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Posts Tagged ‘cognitive load

why do our pupils dilate when we’re thinking hard?

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Canto: So we’re reading Daniel Kahneman’s Thinking fast and slow, among other things, at the moment, and every page has stuff worth writing about and exploring further, it’s impossible to keep up.

Jacinta: Yes with this stuff it’s a case of reading slow and slower. Or writing about it faster and faster, unlikely in our case. A lot of it might be common knowledge, but not to us, though in these first fifty pages or so he’s getting into embodied cognition, which we’ve written about, but there’s new data here that I didn’t know about but which makes a lot of sense to me.

Canto: That’s because you’ve been primed to accept this stuff haha. But I want to focus here more narrowly on experiments Kahneman did early in his career with Jackson Beatty, who went on to become the leading figure in the study of ‘cognitive pupillometry’.

Jacinta: Presumably measuring pupils, which is easy enough, while measuring cognition or cognitive processes, no doubt a deal harder.

Canto: Kahneman tells the story of an article he read in Scientific American – a mag I regularly read in the eighties, so I felt all nostalgic reading this.

Jacinta: Why’d you stop reading it?

Canto: I don’t know – I had a hiatus, then I started reading New Scientist and Cosmos. I should get back to Scientific American. All three. Anyway, the article was by Eckhard Hess, whose wife noticed that his pupils dilated when he looked at lovely nature pictures. He started looking into the matter, and found that people are judged to be more attractive when their pupils are wider and that belladonna, which is used in cosmetics, also dilates the pupils. More importantly for Kahneman, he noted ‘the pupils are sensitive indicators of mental effort’. Kahneman was looking for a research project at the time, so he recruited Beatty to help him with some experiments.

Jacinta: And the result was that our pupils dilate very reliably, and quite significantly, when we’re faced with tough problem-solving tasks, like multiplying double-digit numbers – and they constrict again on completion, so reliably that the monitoring researcher can surprise the subject by saying ‘so you’ve got the answer now?’

Canto: Yes, the subjects were arranged so the researchers could view their eyes magnified on a screen. And of course this kind of research is easy enough to replicate, and has been. My question, though, is why does the pupil dilate in response to such an internal process as concentration? We think of pupils widening to let more light in at times of dim light, that makes intuitive sense, but – in order to seek a kind of metaphorical enlightenment? That’s fascinating.

Jacinta: Well I think you’re hitting on something there. Think of attention rather than concentration. I suspect that our pupils widen when we attend to something important or interesting. As Eckhard Hess’s wife noticed when he was looking at a beautiful scene. In the case of a mathematical or logical problem we’re attending to something intently as well, and the fact that it’s internal rather than external is not so essential. We’re looking at the problem, seeing the problem as we try to solve it.

Canto: Yes but again that’s a kind of metaphorical seeing, whereas your pupils don’t dilate metaphorically.

Jacinta: Yes but it’s likely that our pupils dilate in the dark only when we’re trying to see in the dark. Making that effort. When we turn off the light at night in our bedroom before going to sleep, it’s likely that our pupils don’t dilate, because we’re not trying to see the familiar objects around us, we just want to fall asleep. So even if we leave our eyes open for a brief period, they’re not actually trying to look at anything. It’s like when you enter a classroom and see a maths problem on the board. Your eyes won’t dilate just on noticing the problem, but only when you try to solve it.

Canto: I presume there’s been research on this – like with everything we ever think of. What I’ve found is that the ‘pupillary light reflex’ is described as part of the autonomous nervous system – an involuntary system, largely, which responds ‘autonomously’, unconsciously, to the amount of light it receives. But as you say, there are probably other over-riding features, coming from the brain rather than outside. However, a pupil ‘at rest’, in a darkened room, is usually much dilated. So dilation is by no means always to do with attention or focus.

Jacinta: Well there’s a distinction made in neurology between bottom-up and top-down processing, which you’ve just alluded to, in the sense that information coming from outside, and sensed on the skin, the eye and other sensory organs, is sent ‘up’ to the brain – the Higher Authority, – which then sends down responses, in this case to dilate or contract the pupil, all that is called bottom-up processing. But researchers have found that the pupil isn’t just regulated in a bottom-up way.

Canto: And that’s where cognitive pupillometry comes in.

Jacinta: And here are some interesting research findings regarding top-down influences on pupil size. When subjects were primed with pictures relating to the sun, even if they were’nt bright, their pupils contracted more than with pictures of the moon, even if those pictures were actually brighter than the sun pictures. And even words connected to brightness made their pupils contract. There’s also been solid research to back up the speculations of Eckhard Hess, that emotional scenes, images and memories, whether positive or negative, have a dilating effect on our pupils. For example, hearing the cute sound of a baby laughing, and the disturbing sound of a baby screaming, widens our pupils, while more neutral sounds of road traffic or workplace hubub have very little effect.

Canto: Because there’s nothing, or maybe too much info, to focus our attention, surely? While the foregrounded baby’s noises stimulate our sense of wonder, of ‘what’s happening?’ We’re moved to attend to it. Actually this reminds me of something apparently unrelated but maybe not. That’s the well-known problem that we’re moved to give to a charity when one suffering child is presented in an advertisement, and less and less as we’re faced with a greater and greater number of starving children. These numbers become like distant traffic, they disperse our attention and interest.

Jacinta: Yes well that’s a whole other story, but this brings us to the most interesting of findings re top-down effects on our pupils, and the question we’ve asked in the title. A more scientific name for thinking hard is increased cognitive load, and countless experiments have shown that increasing cognitive load, for example by solving tough maths problems, or committing stacks of info to memory, correlates with increased pupillary dilation. This hard thinking is done in the prefrontal cortex, but we won’t go into detail here about its more or less contested compartments. What I will say is there’s an obvious difference between thinking and memorising, and both of these activities increase cognitive load, and pupillary dilation. Some very interesting studies relating memorising and pupillary dilation have shown that children under a certain age, unsurprisingly, are less able to hold info in short-term memory than adults. The research task was to memorise a long sequence of numbers. Monitoring of pupil response showed that the children’s pupils would constrict from their dilated state after six numbers, unlike those of adults.

Canto: So, while we may not have a definitive answer to our title question – the why question – it seems to be that cognitive load, like any load that we carry, requires the expenditure of energy, which can be manifested in the tightening of muscles in the eye which dilates the pupils. This dilation reveals, apparently, that we’re attending to something or concentrating on something. I can see some real-world applications. Imagine, as a teacher, having a physics class, say. You could get your students to wear special glasses that monitor the dilation and constriction of their pupils – I’m sure such devices could be rigged up, and connected to a special console at the teacher’s desk, so he could see who in the class was paying close attention and who was off in dreamland…

Jacinta: Yeah right haha – even if that was physically possible, there are just a few privacy issues there, and how would you know if the pupillary dilation was due to the fascinating complexities of electromagnetism or the delightful profile of your student’s object of fantasy a couple of seats away? Or how could you know if their apparent concentration had anything much to do with comprehension? Or how would you know if their apparent lack of concentration was to do with disinterest or incomprehension or the fact they were way ahead of you in comprehension?

Canto: Details details. Small steps. One way of finding out all that is by asking them. At least such monitoring would give you some clues to go by. I look forward to this brave new transhumanising world….

References

Daniel Kahneman, Thinking fast and slow, 2012

https://kids.frontiersin.org/article/10.3389/frym.2019.00003

Torres A and Hout M (2019) Pupils: A Window Into the Mind. Front. Young Minds. 7:3. doi: 10.3389/frym.2019.00003

Written by stewart henderson

June 24, 2019 at 11:18 am