The line-of-sight angle (LOSA) was investigated for a simple tracking task. The distance from the eyes of the subject to the image was varied through the use of optical lenses. The subject was seated in a chair with 5 different back angles: 90 degrees, 111.6 degrees, 125 degrees, 158.5 degrees, and 177.1 degrees. No significant difference in the selection of LOSA was found between image distances of .5 meters, 1 meter, 2 meters, and infinity. The subjects' selection of LOSA was affected by the change in seat inclination angles. / Master of Science

Despite extensive research into the concept of mental fatigue there is as yet no “gold standard” definition or measurement technique available. Because of this a large amount of fatigue-related errors are still seen in the workplace. The complexity of the problem lies with the inability to directly measure mental processes as well as the various endogenous and exogenous factors that interact to produce the experienced fatigue. Fatigue has been divided into sleep-related and task-related fatigue; however the task-related aspect is evident both during normal waking hours as well as during periods of sleep deprivation, therefore this aspect is considered important in the understanding of fatigue in general. The concept of task-related fatigue has further been divided into active and passive fatigue states; however differentiation between the two requires careful consideration. Various physiological measures have been employed in an attempt to gain a better understanding of the mechanisms involved in the generation of fatigue, however often studies have produced dissociating results. The current study considered the task-related fatigue elicited by a tracking task requiring sustained attention, in order to evaluate the usefulness of various cardiovascular and oculomotor measures as indicators of fatigue. A secondary aim was to determine whether the behavioural and physiological parameter responses could be used to infer the type of fatigue incurred (i.e. an active versus passive fatigue state) as well as the energetical mechanisms involved during task performance. A simple driving simulator task was used as the main tracking task, requiring constant attention and concentration. This task was performed for approximately two hours. Three experimental groups (consisting of 14 subjects each) were used: a control group that performed the tracking task only, a group that performed a five minute auditory memory span task concurrently with the driving task after every 20 minutes of pure driving, and a group that performed a visual choice reaction task for five minutes following every 20 minute driving period. The secondary tasks were employed in order to evaluate the extent of resource allocation as well as arousal level. Performance measures included various driving performance parameters, as well as secondary task performance. Physiological measures included heart rate frequency (HR) and various time- and frequency-domain heart rate variability (HRV)parameters, pupil dilation, blink frequency and duration, fixations, and saccadic parameters as well as critical flicker fusion frequency (CFFF). The Borg CR-10 scale was used to evaluate subjective fatigue during the task, and the NASA-TLX was completed following the task. A decline in driving performance over time was supplemented by measures such as HR, HRV and pupil dilation indicating an increase in parasympathetic activity (or a reduction in arousal). An increase in blink frequency was considered as a sign of withdrawal of attentional resources over time. Longer and faster saccades were also evident over time, coupled with shorter fixations. With regards to the secondary task influence, the choice RT task did not affect any behavioural or physiological parameters, thereby contesting the active fatigue theory of resource depletion, as well as implying that the increase in demand for the same resources used by the primary task was insufficient to affect the state of the subjects. The increased load elicited by the memory span task improved driving performance and increased measures of HR, HRV, pupil dilation and blink frequency. Some of these measures produced opposite effects to what was expected; an attempt to explain the dissociation of the various physiological parameters was expressed in terms of arousal, effort and resource theories. Overall, the results indicate that the fatigue and/or reduced arousal accompanying a monotonous sustained attention task can, to some degree, be alleviated through intermittent performance of a secondary task engaging mental resources other than the ones used for the primary task. The degree to which such a task is beneficial, however, requires careful consideration as while an immediate increase in arousal and primary task performance is noted, the impact of the task on general attentional resources may be detrimental in the case of reacting should an emergency situation occur.

