Tag Archives: pupil

A window to the brain? Pupil size linked to intelligence

The pupil is the central opening of the iris on the inside of the eye through which light passes before reaching the lens and being focused onto the retina. Credit: Pixabay.

Humans are hardwired to read emotional cues in a person’s facial expressions, including micro-expressions of the eye. In fact, research suggests that if you want to read a person’s true emotional state, stay away from the mouth (fake smiles, anyone?) and pay attention to the eyes, whose sensitive involuntary muscle contractions are much more difficult to conceal. Now, researchers at the Georgia Institute of Technology claim that it may be possible to even gauge a person’s intellect from the eyes, after finding a correlation between pupil size and differences in intelligence between individuals.

The larger the pupil, the higher a person’s fluid intelligence may be

According to the study, which involved more than 500 people aged 18 to 35 from Atlanta, larger pupils were associated with higher intelligence, as measured by standard tests meant to gauge reasoning, memory, and attention.

This relationship is so pronounced that a person should be able to predict with relative confidence who scored the highest or the lowest on an intelligence test just by looking at their pupils with the naked eye, no additional instruments required.

Each subject’s pupil size was assessed using eye trackers that detect light reflecting from the pupil and cornea. Over lengthier eye-tracking, the researchers were able to compute each participants’ average pupil size.

The human pupil is between two and eight millimeters in diameter. However, they’re never fixed. They get bigger or smaller, depending on the amount of light they experience. In low light, your pupils open up or dilate, to let in more light. When it’s bright, they get smaller or constrict, to let in less light.

To normalize pupil measurements, the researchers made sure to assess the pupil at rest when the participants were staring at a blank screen for a couple of minutes. Each participant also went through a barrage of tests that scored them on their ability to solve new problems, remember things over time, and keep focus even when distracted. These combined abilities are often referred to as fluid intelligence.

Pupil size is also known to diminish with age. But after the researchers corrected for age, the pupil size and intelligence link still held up.

The researchers are careful to stress that their association is a correlation and they do not have evidence of a causal link between pupil size and differences in intelligence. That being said, it wouldn’t be that crazy if pupil size did indeed reliably indicate a propensity for scoring high on metrics for intelligence.

Previously, researchers noticed that the pupil is influenced by the locus coeruleus (from the Latin for ‘blue spot’), which communicates closely with the amygdala. Neurons in this region are the main source of the neurotransmitter noradrenaline (norepinephrine), an excitatory chemical that is released in response to pain or stress, stimulating what is referred to as the ‘fight-or-flight’ mechanism.

According to the authors of the new study published in the journal Cognition, the locus coeruleus is heavily involved in organizing brain activity and coordinating distant regions of the brain to work together and accomplish different tasks. Loss of function in this critical brain region is linked to  Alzheimer’s disease, Parkinson’s, and attention deficit hyperactivity disorder (ADHD).

The researchers at the Georgia Institute of Technology speculate that a person’s pupils may be larger due to greater regulation of activity by the locus coeruleus, which may lead to better cognitive performance.

“Additional research is needed to explore this possibility and determine why larger pupils are associated with higher fluid intelligence and attention control. But it’s clear that there is more happening than meets the eye,” Jason S. Tsukahara, Ph.D. student at the Georgia Institute of Technology and lead-author of the study, wrote in an article for Scientific American.

But since pupil size varies so much with the time of day, it might not be a good idea to stare someone dead in the eyes simply to assess whether they’re worth talking to. 

Just thinking about an object’s brightness is enough to change pupil size

Our pupils get bigger in response to dark conditions in order to allow more light into our eyes. Conversely, in bright conditions the pupils contract. Interestingly, a new study found that simply imagining a dark or bright light source is enough to change pupil size, even in the absence of visual stimuli.

Credit: Pixabay.

Nahid Zokaei, a researcher at the University of Oxford, along with colleagues, performed a series of experiments in which 22 men and women were shown dark and light patches. Each patch was associated with a specific sound.

