Searchers typically adopt random-appearing scan patterns when inspecting homogeneous surfaces, presumably because the absence of critical features (pattern irregularities and edges) precludes development of systematic and efficient scanning strategies. The present research attempted to determine whether available modeling tools were appropriate for developing optimal scanning aids for homogeneous displays. Three experiments were conducted to test two critical assumptions that underlie existing models of visual scanning. The first experiment tested the assumption that a static visual lobe, obtained in a task in which the eyes remained fixated at a single location, was the same as a dynamic visual lobe, obtained in a task in which the eyes moved before and after the display presentation. The dynamic lobe was slightly smaller, but no different in shape than the static lobe. The second experiment tested the Independence Model, according to which information acquired in a given fixation cannot be combined with information acquired in a subsequent fixation. Each trial consisted of two tachisoscopic presentations of overlapping portions of the same homogeneous field, controlling target presence on each fixation. Detection performance was compared between conditions on which the target was present on one or two display presentations. The results were consistent with Independence Model. In the third experiment, the Independence Model was tested in a multiple-fixation continuous dynamic scanning task. The subjects' unexpected inability to fixate accurately at specified locations precluded a direct test of the Independence Model, however a Static Independence Model was constructed using a single-fixation continuous lobe model to predict target-detection at each fixation within the dynamic scanning task. Dynamic scanning performance differed systematically from predictions of the Static Independence Model, reflecting an apparent shift in allocation of attentional resources to the center and away from the top and bottom of the display. The attentional shift was embodied in a Dynamic Independence Model which better predicted dynamic scanning performance. Although there was considerable individual variation, the results suggest the requirement to fixate at specified locations may have interfered with target-detection performance at certain target locations. Implications for the development of optimal scanning aids for homogeneous display were discussed.

Enhancing our understanding of the relation that exists between productivity and musculoskeletal disorders is essential to the successful design of person-machine systems for safe and comfortable human use. This research comprises two experiments to study the trade-offs between productivity and shoulder musculoskeletal discomfort in a repetitive task performed at different repetition rates. The objective of the first experiment was to determine from velocity profiles which theoretical movement time model adequately predicted the times for a mail sorting task. Based on the percentage of the total variance explained by the regression models, it was concluded that the optimized initial impulse model (Meyer et al., 1988) using one sub-movement provided the best prediction for the movement times associated with the repetitive task. In addition, the effects of different duty cycles upon movement time were studied. It was found that a decrease in repetition rate produced an increase in mean movement time. In the second experiment a regression model that related biodemographic, anthropometric, workplace and kinematic factors to shoulder musculoskeletal discomfort was developed. Also, the effects of these ergonomic factors upon shoulder musculoskeletal discomfort were studied. It was found that the kinematic variables played the most important role in increasing the percentage of the total variance explained by the regression model. Results showed a significant linear relationship between weight and shoulder musculoskeletal discomfort. High weight values were associated with higher discomfort scores. To diminish the discomfort values it was recommended the improvement of the worker-machine system by designing adjustable equipment within the capabilities of the people to optimize their performance at work. The associations between (1) the number of repetitions, (2) movement time and (3) shoulder musculoskeletal discomfort were studied. It was determined that, if the anthropometry of the working population is considered, an adjustment point for the movement time could be identified (which determines the productivity level of the workers) and a better design of a repetitive task could be achieved. Finally regarding the discomfort-productivity trade-off evaluation, it was found that higher SMD scores were associated with longer movement time values regardless of the experimental population percentile.

Thesis (Ph.D.) --University of Adelaide, Medical School, Dept. of Public Health, 2005. / Title from t.p. of source document (viewed April 2, 2007). "December 2004" Bibliography: leaves 337-352. Also available in print version.

Work-related musculoskeletal disorders (WRMSD), specifically physical and muscular discomfort in the upper arm, lower arm, thigh, lower leg, wrist, shoulders, back, or neck, are among the most frequently reported workplace injuries in the United States. The dearth of knowledge about the types of workloads that may contribute to the development of WRMSD was the impetus of this research. The study aimed to identify antecedents of WRMSD among warehouse workers in order to reduce WRMSDs and increase productivity as expressed in a systems perspective on industrial health. The research questions examined the prevalence of specific WRMSDs, the relationship of high-risk tasks of warehouse personnel with WRMSD incidence, and the relationship of job category and workload with WRMSD incidence. The sample included 82 warehouse workers, stockroom clerks, and forklift drivers. MANOVA was used as the data analysis technique. The results showed that WRMSD was the most prevalent in the upper back, lower back, knees, and lower legs. Various high-risk tasks were linked to WRMSD incidence including repeatedly bending to lift objects was associated with discomfort in the lower back, shoulders, and lower legs. Furthermore, the use of pallets led to reduced discomfort and work interference in the hips and buttocks, upper arms, and knees. Proper lifting form may reduce WRMSD in the shoulders, forearms, lower back, and wrists in particular. The social change implications of this study stem from the notion that increasing the employers' WRMSD prevention awareness will lead to an increase in safety attentiveness and decrease workers' injuries.