When placed in a particular way, the pieces create the illusion of a square, to the adult brain at least. The scientists wanted to find out when babies start to see the square too.
Babies start to see complex objects in the same way as adults at the age of seven months, according to new research.
Scientists at Birkbeck College, London, used a hi-tech hair net and a type of computer game to learn more about what is going on in a baby's brain.
The aim was to find out when infants gain the crucial ability to group together different features of an object to form the whole.
Visual illusion
To do this, the researchers used a visual illusion known as the Kanizsa Square. It involves a group of four shapes resembling the Pacman from the early computer game.
When placed in a particular way, the pieces create the illusion of a square, to the adult brain at least. The scientists wanted to find out when babies start to see the square too.
The special headpiece used in the research is called a geodesic sensor net. It fits over the head like a shower cap and is a safe and child-friendly way of monitoring electrical activity in the brain.
If the babies see the square, the net will pick up a burst of brain activity known as a gamma oscillation.
The researchers report in Science magazine that they found no sign of the brain signals in six-month-old babies, but did detect it in eight-month-olds, indicating that the crucial developmental process takes place around the seven month mark.
Development clues
Dr Gergely Csibra, the lead researcher in the team said: "Understanding how an infant brain develops is obviously fascinating and may have implications for the education and care of babies.
"This new work not only tells us that babies as young as eight months recognise complex objects in the same way an adult does, but also allows us to think of new studies into early infant development.
"The difference between six- and eight-month-old babies is also intriguing and may show that there is an important development in how the brain organises information from the outside world at that age."
The team has studied only healthy babies so far but hopes the research may provide clues as to why some babies are not developing normally.
"We're interesting in understanding normal development of children as well as how brain damage during development may affect our perception, awareness and action," said Dr Greg Davis, also on the research team.
"This could in principle be used to understand disorders of perception and attention that arise in development."