Normalities, abnormalities, and the limits of statistics

Serious abnormalities are mostly rather obvious. At a given point on a scale they count as impairments. But what defines the point? What criteria are used to define it? And what defines the scale?

Tests measure what it is possible to measure.

For example, one widely used scale is the Percentage of Consonants Correct or PCC. Now, the obvious reason for prioritising consonants is that they cause many more developmental issues than vowels. Children have many more difficulties with the consonants than with the vowels. But in respect of any given consonant what counts as ‘correct’? In the considerable literature on children’s mastery of R there is a wide variation in the ages at which a ‘normal’ or ‘correct’ R is said to be acquired (from four to seven). It seems likely that the criteria vary from study to study. And what if a given consonant seems to be pronounced correctly in all but a particular context or a set of words? Do they count in the computation?

A less used scale is the Percentage of Vowels Correct  or PVC. But this is subject to the same problems as as the PCC.

Some children have great difficulties with both vowels and consonants or even more difficulties with vowels than with consonants.

How children say particular words is just one of the more easily testable aspects of ‘phonology‘ – or how the sounds in words are built. But speech is not just about ordering sounds. Speech is also about knowing when and how words change – like the fact the and a both change when the next word begins with a vowel. Such aspects of phonology are not generally tested by standardised tests. But speech entirely based on a linear sequence of speech sounds would be barely recognisable as speech. This became obvious when the first efforts to build speech synthesisers were made in the early 1950s using the new technology of tape recording. Percentages of correctness may give rise to misleading estimates of competence.

Similar issues arise with respect to children’s language, but with one additional issue stemming from the fact that it often seems that children understand more than they can say. This critically involves their grasp of what is known as ‘syntax‘ – or how words fit together.

My clinical focus is on disorders of speech and language and the various interactions between syntax and ‘morphology‘ or how words are built – and phonology. These things may be hard or impossible to represent as points on scales or percentages. The number of words or the ‘lexicon‘ can in principle be counted, but that is only in principle. The number relates only to the words that are said, not the number of words that are understood. These often comprise the main issues which get noticed in children and young people’s speech. But this does not force the conclusion that the only scientific evaluation is statistical.

It is possible that speech and language are just statistically intractable.

Unusual or abnormal development is not, in itself, a disorder. The diagnostic question relates only to the degree of abnormality in any given case. Sometimes a major issue resolves sponaneously and faster than by normal development. But there are issue which do not resolve spontaneously, which without treatment the individual may be left with for life. Such issues can be revealed by extreme degrees of abnormality. To this degree, abnormality can be diagnostic.

Putting things differently, there would seem to be limits to what can be shown by psycholinguistics.

Beyond statistics

Outside the scope of statistical evaluation, there are a number of fundamentals. One of these concerns the development of syllables as parts of words. English happens to have a relatively rich inventory of both vowels and consonants and an unsually complex foot structure. And English is very permissive about how sounds combine in the syllable – what is known as the ‘phonotactics‘. Or they don’t recognise the syllable as a category, treating any consonant before the vowel, what is known as the ‘onset’, as just an extension of the vowel.

Children are not given any guidance or privileged information on which bits of linguistic structure influence which other bits. Nor could they be. Where English stands in the learnability space is not a matter for discourse with children.

In competently spoken English there are interactions between words and between the parts of words inside the words which define the language – like those between an and the and the next word. And there are things which typically developing children commonly way which are most definitely not part of English. Some of these interactions are like points on a pathway. So there is a natural pathway from little, often hard to say even at four, to monopoly, often hard to say at seven or eight or even in adulthood. The T in little and the P in monopoly both get pronounced with more contrast between them and two other sounds – as LIKU and MONOKOLI. This is known linguistically as ‘disharmony’ or ‘dissimilation’. By nine most children can say most words, even the more difficult ones like monopoly. But those who can’t sometimes need help.