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Over the past 18 years, Zelaznik and colleagues have promoted what is known as the event-emergent timing distinction. According to this framework, control of timing can be based upon a neurological clock-like process or upon an emergent process. I review the highlights of this research program that supports this distinction, then describe a new line of research that examines whether timing is a goal of the task or a consequence of other movement constraints. These results highlight the importance of goals in the control of timing.

Fitts’ law has been widely used in the human-computer interaction (HCI) field, especially for Graphical User Interface (GUI) design. However, most studies on Fitts’ law were performed with motion control tasks under visual feedback while only a few endeavor to measure human force control behavior. How quickly humans can exert a constant force with a required accuracy and whether this speed-accuracy tradeoff obeys Fitts’ law still needs to be explored. In this paper, human capabilities for controlling absolute magnitudes of fingertip force with discrete visual/audio/haptic feedback cues were observed and compared. Eighteen participants applied constant forces by pressing a force sensor with their index fingers in the three feedback modes respectively. Response time of 24 pairs (4 × 6) of Magnitude-Tolerance conditions were measured. The results showed that the response time obeyed Fitts’ law within a certain range of force accuracy in all the three feedback modes, while the Linear speed-accuracy tradeoff model was almost superior for the force control process than the Meyer formulation and the Shannon formulation. The response time in the audio feedback mode was the shortest among the three feedback conditions. The results may be used as guidelines for applications that rely on accurate and quick force control under different feedback conditions such as fast tapping tasks on a touch screen.

Although many hand exoskeletons have been developed to provide natural hand movements for patients, extraction of motion intents is one of the challenging issues to perform activities of daily living (ADLs). This paper describes a noninvasive electromyography (EMG)-based proportional control for grasping tasks. To perform grasping tasks in ADLs, three degree of freedoms (DOFs) for thumb adduction/abduction, thumb flexion/extension, and four fingers flexion/extension are required at least. In this work, a 2-D Fitts’ Law test is designed as a suitable alternative of real grasping tasks to perform a real-time EMG control for three DOFs required for grasping. The test setup was built to evaluate a user can generate three commands for direct proportional EMG control. Three EMG signals induced by voluntary wrist and thumb movements were recorded to extract users’ intentions, and each signal was used to activate each degree of freedom in Fitts’ law task. A user was asked to move the cursor into the target using three commands such as cursor right, cursor up, and cursor to the initial position. Healthy subjects were performed our developed interface and the results show that the developed interface performed better than that of our previous study using a pattern recognition method. Although there are several issues remain to be resolved, we expect that proportional EMG control could be used to help SCI or stroke patient for controlling a hand exoskeleton.

This study focuses on testing the usability of 3 different sizes of smartphones by children, adults, and the elderly. Forty-seven participants from each age group were recruited. The research consisted of two stages of experiments. In the first experiment, three existing gestures used by the Android system were evaluated: drag, pinch, and double-touch drag. In the second experiment, two additional re-design gestures were tested: multi-long press and slide down. The users' performances were measured based on their overall time, success time, accuracy, Fitts' Law values, and a subjective questionnaire. Among the five gestures, drag and multi-long press were categorized as the drag gesture, and pinch, double-touch drag and slide down were categorized as the enlarging gesture. The results show that children and adults outperformed the elderly in gesture operation. With respect to smartphone size, the subjects had faster response times and better Fitts' Law values on 6-inch phones. When comparing the subjective preference and the objective use measurement values of the two drag gestures and three enlarging gestures among the different age groups, it was found that children and adults were consistent, whereas the elderly were inconsistent. Overall, in operating the original drag and pinch gestures, the elderly exhibited better objective use measurements, but they preferred the improved gestures, such as slide down.

