a, Spectrogram of examples of the pure tones used in the task for temporal (T) and spectral (S) series; time increases horizontally and frequency increases vertically; colour intensity reflects the energy of the stimuli. Each tone pair shows a representative example of stimuli used in each of the nine conditions, chosen here with a rising pitch from the first to the second tone. The two tones in each pair were always presented in succession; the impression of temporal overlap for the most rapid conditions (temporal series) is an artefact related to the influence of the acoustic uncertainty principle on the time–frequency representation. b, Proportion of correct answers (±s.e.m.) given by early-blind (blue bars), late-blind (red bars) and sighted (white bars) subjects for the nine conditions. c, Significant negative correlation between age of blindness onset and behavioural performance in the pitch-direction task in temporal (left; T6 to T48) and spectral (right; S16 to S128) conditions. Blue and red dots represent early- and late-blind groups, respectively.