From CNN:
Internet users can give Web sites a thumbs up or thumbs down in less than the blink of an eye, according to a study by Canadian researchers.
In just a brief one-twentieth of a second — less than half the time it takes to blink — people make aesthetic judgments that influence the rest of their experience with an Internet site.
The study was published in the latest issue of the Behaviour and Information Technology journal. The author said the findings had powerful implications for the field of Web site design.