Although several Predetermined Motion time Systems mention the effects of change of path angle during a movement, there does not appear to be any experimental evidence for the quoted effects. Here we report effects of angle changes between zero and 180° during the movement, with and without an intervening target at the end of the first component of the movement. The effects are variable: with ballistic movements without an intervening target there is an increase of MT with path angle change; when there is an intervening target the MT of the first component decreases with change of path angle, while that of the second component increases, so that the total movement time is independent of the change in path angle. When the movements are made under visual control, with no intervening target, MT increases with change of path angle, whereas when there is an intervening target, there is no effect of change of path angle, either on the first or second component of the movement. Thus the occurrence of movement time increments is dependent on the form of motor control and the way in which the path angle change occurs.

Fitts' Law is one of the most robust and well-studied principles in psychology. It holds that movement time (MT) for target-directed aiming movements increases as a function of target distance and decreases as a function of target width. The purpose of this study was to determine whether Fitts' Law is affected not only by the demands of the target on the current trial but also by the requirements for performance on the previous trial. Experiments 1 and 2 examined trial-to-trial effects of varying target width; Experiment 3 examined trial-to-trial effects of varying target distance. The findings from Experiments 1 and 2 showed that moving a finger or cursor towards a large object on a previous trial shortened the movement time on the current trial, whereas the opposite occurred with a small object. In contrast, target distance on the previous trial had no effect on movement time on the current trial. These findings suggest that performance on trial n has a clear and predictable effect on trial n+1 (at least for target width) and that Fitts' Law as it is normally expressed does not accurately predict performance when the width of the target varies from trial to trial.

A hybrid gaze and brain-computer interface (BCI) was developed to accomplish target selection in a Fitts’ law experiment. The method, GIMIS, uses gaze input to steer the computer cursor for target pointing and motor imagery (MI) via the BCI to execute a click for target selection. An experiment (n = 15) compared three motor imagery selection methods: using the left-hand only, using the legs, and using either the left-hand or legs. The latter selection method (”either”) had the highest throughput (0.59 bps), the fastest selection time (2650 ms), and an error rate of 14.6%. Pupil size significantly increased with increased target width. We recommend the use of large targets, which significantly reduced error rate, and the ”either” option for BCI selection, which significantly increased throughput. BCI selection is slower compared to dwell time selection, but if gaze control is deteriorating, for example in a late stage of the ALS disease, GIMIS may be a way to gradually introduce BCI.

Speed-accuracy trade-off (SAT) is the tendency for decision speed to covary with decision accuracy. SAT is an inescapable property of aimed movements being present in a wide range of species, from insects to primates. An aspect that remains unsolved is whether SAT extends to plants' movement. Here, we tested this possibility by examining the swaying in circles of the tips of shoots exhibited by climbing plants (Pisum sativum L.) as they approach to grasp a potential support. In particular, by means of three-dimensional kinematical analysis, we investigated whether climbing plants scale movement velocity as a function of the difficulty to coil a support. Results showed that plants are able to process the properties of the support before contact and, similarly to animal species, strategically modulate movement velocity according to task difficulty.

The tradeoff between speed and accuracy of human movements has been exploited from many different perspectives, such as experimental psychology, workspace design, human–machine interface. This tradeoff is formalized by Fitts’ law, which states a linear relationship between the duration and the difficulty of the movement. The bigger is the required accuracy in reaching a target or farther is the target, the slower has to be the movement. A variety of computational models of neuromusculoskeletal systems have been proposed to pinpoint the neurobiological mechanisms that are involved in human movement. We introduce a neurocomputational model of spinal cord to unveil how the tradeoff between speed and accuracy elicits from the interaction between neural and musculoskeletal systems. Model simulations showed that the speed–accuracy tradeoff is not an intrinsic property of the neuromuscular system, but it is a behavioral trait that emerges from the strategy adopted by the central nervous system for executing faster movements. In particular, results suggest that the velocity of a previous learned movement is regulated by the monosynaptic connection between cortical cells and alpha motoneurons.

