• Our neurons were clearly misfiring when describing one of four illusions we used to show how synchronisation of neurons affects vision (10 July, p 28). The brighter centre in circle C is in fact down to an increase in the firing rate of neurons, not tighter synchrony.
• In our story on biometric identification using iris recognition (31 July, p 22), we inadvertently confused two statistical measures, the false match rate (FMR) and the failure-to-match rate (also called false reject rate, or FRR). This resulted in the incorrect attribution of a statement on FRR to John Daugman of the University of Cambridge, where we said iris recognition would have a real-world FRR of the order of 1 in 250 million. In fact this number describes instead the FMR, when a decision threshold is used which allows up to 31 per cent of the bits in an iris template to be corrupted while still accepting the match.
