The test participant in the top gaze plot fixated a few times within the big empty color block before the content downloaded, then spent the remaining time looking at the rest of the page. This user never looked at the big promotional space after it had rendered. The second user (bottom gaze plot) happened to be looking away from the screen during the 8 seconds when the promotional content downloaded. Thus, the first time he looked at the page he saw it as intended, complete with the entire promo. (via Website Response Times (Jakob Nielsen’s Alertbox))
