Sometimes seeing means deceiving before believing, depending on your age. Children and adults size up objects differently, giving youngsters protection against a visual illusion that bedevils their elders, a new study suggests.
This unusual triumph of kids over grown-ups suggests that the brain’s capacity to consider the context of visual scenes, and not just focus on parts of scenes, develops slowly, say psychologist Martin Doherty of the University of Stirling in Scotland and his colleagues. Even at age 10, children lack adults’ attunement to visual context, Doherty’s team concludes in a paper published online November 12 in Developmental Science.
As a result, visual context can be experimentally manipulated to distort adults’ perception of objects’ sizes. But Doherty’s group finds that children, especially those younger than 7, show little evidence of altered size perception on a task called the Ebbinghaus illusion.
“When visual context is misleading, adults literally see the world less accurately than they did as children,” Doherty says.
This pattern holds for Scottish children and adults in the new study as well as for Japanese children and adults who participated in other investigations conducted by Doherty’s team.
Some researchers argue that East Asians focus broadly on the context of what they see while Westerners focus narrowly on central figures. Doherty says the new findings instead indicate that adults in both Scotland and Japan can’t help but track visual context, although this tendency was stronger in the Japanese adults.
Other investigators have noted that children with autism don’t succumb to visual size illusions, consistent with the idea that autism involves an excessive focus on details. But visual context largely eludes all young children, not just those with autism, Doherty asserts.
Even if the new findings hold up, it’s still possible that further research will show that children with autism develop a susceptibility to size illusions more slowly than those without it, remarks psychologist Danielle Ropar of the University of Nottingham in England.
Psychologist Carl Granrud of the University of Northern Colorado in Greeley calls the new study convincing but “somewhat surprising.” Children exhibit sensitivity to visual context on some other visual tasks, he says, such as one in which two equal-sized horizontal lines are perceived as differing in length when flanked by diagonal lines.
Earlier research has yielded conflicting evidence that children fall prey to the Ebbinghaus illusion, partly because of weaknesses in study designs, Doherty says.
His team studied 151 children, ages 4 to 10, recruited from a Scottish primary school and nursery school. Another 24 volunteers, ages 18 to 25, were college students.
Participants viewed a series of images containing pairs of orange circles in which one circle was 2 percent to 18 percent larger than the other. An experimenter asked participants to point to the circle that “looked bigger.”
Control images showed only two orange circles. In other images, each orange circle was surrounded by gray circles intended either to hinder or aid accurate size perception.
Misleading images showed the smaller orange circle surrounded by even smaller gray circles to boost its apparent size. Large gray circles surrounding the larger orange circle were intended to shrink its apparent size.
In helpful images, large gray circles surrounded the smaller orange circle to make it appear smaller than it actually was. Small circles surrounded the larger orange circle to magnify its apparent size.
Four-year-olds correctly identified the larger circle in 79 percent of control images. That figure rose with age, reaching 95 percent in adults.
For 4- to 6-year-olds, accuracy of size perception for misleading images remained at about what it was for control images. Misleading images increasingly elicited errors from older children and tricked adults most of the time. Adults made almost no errors on helpful images. Kids from age 7 to 10 erred on a minority of helpful images, while 4- to 6-year-olds performed no better than chance.
Above: (a) Most people see the further circle as being larger than the nearer one, though they are equal. (b) Adding surrounds, as in the Ebbinghaus illusion, increases the perceived size difference between the two circles. (c) The large element in the centre of the second row from the top may be seen as being larger than that arrowed below, but they are equal.