Accessible Digital Musical instruments (ADMIs) dedicated to people with motor disabilities represent a relevant niche in accessibility research. The designer is often required to exploit unconventional physical interaction channels, different from hands and fingers. Although comprehensive evaluation methods for Digital Musical Instruments in general are found in literature, little has been done both in ADMIs evaluation and the analysis of suitable interaction channels from a Human-Computer Interaction perspective. In this work the performance of breath, gaze pointing and head movements is analyzed, in terms of movement speed and stability, through a simple experiment. These interaction channels could be exploited in the design of ADMIs dedicated to quadriplegic musicians. The proposed experiment has similarities with past Fitts Law evaluation tests. Results are discussed proposing possible mappings between channels and musical performance parameters. These results could also be useful to inform the design of different interface types.

In this paper we examine physical collaboration between two individuals using a dual-arm robot as a haptic interface. First, we design a haptic controller based on a virtual dynamic model of the robot arms. Then, we analyse dyadic human-human collaboration with a reaching task on a 2D plane, where the distance and size of the target changed randomly from a pool of nine reachable positions and sizes. Each subject performed the task individually and linked through the guided robot arms with a virtual model to perform the same task in collaboration. We evaluated both, individual and collaborative performances, based on Fitts’ law, which describes the relation between the speed of motion and its accuracy. The results show that the Fitts’ law applies to both, individual and collaborative tasks, with their performance improving when in collaboration.

Fitts proposed the Fitts Law, a human motion behavior prediction model based on information theory, which established the functional relationship between motion time, motion amplitude and target area width, and became one of the few quantitative models in the field of human-computer interaction. However, the parameters related to devices of a and b need to be tested in combination with specific population and devices. Based on the hardware equipment such as mouse and eye tracker, this paper carried out the experimental design and implementation of interactive motion data collection for command and control system operators, and collected data of 20 people in total. The analysis of experimental data shows that the average value of 20 person-times is: a = 160.7, b = 227. The above research not only improves Fitts Law in the field of command and control system, but also provides a quantitative model targeted at specific groups for later cognitive and behavioral modeling of operators and human-machine interface design.

Placement of alphabets in any keyboard layout requires extensive analysis on several key features of that specific language. Vocabulary size, the correlation between alphabets and punctuation marks, user group based on cultural diversity and many other issues often make the layout optimization method extremely challenging. And when it comes to generalizing the solution for a user group who need to access buttons via feet due to physical disability, additional parameters like assuring minimum movement and analyzing letter frequency chart while placing keys needs to be considered with utmost precision. In this paper, we propose a keyboard layout for Bengali language-speaking physically handicapped group with a vision to assist them in achieving maximum typing speed with less typing error occurrence.

It is not widely known that visual illusions that cause misrecognition with regard to the perception of length or width of figures affect human behavior. Thus, we investigate the influence of the Delboeuf illusion on pointing performance in this study. If the control circle of the Delboeuf illusion, which is the central circle of the Delboeuf illusion figure, is surrounded by a slightly larger circle, it is perceived to be larger than its actual size. On the contrary, if the control circle is surrounded by a much larger circle, it is perceived to be smaller than its actual size. Therefore, the Delboeuf illusion figure affects the perception of circle sizes and can also affect the movement time of pointing movements. The result indicates that there is no significant difference in the movement time and the error rate among three tasks---two tasks with the Delboeuf illusion and the other task without the Delboeuf illusion. Moreover, Fitts' law showed sufficient fits for all conditions. From these results, it can be said that the participants conducted the trials with the Delboeuf illusion as same as the trial without the Delboeuf illusion. This is because the participants saw the circles of the Delboeuf illusion at once in the questionnaire, but they saw the circles one by one during the trials so the illusion magnitude was difference between trials and a questionnaire.

We investigated the performance of 3D pointing using direct touch in a planar surface condition (PC) and a spherical surface condition (SC). In addition, we examined the performance in terms of Fitts’ law. Although the results showed that the performance in SC was slightly worse than PC, SC was higher conformed to Fitts’ law than PC without the conditions involving head rotation (PC’s and SC’s R2 is 0.945 and 0.971, respectively).

