The volunteers then had to rate the websites in terms of their aesthetic appeal.
The researchers found that the speedily formed conclusions closely tallied with opinions of the websites that had been made after much longer periods of examination.
Gitte Lindgaard of Carleton University in Ottawa, Canada, and lead researcher of the paper expressed her surprise at the results.
"My colleagues believed it would be impossible to really see anything in less than 500 milliseconds," she told the website of the Nature journal, which reported the research.
The judgements were being formed almost as quickly as the eye can take in information.
Lasting impressions
The researchers also believe that these quickly formed first impressions last because of what is known to psychologists as the "halo effect".
If people believe a website looks good, then this positive quality will spread to other areas, such as the website's content.
Since people like to be right, they will continue to use the website that made a good first impression, as this will further confirm that their initial decision was a good one.
As websites increasingly jostle for business, Dr Lindgaard added that companies should take note.
"Unless the first impression is favourable, visitors will be out of your site before they even know that you might be offering more than your competitors," she warned.
