We're highly tuned to emotional signals. So whereas most of the information bombarding our brain is filtered, emotion-related signals seem to strike home regardless. Take fearful faces - research has shown these trigger the same activity in a fear-sensitive brain region, the amygdala, regardless of whether we're paying attention to them. This is in contrast to how the brain normally works. For example, a face will trigger a different amount of activity in the brain's fusiform gyri – a kind of face-processing module - depending on whether that face is being attended to. Didier Grandjean and colleagues at the University of Geneva wanted to find out whether the brain treats emotional sounds with the same priority as emotional sights.
Fifteen participants had their brains scanned while they were played two meaningless but word-like utterances to both their ears at once. These utterances were either neutral in their stress, tone and timing or they could convey anger. The participants' attention was always directed to one ear at a time by a task which required them to identify the gender of the voice at either their left or right ear.
An angry utterance at one ear triggered the same enhanced activity in the right middle superior temporal sulcus, regardless of whether a person was paying attention to that ear. "This suggests the right superior temporal sulcus...(is) finely tuned to extract socially and affectively salient signals from conspecficis (others of the same species)", the authors said. Together with past research, this points to a system that prioritises "orienting towards significant stimuli even when these are not the focus of attention".
Grandjean, D., Sander, D., Pourtois, G., Schwartz, S., Seghier, M.L., Scherer, K.R. & Vuilleumier, P. (2005). The voices of wrath: brain responses to angry prosody in meaningless speech. Nature Neuroscience, 8, 145-146.