, results of the two tasks support our previous finding that gross submovements are not necessarily related to accuracy regulation. They also provide evidence that challenges the interpretation of fine submovements as corrections performed voluntarily to improve pointing accuracy. Alternative interpretations of accuracy regulation mechanisms, such as regulation of muscle stiffness and of the muscle co-contraction level are discussed in light of the present results.

The role of vision in the control of continuous multijoint movements

The authors investigated whether visual fixations during a continuous graphical task were related to arm endpoint kinematics, joint motions, or joint control. The pattern of visual fixations across various shapes and the relationship between temporal and spatial events of the moving limb and visual fixations were assessed. Participants (N=16) performed movements of varying shapes by rotating the shoulder and elbow joints in the transverse plane at a comfortable pace. Across shapes, eye movements consisted of a series of fixations, with the eyes leading the hand. Fixations were spatially related to modulation of joint motion and were temporally related to the portions of the movement where curvature was the highest. Gathering of information related to modulation of interactive torques arising from passive forces from movement of a linked system occurred when the velocity of the movement (a) was the lowest and (b) was ahead of the moving limb, suggesting that that information is used in a feedforward manner.

Aging and longitudinal change in perceptual-motor skill acquisition in healthy adults

Knowledge about aging of perceptual-motor skills is based almost exclusively on cross-sectional studies. We examined age-related changes in the retention of mirror-tracing skills in healthy adults who practiced for 3 separate days at baseline and retrained 5 years later at follow-up. Overall, the speed and accuracy of an acquired skill were partially retained after a 5-year interim, although the same asymptote was reached. Analyses with individual learning curves indicated that the effects of age on mirror-tracing speed were greater at longitudinal follow-up than at baseline, with older adults requiring more training to reach asymptote. Thus, although the long-term retention of acquired skills declines with age, older adults still retain the ability to learn the skill. Moreover, those who maintained a processing speed comparable with that of the younger participants evidenced no age-related performance decrements on the mirror-drawing task.

Influence of biomechanical factors on substructure of pointing movements

Irregularities in the velocity profile near the end of pointing movements have been interpreted as corrective submovements whose purpose is to provide accuracy of pointing to the target. The purpose of the present study was to investigate whether two additional factors related to biomechanical properties of the arm also cause submovements. First, motion termination and stabilization of the limb in the final position required by a discrete pointing task may contribute to submovements. Second, inaccurate regulation of interactive torque at the joints may also cause submovements. To investigate the contributions of these two biomechanical factors and the traditionally considered factor of pointing accuracy, the incidence of submovements was analyzed during three types of experimental manipulations. In addition to target size manipulations (small and large targets), conditions for motion termination were manipulated by examining discrete movements (which terminated at the target) and reciprocal movements (which reversed direction without dwelling on the target). Interaction torques were varied by using targets that require different shoulder-elbow coordination patterns. Submovements were detected in 41% of all analyzed movements. Data supported influences from the accuracy and motion termination factors but not from the interactive torque regulation factor on submovement incidence. Gross submovements were associated with motion termination; fine submovements primarily with accuracy demands. These findings and the analysis of temporal movement characteristics suggest that motion termination is an extra movement component that makes control of discrete movements different to control of reciprocal movements. Implications of the findings to a noise-related interpretation of Fitts' law are discussed. The study emphasizes the influence of arm biomechanics on endpoint kinematics.

Touch a screen or turn a knob: choosing the best device for the job

Input devices enable users to interact with systems. In two experiments, we assessed whether and how task demands and user age influenced task performance for a direct input device (touch screen) and an indirect input device (rotary encoder). In Experiment 1, 40 younger (18-28 years) and 40 middle-aged to older adults (51-65 years) performed tasks using controls such as sliders, up/down buttons, list boxes, and text boxes while using a system. The optimal input device to facilitate performance was dependent on the task being performed and the age of the user. In Experiment 2, touch screen use was assessed for 20 younger (19-23 years) and 20 older adults (51-70 years). Task demands were manipulated through button size, movement distance, direction, and type of movement. Performance was moderated by the age of the user and by task demands. Actual or potential applications of this research include guidance for the optimal selection of input devices for different user populations and task characteristics.