After they learned to associate the sounds with the patches, during one experiment the patches flashed on a screen and would disappear after being displayed for only two seconds. The participants then had to imagine the correct corresponding patch when they heard a certain sound.

Amazingly, the study revealed that simply by thinking of a dark patch, the participants’ pupils would enlarge. The same would happen in the case of imaginary bright patches, which prompted the pupils to contract.

“The results provide surprising and consistent evidence that pupil responses are under top-down control by cognitive factors, even when there is no direct adaptive gain for such modulation, since no visual stimuli were presented or anticipated. The results also strengthen the view of sensory recruitment during working memory, suggesting even activation of sensory receptors,” the researchers wrote in the journal PNAS.

These are exactly the same results you would expect to see when physically looking at bright or dark objects — another testament to the power of our minds.

“The thought-provoking corollary to our findings is that the pupils provide a reliable measure of what is in the focus of mind, thus giving a different meaning to old proverbs about the eyes being a window to the mind,” the authors remarked.

Older adults less likely to recognize their errors

Here’s a concern: the older you get, the less likely you are to recognize your mistakes. A new study found that conscious error detection is impaired in older age, a process which seems to be associated with a decrease in self-awareness.

The generational conflict is not new; it’s likely been around since the dawn of man and will continue to lurk in our society for the foreseeable future. But while much of the debate is needlessly entrenched in an ‘us vs them’ rhetoric, there are some objective and significant differences between generations — and one of them may be related to how willing people are to admit their own shortcomings.

To test this, researchers asked younger (<30 years) and older (60-80 years) healthy adults to carry out an eye movement task. The task required a subjective assessment of response accuracy, as well as a “meta-judgment” of the certainty. This allowed scientists to see how aware participants were when they made an error in the task.

They tracked these errors by measuring pupil dilation. In humans and most animals, pupils dilate when something unexpected occurs — pupil dilation is associated (among others) with surprise, fright, and arousal. Pupil dilation also happens when people think they’ve made a mistake, which is what researchers were looking for.

First, the good news: both groups performed the task equally well.

“The good news is older adults perform the tasks we assigned them just as well as younger adults, albeit more slowly,” says Jan Wessel, assistant professor in the University of Iowa and the study’s corresponding author. “But we find there is this impaired ability in older adults to recognize an error when they’ve made one.”

However, when it came to errors — and particularly, recognizing one’s own errors — things were quite different. Younger people’s pupils dilated significantly when they thought they made a mistake. When they made a mistake but didn’t recognize it, their pupils also dilated, though to a lesser degree. Older adults, on the other hand, also exhibited dilated pupils when they made mistakes they recognized. But when they made a mistake they didn’t recognize, their pupils didn’t dilate. Researchers interpret this as a sign of reduced self-awareness. In other words, older people were less likely to realize when they were making a mistake, whereas younger adults seemed to have at least an inkling that they might have erred, says Wessel.

“Greater pupil dilation to reported errors was correlated with greater subjective certainty of error detection, and greater pupil dilation to unreported errors was correlated with greater “residual” awareness of unreported errors,” the study concludes. “Notably, older adults showed no pupil dilation to unreported errors, in line with their lack of “residual” error awareness on such trials. Taken together, our results suggest that reduced autonomic reactivity may contribute to age-related error awareness deficits.”

The study “A blunted phasic autonomic response to errors indexes age-related deficits in error awareness” was published in Neurobiology of Aging. doi: 10.1016/j.neurobiolaging.2018.06.019

What your pupil says about your language

A simple word is enough to trigger a reaction in your pupil.

The pupillary dilation. Image credits: Greyson Orlando.

A surprising new study found that when we hear words associated with a strong luminosity (ie “sun” or “shine”) our pupils contract as if we were actually exposed to them. The same thing happens to words we associate with darkness — our pupils dilate. The responses can have a variety of causes, from an involuntary reflex reaction to feelings of arousal to exposure to light. The latter is most common and often most pronounced.

