The eyes as a window into the mind

What can you tell by about what someone is thinking by looking them in the eyes? Sadly, I can tell nothing. I know what to look at – the size of the pupils, not the mythical direction they are looking – but now I know too many things the eyes might be saying.

Our pupils will shrink or dilate in response to ambient light...and many different mental activities.

Our pupils will shrink or dilate in response to ambient light…and many different mental activities.

There is always the possibility that pupil size can tell you if someone is sexually attracted to you; this fact has pervaded the common knowledge, and may even be the kernel of truth behind “gaydar” as the pattern of pupil dilation  reveals your sexual orientation.

This doesn’t mean that anyone staring at you with wide pupils is hoping for a date. In fact, they could be thinking about almost anything at all, as long as they are thinking hard. Scientists have known that pupils dilate in response to mental effort since 1964, and have used this to investigate everything from  when children start trying to remember something to the challenge of understanding and interpreting language.

And now, we have yet another mental activity that will show in the pupils: imagining a sunny beach. Mental imagery uses many of the same brain regions as actual vision does, so much so that just imagining bright light will prompt the pupils to shrink. When people are asked to imagine “looking at a sunny sky”, their pupils will contract; when they imagine “looking at the night sky” instead, their pupils dilate a, even though they reported the same mental effort needed to imagine both.

All of this sets the stage for an interesting chain reaction at the dinner table. If I notice my date’s pupil’s dilate, I’ll start wondering if they are enjoying the date, or completely distracted by some complex work problem, or perhaps imagining some favorite cave-spelunking vacation. The mental effort of trying to figure this out will probably cause my own pupils to dilate. Perhaps this will be helpful in letting someone else see into my soul.


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