I just came across this discussion on Bruce Charlton’s Miscellany. Charlton cites a paper by Irwin Silverman which shows a secular increase in simple reaction time. I plotted the data points below. Different methods were used across studies, so there’s a lack of method invariance and the results are not compelling. But they agree with other findings in showing no ECT Flynn effect. (Increased intelligence should correspond with decreased reaction time.) The results are interesting for three reasons: (1) ECTs are based on a ratio scale, which more readily allows for cross temporal and spatial comparisons (see: Jensen (2011)’s discussion of the Flynn effect in this respect); (2) the correlation between ETC and IQ is largely genetic;（3）and relatively consistent racial differences in ECTs have been found.
If you are not familiar with the subject, you can read Jensen’s 2006 book on the topic. PDF, for your reading pleasure, here: Jensen, A. R. (2006). Clocking the mind: Mental chronometry and individual differences. Elsevier Science.