Multijoint movement control: the importance of interactive torques

The underlying mechanisms of the neural control of movement have long been explored, with a focus primarily on central control aspects and often overlooking the intrinsic mechanical properties of the motor system. To fully understand the control and regulation of movements, the biomechanical properties of the moving subject, specifically interactive torques, must be considered in the design, evaluation, and interpretation of empirical data. We first discuss the difficulty of extrapolating information from a wide variety of tasks due to their varying inherent task constraints. Examples are subsequently given where a biomechanical perspective provides a more informative interpretation of existing data. Finally, we focus on research examining the role of interactive torques with a discussion of how discoordinated movements may be explained by an inability to modulate interactive torques. Inclusion of biomechanical considerations in motor control research is a step toward incorporating multilevel methodologies and interpretations into the field, and providing a more comprehensive understanding of the neural control and regulation of movement.

Light pen use and practice minimize age and hand performance differences in pointing tasks

We contrasted performance with mouse and light pen input devices for younger, middle-aged, and older adults (N = 72) who were experienced mouse users. Participants used both preferred and nonpreferred hands to perform a menu target selection task. The light pen minimized age differences in performance relative to the mouse. Older adults were more lateralized on a handedness test than young adults and were less efficient using their nonpreferred hand. With practice, older adults improved their response time more than other age groups did. The mouse was rated as more acceptable and easier to use than the light pen across trials, despite the performance advantage of the light pen for all age groups. Usability ratings correlated moderately with performance. A benefit-cost analysis indicated that the more efficient light pen might cover its greater initial cost within 11 months for an older adult and within 23 months for a younger adult. Actual or potential applications of this research include advising older adults to persist with practice for new input devices, advising those who must switch to their non-preferred hand to select a direct positioning device, and providing a methodology for determining the potential payback interval when switching to a faster, though more expensive, input device.

Physical activity, physiological, and psychomotor performance: a study of variously active older adult men

This research examined varying levels of physical activity and psychomotor and physiological function in variously active older men. Very active moderately active, and low active participants were tested on simple (SRT) and choice reaction time (CRT), coincidence-anticipation timing (CAT), and VO2max. No significant differences for age or height were found, although percentage of fat, and weight were statistically different. Active groups were leaner and lighter. VO2max was significantly different between groups, as physically active groups yielded geater values. SRT and CAT also yielded significantly different results with more active participants showing better performance. No between-groups significant differences resulted for CRT. Generally, increased levels of physical activity were related to superior physiological outcomes and improved psychomotor peformance.

How quickly can healthy adults move their hands to intercept an approaching object? Age and gender effects

BACKGROUND

The upper extremities are often used to protect the head and torso from impact with an object or with the ground. We tested the null hypotheses that neither age nor gender would affect the time required for healthy adults to move their upper extremities into a protective posture.

METHODS

Twenty young (mean age 25 years) and twenty older (mean age 70 years) volunteers, with equal gender representation, performed a seated arm-movement task under three conditions: Condition 1, in which subjects were instructed to raise the hands upon cue as quickly as possible from thigh level to a shoulder height target; Condition 2, in which subjects were instructed as in Condition 1 with the addition of intercepting a swinging pendulum at the prescribed hand target; and Condition 3, in which subjects were instructed as in Condition 2 but were asked to wait as long as possible before initiating hand movement to intercept the pendulum. Arm movements were quantified using standard kinematic techniques.

RESULTS

Age (p <.01) and gender (p <.05) affected hand movement times. In Conditions 1 and 2, the older women required 20% longer movement times than the other subject groups (335 vs 279 milliseconds; p <.01). In Condition 3, shorter movement times were achieved by young men (20%; p =.002) and older women (10%; p =.056) as compared with their respective performance in Conditions 1 and 2 because they did not fully decelerate their hands. The other groups slowed their movements in Condition 3.

