One of the most important things a parent can do for a child is to be positive, to show enthusiasm and reward good behavior. There’s plenty of evidence to support the value of this (mercifully) natural impulse. [See: Listen, pay attention – the ingredients of good parenting]

So, given the importance of the affirming and affirmative, what should one make of evidence that children actually pay more attention to the darker side of their experience – and therefore to their parents’ negative comments and actions?

Amrisha Vaish of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, along with colleagues in the UK and US, maintain that children and adults alike, tend to focus more keenly on negative than on positive information and input.

After combing through the existing research, they concluded that by 12 months, infants display what they call a strong “negativity bias”. One can detect and observe it in how infants and children use, communicate about, and recall emotional events and information.

Vaish and company go on to argue that attention to the negative serves important evolutionary functions. Children who attend to fear or anger more so than to “happy expressions” might be more aware of dangers in their midst. Thus those who are wary of strangers and unfamiliar objects might do better in the long run because, while avoiding new experiences might mean a missed opportunity for learning, it is more difficult to reverse the consequences of a harmful event.

That’s not to say the authors believe that parents should start criticizing their children. In fact, they suggest that early and frequent exposure to positive emotions might be a prerequisite for the healthy development of a negativity bias.

In other words, children might pay more attention to negative events because they are less common and stand out in sharp relief against their usual happier interactions. More adventurously, Vaish and her team also speculate that children who do not receive enough positive input, for example from depressed or abusive caregivers, might "tune out" negative events in other contexts and, by doing so, neglect to protect themselves adequately .

As is often the case there is much unremarkable commonsense in these data-driven arguments. Nevertheless, the so-called “negativity bias in children” is a field of research relatively untilled, and plenty more remains to be discovered before the range of practical implications is understood. As it stands, the research only highlights the importance of positivity in childhood.

• Summary of “Not All Emotions Are Created Equal: The Negativity Bias in Social–Emotional Development” by Amrisha Vaish, Tobias Grossmann, and Amanda Woodward in Psychological Bulletin, May 2008, Vol. 134, No. 3, pp 383–403.