What makes a scream alarming?

1 August 2015

Researchers from Switzerland and Germany have just published a paper in which they describe using brain imaging and a cool way of looking at sound, called the modulation power spectrum (MPS) to understand just why screams are so alarming. Rather than looking at the amplitude and frequency of sounds over time, the MPS plots the modulation frequency against the number of cycles per octave, shown as a kind of heat map. On this kind of spectrum, there is a clear zone that gives clues to the gender of the speaker, and another distinct zone that gives information about meaning. But there is also a zone that until now hadn't been associated with any function. In fact, it has been thought to be irrelevant to human communication. This region corresponds to a perception of sound called roughness, which is thought to be unpleasant.