This mechanism is done through the optic and oculomotor cranial nerve. Many creatures, humans included, exhibit a pupillary response. This is basically a mechanism through which the brain tries to adapt the body to new conditions, but it’s not totally clear why the reaction is also associated with psychological responses. What this study did is to open new avenues of research, and show that the dilation and contraction mechanism might be more complex than we thought.

“Theories about embodiment of language hold that when you process a word’s meaning, you automatically simulate associated sensory input (e.g., perception of brightness when you process lamp) and prepare associated actions (e.g., finger movements when you process typing),” the study reads. “To test this latter prediction, we measured pupillary responses to single words that conveyed a sense of brightness (e.g., day) or darkness (e.g., night) or were neutral (e.g., house).”

When confronted with a word, the pupils begin by dilating (0 — 0.5 s), following the general activation of the brain. When this initial activation has passed, the pupils retract (0.5 — 2 s). But the size of the pupil is also determined by the luminosity evoked by the words: when we read a luminance-associated word, the pupils become smaller than when we read a word associated with darkness (1 — 3 s). Image credits: Sebastiaan Mathot, University of Groningen.

Not all responses were alike. The brighter (or darker) the word people heard, the stronger the response, which in itself seems to raise more questions than it answers.

It seems to fit with a theory called the ’embodiment of language’. Basically, the theory says that whenever we hear a word or a group of words, we mentally simulate it in our mind. If someone would say ‘keyboard,’ your brain would project an image of the keyboard, as well as the gesture of typing at a keyboard; even if you might not realize it. The same thing happens with ‘sun’ — you visualize a big ball of fire, and your pupil adapts. However, researchers say, behavioral studies have so far not directly tested one of the central predictions of embodied language: that word meaning by itself can trigger, at least in some cases, associated involuntary actions. This is why this particular study is so important: it can be a definite proof for a long-standing but still challenged theory.

Journal Reference: Sebastiaan Mathôt, Jonathan Grainger, Kristof Strijkers. Pupillary Responses to Words That Convey a Sense of Brightness or Darkness. Psychological Science, 2017; 095679761770269 DOI: 10.1177/0956797617702699


Arousal makes us more confident in what we perceive, study finds

A new study found that even imperceptible changes in our state of arousal can influence the confidence we have in our visual experiences.

Image credits Nan Palmero / Flickr.

A team from University College London has found that subtle increases in arousal — even ones so slight we aren’t even consciously aware of — affect how confident participants felt about what they were seeing when asked to complete a simple task.

The team asked 29 volunteers to follow a cloud of moving dots on a screen, decide whether they were moving to the left or to the right, then rate how confident they are in their answer. Without the volunteers knowing, some of the challenges started with a disgusted face appearing on the screen — too briefly for the participants to consciously perceive it.

But their unconscious did pick up on the image, causing their heart rate to increase and their pupils to dilate. The team found that even when the dots were made noisier and harder to make out, participants in this aroused state maintained their confidence in the answers they were giving.

“Typically when we see something, we have insight not only into what it is that we’ve seen, but also how clearly we’ve seen it,” explains lead author Micah Allen from the UCL Institute of Neurology.

“If the picture is clouded or obscured, our feeling of confidence in what we’ve seen is lessened. This ability to accurately appraise our own experiences is an important part of our everyday lives.”

Previously, Allen explains, researchers have viewed the brain like “a scientist or statistician” who evaluates the quality of our experiences — and, based on this, it gives us our feeling of confidence. The study challenges this view by tying our confidence to physical states .

“Our results suggest that subtle, unconscious changes in the physiological state of our bodies impact how we perceive uncertainty. Interestingly, we found that not only did confidence correlate with how fast a participant’s heart beat on each trial, but that artificially increasing arousal actually caused participants to act as if they were blind to the quality of their visual experiences,” said Allen.

