Visual demand in manual task performance - Towards a virtual evaluation

Visual information is crucial for carrying out motor activities. However, knowledgeabout the effects of visual demand on the performance of manual tasks is not welldocumented. Visual determinants must be identified in order to be used in visualisationand simulation tools (e.g. computer manikins) as well as considered during ergonomicevaluations of workplaces and products. This thesis developed a visual demand modelin which the characteristics of the task, the operator and the environment have aninfluence on the visual demand related to the performance of a task and result in aspecific behaviour. This model has been used for the design of the five appendedpapers. The overall aim was to identify the determinants of visual demand in manualtask performance. Two scenarios were investigated: car driving and manual assemblywork. Paper I was an inductive study where the visual demand model was used toexamine how the task, environment and operator characteristics influence the visualdemand involved in assembly work. Paper II dealt with the effect of the taskcharacteristic, e.g. precision, as determinants of visual demand on working posture andmovement paths in a laboratory study. Paper III investigated the influence of the taskand the environmental characteristics, i.e. time pressure, real motorway and interior cardesign as determinants of the visual demand on drivers visual behaviour and primarytask performance. Paper IV examined the influence of the environment, the task andoperator characteristics, i.e. time pressure, real motorway, interior car design, driversage and skill as determinants of the visual demand on a drivers visual behaviour andprimary task performance. Paper V studied how visual demand can be predicted usinga visualisation tool such as a computer manikin. Numerous methods have been used tohighlight the relation between visual demand and the behaviour produced by operators:an eye tracking system, motion tracking, observations, and interviews. Designing thestudies with high level of validity was a priority and the majority of the studied focusedon the subjects in their own environment, e.g. secondary task performance whilstdriving in motorway traffic and assembly work in an industrial plant. The followingvisual determinants of manual task performance were identified: degree of precisiondegree required in manual assembly, fine-tuned activity in manual assembly, location ofin-car controls, drivers age and experience. Vision analysis carried out with computermanikin software does not really facilitate detection and consideration of visualdemand, as it does not provide a method for analysing the visual determinants for aspecific task. Suggestions concerning the design of the vision module and a method forhow to use it are proposed. A further step will be to take into account psychomotortasks and mental load into account in order to evaluate visual demand, i.e. study theinfluence of cognition on motor activity as well as its effect on task and workplacedesign