Structural equation modeling approach for the analysis of ergonomics risk factors and occupational injuries among building construction workers in Bahir Dar City-Ethiopia.

Ergonomic risk factors are a prominent cause of fatality and severe injuries in building constructions. Hence, this study applies a Structural Equation Modeling (SEM) approach to analyze ergonomics risk factors and occupational injuries among building construction workers in Bahir Dar City, Ethiopia. The results indicate significant relationships between ergonomics risk factors and the prevalence of occupational injuries. This study's findings contribute to the understanding of occupational health and safety in the construction industry, highlighting the need for targeted interventions. A cross-sectional study has been carried out, where data was collected through direct observations and standardized pretested questionnaires. The study recruited 220 participants in the construction industry. The data was analyzed using AMOS to study the direct and indirect effects of the identified variable. SEM has shown that the magnitude of the prevalence of occupational injury was 65.2 %. The results also revealed that the mostly affected body parts were lower arm, lower leg, hand, toe, and knee. Carpenter & roofers, plasterer and daily labors & other helpers were highly injury subjected occupations in respective order. The six leading significant risk factors were, do not tie belt at scaffold, falling stairways & ladders, exposure hazardous substances, tools & machinery, electricity (electric power accidents), repetitive tasks, the layout didn't consider health & safety aspects in the site, and do not provide safety orientation for new workers engaging the job. Employees are mostly affected on their lower body parts which needs more focus to prevent it, especially carpenter & roofers, plasterer and daily labors. Also the findings show that 50 % of respondents agree that the higher priority for safety and health management practices should be given to finishing part of the construction followed by excavation and earth work, masonry, and electrical installations. Therefore, it is recommended that the contractors must focus more on the finishing phase.

The accuracy of the frontal extent in stereoscopic environments: A comparison of direct selection and virtual cursor techniques.

This experiment investigated the accuracy of distance judgment and perception of the frontal extent in a stereoscopic environment. Eight virtual targets were projected in a circular arrangement with two center-to-center target distances (18 cm and 36 cm) and three target sizes (0.6 cm, 1.5 cm, and 3.7 cm). Fourteen participants judged the positions of virtual targets presented at a distance of 90 cm from them by employing two different interaction techniques: the direct selection technique and the virtual cursor technique. The results showed overall higher accuracy with the virtual cursor technique than with the direct selection technique. It was also found that the target size significantly affected the frontal extent accuracy. In addition, significant interactions between technique and center-to-center target distance were observed. The direct selection technique was more accurate at the 18 cm center-to-center target distance along the horizontal (x) and vertical (y) axes, while the virtual cursor technique was more accurate for the 36 cm center-to-center target distance along the y axis. During the direct selection, estimations tended to converge to the center of the virtual space; however, this convergence was not observed in the virtual cursor condition. The accuracy of pointing estimations suffered on the left side of participants. These findings could provide direction for virtual reality developers in selecting proper interaction techniques and appropriately positioning virtual targets in stereoscopic environments.

Impact of parallax and interpupillary distance on size judgment performances of virtual objects in stereoscopic displays.

Effective interactions in both real and stereoscopic environments require accurate perceptions of size and position. This study investigated the effects of parallax and interpupillary distance (IPD) on size perception of virtual objects in widescreen stereoscopic environments. Twelve participants viewed virtual spherical targets displayed at seven different depth positions, based on seven parallax levels. A perceptual matching task using five circular plates of different sizes was used to report the size judgment. The results indicated that the virtual objects were perceived as larger and smaller than the corresponding theoretical sizes, respectively, in negative and positive parallaxes. Similarly, the estimates from participants with small IPDs were greater than the predicted estimates. The findings of this study are used to explain human factor issues such as the phenomenon of inaccurate depth judgments in virtual environments, where compression is widely reported, especially at farther egocentric distances. Furthermore, a multiple regression model was developed to describe how the size was affected by parallax and IPD. Practitioner Summary: The study investigates the effects of parallax and interpupillary distance on size perception of virtual targets in a stereoscopic environment. Virtual objects were perceived as larger in negative and smaller in positive parallax. Also, size estimates were greater than the theoretical sizes for participants with smaller IPD. A multiple-regression model explains the impact of parallax and measured IPD. Abbreviations IPD interpupillary distance VR virtual eality HMD head mounted-displays 2AFC two-alternative forced choice IOD interocular distance PD pupillary distance ANOVA analysis of variance.

Kinematic analysis of direct pointing in projection-based stereoscopic environments.

This work investigated the effects of visual information, parallax, and target positions on movement performances in projection-based stereoscopic displays (PSDs). Fifteen (26.5 ±â€¯3.83 years) self-declared right-handed individuals, with normal or corrected to normal visual acuity, completed pointing tasks in stereoscopic and real environments (RE). Three-dimensional spatial data, recorded by a motion system composed of six infrared cameras, was used to compute kinematics of reaching a real/virtual object at a combination of three parallax and nine frontal planar positions. The results indicated that movement in the PSD was slower and needed longer confirmation time than that in the RE. This might be because of the difficulty and misperception of distance associated with PSD. The motions were initiated faster but took longer to complete in vision-based conditions. The overall kinematic parameters were better as targets were presented closer to participants and around the center of displays. However, during pointing at a target that was continuously visible or presented briefly and disappeared, participants applied similar movement strategies to approach the visual objects. The comparable kinematics and movement behaviors in stereoscopic displays encourage the use of direct pointing that would enhance reaching and grasping tasks - which are important in applications such as rehabilitation, surgical training, and other programs that employ upper limbs. In addition, the more natural interaction by direct pointing minimizes the effort of learning new skills to use other devices.