Piloting an experiment, ALL participants show a difference between static vs. illusory motion conditions following the initial light reflex. 6/9 participants show greater dilation to illusory motion (as predicted), 3/9 show greater dilation to static images (strong reverse effect).
This is counter-intuitive to literature on pupil-dilation as an exploratory/arousal mechanism...have any studies been conducted on vast individual variability in the pupil's arousal response to this extent? In essence, is there anything to support testing the absolute difference in pupil response given that every participant shows a difference between conditions?
Any insight appreciated!
Dear Steve
I have done several pupillary response experiments on how pupil size (constriction or dilation) changes with the size and spatial frequency of visual stimuli. I suspect that the luminance or other visual property difference of the static and illusory motion conditions affected your results. To study the effect of arousal, you should first make sure that the visual properties of these two conditions are balanced. Otherwise, it is hard to draw any conclusions.
I hope this helps. I am working at BMI as well. Let me know if you need further information.
Juan
Dear Steve,
Following up on Abdul Aziz's comment, I think it would be worth having a look at the eye movements in your task. They could certainly affect your pupil size estimates. Was fixation enforced?
Another important question is how you test the significance of your effect subjectwise. Pupillary data is a bit dangerous because of strong autocorrelation. This could enflate your effects artifically...
Best,
Alex
We are actually currently doing some eye-tracking research comparing moving and static faces however our primary focus is on fixation patterns rather than pupil dilation I am afraid. There is some literature (e.g. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102463) that suggests that pupil dilation is indicative of overall attentional effort though. Do you have behavioural / performance measures in your study too? It might be that the behavioural data can shed light on why some of your participants are showing this reverse pattern e.g. if they are finding the static condition harder than the other participants and harder than the moving condition it may be that they are exerting more attentional effort in the static condition...could this be possible?
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