Aggressive kids don't respond to maternal affection

"A healthy brain is drawn to biologically relevant cues and the eyes of other people provide so many of those," says Mark Dadds of the University of New South Wales' School of Psychology in Australia, who led the research.

"But this is a sub-group of kids who are quite different. They are low on emotion and they don't connect with authority figures," he said, according to a New South Wales  university release.

The team -- including psychiatrists John Brennan, David Hawes, University of Sydney and colleagues from the Institute of Psychiatry at King's College, London -- is studying children with repetitive patterns of aggressive, hostile and anti-social behaviour.

Most are emotionally "hot" -- they are impulsive, emotional and given to overly hostile interpretations of the world, but they have normal levels of empathy and are largely reactive in their aggression.

Those in the much smaller "cold" group are under-emotional, show problems with empathy and may also be proactive or even predatory in their aggression -- many go on to become involved in serious crime, violence and drug-taking.

The team conducted pioneering lab experiments using eye-tracking devices and video cameras to record how much eye contact such children made while interacting with their parents.

The studies involved more than 100 British and Australian children aged between four and 16 who were diagnosed with Oppositional Defiant Disorder (ODD) and with no other significant mental, medical or developmental issues. They were compared with control groups of children with no mental health or behavioural problems.