The objective of this paper is to explore three different interaction methods in a confirmation task on a head-mounted Augmented Reality (AR) device with a population of children aged 9-11 years. The three interaction methods we look at are voice recognition, gesture recognition, and controller. We conducted a within-subjects study using a Fitts’ Law confirmation task performed by children with a Microsoft HoloLens. We measured elapsed time during the completion of the tasks. Also, we collected usability and fatigue measures using the System Usability Scale and the OMNI RPE (Ratings of Perceived Exertion) scale. We found significant differences between voice and controller for time, fatigue and usability. We also found significant differences between gesture and controller for time, fatigue and usability. We hope to apply the results of this study to improve augmented reality educational tools for children in the future.

Testing software with individuals who have differing abili­ ties such as motor impairments allows developers to create more accessible applications. Unfortunately, these individuals are not always available to assist with research or software development testing. To help address this issue, we propose a system which simulates the difficulties demonstrated by a motor-impaired user interacting with a head-controlled mouse pointer system. Through an evaluation using a Fitts' law ex­ periment, we compare the throughput rate in bits per second and percent error rate of our system between users with and without motor impairments.

A 3D user interface can be adapted in multiple ways according to each user’s needs, skills and preferences. Such adaptation can consist in changing the user interface layout or its interaction techniques. Personalization systems which are based on user models can automatically determine the configuration of a 3D user interface in order to fit a particular user. In this paper, we propose to explore the use of machine learning in order to propose a 3D selection interaction technique adapted to a target user. To do so, we built a dataset with 51 users on a simple selection application in which we recorded each user profile, his/her results to a 2D Fitts Law based pre-test and his/her preferences and performances on this application for three different interaction techniques. Our machine learning algorithm based on Support Vector Machines (SVMs) trained on this dataset proposes the most adapted interaction technique according to the user profile or his/her result to the 2D selection pre-test. Our results suggest the interest of our approach for personalizing a 3D user interface according to the target user but it would require a larger dataset in order to increase the confidence about the proposed adaptations.

We present the performance analysis for the three devices Leap Motion, Myo, and Space Navigator under the framework of Fitts’ law in two and three dimensional applications. One experiment was carry on to evaluate the selection task in a 2D software application, in which is request to the user to select a green rectangle. A second experiment was a 3D game in which an object is displaced until the position of the same object form situated in a different position. The usability of each device is evaluated with the aim of a questionnaire. Based on the results of the conducted experiments, we suggest for which 2D or 3D applications are more suitable the use of these devices: LM and Space Navigator devices can be used in 3D applications; LM is avoided to use it by long periods of time; Myo device can be used in 2D applications.

When users operate smartphones and desktop interfaces with their fingers, there are differences between the motor and visual widths. For example, when a user selects an item from a vertical menu, the area that is physically touched by the user is often larger than the visual width (e.g., of the label for the item selected). Therefore, the user aims for the label assuming that the label width (the visual width) means the motor width. Consequently, the user performs operations more carefully than necessary. We conducted an experiment to investigate the effect of the motor and visual widths on finger pointing. After asking participants to explore the motor width, they performed an experimental task. Our experiment shows that the users' movement time depends on the motor width and can be predicted. We also analyze existing interfaces and discuss the implications.

Although much work has been done and improved solutions have been proposed towards the design and development of keyboard layouts for non-disabled people, very few approaches have addressed the same issue for the physically handicapped group. In this paper, we propose a novel text entry system, namely BADHON, for a specific user base who are unable to use regular keyboards because of limited hand mobility and require a solution to interact with the computer using thumb toe and ankle movement. In order to resolve the inevitable trade-off between faster typing speed acquisition and inconvenience of memorizing a new layout, two different layouts have been proposed. One combines movement time model and linguistic model to ensure good words per minute (WPM) count and other significantly reduces the burden of carrying manual while using the layout by keeping the alphabet’s orientation as easy as possible.

