Effects of target location, stature and hand grip type on in-vehicle reach discomfort

Effect of object and human-factor characteristics on the preference of thumb-index finger grasp type

This work is to investigate the factors affecting the preference of human thumb-index finger grasping type. A multinomial logistic regression analysis shown that the object characteristics (equivalent diameter and shape) and human-factor characteristics (hand-used, finger-length sum and finger-length ratio) had significant contributions on the preference of thumb-index finger grasp type (p < 0.05) but the gender had not (p > 0.05). Subsequently, two mathematical equations were proposed for predicting the probability at which the precision-pinch and power-grasp were chosen for grasping an object. The probability at which the precision-pinch was chosen gradually decreased with the increase in the equivalent diameter of objects, but it is opposite for the power-grasp case. The shorter the finger-length sum, the more likely the participant was to select the power-grasp for grasping an object compared to the precision-pinch. The power-grasp was the most frequently chosen for the finger-length ratios of 1.0-1.25 and 1.75-2.0. Practitioner summary: This fruitful study gave explanation of the relationship between the object and human-factor characteristics and the preference of human thumb-index finger grasp type, which would be helpful to make intelligent grasping planning strategies for two-finger bionic mechanical hands.

Future technology on the flight deck: assessing the use of touchscreens in vibration environments

Use of touchscreens in the flight deck has been steadily increasing, however, their usability may be severely impacted when turbulent conditions arise. Most previous research focusses on using touchscreens in static conditions; therefore, this study assessed touchscreen use whilst undergoing turbulent representative motion, generated using a 6-axis motion simulator. Touchscreens were tested in centre, side and overhead positions, to investigate how turbulence affected: (1) error rate, movement times and accuracy, (2) arm fatigue and discomfort. Two touchscreen technologies were compared: a 15" infra-red and a 17.3" projected capacitive touchscreen with force sensing capability. The potential of the force sensing capability to minimise unintentional interactions was also investigated. Twenty-six participants undertook multi-direction tapping (ISO 9241; ISO 2010 ) and gesture tasks, under four vibration conditions (control, light chop, light turbulence and moderate turbulence). Error rate, movement time and workload increased and usability decreased significantly, with screen position and increasing turbulence level. Practitioner Summary: This study evaluated the use of infra-red and projected capacitive touchscreen technologies using multi-directional tapping and gesture tasks, whilst being subjected to different levels of turbulence representative motion. Performance degraded significantly with increasing turbulence level and touchscreen location. This has implications for future flight deck design.

Limiting disproportionate disaccommodation in design for human variability

In the design of artefacts, tasks and environments for human use, the body dimensions of the target population are a critical element in spatial optimisation of the design. This study examines how the choices designers make affect the ability of different user groups to safely and effectively interact with a designed artefact. Due to the variability in body size and shape across different demographic groups, heterogeneous user populations are unlikely to experience uniform levels of performance. The associated variability in the rate of unacceptable user conditions is referred to here as disproportionate disaccommodation. This is both an ethical and a performance concern that can partially be addressed through improved design practice. Three methods for incorporating the consideration of user demographics and the corresponding variability in body size and shape are presented. They are compared with a baseline strategy in terms of accommodation and cost.

To twist, roll, stroke or poke? A study of input devices for menu navigation in the cockpit

Modern interfaces within the aircraft cockpit integrate many flight management system (FMS) functions into a single system. The success of a user's interaction with an interface depends upon the optimisation between the input device, tasks and environment within which the system is used. In this study, four input devices were evaluated using a range of Human Factors methods, in order to assess aspects of usability including task interaction times, error rates, workload, subjective usability and physical discomfort. The performance of the four input devices was compared using a holistic approach and the findings showed that no single input device produced consistently high performance scores across all of the variables evaluated. The touch screen produced the highest number of 'best' scores; however, discomfort ratings for this device were high, suggesting that it is not an ideal solution as both physical and cognitive aspects of performance must be accounted for in design.

PRACTITIONER SUMMARY

This study evaluated four input devices for control of a screen-based flight management system. A holistic approach was used to evaluate both cognitive and physical performance. Performance varied across the dependent variables and between the devices; however, the touch screen produced the largest number of 'best' scores.

The influence of seat backrest angle on human performance during whole-body vibration

This study investigated the effects of reclined backrest angles on cognitive and psycho-motor tasks during exposure to vertical whole-body vibration. Twenty participants were each exposed to three test stimuli of vertical vibration: 2-8 Hz; 8-14 Hz and 14-20 Hz, plus a stationary control condition whilst seated on a vibration platform at five backrest angles: 0° (recumbent, supine) to 90° (upright). The vibration magnitude was 2.0 ms(-2) root-mean-square. The participants were seated at one of the backrest angles and exposed to each of the three vibration stimuli while performing a tracking and choice reaction time tasks; then they completed the NASA-TLX workload scales. Apart from 22.5° seat backrest angle for the tracking task, backrest angle did not adversely affect the performance during vibration. However, participants required increased effort to maintain performance during vibration relative to the stationary condition. These results suggest that undertaking tasks in an environment with vibration could increase workload and risk earlier onset of fatigue.

PRACTITIONER SUMMARY

Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This paper reports new experimental data systematically investigating the effect of backrest angle on human performance. It demonstrates how workload is elevated with whole-body vibration, without getting affected by backrest angle.

The manipulability: a new index for quantifying movement capacities of upper extremity

In this work, it is proposed to evaluate the upper-limb movements through a global index of performance borrowed from the field of robotics: the manipulability. For a given posture, this index quantifies the set of velocities that can be achieved at the wrist in all the Cartesian directions. The manipulability can be represented by an ellipsoid from which the volume and shape related parameters can be derived. During a reach to grasp movement, the ellipsoid obtained from experiment presented a flattened shape along the forearm longitudinal axis and an increased volume as the arm was extended. From this study, it is concluded that: (1) the ellipsoid volume reflects well the ability to generate speed at the wrist which is effectively maximal for an extended posture; (2) if maximal velocity is an important parameter it might be advisable to primarily move the hand perpendicularly to the forearm longitudinal axis.

PRACTITIONER SUMMARY

The interest of manipulability indices is that they evaluate globally a posture of the upper-limb in relation to a given task. This original parameter could help to design environments or devices in order that the adopted postures maximise one particular aspect of the performance, i.e. the velocity of the hand.