from msnbc:

Scientists unlock Zen garden’s secret
Analysis reveals a hidden tree among rocks

Sept. 25 ˜  For centuries, visitors to the renowned Ryoanji Temple garden in Kyoto, Japan, have been
entranced by the simple arrangement of rocks. The five sparse clusters on a rectangle of raked gravel are said to be pleasing to the eyes of the hundreds of thousands of tourists who visit the garden each year. Scientists now believe they have discovered its mysterious appeal.

       
“WE HAVE UNCOVERED the implicit structure of the Ryoanji garden’s visual ground and have shown that it includes an abstract, minimalist depiction of natural scenery,” said Gert Van Tonder of Kyoto University.
      
The researchers discovered that the empty space of the Zen Buddhist temple’s garden evokes a hidden image of a branching tree that is sensed by the unconscious mind.

 “We believe that the unconscious perception of this pattern contributes to the enigmatic appeal of the garden,” Van Tonder added.

He and his colleagues believe that whoever created the garden during the Muromachi era between 1333-1573 knew exactly what they were doing, and that the placement of the rocks was “not accidental.“
      
Through the centuries, various meanings have been read into the rock placement — one view holds that the rocks symbolize a tigress crossing the sea with her cubs, while another contends that the pattern represents the strokes of a Chinese character meaning “heart” or “mind.”
      
However, such interpretations don’t explain the attraction the garden holds even for the uninitiated, the researchers reported in Thursday’s issue of the journal Nature.

To look for deeper patterns, the scientists used a concept called medial-axis transformation, a scheme for analyzing shapes that is widely used in image processing and studies of visual perception.
    
To understand the concept of medial-axis transformation, imagine drawing the outline of a shape in a field of dry grass and then setting it alight: The medial axis is the set of points where the inwardly propagating fires meet, the researchers explained. It has been shown that humans have an unconscious visual sensitivity to the axial-symmetry skeletons of stimulus shapes.
      
The analysis revealed what appeared to be a tree with branches that separated the elements of the rock arrangement. A widening trunk leads to a point in the garden’s main hall that is considered the prime viewing spot — as well as to an alcove containing a Buddhist statue.
       
Random changes in the location of the five rock clusters would destroy the image, the researchers said.
      
They said abstract art may have an impact similar to that of the Ryoanji Temple’s garden, which has helped earn Kyoto’s monuments the status of a UNESCO World Heritage Site.
   
“There is a growing realization that scientific analysis can reveal unexpected structural features hidden in controversial abstract paintings,” Van Tonder and his colleagues observed.