Pattern recognition is dependent upon the culture of the child.
The point here is that Pattern Recognition is highly influenced by culture. It is very dependent upon experience and learning. Because of this you would not expect children from the Amazon or Borneo Jungles perform tasks like these until they were 8 or 9 years old, allthough they could recognize many other things we couldn't much earlier.
In our society, children are born on rectangular tables in square (or round) rooms.
They leave through rectangular doors to live in rectangular cribs. They eat off round plates, live on city blocks in houses with triangular roofs. These forms are very much a part of their world. Why wouldn't they learn to recognize them earlier.
Even the symbolic letters, which will be such an important part of their future, are nothing but intricate combinations of bits and pieces of crosses, circles, squares and triangles.