Occupational injuries and illnesses remain to be a heavy burden on workers and employees in industrial developing and industrially developed societies, and health and safety in workplaces continues to be an important issue for ergonomists. Steps are being taken to stimulate health and safety agendas and to discover ways in which health and safety in industries can be improved. The main responsibility of employers is to provide employees with information, instructions and training that they required to carry out their work tasks in a healthy, practical and safe manner. The role of education as a countermeasure to occupational injury and illness is being re-examined by health and safety practitioners and safety training is being considered as a vital part of accident prevention strategies. Effective training programmes should guarantee that workers possess the skills they require to complete their tasks in a safe and healthy manner. Very little is known about the type and quality of training workers undergo and how that training affects the safety outcomes of companies. There has been an attempt over the past 20 years to increase the research on safety communications and a great deal of this research has been focused on safety warnings; with the greatest attention been placed on the components of safety signs, such as colours, size, shapes and icons. The effects of these components on comprehension with relation to age and education have not received the same amount of attention. The impact of familiarity on safety warnings with respect to age and education has also received very little attention; despite the knowledge that familiarity has been shown to increase the noticing of warnings and the comprehension of safety information. Despite the increase in the research on safety communication, the literature and research in South Africa is scarce. Studies present in South Africa do not encompass the comprehension of safety signs or the ability of individuals with different age and education levels to learn the information included in the signs. Due to the multi-linguistic nature of South Africa and the fact that South Africa is an Industrially Developing Country (IDC) with high levels of illiteracy, issues such as the comprehension of safety information must be addressed. Therefore, the objectives of this study were to investigate the effects of safety sign attributes on learning and familiarity, in subjects that differed in age and education levels. These effects were investigated through measuring the reaction and response times of the different subject groups, as well as the number of components in the safety signs that were recalled correctly. The combined results of these responses were used as a measure for familiarity. A set of signs was designed for the study by the researcher using three different colours, three different shapes, three different icons and text. Certain variables were omitted from some signs to create the test pool and the eight conditions that were tested in a laboratory setting. Each condition contained different components of the designed signs and 60 subjects were used to test these conditions. The subjects were placed in groups according to their age and level of education. Subjects were required to learn a set of 64 signs, either “With Occlusion” or “Without Occlusion”, and asked to recall the meanings of the components in the signs. Reaction time, response time and error rate were measured from the responses. The results showed that the conditions resulted in different reaction times, response times and error rates for all subjects. The signs containing a combination of shapes and text resulted in the best performance. Age and education were found to have a significant effect on various performance criteria as did the method in which the signs were displayed (Occlusion and No Occlusion). The increased repetitions and sessions elicited lower reaction times, response times and error rates. The conclusions drawn from this study suggest that different attributes be considered carefully when subjects are expected to learn and recall information in safety signs. The results also highlighted the need to increase the exposure of individuals to safety signs in order to increase familiarity and ultimately improve the recall and comprehension of the attributes.

In 2008, there were more than 5,200 workplace fatalities in the United States (BLS, 2010b). During the same time period, U.S. employees missed almost 1.1 million days from work (BLS, 2010c). Accidents are unexpected outcomes that result not only from individuals' behaviors, but from contextual factors (Krause, 1997; Reason, 1990). Therefore, unsafe behaviors have to be interpreted according to a combination of what is occurring in the environment and what the individual is doing in that environment. The present study sought to create a more comprehensive model of safety by means of macroergonomics. Macroergonomics utilizes sociotechnical systems theory to posit that a work system is composed of a personnel subsystem (i.e., ways individuals perform tasks), a technological subsystem (i.e., tasks to be performed), and external factors (Hendrick, 2002a). Perceived control over work hours, an aspect of the technological subsystem, was examined as an antecedent of work-family conflict. Supervisor instrumental support, an aspect of the personnel subsystem, was examined as a moderator of the relationships between perceived control over work hours and work-family conflict. Supervisors have an imperative role in employees' perception of control over their work hours (Kelly & Moen, 2007). Supervisor instrumental support was also hypothesized to moderate the relationships between work-family conflict and safety performance. Supervisors who support their employees in their work-family matters exceed mandatory requirements set forth to protect workers' safety and health (Mearns, Hope, Ford, & Tetrick, 2010). A majority of the 360 participants in the present study were grocery store employees who worked in the front end of the store as cashiers. Job tenure in this particular grocery store chain was an average of 7 years (SD = 5.96) and the average number of hours worked per week was 31 (SD = 8.55). The employees were an average age of 38 years old (SD = 15.25). Two hundred and sixty-two (73%) of the participants were female, 330 (92%) were White, 196 (55%) employees were married or living as married, 146 (41%) employees identified themselves as parents with children living at home, and 58 (16%) employees provided elder care. The data were analyzed using a moderated mediation model. An employee's perceived control over his/her work hours was negatively associated with work-to-family and family-to-work conflict. Work-to-family conflict was not significantly associated with either safety compliance or participation. In contrast, family-to-work conflict was significantly associated with both safety compliance and participation. These findings replicate Cullen and Hammer's (2007) findings that family-to-work conflict, but not work-to-family conflict, is negatively associated with safety compliance and participation. The replication of these significant findings gives support to macroergonomics' assertion that external forces (i.e., family) can affect the safety of employees. All of the meditating and moderating relationships proposed in this dissertation were not significant. I conducted post hoc analyses to determine other possible significant paths in the model examined. The FSSB dimension of supervisor instrumental support was found to positively affect both safety compliance and participation. Supervisor instrumental support was also found to directly affect work-to-family conflict. Overall FSSB and its subdimensions demonstrated similar patterns in the hypothesized relationships and in additional relationships examined. Numerous implications can be recognized from this dissertation. First, interdisciplinary approaches to safety research are emerging and important in the pursuit of safer work environments. Macroergonomics and I/O psychology have commonalities that lend themselves to a good partnership where researchers can learn from each other and collaborate to advance the study of safety. Second, organizations need to focus on the stressors their employees experience as part of their safety programs, and numerous studies, including this dissertation, have found that family-to-work conflict impacts safety compliance and participation. Future safety research may incorporate macroergonomics, which emphasizes that focusing on one adverse aspect of the system may not be enough to create valuable change if there are other adverse factors still creating demands elsewhere in the system. This will allow for a more comprehensive model that ensures certain aspects of the system are not neglected, which can reduce effectiveness of constructs used to create positive changes.