Yesterday I blogged about three new measures of mental function that I have recently started to use. Here are the first results.
Each point is a mean; the error bars show standard errors. I expected a within-session warm-up effect (Trial 1 slower than Trials 2-5) but there isn’t one so I use variation across the 5 trials (100 digits each) to get a standard error.
2. Digit span.
The program increases the number of digits to remember by one when I’m right and decreases that number by one when I’m wrong. The test continues until there have been six reversals in direction of the number of digits (e.g., the sequence 5, 6, 7, 8, 7, 6, 7, 8, 9, 8 contains three reversals). Each pair of reversals is averaged to get an estimate of digit span; I use between-average variation to get a standard error.
Digit span slowly improves with practice, other researchers have found. The increase is slow, however — one digit for every two hours doing the task.
3. Speeded arithmetic.
The questions differ greatly in how long they take (7*9 much slower than 1+0) so I fit a model to remove obvious effects and use the variation of the residuals to get standard errors. I think these results are so erratic because I did the test in several different places and in some cases I corrected mistakes (which is very slow). Now I don’t correct mistakes.