New York, March 1 (IANS): Cannabis significantly affects users' ability to recognise, process and empathise with human emotions like happiness, sadness and anger, suggests new study.

"We're not taking a pro or anti stance; but we just want to know, what does it do? It's really about making sense of it," said one of the researchers Lucy Troup, assistant professor of psychology at Colorado State University in the US.

The findings were published in the journal PLOS ONE.

For the study, involving 70 participants, the researchers measured electrical activity in the brain triggered by visual attention -- when one notices something.

The participants self-identified themselves as chronic, moderate or non-users of cannabis.

The experiments consisted of the following: With participants connected to an electroencephalogram (EEG), they were asked to view faces depicting four separate expressions: neutral, happy, fearful and angry.

Cannabis users showed a greater response to faces showing negative expression, particularly angry, than controls.

Conversely, cannabis users showed a smaller response to positive expressions -- the happy faces -- compared with controls.

Also, the participants were asked to pay attention to the emotion, and then identify it -- to "explicitly" identify the emotion.

In those cases, users and non-users of cannabis were virtually indistinguishable. But when asked to focus on the sex of the face, and later identify the emotion, cannabis users scored much lower than non-users.

This signified a depressed ability to "implicitly" identify emotions, the researchers said.

Cannabis users were also less able to empathise with the emotions, said the study that seems to suggest that the brain's ability to process emotion is affected by cannabis.