I did this by making 2 different articles for the same news story. The first simply had text content:
http://stephengreig.co.uk/xperia-part-one/
The second had text content plus pictures and a video:
http://stephengreig.co.uk/xperia-part-two/
The participants then completed 1 of 2 surveys (depending on which article they read) to indicate how they rated various aspects of the article they read.
I have made an infographic to show the results and conclusions of my 3rd artefact:
(Click to enlarge)
