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Purpose: The perception of effort (PE) is widely used to prescribe and monitor exercise during locomotor and resistance tasks. The present study examines the validity of PE to prescribe and monitor exercise during upper-limb motor tasks under various loads and speed requirements. Methods: Forty participants volunteered in two experiments. In experiment 1, we used four PE intensities to prescribe exercise on a modified version of the box and block test (BBT) and a pointing task. We investigated the possibility of monitoring the exercise intensity by tracking changes in PE rating in response to three different tempos or additional weights. Experiment 2 replicated the possibility of prescribing the exercise with the PE intensity during the BBT and explored the impact of additional weights on performance and PE during the standardized version of the BBT. Muscle activation, heart rate, and respiratory frequencies were recorded. Results: In experiment 1, increasing the PE intensity to prescribe exercise induced an increased performance between each intensity. Increasing task difficulty with faster movement tempo and adding weight on the forearm increased the rating of PE. Experiment 2 replicated the possibility to use PE intensity for exercise prescription during the BBT. When completing the BBT with an additional weight on the forearm, participants maintained performance at the cost of a higher PE. In both experiments, changes in PE were associated with changes in muscle activation. Conclusion: Our results suggest that PE is a valid tool to prescribe and monitor exercise during upper-limb motor tasks. [ABSTRACT FROM AUTHOR]

Human–virtual target interactions are becoming more and more common due to the emergence and application of augmented reality (AR) devices. They are different from interacting with real objects. Quantification of movement time (MT) for human–virtual target interactions is essential for AR-based interface/environment design. This study aims to investigate the motion time when people interact with virtual targets and to compare the differences in motion time between real and AR environments. An experiment was conducted to measure the MT of pointing tasks on the basis of both a physical and a virtual calculator panel. A total of 30 healthy adults, 15 male and 15 female, joined. Each participant performed pointing tasks on both physical and virtual panels with an inclined angle of the panel, hand movement direction, target key, and handedness conditions. The participants wore an AR head piece (Microsoft Hololens 2) when they pointed on the virtual panel. When pointing on the physical panel, the participants pointed on a panel drawn on board. The results showed that the type of panel, inclined angle, gender, and handedness had significant (p < 0.0001) effects on the MT. A new finding of this study was that the MT of the pointing task on the virtual panel was significantly (p < 0.0001) higher than that of the physical one. Users using a Hololens 2 AR device had inferior performance in pointing tasks than on a physical panel. A revised Fitts's model was proposed to incorporate both the physical–virtual component and inclined angle of the panel in estimating the MT. This model is novel. The index of difficulty and throughput of the pointing tasks between using the physical and virtual panels were compared and discussed. The information in this paper is beneficial to AR designers in promoting the usability of their designs so as to improve the user experience of their products. [ABSTRACT FROM AUTHOR]

Shannon’s Index of Difficulty ( $ID$ ), reputable for quantifying the perceived difficulty of pointing tasks as a logarithmic relationship between movement-amplitude ( $A$ ) and target-width ( $W$ ), is used for modeling the corresponding observed movement-times ( $MT_{O}$ ) in such tasks in controlled experimental setup. However, real-life pointing tasks are both spatially and temporally uncontrolled, being influenced by factors, such as – human aspects, subjective behavior, the context of interaction, the inherent speed-accuracy trade-off, where, emphasizing accuracy compromises speed of interaction and vice versa. Effective target-width ( $W_{e}$ ) is considered as spatial adjustment for compensating accuracy. However, no significant adjustment exists in the literature for compensating speed in different contexts of interaction in these tasks. As a result, without any temporal adjustment, the true difficulty of an uncontrolled pointing task may be inaccurately quantified using Shannon’s $ID$ . To verify this, we propose ANTASID (A Novel Temporal Adjustment to Shannon’s ID) formulation with detailed performance analysis. We hypothesized a temporal adjustment factor ( $t$ ) as a binary logarithm of $MT_{O}$ , compensating for speed due to contextual differences and minimizing the non-linearity between movement-amplitude and target-width. Considering spatial and/or temporal adjustments to $ID$ , we conducted regression analysis using our own and Benchmark datasets in both controlled and uncontrolled scenarios of pointing tasks with a generic mouse. ANTASID formulation showed significantly superior fitness values and throughput in all the scenarios while reducing the standard error. Furthermore, the quantification of $ID$ with ANTASID varied significantly compared to the classical formulations of Shannon’s $ID$ , validating the purpose of this study.

In pen + touch interfaces, two-handed pointing tasks are quite basic. We focus on two-handed pointing tasks on a stationary touchable tablet under asynchronous conditions, in which another target will not appear until one target is touched and dwelled. Fitts' law cannot accurately model such pointing tasks based on the results of our pilot study. This paper seeks to establish an ergonomics model for bimanual pointing tasks under asynchronous interaction. We designed and implemented three experiments with bimanual pointing tasks varying the target widths and distances. A series of bimanual pointing tasks with ten different IDs (Index of Difficulty) were carried out by 18 participants. The movement time (MT) and errors were collected and analyzed. Through experiments, we found that the index of difficulty of pointing tasks has a significant impact on MT (F9,170 = 6.276, p 2 = 0.973, while the Fitts' law model only achieves a fit of R2 = 0.623. The experimental results show that our model has a strong effectiveness and applicability for bimanual pointing tasks in pen + touch interfaces.

