The way humans talk is hugely complicated. In fact, the complex ways in which we produce speech - the variety of sounds and noises we make, along with the different emphases we place on sounds when talking - are unparalleled in the animal world.

As adults, we can fail to appreciate this. Speaking and listening appears to be so natural, and easy, that we take it for granted. But speech perception and speech production - the two facets of what is known as “speech processing” - are hard. They involve complicated neurological processes, and ones that have to be learned, just like any other skill. And that learning process will develop at different rates for different children, which is why speech processing is something about which every teacher should be aware.

Sophie Scott, professor of cognitive neuroscience at University College London, is a good person to turn to for information. Her research concerns the neurobiology of speech perception, including the evolution of speech and the difference between intelligibility and comprehension.

“There are multiple things going on, even with just the straightforward listening side of things,” she explains.

For example, research shows there are areas of the brain that appear to be particularly important in determining how we perceive and process speech. “On the whole, the left side of the brain is very good at listening for things that are to do with language: from speech sounds through to words and syntax ... whereas the same areas on the right side of the brain are a lot more interested in the non-verbal aspects of speech communication: so, speaker identity, speaker emotion, melody in speech, or the use of irony and humour,” says Scott.

This suggests that, at an early age, the brain effectively separates out the linguistic elements of language from the other aspects of a voice and processes them separately.

“So, right hemisphere damage might leave you with a problem understanding not the words that someone is saying, for example, but what they really mean - did they mean to be funny or did they mean to be sarcastic?” explains Scott.

Understanding before saying

Perhaps unsurprisingly, given the many aspects involved, different children develop speech perception and production at different rates - although the research is not conclusive on why this should be so.

“What we can say is that speech perception [rather than production] tends to come in earlier,” Scott says. “I can remember being really shocked by my baby when he was still nursing, hearing me say to another baby, ‘Oh, that’s good clapping,’ and immediately making eye contact with me, raising his hands above his head, and clapping - as if to say, ‘I think you’ll find I can do that!’ ”

Perception comes first because speech production relies on developing both the understanding of speech and motor skills.

“So, there is that discrepancy - but then beyond that, [development speed] varies a lot,” Scott says.

How can you work out if a child is struggling with understanding or producing speech? It’s tricky, as environmental factors get in the way, Scott acknowledges.

“For a start, you are very rarely listening to speech in silence - there is normally some sort of background noise going on,” she says. “Children struggle much more than adults to understand speech when there are other people talking in the background. Adults get quite good at ignoring other talkers, but children are not good.”

In fact, children are disproportionately disadvantaged by background talkers who are adults, Scott says - meaning that if a classroom assistant is speaking in the background at the same time as a teacher is addressing the class, for example, then that might pose some difficulties for the children.

“That is speaking to part of the speech perception system that is basically attentional - being able to pay attention and not be distracted by something else,” adds Scott. “All the interfering sounds that you are listening to will be processed to some extent,” she explains, and while adults are good at focusing on what they need to listen to, “it takes children a while to get there”.

Bearing this in mind when teaching seems as good a place to start as any when trying to be more aware of these issues. You might think that a natural extension of this would be that differing accents and languages would make things even more complicated. Unlike with much speech perception and production, however, it seems that children are better able to learn the differences between verbal pronunciations than adults.

“Part of learning a language is learning the speech sound contrasts that are relevant to that language,” Scott explains. “So, in English the sounds ‘r’ and ‘l’ are two different phonemes - ‘red’ is a different word from ‘led’. If you were a speaker of Japanese, though, the ‘r’ in red and the ‘l’ in led are just different variations of the same phoneme.

“An example in English is if I say the word ‘leaf’, and then the word ‘cell’ - both have an ‘l’ sound and we hear them both as ‘l’, even though they are very different speech sounds. If we, like a Japanese speaker learning English, were confronted with a language where we had to learn the two different ‘l’ sounds as separate, distinct, we would struggle.

“[Fortunately], when you are still at school, your brain is still learning those contrasts, and it is a much better age at which to learn second languages. You tend to find that children are less hampered by being tied into one particular language system - they are still more flexible, and able to deal with entirely different sets of relevant sounds.”

That is a strong case for teaching languages as early as possible in the school system.

Link to literacy

But what about reading? The interaction between speech processing and reading development is another area that neuroscientists have studied closely, and it is well established that those who have difficulty mapping between speech perception and speech production often struggle with reading, too.

“The interactions between perception and production are really important in learning to read, and if you have difficulty with that it can predict reading difficulties later on,” Scott says.

There are other areas, though, where reading and speech processing seem less closely linked. Take phonics, for example.

“You don’t need to be able to break a word up into its constituent speech parts to be able to understand it,” Scott says, pointing out that babies and dogs can understand plenty of words, but cannot read.

“So to understand ‘cat’, I don’t need to hear ‘c, a, t’, and, as far as we can tell, there is no point in your brain, when you are listening to speech ... when that word gets broken down [into those letter sounds].”

As a result, it is quite common for children - and, indeed, adults - to have incredibly proficient speech-processing ability but to struggle with relatively basic reading tasks: the correlation between good oral ability and good reading is not as clear-cut as some believe.

“If you look at people who have never learned to read, they cannot hear the sounds ‘c, a ,t’ in the word ‘cat’,” Scott continues, “because the person who has learned to read has done that segmentation, which you don’t have to do to understand [spoken words].”

This can be demonstrated by looking at children who have a recognised reading disorder. “If you had a group of children with dyslexia, and a group of the same age [without dyslexia], those children would show very little if any difference in their ability to understand speech,” Scott says. “And that seems to be because you don’t need to be able to access those kinds of representations to be able to learn to understand speech.”

While there are some disorders in speech processing that are difficult to overcome, such as developmental language disorder, Scott says that most children will develop speech-processing abilities over time.

What is important for teachers is that the differences in speed of development in this process - and the links between this and other challenges a child might have - are acknowledged.

Also key is the knowledge that multiple adult voices can make things far harder. And, most of all, we need to remember that understanding speech and being understood vocally are far more complicated than we often imagine.

Chris Parr is a freelance writer

This article originally appeared in the 5 July 2019 issue under the headline “Tes focus on… Speech processing”