The visual demand of finger-touch based interactions with touch screens has been increasingly modelled using Fitts' Law. With respect to driving, these models facilitate the prediction of mean glance duration and total glance time with an index of difficulty based on target size and location. Strong relationships between measures have been found in the controlled conditions of driving simulators. The present study aimed to validate such models in naturalistic conditions. Nineteen experienced drivers carried out a range of touchscreen button-press tasks in an instrumented car on a UK motorway. In contrast with previous simulator-based work, our on-road data produced much weaker relationships between the index of difficulty and glance times. The model improved by focusing on tasks that required one glance only. Limitations of Fitts' Law in the more complex and dynamic real-world driving environment are discussed, as are the potential drawbacks of driving simulators for conducting visual demand research.

The aim of public and private health institutions is to prevent, mitigate or suppress the effects that endanger the lives and health of populations. Rare diseases are generally genetic and hereditary diseases that appear in pediatric age. Rare diseases are chronic diseases with a risk of causing death or physical, neurological and/or cognitive impairment.Virtual Reality applications are tools to improve the cognitive rehabilitation process. The aim of this paper is to apply the Perfetti method and the Fitts Law in a Virtual Reality application. The application is oriented for patients with rare diseases and allows teaching, learning and measuring the level of learning in processes of memorization and location of objects using Leap Motion Technology.

Virtual reality (VR) is becoming more and more ubiquitous to interact with digital content and often requires renderings of avatars as they enable improved spatial localization and high levels of presence. Previous work shows that visual-haptic integration of virtual avatars depends on body ownership and spatial localization in VR. However, there are different conclusions about how and which stimuli of the own appearance are integrated into the own body scheme. In this work, we investigate if systematic changes of model and texture of a users' avatar affect the input performance measured in a two-dimensional Fitts' law target selection task. Interestingly, we found that the throughput remained constant between our conditions and that neither model nor texture of the avatar significantly affected the average duration to complete the task even when participants felt different levels of presence and body ownership. In line with previous work, we found that the illusion of virtual limb-ownership does not necessarily correlate to the degree to which vision and haptics are integrated into the own body scheme. Our work supports findings indicating that body ownership and spatial localization are potentially independent mechanisms in visual-haptic integration.

This paper acquaints a head gesture and eye blink controlled human-computer interaction device to obstruct carpal tunnel syndrome (CTS) and making the computer mouse accessible for the differently able individuals. Traditional computer mouse puts a user’s hand for too long in a pronation posture which increases inflammation in the wrist and hand. To solve this problem, in this paper as an alternative to the customary computer mouse is introduced. The system uses three-axis accelerometer and gyroscope to detect the head gesture and translate it into the position of the mouse cursor on the computer screen. The complementary filtering technique obtains a smooth and accurate output from the inertial measurement unit (EMU). To perform the left and right clicking event, the user’s need to shut the left and right eye for a moment while opening another eye. The system usages the deep convolutional neural network (CNN) to classify the individual openness and closeness of both eyes. The implementation details along with the performance evaluation results are delineated in this paper show that the system has extensive control over its performance.

Quantifiable differences among fingers in force control capability have both important practical and theoretical values in characterizing force control of accurate finger-tapping tasks. Following the classical Fitts’ law paradigm, we quantified the differences among ten fingers in term of speed–accuracy trade-off (SAT) in performing repetitive discrete force control tasks. Visual cues displaying targeted force magnitudes and tolerances were provided. Users were required to apply the targeted force within the given tolerance quickly and accurately by pressing a force sensor using the specified finger. We found that ten fingers obeyed the Meyer model in the SAT performance and they differed in reaction time, the index of performance (IP), and the goodness of fit for the Meyer model. A modified Meyer model was proposed to quantify the difference between ten fingers in the SAT performance using only one parameter, making the quantification easier than using the original Meyer model. Pairwise comparisons showed that the differences between symmetrical fingers on both hands were insignificant except for the pair of index fingers. These findings provided us with multiple perspectives on the differentiation among ten fingers in the force control capabilities. Our study helps lay the foundation for engineering systems that rely on finger force control ability.

