Thus, adding the cognitive load magnifies the difference in salience. The change in relative salience leads to a corresponding difference in attributions. So, you do a study in which you look at attributions to more and less salient actors under conditions of light cognitive load and heavy cognitive load. Your light load condition is a replication of one of the original studies, say the one in which one actor was sitting under a bright light while the other is not. Extent of dispositional attributions for salient and non-salient actors under light and heavy cognitive loads.
Larger numbers refer to greater dispositional attributions.
What you read above should be considered to be the beginning of how you might think about your experiment. Your own proposal will be much more detailed than this sketchy outline. Here is a more abstract description of what you should be doing. You are expecting that one of these conditions will produce different behavior on the part of your subjects than the other. By the time you've reached this point, you should have a study roughly mapped out in your mind.