Yep, it has been scientifically proven: the accuracy of people in describing charts with 'chart junk' is no worse than for plain charts, and the recall after a 2-3 week gap was actually significantly better. In addition, people overwhelmingly preferred 'chart junk' diagrams for reading and remembering over plain charts. In all, the researchers conclude that if memorability is important, elaborate visual imagery has the potential to help fix a chart in a viewer's memory.
I am sure Tufte is not going to like this...
The findings have been described in the paper "Useful Junk? The Effects of Visual Embellishment on Comprehension and Memorability of Charts" [hci.usask.ca]. About 60 participants were asked to look to 14 different information graphs created by Nigel Holmes (see also his book Designer's Guide to Creating Charts and Diagrams) and their equivalent, custom-made 'plain' versions. The 'chart junk' charts were all designed to attract the eye, engage the reader, and sometimes provide a particular value message over and above the presentation of the data itself. In fact, the researchers deliberately chose the most extreme type of visual embellishment that they could: namely, the full cartoon imagery used by Holmes.
The participants then answered questions about each chart's topic and details, such as 'What is the chart is about?', 'What are the displayed categories and values?', 'What is the basic trend of the graph?' and 'Is the author trying to communicate some message through the chart?'. Half of the participants then answered the same questions again, after about 5 minutes of playing a game, and half after around 12 days. The experimenters then recorded any correctly recalled charts (e.g. 'I remember one about the price of diamonds').
"The illusion of objectivity (as used in minimalist charts) and the use of evocative imagery (as used in Holmes charts) are perhaps just different approaches that work at different ends of the rhetorical spectrum. Designers and readers should remember that a Holmes chart is not necessarily more biased than its plain counterpart - but it may be more effective at conveying the value message that is part of the overall argument."
Via Eager Eyes.