M. Suwa, and B. Tversky. Design studies, 18 (4):
385-403(1997)"sketches serve as a 'perceptual interface' through which one can discover non-visual functional relations underlying the visual features." p 401.
M. Johansson, and M. Arvola. Proceedings of the 21st British HCI Group Annual Conference on People and Computers: HCI...but not as we know it - Volume 1, page 177--184. Swinton, UK, UK, British Computer Society, (2007)