Human brains notice a voice much faster when it is considered threatening or aggressive than when it is perceived as normal or happy in an auditory environment, according to a new study.

The study demonstrated that in a few hundred milliseconds, our brain becomes sensitive to the presence of angry voices. Sight and hearing are the two senses that allow human beings to detect threatening situations. "We are interested in how fast our attention responds to the different intonations of the voices around us and how our brain deals with potentially threatening situations," said Nicolas Burra, researcher from the University of Geneva in Switzerland. 

The researchers presented 22 short human voice sounds (600 milliseconds) that were neutral utterances or expressed either anger or joy to a small group of people while an electroencephalogram (EEG) -- diagnostic test -- measured electrical activity in the brain down to the millisecond. 

The findings, published in the journal Social Cognitive and Affective Neuroscience, revealed that when the brain perceives an emotional target sound, N2ac activity is triggered after 200 milliseconds. However, when it perceives anger, the N2ac intensifies and lasts longer, which is not the case for joy.

N2ac is a component related to the focusing of attention within an auditory scene. Also, LPCpc activity -- a cerebral marker of auditory attention -- is also stronger for angry than for happy voices, findings revealed. This rapid detection of the source of a potential threat in a complex environment is essential as it is "critical in crisis situations and a great advantage for our survival", noted Leonardo Ceravolo, researcher from the varsity.