Hunting for the source, I posted a query on the Infodesign Cafe, which put me in touch with Michael Molenda of Indiana University, who was on a similar hunt. He eventually published a short paper with his findings (you can find it here). He traced it to Edgar Dale's 'cone of experience', published in the late 40s. Dale used a schematic diagram (below) to illustrate his view that increasing richness of experience would lead to greater learning.
Somewhere along the way, someone has added the figures, and these have been repeated endlessly ever since, deeply embedded in the teacher training curriculum. Tony Betrus and Al Januszewski of the State University of New York have published a collection of bad cones.
It seems unlikely that a 'quotation' like this would have survived for so long unless there is some truth in it - in other words, it chimes with people's experience in some way, just as a saying such as 'a picture is worth a thousand words' does. Perhaps this is just a modern version of a proverb – it's just that these days we need statistics.
The Education department at Cisco Systems have looked into the evidence that actually does exist, and produced a useful metareview .