Age Of Vocabulary Acquisition

There was a large amount of anecdotal evidence that dyslexics were late in learning to talk, but I owe to my colleague John Done an ingenious way of establishing the matter experimentally and quantifying the amount of lateness.

The argument is a somewhat complex one, and for full details readers should consult the original paper (Done and Miles, 1988). In brief, the starting point was an earlier finding that, in adults, there was a high correlation between the time which it took to name a picture (the 'response latency') and the age at which the name had been learned. We wondered if the same would be true in the case of dyslexic children. John started by giving 65 pictures to 101 children aged two, three, four and five years and noting in which age band (six-monthly intervals) 75% of the pictures could be named; the children were simply asked to say 'what the picture was called'. Some of the pictures were of objects likely to be known to the children but where the names were not all that high in tables of word frequencies, for example 'bicycle', 'giraffe' and 'windmill'. This was because John wanted to determine whether word frequency or age of acquisition was the more important factor. By a suitable statistical technique it was possible to study the influence of these two factors separately, and, although there was, of course, a correlation between the two, statistical analysis showed that age of acquisition was the more important.

After initially presenting these pictures to children John started on the main experiment. This involved giving the same 65 pictures to dyslexic and control subjects aged about 14.6. (The controls were marginally younger, so that, if there were any effect of age, it would count against the hypothesis which we were testing.) The response latencies of both groups correlated highly with the previously determined age of acquisition. However, the response latencies of the dyslexics were considerably longer than those of the controls. Overall, when he took into account the age of acquisition of the different words, John found that the difference in response latencies between the two groups produced an overall difference score of 67 milliseconds; this was found to represent a relative lateness in word acquisition score for the dyslexics of 10.8 months (note 15.6). This would seem to make sense as an overall measure of dyslexics' relative lateness in acquiring vocabulary.

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Adult Dyslexia

Adult Dyslexia

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