Does pupil dilation during exercise predict effects on cognition?

There is a lot of interest in the eye as a window into the brain.  In a couple of weeks, we travel to Seattle for another installment in my participation on a study of the eye and Alzheimer's disease.  We said before that some scientists consider the eye to be an extension of the brain, and bad things happening in the brain might also be happening visibly in the eye.  So they are looking inside my eyes for evidence of the advance of Alzheimer's disease.

I came across another study of an association between the eye, the brain, and neurodegenerative disease.  This one found an association between pupil dilation during light exercise (yoga or walking on the treadmill) and cognitive improvement.  The researchers reported that they could associate the dilation of the eyes during light exercise with improvements in cognition.  The amount of change in pupil dilation could be associated with improved cognitive test scores.  They propose that the part of the brain controlling pupil dilation is also involved in cognition.  While this area of the brain is improving (during exercise), the pupils are dilating.

The researchers wanted to reassure people that even light exercise would improve their brain function. 

This is interesting, and it's in line with was learned by the HABIT study.  You will recall from Beating the Dementia Monster that Dr. Phatak was principal investigator for the Seattle site for the HABIT study, and she said that the only lifestyle change they measured that improved cognition was taking up yoga.  The HABIT study has since advanced from being a scientific study to being a regular program at the Mayo Clinic.

On the other hand, other research we discussed in Beating the Dementia Monster found that six or so hours a week (quite a lot for most people) was required to maximize the effect of exercise among patients with young onset Alzheimer's disease.  The study did not say how light or hard the exercise was.  And I've seen varying opinions on how hard exercise must be to produce results.  

In my case, I go kind of hard, but I'm really happy with my results.  Would my results be just as good if I went 2.5 mph on the treadmill with zero degree incline, rather than the 3.5 mph at the 15 degree incline that I do now?  There's only one way to find out, but I'm not willing to pursue it.