Why does a single red light in a row of green ones seem to last longer than the rest? This trick of the brain is called the oddball effect. To test it, set up a slideshow of 15 to 20 images that share a theme, like nature scenes or pets. Hide one "oddball" slide near the end that breaks the pattern. Each slide shows for the same amount of time. After the slideshow, ask each participant how long the oddball slide lasted. Most people will guess it stayed on screen longer than the matching slides, even though every slide had the same duration.