The WAIS test (Wechsler Adult Intelligence Scale) measures perception and memory, and determines the ability to make a distinction between essential and non-essential details. The test person has to identify the missing component in images of a broken comb, a face in profile without a nose, a vase of flowers where the stems have been erased, a table with three legs, and so on. The ‘incomplete’ drawings can be completed through logic, but they also appeal to the imagination...