Objective Use Fitts’ law to compare accuracy and throughput of three flight deck interfaces for navigation. Background Industry is proposing touch-based solutions to modernize the flight management system. However, research evaluating touchscreen effectiveness for navigation tasks in terms of accuracy and throughput on the flight deck is lacking. Method An experiment was conducted with 14 participants in a flight simulator, aimed at creating Fitts’ law accuracy and throughput models of three different flight deck interfaces used for navigation: the mode control panel, control display unit, and a touch-based navigation display. The former two constitute the conventional interface between the pilot and the flight management system, and the latter represents the industry-proposed solution for the future. Results Results indicate less accurate performance with the touchscreen navigation display compared to the other two interfaces and the throughput was lowest with the mode control panel. The control display unit was better in both accuracy and throughput, which is found to be largely attributed to the tactile and physical nature of the interface. Conclusion Although performance in terms of accuracy and throughput was better with the control display unit, a question remains whether, when used during a more realistic navigation task, performance is still better compared to a touch-based interface. Application This paper complements previous studies in the usage of aircraft touchscreens with new empirical insights into their accuracy and throughput, compared to conventional flight deck interfaces, using Fitts’ law.

Aimed movement is ubiquitous and has been extensively investigated. However, little research exists when the hand movements are incompatible with eye movements such as when viewing through a mirror or when performing laparoscopic surgery. An experiment was designed to investigate how individuals perform under one-dimensional and two-dimensional inversion with direct viewing as a reference condition. Twenty-four right-handed university students participated in this experiment and completed all aimed movements with a full-factorial design of movement amplitude at three levels and index of difficulty at 10-levels in three visual conditions of direct, viewing through a mirror (1D inversion) and observing through a right-angled mirror (2D inversion). Learning is rather rapid with direct viewing and with 1D inversion. However, participants take a longer time to stabilize their performance in the 2D inversion condition. Fitts' law is robust under all visual conditions. The eye-hand incompatibility increases movement time with 2D inversion taking the longest movement time. Movement time (MT) was split into initiation time (IT), distance covering time (DCT) and acquisition time (AT) based on submovements. The distance covering part is the first submovement that is primarily ballistic and covers around 90% or more of total amplitude. Furthermore, AT allows the aimed movement to be split into two phases: ballistic and visual control. The results show that the transition from ballistic to visual control happens at lower Index of difficulty (ID) values as the level of incompatibility increases. Based on the experiment and prior research, it is appropriate to use the model MT = a + b ID + c√A as it can account for the two phases of ballistic and visual control.

Background People after stroke often have postural impairments that can increase their risk of falling. Anticipatory postural adjustments (APAs) are changes in the activity of postural muscles prior to a voluntary movement in order to maintain vertical equilibrium. Previous research suggests that improving APAs leads to better postural control and reduces the risk of falls. Despite the importance of APAs and their impairment among people post-stroke, studies that aim to investigate methods for improving APAs are limited. Consistent evidence supports that an external focus of attention compared to an internal focus of attention, yields superior performance of motor skills that include postural control. Research question What are the effects of adopting different foci of attention on measures of APAs and movement parameters when performing a lower extremity Fitts’ task among people post-stroke? Methods Twelve individuals post-stroke performed a lower extremity stepping movement (Fitts’ task) while adopting an external focus or an internal focus of attention in a within-subject design. A motion capture system was used to record participants’ movement data. Custom software derived movement time (MT), peak velocity (PV), time to peak velocity (ttPV) and variability at endpoint (SDT). Electromyography was used to measure muscle activity and determine APAs onset and magnitude. For all dependent variables separate repeated measures ANOVAs were conducted to compare performance between foci of attention. Results The results showed that an external focus of attention yielded significantly better performance on all outcome measures. The improvement in performance was seen in shorter MT, higher PV, shorter ttPV, smaller SDT, earlier APAs onset and more efficient APAs magnitude. Significance The changes in outcome measures suggest that adopting an external focus of attention during postural tasks could be an effective strategy for improving balance control among people post-stroke.

