Ballistic movements on data-entry keypads

Research to date on movement times on data-entry keypads has assumed that the movements are made under visual control [Drury, C.G., Hoffmann, E.R., 1992. A model for movement times on data-entry keyboards. Ergonomics 35, 129-147; Hoffmann, E.R., Tsang, K.T., Mu, A., 1995. Data-entry keyboard geometry and keying movement times. Ergonomics 38 (5), 940-950; Silfverberg, M., MacKenzie, I.S., Korhonen, P., 2000. Predicting text entry speed on mobile phones. In: Proceedings of the ACM Conference on Human Factors in Computing Systems - CHI 2000. ACM, New York, pp. 9-16]. This is often not the case; where the value of Fitts’ Index of Difficulty is low, it is likely that movements will be made ballistically. A survey of commonly used keypads on devices such as mobile phones and ATMs shows that there is a need to study movement times when these ID values are less than those for which movements are likely to be made under visual control [Gan, K.-C., Hoffmann, E.R., 1988a. Geometrical conditions for ballistic and visually-controlled movements. Ergonomics 31, 829-839]. A series of experiments on simulated and real keypads indicates that the ballistic form of movement is generally valid and may be modelled by a modification of the ballistic movement time model of Hoffmann [1981. An ergonomics approach to predetermined motion time systems. In: Australian Institute of Industrial Engineers, Proceedings, Ninth National Conference, pp. 33-47] and of Gan and Hoffmann [1988a. Geometrical conditions for ballistic and visually-controlled movements. Ergonomics 31, 829-839l; 1988b. Sequential ballistic movement. Ergonomics 31 (10), 1421-1436]. A model is developed for the time to complete sequences of number entries containing up to 5 numbers. In this model, the movement times are related to the square-root of the sum of the movement amplitudes.

Relevance to industry

Many industrial applications require the use of keypads for data entry. Movements may be made ballistically or visually controlled, depending on the geometry of the keypad. As the time for data entry is dependent on geometry, a model for time taken is necessary for predicting human performance.     

Seated leg/foot ballistic and visually-controlled movements

An experiment with 52 participants investigated the relationship between movement time of the leg/foot for seated persons when moving in the transverse and sagittal planes. Four amplitudes of movement and 11 values of Fitts' Index of Difficulty (ID) were used to determine conditions under which ballistic movements could be made along with the need for visual control at higher ID values. Vision of the foot was available in all movements. As with arm movements (Gan and Hoffmann, 1988) there was a critical ID value below which it was possible to use ballistic movements and where movement times were approximately linear with the square-root of movement amplitudes. Above these ID values, Fitts' law applied, with gradients dependent on the amplitude of movement, suggesting that the muscle torque applied to the leg varied with movement amplitude. The critical ID varied with the amplitude of movement as previously found for arm movements.Relevance to industryThere is increasing use of the foot/leg for input to various controlling devices. Consequently it is necessary to have detailed information on the capacity of the leg/foot system to provide accurate input to a machine via a control pedal or other device. The present research provides such information over a wide range of control sizes and spacings.     

Movement of loads with trunk rotation

Movements with participants standing at a bench and moving loads up to 6 kg were studied, with participants using two hands to hold the load and trunk rotation in order to move the loads to specified locations. Tasks were performed with rapid ballistic movements and also with ongoing visual control. Data for ballistic movements were modelled in terms of a modified form of the (Gan, K.-C. and Hoffmann, E.R. 1988. “Geometrical conditions for ballistic and visually controlled movements.” Ergonomics 5 (31): 829–839) model for ballistic movements, taking into account the inertial properties of trunk rotation. Visually-controlled movements were modelled in terms of Fitts' law and a term that allowed for the ballistic form of the first submovement of the visually-controlled movement.

Practitioner Summary: Movement times to move masses up to 6 kg, for workers at a bench using trunk rotation, are given. Theoretical models fit the experimental data very well and allow prediction of movement times.     