He added that the findings suggest our ability for conscious introspection is much more dependent on our body’s state than previously assumed. Professor Geraint Rees, Dean at the UCL Faculty of Life Sciences and co-author of the paper, believes that the findings could help understand people struggling with depression. Because anxiety and depression alter the body’s state of arousal, patients suffering these conditions might perceive a too certain or uncertain world.
The full paper “Unexpected arousal modulates the influence of sensory noise on confidence” has been published in the journal eLife.


goat eyes

Why goats have really weird rectangular pupils

Ever took a moment to stare a goat in the eyes? If you have, you might have noticed something really weird: their pupils are horizontal, or rectangular. It’s one of those things that baffles the mind once it hits you because we’re so used to circular pupils or even vertical slit ones, on account of cats or snakes.

goat eyes

Credit: Pinterest user Leta Sparks

It’s always about survival

UC Berkeley and Durham University researchers were also intrigued by these somewhat atypical shape. Being scientists, they decided to investigate and analyzed pupil shapes of no fewer than 214 land species.

What they eventually found was that pupil shape is linked to the ecological niche or role of the animal. The general pattern is predators have vertical slit pupils because these help them judge distance better, making it easier to pounce on prey. Meanwhile, herbivores — which are the target of carnivores — have rectangular slit pupils as a line of defense, offering them a broader field of vision.

As a herbivore, apart from some antlers and hooves, there’s not that much you can do to fend back a predator. The best thing they can do is run away, which is why many herbivores are also fast. Before you can run, though, you need to know when it’s time to make an exit which is where the goat’s rectangular eyes come in. These enable a panoramic vision which can detect intruders approaching from various directions.

The horizontal pupils also enhance the image quality of objects directly ahead of the animal. This clear front-image helps guide rapid locomotion over a potentially rough terrain, the researchers noted in Science Advances.

Grazing animals like goats also rotate their eyes when they bow their heads down so their eye slits are parallel to the ground at all times. They can rotate more than 50 degrees per eyes or 10 times more than the human eye. This way, even when they’re grazing, goats can always keep a good eye on the world and lurking predators.

Rectangular pupils are typically employed by equines and ruminants, such as sheep, deer, and horses.

Good quality breakfast linked to better performance in school

Cardiff University public health experts have discovered a powerful link between a pupil’s breakfast quality and their performance at school. The study – the largest to date looking at how nutrition influences school performance — recorded the breakfast habits of 5000 pupils aged 9 through 11, and their results in the Key Stage 2 Teacher Assessments 6-18 months later. The pupils who ate breakfast, and had better quality food at breakfast, achieved higher academic outcomes that the ones attending classes on an empty stomach.

Image via freestockphotos

“While breakfast consumption has been consistently associated with general health outcomes and acute measures of concentration and cognitive function, evidence regarding links to concrete educational outcomes has until now been unclear,” said Hannah Littlecott, lead author of the paper.

“This study therefore offers the strongest evidence yet of links between aspects of what pupils eat and how well they do at school, which has significant implications for education and public health policy – pertinent in light of rumours that free school meals may be scrapped following the November spending review.”

The pupils were asked to remember all the food and drinks they consumed over a 24 hour period, noting what they had and the specific time of the meals throughout the day as well as what they ate in the morning of the reporting.

The data shows that beside the quality and number of healthy items consumed for breakfast, other dietary habits — such as the ratio of sweets to fruits and vegetables each pupil had daily, for example — also had a positive effect on educational performance. Eating unhealthy items like sweets and crisps for breakfast, which was reported by 1 in 5 children, had no positive impact on educational attainment.

“For schools, dedicating time and resource towards improving child health can be seen as an unwelcome diversion from their core business of educating pupils, in part due to pressures that place the focus on solely driving up educational attainment. But this resistance to delivery of health improvement interventions overlooks the clear synergy between health and education. Clearly, embedding health improvements into the core business of the school might also deliver educational improvements as well,” Hannah concluded

Professor of Sociology and Social Policy Chris Bonell, from the University College London Institute of Education, welcomed the study’s findings.

