How our Sensorimotor System May Affect Speech Perception

Hello fellow SLPs

Ok this post goes a little deep but it’s pretty interesting and worth the read (in my humble opinion), especially for those of  you working with children with speech sound disorders.

It’s pretty well accepted that when we don’t perceive sounds accurately, we have little chance of producing them accurately. You’ve seen this firsthand when you try to imitate something in a language you don’t speak and a native speaker shakes his head as you stumble through his language. In your mind, your pronunciation was fairly good. But, unless you were exposed to Italian as a baby, it’s obvious as soon as you say bongiorno that you are not a native speaker. (By the way, for any of you who have seen Inglourious Bastards, do you not crack up as Brad Pitt’s character tries to pass for a native Italian speaker?!) Our brains weren’t primed as infants to hear the phones in non-native languages and so we have little chance of imitating them with native-like speech. We also know that for babies with hearing loss, their vowel shapes and babbling are not the same as their normally hearing peers. So, when we don’t perceive phones, we don’t produce them accurately. This is a given.   What may come as news to many SLP’s though is how articulation of sounds may affect perception of sounds, according to a recent study.

What do I mean by that?

In this study, researchers wanted to see how restriction of the articulators would impact a baby’s ability to perceive a speech sound.   In an infant’s brain there are pathways that support the “auditory-to-motor” mappings meaning that the brain sends cues down to the articulators when certain sounds are heard. This study proposes that there is a loop with speech perception and speech production. New sounds are processed in the brain and then produced by the articulators and that the articulators being able to produce the sound also reinforces recognition of that sound by the brain.

When a novel sound is introduced to an infant, they attend more to this sound.  This study divided babies into groups who were exposed to a speech sound that is not discriminated by adults because of neural pruning that happens usually around 9-12 months of life. But, small babies who have not yet had neural pruning do identify subtle differences in phones across languages. In one group, the researchers “restricted” the tongue by placing a baby mouthing toy in the babies’ mouths where they would typically produce the sound. The babies were then exposed to the nonnative phoneme (a sound in Hindi). In another group, the babies were not given anything to mouth so their articulators were not blocked. They were then exposed to the nonnative sound. Babies whose articulatory placement was blocked attended less to the nonnative sound (which was measured by babies trying to localize the sound).  The sound was a lingual alveolar sound, so having a chewy toy effectively blocked placement. Well, what if the babies weren’t attending because they had something in their mouths which focused their attention on mouthing rather than locating sounds? So a third group was designed to rule this out. In the third group, the babies were given a mouthing toy that was gummy and flexible and allowed their tongue to move to the alveolar ridge. And this group of babies did attend to the novel sound similar to the group with no chewy toy. So, what does this study mean about what we think is a unidirectional learning of sounds (i.e. only from the brain to the articulators rather than a feedback loop.)  

This study indicates that the ability to articulate a sound can influence how it is perceived in the auditory system.

The authors of this study hypothesize that impairments in the motor function of the articulators can also affect speech perception. If speech perception were affected, wouldn’t language also be affected as children with oral-motor differences may not be perceiving the phonemes of their own language that they are hearing.  They also state that, “This raises the question of whether speech perception is compromised in clinical populations with congenital oral–motor deficiencies or dysmorphologies. At present, these children are given speech therapy to improve their production skills, but no consideration is given to whether their perception is also affected by differences in their
productive systems (i.e. Bruderer, et al.”

I find this study interesting and there are few others that I have found like it, but I’m hoping that this area will continue to gain interest among researchers as many clinicians attest to seeing an oral-motor difference linked to a speech perception connection. My next post will be a follow up on this one as well as discussing a relationship between the sensorimotor system and language delays. Grazie!

 

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