Underwater movement times with ongoing visual control

Arm movements made in a water environment take longer to perform than in an air environment due to the drag forces experienced by the arm. Movement times for ballistic underwater movements have been accurately modelled by Hoffmann and Gan (1988 Hoffmann, E.R. and Gan, K-C. 1988. Underwater ballistic movements. Ergonomics, 31(9): 1305–1316. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). The present work models the movement time for movements that require ongoing visual control. In these movements, the ‘distance-covering’ phase is carried out at high speeds and will be affected by the fluid characteristics, while the ‘homing-in’ phase, where speeds are low, is less affected. An experiment is reported that models these effects and which indicates that a ballistic component needs to be added to the standard Fitts model in order to account for the drag forces in the distance-covering phase of the movement.

Practitioner Summary: Many tasks, such as maintenance and salvage work, require work to be done underwater. Times for performing underwater tasks are generally longer than on land. This article is one step in modelling the difference in task times for land and underwater movements.     

Hybrid evaluation method for Korean Character input system in mobile phones

In this study, hybrid evaluation incorporating the Hick–Hyman law was proposed to predict input performance of a Korean input system applied to the number pads of mobile phones. The hybrid model, calculated based on the Hick–Hyman law, is a combination of reaction time (RT) and movement time (MT) model, which is a better model for predicting user performance than the conventional models that were used to assess Korean input system evaluation such as the Fitts' and the KLM-GOMS models. Along with Fitts' model (of visual-controlled movements), the simple movement time (SMT) and ballistic movement time (BMT) models (of ballistic behavior movement) were also evaluated to measure MT. Results showed that ballistic behavior movement was more compatible than visual-controlled movement. In ballistic behavior movement, a thumb-movement distance of <21 mm was closer to the SMT than the BMT model. These results indicate that when applying hybrid model movement, the displacement, and the target size properties of mobile phone users is required in the engineering of a predictive model. Thus, the suggested hybrid evaluation is meaningful in that it can evaluate users' input behaviors very appropriately in the case of hand-held input devices.Relevance to industryA hybrid model based on Hick–Hyman law was determined to be effective to evaluate text input systems for the hand-held input device. This effective hybrid model can provide more accurate prediction time for text input behaviors to its designers for efficient system design. To its usability engineers, this hybrid model for more accurate prediction time can also provide an effective quantitative tool for usability evaluations for hand-held input device manufacturing industries because this model can save efforts as well as time for usability testing.     

The use of ballistic movement as an additional method to assess performance of computer mice

This study investigates an additional method for independently evaluating performance of speed and accuracy of computer mice, based on five parameters of the initial submovement when aiming at a target. This first submovement is known to be carried out in a ballistic manner and hence the Fitts-type aiming movement may be studied by means of the established relationships for ballistic movement. To test the ballistic movement method, eight participants used four different computer mice to execute ballistic movements and Fitts-type aiming movements. Regression tests showed that the Fitts movement time was well correlated with the time and stopping-variable error of ballistic movement, implying that measuring ballistic movement parameters can predict the performance of Fitts-type aiming movements. More importantly, the use of ballistic movement method allows independent assessments of the speed and accuracy, providing additional information for input devices assessment and designs.Relevance to industryThe study illustrates the close correspondence between input device evaluation using the proposed ballistic movement method and Fitts' law. The ballistic movement method allows independent measures of speed and four types of accuracy, which should benefit input devices assessment and designs.     

Goal-directed aimed movements with path obstructions

Studies are reported in which participants moved from a starting position to a final target, but moved around obstacles that prevented a direct path being taken. Seven experiments are reported in which subjects made multiple-component movements, defined by changes in the direction of movement, but without intervening targets (or stopping points) between components. It was found that components of movement time did not interact, contrary to the results of Gan and Hoffmann (1988b) for cases where there was an intervening target, and that component times could be added. For ballistic components, the time for the movement was linearly related to the square root of the total amplitude of movement; for components that were visually controlled, the time was related to Fitts' Index of Difficulty based on the total amplitude of movement and the final target size. Results are compared to data for movements with intervening targets, where the movement integration hypothesis is valid. PRACTITIONER SUMMARY: Many movements, particularly to inaccessible places, cannot be made directly, but must be made about obstacles in the path. This research shows how times for these movements can be quantified in terms of the direct path length and the size and location of the obstacles.     

