Researchers have revealed fresh evidence for an earthquake-induced mental fog that affected Canterbury residents, dubbed "quake brain".

Research by Otago University scientists found a group of people affected by the traumatic events of the Christchurch earthquake made 13 per cent more errors on assigned tasks.

These included having affected people learn the way through a maze, alongside others who had not experienced the disruptive, ongoing natural phenomenon.

The quake-affected group were identified as having experienced a degree of trauma during the February 22, 2011 quake, and included emergency responders, those who were injured, or had a family member injured during the quake or whose property or neighbourhood had been badly damaged.

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Despite having experienced trauma, this group of people all identified themselves as being "resilient".

They were tested two years after the February earthquake, and their results compared to a group of people who had done the same test but had no experience of quakes.

The findings of the research were preliminary, meaning they had been analysed but results had not yet been published in any scientific journal.

Psychiatrist Professor Richard Porter, the head of Otago's department of psychological medicine, said the research showed the ongoing effect of quakes even two years after the February event and that there was likely to have been a significant effect on memory for a large percentage of the population, since many were exposed to these types of traumas.

This problem was even greater for people who developed post-traumatic stress disorder after the earthquakes.

The research emphasised that these problems are common and others should make allowances for these sorts of difficulties.

"We do not know how long this effect is likely to have lasted," Porter said.

"We are currently seeking funding to re-test the group of people to see if their memory has now returned to normal."

The research, funded by Otago University and the Canterbury Medical Research Foundation, follows another recent study by Otago scientists that unexpectedly found no negative trends relating to Christchurch school-leavers.

The absence of negative effects on teenagers leaving high school when the 2010 and 2011 quake sequence struck was put down to resilience, despite widespread research showing how natural disasters increased rates of depression, anxiety, and post-traumatic stress disorder.