"More attention is elicited by things that are not expected," said Wise, who was a doctoral student at Stanford when he conducted the research.

One implication for online media is that users might be more interested in content when it appears without warning, such as in the form of sudden bursts of motion and sound, or the much-disliked pop-ups, Wise said.

For the study, Reeves and Wise showed a series of images to 22 undergraduates. The pictures included photos of people having a good time--at the top of a roller coaster, for instance--as well as images likely to elicit unpleasant feelings--such as an empty cemetery.

The researchers then compared reactions of students who initiated the photos by pressing a play button with those who had no control over the presentation of the images. Students had a greater physiological reaction--as measured by heart rate deceleration--to pictures that were not user-initiated. Reeves and Wise found that students also rated the positive pictures more appealing when they were not user-initiated.

The study is slated for publication in an upcoming issue of Media Psychology.

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