Head-mounted displays offer full control over lighting conditions. When equipped with eye tracking technology, they are well suited for experiments investigating pupil dilation in response to cognitive tasks, emotional stimuli, and motor task complexity, particularly for studies that would otherwise have required the use of a chinrest, since the eye cameras are fixed with respect to the head. This paper analyses pupil dilations for 13 out of 27 participants completing a Fitts' law task using a virtual reality headset with built-in eye tracking. The largest pupil dilation occurred for the condition subjectively rated as requiring the most physical and mental effort. Fitts' index of difficulty had no significant effect on pupil dilation, suggesting differences in motor task complexity may not affect pupil dilation.

Fitts’ law is a performance model of human movement especially the act of pointing which is widely used in Ergonomics and Human-Computer Interaction. The aim of this review is to provide an overview of the discussions and extensions of Fitts’ law as well as the relevant applications in recent years (2013–2018). The present paper shows that the related discussions mainly focus on the theoretical basis and performance of Fitts’ law. In addition, several new predictive models are proposed to improve accuracy or extend the law to three-dimensional space. The applications apply Fitts’ law into different input methods and user populations to explore the feasibility of it in specific conditions. The review shows that despite the theoretical and practical development about this topic, differences of views still remain and further research is needed.

The aims of this study were to investigate the effects of throwing instruction (i.e., velocity and accuracy) and testing order (random or blocked) on dart throwing performance testing and on the movement strategies leading to this performance. Twelve physical education students (nine men and three women, age: 24 ± 7.5; mass: 77.7 ± 15.8, height: 1.77 ± 0.06 m) performed dart throws with four different instructions, varying in priority regarding velocity and accuracy, instructed in a blocked and random manner. The main findings were that dart velocity decreased when the priority of accuracy increased. However, when accuracy was the main priority, accuracy increased only when measured for consistency. Testing order influenced peak joint kinematics of wrist flexion in addition to finger extension and the time of occurrence of elbow extension. Instructions emphasizing velocity and/or accuracy showed a clear speed-accuracy trade-off in dart throwing and thereby followed Fitts' law. Testing order had a minor effect on the speed-accuracy trade-off. The blocked testing order appeared to increase performance outcomes that favored the priority set by the instruction in contrast to the random test order. These differences were based upon adjustments of joint movements, which were based upon the knowledge of the previous attempts. These adjustments were visible between the different instructions through changes in the execution timing of peak wrist flexion and elbow and finger extension.

Why does Fitts’ law fit various human behavioural data well even though it is not a model based on human physical dynamics? To clarify this, we derived the relationships among the factors applied in Fitts’ law—movement duration and spatial endpoint error—based on a multi-joint forward- and inverse-dynamics models in the presence of signal-dependent noise. As a result, the relationship between them was modelled as an inverse proportion. To validate whether the endpoint error calculated by the model can represent the endpoint error of actual movements, we conducted a behavioural experiment in which centre-out reaching movements were performed under temporal constraints in four directions using the shoulder and elbow joints. The result showed that the distributions of model endpoint error closely expressed the observed endpoint error distributions. Furthermore, the model was found to be nearly consistent with Fitts’ law. Further analysis revealed that the coefficients of Fitts’ law could be expressed by arm dynamics and signal-dependent noise parameters. Consequently, our answer to the question above is: Fitts’ law for reaching movements can be expressed based on human arm dynamics; thus, Fitts’ law closely fits human’s behavioural data under various conditions.

