Differential magnification methods and interface factors for improving visual inspection performance


Student thesis: Doctoral Thesis

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  • Choi Hung LEE


Awarding Institution
Award date16 Feb 2009


Magnification is a commonly used means of improving task visibility in quality inspection tasks. In this study, two novel differential magnification methods, namely differential linear and differential nonlinear magnifications, were developed. With differential magnification, a lower scaling is applied in the high resolution central fixation area while the more peripheral objects are scaled with a higher magnification power. The idea is well supported by the variable visual acuity nature of human vision across fovea and periphery and the effectiveness of linear and nonlinear magnification on target detection performance. The differential magnifications which match the psychophysical properties of human eyes are expected to improve the interface design of video magnifiers and ultimately the visual inspection performance. In order to investigate the effectiveness of differential magnification methods, versatile computer software was developed to simulate the visual inspection task and to produce the desired magnification effects. A series of experiments were then conducted, focusing on the learning effect and the auditory cueing effect in using the two differential magnifying lenses. For the examination of learning effects with the novel magnification methods, a learning programme was designed with performance and process feedback given to learners in order to facilitate their learning process. Exponential learning curves were established and greater improvement from repeated practice was noted for the two novel differential magnification methods than the traditional linear magnification method. Based on the learning curve models, the traditional linear magnification method was outperformed by the differential linear and nonlinear methods after four and ten repeated practice sessions, respectively. Given the favorable influence of sensory cueing on attention orientation, the effectiveness of auditory cues for directing subjects’ attention from the peripheral to the neglected foveal areas on visual inspection performance was also examined in this study. The results showed positive cueing effects on attention orientation and the auditory cues proved to be useful for improving inspection performance with the two novel differential magnification methods. Detailed discussion on the effectiveness of the auditory cues was made with reference to the Wickens’ multiple resources model and Wolfe’s Guided Search model. In addition to the novel design and testing of differential magnification methods, other probable magnification interface factors including magnification mode, location cues, magnifier shape, magnification power, and target difficulty were examined together with subject factors including visual acuity and visual lobe area. It was found that considerations of screen space design for displaying magnified window and original product image were important concerns for video magnifiers. And, the results suggested that the use of location cues was particularly useful when the visual task demanded a high level of search memory and the subjects employed an unsystematic search strategy. To summarize, the effectiveness of the differential magnification methods was found greatly improved with repeated practices and the aid of auditory cues. Second, the study furnishes specific knowledge of magnification interface factors for improving visual inspection performance. The findings of this research have useful implications for the interface design of video magnifiers, and provide vital information for establishing more optimal inspection system designs which will be particularly beneficial to industrial inspection tasks.

    Research areas

  • Optical methods, Quality control, Engineering inspection