I subscribe to the excellent: psyblog. I’ve flagged this up before and I strongly encourage you to subscribe if you’re fascinated by psychology and how our amazing mind works – for us as much as against us at times!
Quoting from the site:
According to an fMRI imaging study, change in pupil size may be difficult for us to notice consciously, but we do seem to pick up on these very small changes unconsciously (Demos et al., 2008).
The report found that no people detected that their pupil size had changed; yet, the evidence clearly showed that they had been manipulated, changing in size depending upon what image they were shown. A constriction of the pupil appears to indicate, among other things, disgust and disapproval and conversely a dilution indicates approval. Interestingly though, shock causes a widening of the pupils and will be followed by a narrowing. The narrowing is a protection mechanism, literally preventing as much light from the object entering our eyes. In effect we are protecting ourselves from the experience.
There is a great deal in their article and others on the eyes. Many people say our eyes are ‘the window to the soul’. It is something that I agree with too. Perhaps it might be worth while ‘keeping an eye’ on what you expose your mind to. Hedonistic habituation will lead to an ever-increasing need for greater stimulation.