I can remember reading that computer intelligence is heading (or maybe the most powerful ones already have) towards the Natural intelligence of a four-year-old child. But how are the two kinds of intelligence compared?
You are probably referring to ConceptNet (created by the Massachusetts Institute of Technology under its Artificial Intelligence program).
It's a software system / semantic network containing lots of things computers should know about the world, especially when understanding text written by people.
Researchers from the University of Illinois (research team led by Stellan Ohlsson) did a study on the ConceptNet 4 version of the AI and they discovered that its IQ level is the same as that of a 4-year-old child (somewhat... see below).
The chosen IQ test is known as the Wechsler Preschool and Primary Scale of Intelligence (third edition, WPPSI-III). It's commonly used in schools across the United States and is designed to measure the level of intelligence in five key categories and consists of 14 subtests (picture memory, similarities, object assembly, picture naming...).
The test questions (e.g. "Why do we shake hands?") were translated into ConceptNet 4 inputs using a combination of the simple natural language processing tools that come with ConceptNet together with short Python programs that we wrote. The question answering used a version of ConceptNet based on spectral methods.
The ConceptNet system scored a WPPSI-III VIQ that is average for a four-year-old child, but below average for 5 to 7 year-olds
The large variations among subtests and ordinary common sense strongly suggest that the WPPSI-III VIQ results do not show that "ConceptNet has the verbal abilities a four-year-old."
Rather, children's IQ tests offer one objective metric for the evaluation and comparison of AI systems
(From Measuring an Artificial Intelligence System's Performance on a Verbal IQ Te st For Young Children - Stellan Ohlsson, Robert H. Sloan, György Turán, Aaron Urasky)