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Our article "Shards of Genius" (THES, March 29) was both truncated and garbled in the sub-editorial process.

Christopher's genius for learning languages is in marked contrast with his poor performance on some other tasks such as those involving pattern recognition or the "conservation of number". Such contrasting abilities prompted the claim that "assigning someone, anyone, a single IQ is silly", to which Professor Radford (THES, April 12) takes exception. We do not deny that some people have "all-round ability" and that others are uniformly inept, but such (un)fortunate beings are hardly the norm.

Christopher's case is an extreme one, with his score on various standardised "intelligence tests" ranging from 40 to more than 120. As our book, The Mind of a Savant (Blackwell), and the uncut version of our contribution made clear, he is even good at abstract reasoning, though only in linguistic and not in other domains. This unusual profile of talent and disability led to our conclusion that the mind is too complex to be characterised by a single index. This conclusion still seems to us to be inescapable.

Neil Smith Department of Phonetics and Linguistics University College London