Speaking rhythmically can enhance auditory perception

To perform the motor action of speech and auditory perception, well-identified parts of the brain are activated. These two specific and differentiated areas used to be considered independent from each other, but for some years now we know that they interact in a coordinated and complex way.

Florencia Assaneo, researcher at the Universidad Nacional de México and first author of the study that was published in Nature Human Behaviour worked with Yonatan Sanz Perl, CONICET assistant researcher at the ‘School of Mathematics and Sciences of the Universidad de San Andrés. The scientists proved the existence of this interaction between hearing and the motor part in a group of individuals that identified themselves as ‘high synchrony’ people.

During the experimentation, the researchers observed that these people produce syllables, stimulate their system of perception of sounds and enhance their ability to listen. Although scientists suspected it to occur but there was no evidence supporting the fact that the production of speech modulates auditory perception.

“Our study was based on rhythm, as my area of expertise is rhythmicity in speech. We observed that when we produce speech at a certain rhythm -the cadence of what you are say- is translated into the perception system,” Assaneo explains.

The researcher explains that they gave participants one syllable -po or pu- in between a noise adjusted to each individual -not all have the same ability to abstract from the sound that surrounds them-, while repeating the syllable ‘ta’ at a certain rhythm, the rhythm that each one uses naturally.

“We observe if they are better at understanding the syllable that is in the noise, according to what moment of repetition production it is. If the syllable occurs when the individual has been saying the ‘ta’ that has been produced in that same rhythm, it improves the perception of the subjects with high synchrony. Besides, we distinguish that there are subjects of high or low synchrony that are completely different. Although the rhythm of production is reflected in perception, this happens only for those with high synchrony but not with those of low,” explains the scientist.

The mathematical modeling to validate the experimental results arose from the collaboration with Sanz Perl, who used to work together with Assaneo as CONICET doctoral fellows at the Laboratorio de Sistemas Dinámicos del Departamento de Física, Universidad de Buenos Aires. “The modelling provides an approximation of how what one observes works and some predictions. It is a simple model in which the motor and auditory nuclei are two oscillators, which have a phase that characterizes the oscillation. It is considered to be an abstraction of the functioning of those excitatory and inhibitory neurons of these nuclei, and that they are coupled to each other through a cable, and what happens to one affects the other,” the researcher describes.

These cables, which are the connection between neurons -axons-, are the ones that join the areas of the brain in play -the motor of speech and the auditory- and are ‘thicker’ in individuals with high synchrony. This variability needs to be reproduced in the mathematical model to reproduce the experimental results. It is the mathematical corroboration that individual differences are key, that the connection between motor and auditory areas is not equally strong for all subjects.

“This shows the importance of taking into account individual differences when doing science, which is something that very often we scientists do. We tend to believe that all brains work in the same way. There are a lot of phenomena that occur but not in the entire population,” concludes the scientist.