Abstract
As more designers allow users to customize the look and feel of interfaces, users will be required to recognize the implications of their choices on their future performance, comfort, and enjoyment. Understanding the limits of people’s predictive capabilities may be an important component in identifying why people choose one product over another based on ease of use or why people have difficulties identifying tasks that can be performed together. The purpose of this study is to further explore users’ biases for utilizing the amount of white space in the stimulus as a predictor of task difficulty, to validate discrepancies between predicted task difficulty and performance outcomes found in previous research and the human factors literature, and to identify task-specific strategies that are used to anticipate task difficulty. The study uses the NASA Task Load Index (NASA-TLX) in prospective difficulty judgments for these three types of tasks: 1) a stimulus-response compatibility task, 2) a target acquisition task and 3) a perceptual search task. In general, participants predicted lower task demand for designs with more intervening white space. For the visual search task, these estimates of demand were consistent with participants’ actual performance reaction times. However, for the stove design and Fitts’ tasks participants rated tasks that were likely to result in more errors as less challenging suggesting that the type of task is an important factor in participants’ abilities to predict relative task difficulty.
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