Stimulus salience refers to bottom-up factors that determine and attract attention to elements or objects in a scene. The term salient, itself, means to be noticeable or stand out. Salient features are physical properties and can include things like color, movement, and pitch. Attentional capture is when attention due to stimulus salience causes an involuntary shift of attention. For example, advertisers may use attentional capture as a marketing strategy on websites by placing flashing ads for a product on the side of the news article you are attempting to read. It is difficult to attend to plain news text when there is a flashing advertisement in your field of vision.
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Simola, J., Kuisma, J., Öörni, A., Uusitalo, L., & Hyönä, J. (2011). The impact of salient advertisements on reading and attention on web pages. Journal of Experimental Psychology: Applied, 17(2), 174