CONCLUSIONS

Age, gender, and perceived threat significantly affected movement times. However, even the slowest movement times were well within the time available to deploy the hands in a forward fall to the ground.

Patterns of transfer of adaptation among body segments

Two experiments were conducted in order to determine the patterns of transfer of visuomotor adaptation between arm and head pointing. An altered gain of display of pointing movements was used to induce a conflict between visual and somatosensory representations. Two subject groups participated in Experiment 1: group 1 adapted shoulder pointing movements, and group 2 adapted wrist pointing movements to a 0.5 gain of display. Following the adaptation regimen, subjects performed a transfer test in which the shoulder group performed wrist movements and the wrist group performed shoulder movements. The results demonstrated that both groups displayed typical adaptation curves, initially undershooting the target followed by a return to baseline performance. Transfer tests revealed that both groups had high transfer of the acquired adaptation to the other joint. Experiment 2 followed a similar design except that group 1 adapted head pointing movements and group 2 adapted arm pointing movements. The arm adaptation had high transfer to head pointing while the head adaptation had very little transfer to arm pointing. These results imply that, while the arm segments may share a common target representation for goal-directed actions, individual but functionally dependent target representations may exist for the control of head and arm movements.

Word-processing training and retraining: effects of adult age, experience, and interface

Novice (Experiment 1) and experienced (Experiment 2) young, middle-aged, and older adults learned a new word-processing application in keystrokes, menus, or menus-plus-icons interface conditions. Novices showed strong age differences in the time to complete the 3-day tutorial and in declarative and procedural tests of word-processing knowledge. Menus and menus-plus-icons were superior to keystrokes condition. though interface did not interact with age. Experienced users showed age-related slowing in learning rate but minimal age differences in test performance when retrained on a new word-processing program. Age and computer experience accounted for much of the variance in both learning time and word-processing performance; interface type, speed of processing, and spatial generation ability made additional contributions. Experience interacted with age to predict performance. Implications for training and retraining older workers are discussed.

Effects of aging on linear and curvilinear aiming arm movements

This research was designed to test the hypothesis that seniors may have deficits in their movement planning and execution of rapid target oriented arm movements. Twenty senior adults (M = 81.2 years, SD = 1.8) and 20 young adults (M = 25.2 years, SD = 2.5) performed two types of fast aiming arm movements (linear and curvilinear) on a digitizer in a counterbalanced order. Age effects on the variables of movement time, movement jerk, as well as on the profiles of movement displacement, velocity, and acceleration were examined. The outcomes of analysis of variance (ANOVA) with repeated measures indicated that the seniors executed both movement tasks more slowly and had higher movement jerk than the young adults. This suggests that aging is not only associated with slower but less smooth movements. In addition, the examination of movement profiles indicated that the young adults implemented the curvilinear task as one smooth and integrated motion, whereas the seniors executed the task in two segments. One possible reason of this "segmental" execution of curvilinear movement is that seniors may compensate for their deficits in movement planning by adopting a control strategy that reduces movement complexity. The aging effects on rapid aiming arm movements are discussed from the perspectives of motor planning, the "speed-accuracy trade-off," and task complexity.

Developmental features of rapid aiming arm movements across the lifespan

Using a lifespan approach, the authors investigated developmental features of the control of ballistic aiming arm movements by manipulating movement complexity, response uncertainty, and the use of precues. Four different age groups of participants (6- and 9-year-old boys and girls and 24- and 73-year-old men and women, 20 participants in each age group) performed 7 types of rapid aiming arm movements on the surface of a digitizer. Their movement characteristics such as movement velocity, normalized jerk, relative timing, movement linearity, and intersegment intervals were profiled. Analyses of variance with repeated measures were conducted on age and task effects in varying movement complexity (Study 1), response uncertainty (Study 2), and precue use (Study 3) conditions. Young children and senior adults had slower, more variant, less smooth, and less linear arm movements than older children and young adults. Increasing the number of movement segments resulted in slower and more variant responses. Movement accuracy demands or response uncertainty interacted with age so that the 6- and 74-year-old participants had poorer performances but responded similarly to the varying treatments. Even though older children and young adults had better performances than young children and senior adults, their arm movement performance declined when response uncertainty increased. The analyses suggested that young children's and senior adults' performances are poorer because less of their movement is under central control, and they therefore use on-line adjustments. In addition, older children and young adults use a valid precue more effectively to prepare for subsequent movements than do young children and senior adults, suggesting that older children and young adults are more capable of organizing motor responses than are young children and senior adults.

