with no pressure on response time, regarding which of two parallel, vertical lines of markedly different lengths was longer. The stimuli and psychophysical procedure were the same as those used in Deary et al. (2004a), with a prescribed number of trials given at different stimulus durations. The correctness of each response across the 150 trials was recorded as the outcome variable. A general factor, explaining 59% of variance, was calculated from a principal components analysis of digit symbol, 4-choice RT mean and inspection time.