“This study adds to a growing body of international evidence indicating that investing resources in effective interventions to improve young people’s health is also likely to improve their educational performance. This further emphasises the need for schools to focus on the health and education of their pupils as complementary, rather than as competing priorities. Many schools throughout the UK now offer their pupils a breakfast. Ensuring that those young people most in need benefit from these schemes may represent an important mechanism for boosting the educational performance of young people throughout the UK”.

Dr Graham Moore, who also co-authored the report, added:

“Most primary schools in Wales are now able to offer a free school breakfast, funded by Welsh Government. Our earlier papers from the trial of this scheme showed that it was effective in improving the quality of children’s breakfasts, although there is less clear evidence of its role in reducing breakfast skipping.”

“Linking our data to real world educational performance data has allowed us to provide robust evidence of a link between eating breakfast and doing well at school. There is therefore good reason to believe that where schools are able to find ways of encouraging those young people who don’t eat breakfast at home to eat a school breakfast, they will reap significant educational benefits.”

Pupil shape reveals what kind of animal you are

Your eyes are a window to your soul, or so the saying goes – but a new research suggests that the pupil shape and size have a lot to do with an animal’s nature. Hunters like cats tend to have vertical pupils, while horizontally elongated pupils are generally plant-eaters.

cat pupil

Image via Wiki Commons.

Pupils are the eyes’ aperture – they’re black because light rays entering the pupil are absorbed. Humans have circular pupils, but that’s rather rare in the animal kingdom. Creatures like crocodiles, vipers, cats and foxes have vertical pupils, while for horses, rays, deer, sheep and many others, pupils are horizontal. But why? Why is there such a large variability between different species?

An analysis of 214 species of land animals shows that a creature’s ecological niche is a strong indication of pupil shape. The study, led by vision scientist Martin Banks, a UC Berkeley professor of optometry, found that creatures with vertical pupil slits are more likely to be ambush predators. Among the 65 frontal-eyed, ambush predators in this study, 44 had vertical pupils, and 36 of them had shoulder heights that were less than 42 centimeters (16.5 inches) – so they were close to the ground.

They also have stronger muscles in the eyes which allows them to greatly contract or dilate the pupil, allowing more or less light to enter the eye. For example, the vertical slits of domestic cats and geckos undergo a 135- and 300-fold change in area between constricted and dilated states. Us humans exhibit only a 15 fold change.

Meanwhile, grazers need horizontal pupils so they can better detect predators.

“The first key visual requirement for these animals is to detect approaching predators, which usually come from the ground, so they need to see panoramically on the ground with minimal blind spots,” said Banks. “The second critical requirement is that once they do detect a predator, they need to see where they are running. They have to see well enough out of the corner of their eye to run quickly and jump over things.”

Meanwhile, those with round pupils, like humans, are more likely to be active hunters, chasing down their prey. This raises an interesting question: we have vertical, horizontal, circular… why not diagonal?

“For species that are active both night and day, like domestic cats, slit pupils provide the dynamic range needed to help them see in dim light yet not get blinded by the midday sun,” said Banks. “However, this hypothesis does not explain why slits are either vertical or horizontal. Why don’t we see diagonal slits? This study is the first attempt to explain why orientation matters.”

Well, herbivores need to have a broad field of sight to be able to see incoming predators. For ambush predators, accurately gauging the distance animals would need to pounce on their prey – this is prevalent especially for animals closer to the ground (this is why cats have vertical pupils, but bigger cats, like lions or tigers don’t). Having diagonal pupils simply wouldn’t provide any advantage.

So far, this study has only been conducted on terrestrial animals. It would definitely be interesting to see how their findings fare with flying and water-based creatures.