The commonly held belief is that the human brain is more efficient when processing alarm type screams (fear, pain, anger) than non-alarming screams (sadness, joy, pleasure), as alarm screams are of greater immediate relevance to survival.
Participants took longer to categorise alarm screams than non-alarm screams, which were identified faster and with greater accuracy
A recent study at the University of Zurich does not uphold this belief, suggesting that responses to alarm screams are in fact slower. Participants were asked to differentiate between the six scream types and a seventh neutral scream. One group of participants categorized screams as alarming or non-alarming, whilst a second group were asked to categorize them as fear, pain, anger, sadness, joy, pleasure, and neutral. The results showed participants took longer to categorise alarm screams but responded faster and with greater accuracy for non-alarm screams.
The study also found differences in the brain activity occurring when the magnitude of the alarm scream heard is varied. fMRI scans of a third group of participants showed less alarming screams, compared to screams of a more alarming nature, evoke more activity in the auditory and frontal regions.
fMRI scans also showed the valence of a scream to elicit activity differences, with positive screams (non-alarming) associated with greater activity in the frontal and auditory than negative screams (alarming).
Researchers suggest that non-alarm screams are encountered more frequently in the social environment, and are therefore prioritised when it comes to human scream recognition
The reasons behind why the human brain responds faster to non-alarm type screams are not concrete in the slightest. The researchers behind the study give the possible explanation that non-alarm screams are encountered more frequently in the social environment humans inhabit and are therefore prioritised.
They also suggest that when the misclassification of a scream does occur, it is likely to be misclassified as an alarm type scream. This represents a natural bias for threat perception, as when weighing up the costs and benefits of interpreting a situation as threatening or not, it is of greater benefit to err on the side of caution and interpret a situation as a possible hazard.
Whilst the purpose of greater reactivity in humans to non-alarm screams can only be speculated about, the study is able to overturn previous beliefs about scream processing efficiency, providing a stepping stone for future work.