Dynamic Contrast

The correspondence problems due to perceptual characteristics of a display are compounded when we go from a static to an animated graphic. Because of their dynamic character, educational animations introduce a further challenge to information extraction beyond those found with static graphics. Certain aspects of a display that changes over time have the potential to capture learner attention. If there is sufficient dynamic contrast between one or more items in the display and their surroundings, the effect can be very compelling in a perceptual sense. It seems that a fundamental level, our perceptual system is attuned to detect and follow such changes, irrespective of their importance in terms of the subject matter. As with static displays discussed above, items that are perceptually compelling (in this case because of their dynamic character) may not necessarily be of great thematic relevance to the given learning task. The big orange float in the accompanying animation is far more perceptible than the small gray air valve because of both its visuospatial characteristics, and its high level of dynamic contrast with the rest of the display.

The misleading effects of dynamic contrast are likely to be particularly problematic for learners who lack background knowledge in the content domain depicted in an animation. These learners can be largely in the thrall of the animation's raw perceptual effects and so tend to process the presented information in a bottom-up manner. For example, their attention within the display is likely to be directed to items that have conspicuous dynamic characteristics. As a result, there is a danger that they will attend to unimportant information merely because it is perceptually compelling. However, learners who already have considerable domain specific background knowledge are likely to be less influenced by perception alone. This is because their attention is also directed to a considerable extent by their knowledge of which aspects of the subject matter are of most relevance (irrespective of their perceptibility). As a result, their processing of information in the display has a more top-down character. In the pumping system animation example, the air valve would be noticed by those who are already familiar with pumps in general because their existing background knowledge would put them on the lookout for crucial (but visually insignificant) parts of the mechanism.

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