The shortcuts that I took in the name of time and complexity are mentioned in italics.
People form hierarchical structures for remembering shapes.
These simple shapes, in turn, can be represented as collections of lines. The position and angle of these lines must be remembered in order to understand the simple shapes. People often break up continuous stimuli into arbitrary discrete categories. The first category consisted of lines with slopes from 0 to 45 degrees, while the second consisted of slopes from 45 to 90 degrees. In a similar experiment by Huttenlocher et al.