Human–virtual target interactions are becoming more and more common due to the emergence and application of augmented reality (AR) devices. They are different from interacting with real objects. Quantification of movement time (MT) for human–virtual target interactions is essential for AR-based interface/environment design. This study aims to investigate the motion time when people interact with virtual targets and to compare the differences in motion time between real and AR environments. An experiment was conducted to measure the MT of pointing tasks on the basis of both a physical and a virtual calculator panel. A total of 30 healthy adults, 15 male and 15 female, joined. Each participant performed pointing tasks on both physical and virtual panels with an inclined angle of the panel, hand movement direction, target key, and handedness conditions. The participants wore an AR head piece (Microsoft Hololens 2) when they pointed on the virtual panel. When pointing on the physical panel, the participants pointed on a panel drawn on board. The results showed that the type of panel, inclined angle, gender, and handedness had significant (p < 0.0001) effects on the MT. A new finding of this study was that the MT of the pointing task on the virtual panel was significantly (p < 0.0001) higher than that of the physical one. Users using a Hololens 2 AR device had inferior performance in pointing tasks than on a physical panel. A revised Fitts’s model was proposed to incorporate both the physical–virtual component and inclined angle of the panel in estimating the MT. This model is novel. The index of difficulty and throughput of the pointing tasks between using the physical and virtual panels were compared and discussed. The information in this paper is beneficial to AR designers in promoting the usability of their designs so as to improve the user experience of their products.

Pointing and gesturing with the dominant thumb (DT) and the non-dominant thumb (NT) are two common tasks for bimanual tablet gripping interaction. Understanding the differences between DT and NT is important to pointing and gesturing based interface design on tablets, but is overlooked by previous studies. We therefore conducted two experiments. In the first experiment, participants carried out pointing tasks with DT and NT, respectively, on a tablet. We found DT and NT input differed in pointing time (DT had average shorter time than NT) and required target sizes for fast and accurate pointing (7.7mm and 9.4mm in diameter for DT and NT). On the other hand, DT and NT were alike in pointing accuracy. They performed about the same for target size larger than 9.6mm and distance shorter than 21mm. Both DT and NT pointing can be modeled by Fitts' law. In the second experiment, participants performed gesturing tasks with DT and NT respectively on a tablet. The collected data were analyzed using a set of gesture features. Results showed DT and NT were different in features such as articulation time, size ratio and indicative angle difference, but similar in features like aperture, axial symmetry and shape distance. The differences of time and accuracy between DT and NT depended on gesture complexity but not gesture sizes. We discuss these findings with implications for future bimanual thumb interaction design and research. [ABSTRACT FROM AUTHOR]

Many handheld devices with stylus pens are available in the market; however, there have been few studies which examine the effects of the size of the stylus pen on user performance and subjective preferences for handheld device interfaces for various age groups. Two experiments (pen-length experiment and pen-tip width/pen-width experiment) were conducted to determine the most suitable dimensions (pen-length, pen-tip width and pen-width) for a stylus pen among young adult, child and older users. In pen-length experiment, five pen-lengths (7, 9, 11, 13 and 15 cm) were evaluated for young adult, child and older users, respectively. In pen-tip width/pen-width experiment, six combinations of three pen-tip widths (0.5, 1.0 and 1.5 mm) and two pen-widths (4 and 7 mm) were compared for young adult, child and older users, respectively. In both experiments, subjects conducted pointing, steering and writing tasks on a PDA. The results were assessed in terms of user performance and subjective evaluations for all three pointing, steering and writing tasks. We determined that the most suitable dimensions of the pen are as follows: pen-length 11–15 cm, pen-tip width 1.0–1.5 mm and pen-width 7 mm for older users; for child users, pen-length 7–13 cm, pen-tip width 1.0–1.5 mm and pen-width 4 mm; and for young adult users, pen-length 11 cm, pen-tip width 0.5 mm, and pen-width 7 mm. [ABSTRACT FROM PUBLISHER]

Surgical overhead luminaires and head-mounted luminaires are important tools for surgeons. The optical design of these luminaires focuses on providing shadow free light. Shadows, however, are reported as important cues for depth perception in mono- and stereo-visual situations. Because surgeons repeatedly touch delicate tissue with their instruments, their depth-perception should not be hampered. Two experiments were performed to evaluate the influence of shadow on human performance when executing stereo-visual pointing tasks. Experiment 1 studied the effect of the existence of shadows and Experiment 2 studied the effect of the direction of shadows. Subjects were instructed to point random sequences of virtual targets accurately under different shadow situations. Performance was characterized with spatial error E (distance to target, mm). Experiment 1 showed that both large and small high-contrast shadows gave significantly smaller spatial error E (4.8, 4.6 mm, respectively) than either low-contrast shadows (5.6 mm) or no shadows (6.3 mm). Experiment 2 showed that the Error varied (2.1 to 3.2 mm) for different illumination directions. The Error decreased with an increasing angle between the line-of-sight and line-of-light. Illuminating from the center or from the left side of the observer gave better results then from the right side. To maximize depth-perception, surgical luminaires should provide a clear shadow from a light source that illuminates from within the vertical plane through the line-of-sight, and with a 90° angle with respect to the line-of-sight. [ABSTRACT FROM AUTHOR]

The steering law is an excellent performance model for trajectory-based tasks, such as drawing and writing in GUIs. Current studies on steering tasks focus on the effect of system factors (i.e. path width and amplitude) on the movement time and steering law's related applications. We conducted a series of experiments to further explore the effect of different operational biases (bias speed or accuracy) on steering completion time and standard deviation for two steering trajectory shapes, i.e. a straight steering task and a circular steering task, and then establish a new model accommodating system and subjective factor in steering tasks. Empirical results showed that the new model is more predictive and robust than the traditional steering law. [ABSTRACT FROM AUTHOR]