Directional ballistic movement with transported mass

By applying Newton's Law of motion and assuming an approximate sinusoidal or trapezoidal waveform for the acceleration pattern, time for a ballistic movement is shown to be a function of the square root of movement amplitude and total moment of inertia. This equation is the ballistic equivalent of Fitts' equation for visually controlled movements. The experimental data gave excellent correlation with the mathematical models. Direction of movement had no significant effect on movement time for the loads used in this experiment. Even though the models were developed for movement about the elbow, the models were applicable to movement using both the shoulder and elbow. It was adequate to assume a constant average maximum muscle torque in the model.     

Underwater ballistic movement

A mathematical model is developed for ballistic arm movements in an underwater environment. Characteristics of the arm moving in water, the ‘induced’ moment of inertia and drag coefficient, are found from experiments on an artificial arm. These data, along with the mathematical model, are used to predict underwater movement times from experimental data for movement times in air.

Experiments on two groups of subjects, in both air and water environments, show that the model yields a good prediction of ballistic movement times in an underwater environment.     

A comparison of hand and foot movement times

Three experiments are reported in which a comparison is made between the times for movement of the hand and the foot. Both ballistic and visually-controlled movements were studied. It was found that execution time for foot movements is generally about twice as long as that for the equivalent arm movement. The times for foot movements were described well by the Welford, Norris and Shock modification of Fitts' Law for visually-controlled movements and, for ballistic movements, by the square-root-of-amplitude equation found by Hoffmann for arm movements.     

Effects of task characteristics on unimanual and bimanual movement times

Fitts' law cannot be used to predict movement times (MTs) of bimanual tasks since no empirical relationships associating task difficulty and bimanual MT have been demonstrated yet. Development of a ‘bimanual task difficulty index’ has been challenged by the complex patterns of coordination involved in simultaneously performing two tasks, one with each hand, under a control system with limited visual and attentional resources. To address this fundamental issue in human motor performance, bimanual object transfers with the left and right hands to targets of various precision requirements and separated by different distances were studied in six healthy subjects. Visual resource allocation during task performance was used to identify ‘primary’ and ‘secondary’ hand movements in bimanual tasks. While the primary movement was similar to a unimanual movement, the secondary MT varied with its own, as well as the contralateral hand's task constraints. These results, which were stable and consistent across six subjects, provide preliminary evidence that visual behaviour, indicating closed-loop control, can be used to systematically derive bimanual MTs.

Practitioner summary: A simple extension of Fitts' law cannot be used to predict movement times (MTs) of bimanual tasks since there is no consensus on the definition of a ‘bimanual task difficulty index’ in the literature. In this paper, we have approached this problem by using visual resource allocation patterns to systematically derive bimanual MTs.     

Mathematically modelling the effects of pacing,finger strategies and urgency on numerical typing performance with queuing network model human processor

Numerical typing is an important perceptual-motor task whose performance may vary with different pacing, finger strategies and urgency of situations. Queuing network-model human processor (QN-MHP), a computational architecture, allows performance of perceptual-motor tasks to be modelled mathematically. The current study enhanced QN-MHP with a top-down control mechanism, a close-loop movement control and a finger-related motor control mechanism to account for task interference, endpoint reduction, and force deficit, respectively. The model also incorporated neuromotor noise theory to quantify endpoint variability in typing. The model predictions of typing speed and accuracy were validated with Lin and Wu's (2011) experimental results. The resultant root-mean-squared errors were 3.68% with a correlation of 95.55% for response time, and 35.10% with a correlation of 96.52% for typing accuracy. The model can be applied to provide optimal speech rates for voice synthesis and keyboard designs in different numerical typing situations.

