He found that younger people were more likely to restrain themselves from answering the trick question, whereas older people were more likely to blurt out "black" and then realize it was a trick.
Von Hippel said evidence from these two experiments shows that the same older people, who were more likely to be blunt, have lower inhibitory power in their frontal lobes.
Future Studies
Von Hippel would now like to do similar tests on a larger number of people using magnetic resonance imaging, or MRI, to check if atrophy in the frontal lobes correlates with bluntness in older adults.
For now, he can not rule out other causes for the bluntness, such as early stage dementia.
But he said the frontal lobe theory is supported by other research showing the people with frontal lobe brain damage are often more socially inappropriate.
An Uncomfortable Idea?
But von Hippel said his work has been criticized.
"I think it's perceived as an attack on older adults," he said. "I don't believe it is."
He said it was already accepted that atrophy of the frontal lobes occurs as you age and this affects memory and slows down brain processing.
"What our research is showing is that there are social consequences as well," he said.
