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This technique of ink-blot psychological analysis was developed by Hermann Rorschach in 1918-1922. He used these and similar form detection tests as ways of prompting his subjects to make free mental associations and 'see' shapes and images in the ink blot patterns. These were then interpreted as direct projections of the subconscious mind. Rorschach died in 1922. Although his test enjoyed a resurgence of interest in the 1940s and 1950, it is no longer thought psychologically significant.

Many surrealist artists, notably Mirs, have used random or almost random patterns as springboards for creating pictures that feature landscapes and living subjects. This was first suggested as a technique by Leonardo da Vinci in 1500 in his Treatise on Painting.

In his Treatise Leonardo writes that he was inspired by looking at “a wall which is marked with all kinds of stains. If you have to invent a situation, you can see things in it that look like various landscapes. Through confused and vague things the spirit wakes to new inventions”. Recently, it has been shown how the human eye's responses to complicated scenes can be understood in terms of the fractal dimension of the pattern being viewed. This dimension lies between 1 and 2 for a pattern on a flat surface.

A simple smooth line has fractal dimension equal to 1 but a complicated jagged line that eventually fills a two-dimensional area will have dimension 2. In between there are patterns of growing complexity as the dimension grows in value. We are able to pick out faces, shapes, apparent canals on the surface of Mars, from fractal patterns that have a small enough dimension.

As the dimension rises the complexity of the pattern becomes overwhelming and we no longer 'see' coherent recognisable images any more. Investigations have shown that Rorschach's ink blots all had modest fractal dimensions close to 1.25, comfortably below the threshold where image recognition is lost because of complexity and not far from the value of approximately 1.3 where it appears that human interest is attracted most strongly - a happy medium between too much order and too much randomness.

If the ink blots had happened to have had much larger fractal dimension no one would probably have 'seen' any images in them at all.

Text by John Barrow.

H. Rorschach, 'Psychodiagnostics', Grune and Straton, NY, (1921).

R.E. Rogowitz and R.F. Voss, Proc. Conference on Human Vision, S.P.I.E. 1249, 387 (1990).

R. Taylor & B. Newell, 'Fractals: A resonance between art and Nature' (2000).