In adults, previous studies have suggested that stress promotes habits and reduces cognitive flexibility. Psychologists from Germany's Ruhr University Bochum have revealed that the same is true for infants. While under stress, even infants are inclined to resort to habits, rather than try out new things.
Lead researcher Sabine Seehagen said, "If infants are repeatedly exposed to stress and therefore don't try out alternative behaviors, this may have a negative impact on their knowledge acquisition."
For the study, researchers analyzed 26 infants at the age of 15 months who underwent a learning task. Around half of the infants in the study had previously been subjected to stressful situations such as they may occur in their everyday life - a stranger sat down next to them, a dancing robot played loud music and moved around, their parents left the room for a maximum of four minutes. These events lead to an increase in the stress hormone cortisol. On the other hand, infants in the control group spent the same period of time playing with their parents.
Then, all the infants participating in the study were presented with a box containing two lamps and learned that one of them emitted a red light when pressed and the other one a blue light. They were allowed to press one of the lamps as often as they liked but access to the other lamp was blocked.
In the subsequent experiment, the infants were free to choose which lamp they wanted to play with, but now neither of them lit up. Even though the lamps worked no longer, infants in the stressed group continued to press the lamp that they had got used to pressing, while children in the control group exhibited more flexible behavior and pressed the other lamp significantly more frequently.
The findings were published in PNAS.