Two days ago I explained why the test I was using to measure my mental function many times/day had room for improvement. I wanted a new test much like the old test but with which my accuracy was higher.

I was more accurate with the simple arithmetic test (e.g., 3 + 6) than with the memory test I described two days ago. The crucial difference might have been the number of possible answers. The arithmetic test had 40-odd possible answers; the memory test had 2 (yes and no). Saul Sternberg did a reaction-time experiment in which the number of possible answers was varied from 2 to 8. I don’t know what the accuracy data were but the variance of the reaction times was lower with 8 possible answers even though reaction times were longer. A plausible explanation is that there was much more anticipation with 2 possible answers than with 8. Anticipation can cause errors.

The new test I am trying consists of typing how many letters from the set {A, B, C, D} are among a set of four letters chosen from a much larger set (most of the alphabet). The possible answers are “1″, “2″, “3″, and “4,” each equally likely. For example, I might see T B X A. The correct answer is “2″. I am using R (the programming language) to run this test so I type “2″ with one hand and hit Enter with the other as fast as possible.

Here are the results so far from the new test — the training phase.

These values are taken from fit of a linear model; they are similar to means. As I gain experience with the test I am getting faster. The new test is slower than the old test (which is good — more mental processing).

Consistent with what Sternberg found, variation in reaction times is less with the new test than with the old test even though average reaction times are greater:

This graph shows the standard deviation of residuals from the fitted model. The units are reciprocal seconds (x 10) because I did a reciprocal transformation before fitting the model. The reciprocal transformation made the reaction times close to normally distributed.

Here is accuracy:

The new test feels easier than the old test, but so far there is little difference.

Overall it seems to be a step in the right direction. Reduction in variation of reaction times means more sensitive measurements.

The experiments I am planning are very simple: Test myself regularly (say, every half-hour), eat something. If the measurements are steady, it is very easy to see an effect. As far as I know, such experiments have never been done. One reason, I think, is that they require self-experimentation: It is no trouble for me to do the test (which takes 4 minutes) 100 times in a week and thereby reach a steady state. But to have someone else do the test 100 times as preparation — especially if the test were done in a lab — would be very difficult.

During a trip to Los Angeles a few weeks ago, I noticed that my scores on several mental tests were better all of a sudden. The apparent cause was that I had taken flaxseed oil at an unusual time. Normally I took it about 10 hours before the tests; in this case I had taken it about 4 hours before.

Does flaxseed oil have a short-lived effect on brain function? When I got home I tried to find out. Rather than doing a set of four tests once per day I switched to one test many times per day (e.g., 10 times). This would allow detection of short-lived ups and downs in my mental function.

The test I used required nothing but my laptop. I usually have my laptop with me so such a test is much easier to do throughout the day than a task that requires other equipment. The test consisted of four blocks of 50 trials each. For each block I memorized a new set of three digits (e.g., 0 1 7). On each trial I saw 1, 3, or 5 digits and pressed a keyboard key as quickly as possible to indicate if any of the memorized digits is in the displayed set. For example, if the memory set was 0 1 7 and the display set was 3 2 8 the correct answer was “no” (which I indicated by pressing “4″).

The trials were packed together as closely as possible: As soon as I answered, the next set appeared. It took about 3 minutes to do 200 trials.

I did frequent measurements for four or five days. They appeared to confirm what the Los Angeles measurements suggested: Flaxseed oil did have a short-term effect. But two things muddied the water:

1. Baseline measurements were not always as steady as I would like. There were ups and downs that seemed too large to be random variation. The curious and exciting thing was that these ups and downs usually had a possible explanation — something had changed. For example, the measurements would be X1, X2, X3, Y. X1, X2, and X3 are close; Y is quite different. Between X3 and Y I had eaten a meal.

2. The task was difficult. I was about 88% correct and it was hard to do better. With any reaction-time task there is a speed-accuracy tradeoff: If you are slower, you can be more accurate. In this particular case this is a problem because it is an added source of variation and may reduce reaction-time differences: Rather than becoming slower, I become less accurate (or rather than becoming faster I become more accurate).

Problem #1 is easy (if slightly unpleasant) to solve: Keep the situation more constant. Eat less during the measurement period, etc.

To reduce Problem #2 I am learning a new task. I will go into detail tomorrow.

My mother tried drinking flaxseed oil. She measured her balance by standing on one leg; the measure was how long she could do that. She did ten of these measurements per day.

Here is what happened:

When she started taking the flaxseed oil, her balance suddenly started to improve.

Are injury-causing falls “the new scurvy,” I wondered — that is, caused by an easily-preventable nutrient deficiency? These results support that idea. However, I can’t explain the decline in balance during the pre-flaxseed baseline period. Perhaps she had eaten food high in omega-3 and the effects were wearing off.

Here are precautions about flaxseed oil. If you are 70 years old or older and would like to find out if flaxseed oil improves your balance, please contact me.

Directory of my omega-3 research.