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My voice, your voice, our voice | Sonja Kotz

Faculty of Psychology and Neuroscience

Our voices are unique, and a lot of our personality and character is embodied in our voice. But what if we lose connection to our own voice, what if we think it is someone else’s?

Sonja Kotz, professor of Neuropsychology and Translational Cognitive Neuroscience at the Faculty of Psychology and Neuroscience at Maastricht University, has recently published two papers on the perception of the human voice. Our own voice, and the voices of others.

The two papers are: Neural adaptation to changes in self-voice during puberty in Trends in Neuroscience and Entrainment echoes in the cerebellum in Proceedings of the National Academy of Sciences (PNAS) 

We talked to professor Kotz about the work discussed in these papers.

Our own voice

Neural adaptation to changes in self-voice during puberty in Trends in Neuroscience.

“We are very familiar with our own voice, so familiar, that when we hear it, our brain does less work to process it”. This mechanism is useful, allowing our brain more capacity for other perceptions such as the voices of others. Our voice is unique to us, and we are so used to it that it becomes a big part of our self-identity. 

“We are interested in people who experience auditory hallucinations, such as hearing voices. We know that when people hear voices there is a disconnect of recognising your own voice as part of yourself”. Not recognising your own voice is at the root of these auditory hallucinations that often start during puberty. Kotz was brainstorming with her long-term collaborator Ana Pinheiro (Assistant Professor of Neuropsychology and Cognitive Psychology at the Faculty of Psychology – University Lisbon, Lisbon, Portugal) about new projects. “We saw this connection between puberty and the occurrence of auditory hallucinations, and we thought - could this have anything to do with the multiple changes of our voice in puberty”. 

Hormonal changes during puberty cause the voice to change in pitch, character, and tone. In some cases, this can lead to the disruption of hearing our voice as our own. “That, together with other physical and emotional changes during puberty, could make people more susceptible to these auditory hallucinations”. 

The upcoming (at least) five years, Kotz and Pinheiro will look at people going through puberty to measure how their susceptibility to mental disorders develops during this period of great change. 

Predictions and corrections

Entrainment echoes in the cerebellum in Proceedings of the National Academy of Sciences (PNAS)

Our brain knows what’s coming, or at least the cortex thinks it knows. Our brain is constantly making predictions of what’s coming and when something is coming “it uses all factors of someone speaking, such as their tempo, tone, content, and rhythm of speech, to guess what is coming next and when”. This makes it easier for us to listen and be engaged in conversation, as we don’t need to process everything, we just need to verify. “We call these expectations. These expectations work especially well with the rhythmic nature of speech. We sync with the rhythm that we’re hearing”.

“When we speak, we make an effort to speak clearly, so that we’re understood”. Kotz and her colleagues found that when speech is less intelligible, the syncing doesn’t work as well. “This makes it more difficult for our brains to comprehend speech when somebody is, for example, speaking behind a closed door, or we’re in a large group with many people speaking at the same time”. 

“In this study, we looked at the brain activity using Magnetoencephalography, or MEG (reading brain activity via magnetic field), to see what happens when we manipulate these two factors, rhythm and intelligibility. What we found was that our brain is also making these predictions when there is no more input. Even after we’ve stopped hearing another voice speaking, our brain is calculating and ready for what’s to come, but only if speech is intelligible”. This is a strong indication that our brain is continuously making predictions, not only in terms of the content of the speech, but also its timing and rhythm. “Not only what is coming next, but also when it is coming”.

This explains why it takes more effort to listen to a large group of people speaking, than to a one-on-one conversation. Your brain is constantly recalibrating. “This was another big finding. We were able to locate this activity to a specific area in the brain, the cerebellum”. The cerebellum has always been considered to be part of a monitoring system of the cortex. “Monitoring in this case means that the cortex generates certain predictions, and the cerebellum monitors that it fulfils them, and if it doesn’t match up, the cerebellum tells the cortex to make adjustments”.

These papers both contribute to our understanding of the human voice, how we use it in speech, and how our brain perceives voices and speech by using predictions.

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