Movement substructures change as a function of practice in children and adults

An experiment is reported in which participants at 6 (n = 20), 9 (n = 20), and 24 years (n = 20) of age either received or did not receive practice on a rapid aiming task using the arm and hand. The purpose of the experiment was to document the changes in movement substructures (in addition to movement time) as a function of practice. After receiving 10 baseline trials, subjects in the practice groups received 30 practice trials followed by 10 retention trials on each of 5 days, while subjects in the no-practice group had only baseline and retention trials. Retention-only trials were divided into primary (reflecting the ballistic controlled part of the movement) and secondary (reflecting corrective movement adjustments) submovements. In addition, jerk (the 3rd derivative of movement displacement) was calculated as an estimate of the smoothness of the movement. Participants increased the primary submovement as a function of practice; however, the increases were substantially larger in the children (25-30%) than in the adults (10%). Participants also decreased jerk as a function of practice and the decreases were greater in children than in adults. The results suggest that with practice the primary submovement is lengthened so that it ends nearer the target, especially in children. Associated with the primary submovement covering a larger percentage of the movement length and time, movements became smoother.

Application of Cognitive Theory to Training and Design Solutions for Age-related Computer Use

As the prevalence of computer-based technologies increases throughout society, so does the likelihood that older adults will be required to interact with them. Unfortunately, such systems often appear to older adults to be too hard to use and too hard to learn. We provide examples highlighting the opportunities available to behavioural science to affect training and system design through practically relevant research. We focus on our research on ageing, computer use, and training to support our assertion that applied research aimed at designing training materials and system interfaces to enhance the performance of older adults can and should be driven by psychological theory. The data presented and studies reviewed here clearly demonstrate that theory is critical for predicting age differences in computer use, for guiding the development of both training and design interventions for older computer users, and for reconciling conflicting findings in the design-evaluation literature.

Aging, motor control, and the performance of computer mouse tasks

Because of the increased presence of computers in work and everyday life and the demographic "graying" of America, there is a need for interface designs that promote accessibility for older people. This study examined age differences in the performance of basic computer mouse control techniques. An additional goal of the study was to examine the influence of age-related changes in psychomotor abilities on mouse control. A total of 60 participants in 3 age groups (20-39 years, 40-59 years, and 60-75 years) performed 4 target acquisition tasks (pointing, clicking, double-clicking, and dragging) using a computer mouse. The data indicated that the older participants had more difficulty performing mouse tasks than the younger participants. Differences in performance attributable to age were found for the more complex tasks (clicking and double-clicking). Furthermore, age-related changes in psychomotor abilities were related to age differences in performance. We discuss applications to computer interface designs. Actual or potential applications of this research include specifications for computer mouse design to accommodate older populations.

The influence of mental and motor load on handwriting movements in parkinsonian patients

This experiment tested the hypothesis that Parkinson's disease (PD) patients are more vulnerable to a moderate level of secondary task load than elderly or young controls due to heightened variability in the motor system. PD patients, elderly, and young adults performed a handwriting task with different secondary tasks. The secondary task imposed motor load (i.e., speech) and/or a mental load (i.e., ignoring, repeating, or subtracting). The findings showed that, in contrast to young and elderly controls, PD patients tended to increase MT, accumulated pause time, and normalized jerk when the secondary task consisted primarily of motor load. Furthermore, it was shown that PD patients did not reduce writing sizes as result of a high level of mental load which finding suggests that writing in an automated fashion does not result in micrographia. The results are discussed in relation to strategies imposed to contend with reduced signal-to-noise levels in the motor system.