Practitioner Summary: An enhanced QN-MHP model was proposed in the study to mathematically account for the effects of pacing, finger strategies and internalised urgency on numerical typing performance. The model can be used to provide optimal pacing for voice synthesise systems and suggested optimal numerical keyboard designs under urgency.     

A Model of Linear Arm Movements with Preview Constraints

This study extends Fitts's law for linear and serial arm movements to incorporate constraints on the preview (distance) for each movement. A simple first-order linear model relating mean movement time to Fitts's index of difficulty (ID) variable and a preview-constraint ID variable was found to explain 92% of the variation in movement time. The results, which were based on a sample of 12Ss, showed that the preview-constraint variable contributed more to the movement time than did Fitts's ID variable. The information rate generated was 6·2 bits/sec, which was about half that produced by similar tasks involving no preview constraints and about 60% higher than that produced by rotary arm movements with preview constraints.

The relatively large error rates generated were predominantly overshoot errors. The highest error rates occurred for the more difficult tasks as reflected by large ID values. Both movement times, error rates and parameter estimates showed large variations between individual Ss. The mean movement times across Ss were considerably higher than predetermined motion-time systems predictions.     

Effects of age and psychomotor ability on kinematics of mouse-mediated aiming movement

The objective of this research is to understand the influence of age and age-related psychomotor ability on the process of mouse-mediated aiming movement. It is premised on the notions that (1) mouse-mediated aiming movements can be better understood via studying its kinematics and (2) age is a surrogate variable in kinematic differences, and that age-influenced fundamental factors such as psychomotor ability may have a more direct effect. As expected, age kinematic differences were detected. However, when comparing with age, age-influenced psychomotor ability (i.e. manual dexterity) contributed more substantially to the variances of kinematics in the ballistic phase. For homing phase, in addition to manual dexterity, age-influenced wrist–finger speed was also a significant contributor. In future studies, it is suggested that components of visual processing should be included for better understanding of its role as an age-influenced fundamental ability in aiming movements. Applications of this research are discussed.

Practitioner Summary: This paper presents empirical data showing age effects in movement kinematics are chiefly mediated by age-related changes in psychomotor ability. Our findings provide additional data for existing and newer performance enhancement solutions, especially for those targeting older adults.     

Geometrical conditions for ballistic and visually controlled movements

The ballistic movement is defined as a rapid voluntary movement which is motor programmed and in which visual feedback for path correction is not possible. A discrete ballistic movement is of short movement duration (less than about 200 msec) with a triphasic pattern in the electromyograph (EMG) for muscle activity and has an acceleration pattern which approximates a sinusoidal waveform. When the Index of Difficulty for such a movement is less than 3·0, the movement time is found to be related to the square root of the movement amplitude. The occurrence of ballistic movement is determined by the combined factors of Fitts' Index of Difficulty and movement amplitude.     

Macro repositioning movements of pelvis and trunk during simulated driving tasks

Low back pain (LBP)³ is one of the most important features of discomfort in prolonged sitting postures. This is evidenced by an increase in the number of postural changes called macro-movements. The focus of study was the frequencies of macro repositioning movements in prolonged sitting posture resulting from the perception of discomfort caused by low-back pain. Eighteen (18) drivers performed driving tasks for a period of 90 min. The results indicate that LBP participants performed more movements (10.52 rep/h), compared to without low back pain participants (8.52 rep/h). However, the latter moved more than expected due to joint macro movements of the pelvis and trunk. LBP subjects generally performed macro-repositioning movements of the trunk only, while without low back pain (WLBP)⁴ subjects moved pelvis and trunk simultaneously. Although the WLBP participants moved less than those with LBP symptoms, they applied different movement strategies which should be considered in further research. Finally, the authors also propose that future research should be directed towards determining the influence of these lumbo pelvic movements when provided in a controlled manner, to improve comfort in seats and to help manufactures to offer better ergonomic seats.Relevance to industryAccording to the findings of this study, control of lumbo pelvic movements could be used to improve the design and production of ergonomic seats for driving activities.     

