New Zealand psychology researchers have challenged a landmark US study that indicated infants are born with a moral compass that enables them to recognize "good" and "bad" behavior.

Yale University researchers had claimed that their 2007 study provided the first evidence that infants aged 6 to 10 months showed a preference for individuals who helped rather than hindered another individual.

On Thursday, researchers at New Zealand's University of Otago said they had conducted their own experiments that showed the Yale findings could have simply been the result of infants' preferences for interesting and attention-grabbing events, rather than an ability to evaluate individuals based on their actions towards others.

The Yale paper had received a lot of international attention when it was published and had since received more than 100 citations, which had raised the interest of the Otago researchers, lead Otago author Dr Damian Scarf said in a statement.

"Obviously, the idea that morality is innate is extremely interesting and, if true, would raise questions about which components of our moral system are innate and also have implications for the wider issue of the roles that nature and nurture play in development," said Scarf.

In the original experiment, infants watched a wooden toy attempt to climb a hill: in one attempt a "helper" toy nudged the climber up the hill, and in another, a "hinderer" toy nudged the climber down the hill.

Presented with the toys later, most of the infants picked the helper over the hinderer.

The Yale paper concluded that the experiments showed that infants had a "universal and unlearned" ability to evaluate individuals based on how they interacted with another individual.

However, the Otago researchers noticed in the videos of the study two other factors that could influence the infants' choices.

"On the help and hinder trials, the toys collided with one another, an event we thought infants may not like. Furthermore, only on the help trials, the climber bounced up and down at the top of hill, an event we thought infants may enjoy."

The Otago researchers in their experiments manipulated the collisions and bouncing to show that these perceptual events were driving infants' choices, Scarf said.

"For example, when we had the climber bounce at the bottom of the hill, but not at the top of the hill, infants preferred the hinderer, that is, the one that pushed the climber down the hill," he said.

"If the social evaluation hypothesis was correct, we should have seen a clear preference for the helper, irrespective of the location of the bounce, because the helper always helped the climber achieve its goal of reaching the top of the hill."

Although the Yale researchers had followed up their original study with further research findings that appeared to support the original study, these too could be explained under the simple association hypothesis, he said.

The Otago study was published in PLOS ONE, an international, peer-reviewed, open-access, online journal, said the statement.