Eye gaze as an input method has been studied since the 1990s, to varied results: some studies found gaze to be more efficient than traditional input methods like a mouse, others far behind. Comparisons are often backed up by Fitts' Law without explicitly acknowledging the ballistic nature of saccadic eye movements. Using a vision science-inspired model, we here show that a Fitts'-like distribution of movement times can arise due to the execution of secondary saccades, especially when targets are small. Study participants selected circular targets using gaze. Seven different target sizes and two saccade distances were used. We then determined performance across target sizes for different sampling windows ("dwell times") and predicted an optimal dwell time range. Best performance was achieved for large targets reachable by a single saccade. Our findings highlight that Fitts' Law, while a suitable approximation in some cases, is an incomplete description of gaze interaction dynamics.

Although numerous studies have focused on interfaces for maneuvering drones, a method for evaluating these interfaces has not been established. A pointing experiment was carried out with a drone in this study. The results indicate that the target distance and target width affect the movement time and error rate while maneuvering. This is consistent with the results of previous pointing studies. Fitts' law was not a good fit (R^2 = 0.672), while the data fit well to a two-part model (R^2 = 0.993). Based on these results, we propose future experimental work that could contribute to improving drone interfaces.

Tables, desks, and counters are often nearby, motivating their use as interactive surfaces. However, they are typically cluttered. As an alternative, we explore touch input along the 'edge' of table-like surfaces. The performance of tapping, crossing, and dragging is tested along the two ridges and front face of a table edge. Results show top ridge movement time is comparable to the top face when tapping or dragging. When crossing, both ridges are at least 11% faster than the top face. Effective width analysis is used to model performance and provide recommended target sizes. Based on observed user behaviour, variations of top and bottom ridge crossing are explored in a second study, and design recommendations with example applications are provided.

We propose a novel, biologically plausible cost/fitness function for sensorimotor control, formalized with the information-theoretic principle of empowerment, a task-independent universal utility. Empowerment captures uncertainty in the perception-action loop of different nature (e.g. noise, delays, etc.) in a single quantity. We present the formalism in a Fitts' law type goal-directed arm movement task and suggest that empowerment is one potential underlying determinant of movement trajectory planning in the presence of signal-dependent sensorimotor noise. Simulation results demonstrate the temporal relation of empowerment and various plausible control strategies for this specific task.

Even when in a static position, data acquired from 6 Degrees of Freedom (DoF) trackers is affected by noise, which is typically called jitter. In this study, we analyzed the effects of 3D rotational jitter on Virtual Reality (VR) controllers in a 3D Fitts' law experiment, which explored how such jitter affects user performance. Eight subjects performed a Fitts' law experiment with or without additional jitter on the cursor. Results show that while error rate significantly increased above ±0.5° jitter and subjects' effective throughput started to decrease significantly above ±1° jitter, there was no significant effect on users' movement time. Further, the Fitts's law movement time model was affected when ±2° jitter was applied to the tracker. According to these results, ±0.5° jitter on the controller does not significantly affect user performance for the tasks explored here. The results of our study can guide the design of 3D controller and tracking systems for 3D user interfaces.

This paper presents the first investigation into using the goal-crossing paradigm for object selection with virtual reality (VR) head-mounted displays. Two experiments were carried out to evaluate ray-casting crossing tasks with target discs in 3D space and goal lines on 2D plane respectively in comparison to ray-casting pointing tasks. Five factors, i.e. task difficulty, the direction of movement constraint (collinear vs. orthogonal), the nature of the task (discrete vs. continuous), field of view of VR devices and target depth, were considered in both experiments. Our findings are: (1) crossing generally had shorter or no longer time, and higher or similar accuracy than pointing, indicating crossing can complement or substitute pointing; (2) crossing tasks can be well modelled with Fitts' Law; (3) crossing performance depended on target depth; (4) crossing target discs in 3D space differed from crossing goal lines on 2D plane in many aspects such as time and error performance, the effects of target depth and the parameters of Fitts' models. Based on these findings, we formulate a number of design recommendations for crossing-based interaction in VR.