Subjective estimates of times for assembly work

Research by Chan and Hoffmann (2013, 2016) showed that people can estimate task times with reasonable accuracy. That work included experiments on Fitts’ task, a double component movement task, pin-to-hole assembly and ballistic movement tasks. In each case, a linear relationship was found relating subjective estimates of task time and actual task times. In this research, the work has been extended to two industrial assembly tasks: assembly of a U-bolt from components and the more complex task of assembling a hacksaw. These tasks were done in an ergonomically designed work space, with components placed within the Normal Work Area and using jigs for convenience of using two-handed assembly. Actual and estimated component times were obtained from video and voice recordings. Results showed that estimated times were lower than actual assembly times, but higher than times predicted using the MODAPTS predetermined motion time system. Participants appeared to have most difficulty estimating times for task components involving fine manipulation, such as inserting and tightening screws.     

Task and user effects on reading patterns in information search

We report on an investigation into people’s behaviors on information search tasks, specifically the relation between eye movement patterns and task characteristics. We conducted two independent user studies (n = 32 and n = 40), one with journalism tasks and the other with genomics tasks. The tasks were constructed to represent information needs of these two different users groups and to vary in several dimensions according to a task classification scheme. For each participant we classified eye gaze data to construct models of their reading patterns. The reading models were analyzed with respect to the effect of task types and Web page types on reading eye movement patterns. We report on relationships between tasks and individual reading behaviors at the task and page level. Specifically we show that transitions between scanning and reading behavior in eye movement patterns and the amount of text processed may be an implicit indicator of the current task type facets. This may be useful in building user and task models that can be useful in personalization of information systems and so address design demands driven by increasingly complex user actions with information systems. One of the contributions of this research is a new methodology to model information search behavior and investigate information acquisition and cognitive processing in interactive information tasks.     

Open-loop and feedback-controlled mouse cursor movements in linear paths

Path length (A), path width (W) and movement direction (θ) are identified as the main factors affecting visually-controlled movement times in linear paths. Effects of A and W are well described by Drury's ( 1971 . Movements with lateral constraint. Ergonomics, l4 (2), 293-305.) model in which movement time is linearly related to the ratio of A/W. At low A/W values, departure from linearity has been identified but not investigated in detail. Data are presented for both open-loop and feedback-controlled movements in linear paths at 0, 60 and 150° movement directions. Movement amplitude and path width were varied over a wide range to determine the effects of A and (A/W) on movement time. Movements were found to be made ballistically or in open-loop mode when the ratio (A/W) was less than about 8 to 10 and the movement times were linearly related to √A for all angles of movement. Feedback-controlled movements followed Drury's law; ballistic movements had movement speed linear with √A. PRACTITIONER SUMMARY: Many tasks require manoeuvring equipment or devices through a path of limited width. These movements can be made with or without feedback control, depending on the path constraints. The conditions for the two forms of movement are determined in this research.     

Showing a model's eye movements in examples does not improve learning of problem-solving tasks

Eye movement modeling examples (EMME) are demonstrations of a computer-based task by a human model (e.g., a teacher), with the model's eye movements superimposed on the task to guide learners' attention. EMME have been shown to enhance learning of perceptual classification tasks; however, it is an open question whether EMME would also improve learning of procedural problem-solving tasks. We investigated this question in two experiments. In Experiment 1 (72 university students, M_age = 19.94), the effectiveness of EMME for learning simple geometry problems was addressed, in which the eye movements cued the underlying principle for calculating an angle. The only significant difference between the EMME and a no eye movement control condition was that participants in the EMME condition required less time for solving the transfer test problems. In Experiment 2 (68 university students, M_age = 21.12), we investigated the effectiveness of EMME for more complex geometry problems. Again, we found no significant effects on performance except for time spent on transfer test problems, although it was now in the opposite direction: participants who had studied EMME took longer to solve those items. These findings suggest that EMME may not be more effective than regular video examples for teaching procedural problem-solving skills.