The Meaning of Pupil Dilation

Scientists are using pupil measurements to study a wide range of psychological processes and to get a glimpse into the mind.

What do an orgasm, a multiplication problem and a photo of a dead body have in common? Each induces a slight, irrepressible expansion of the pupils in our eyes, giving careful observers a subtle but meaningful signal that thoughts and feelings are afoot.

Wikimedia, Steve Jurvetson

For more than a century, scientists have known that our pupils respond to more than changes in light. They also betray mental and emotional commotion within. In fact, pupil dilation correlates with arousal so consistently that researchers use pupil size, or pupillometry, to investigate a wide range of psychological phenomena. And they do this without knowing exactly why our eyes behave this way. “Nobody really knows for sure what these changes do,” said Stuart Steinhauer, who directs the Biometrics Research Lab at the University of Pittsburgh School of Medicine.

While the visual cortex in the back of the brain assembles the images we see, a different, older part of our nervous system manages the continuous tuning of our pupil size, alongside other functions—like heart rate and perspiration—that operate mostly outside our conscious control. This autonomic nervous system dictates the movement of the iris, like the lens of a camera, to regulate the amount of light that enters the pupil.

The iris is made of two types of muscle: in a brightly lit environment, a ring of sphincter muscles that encircle and constrict the pupil down to as little as a couple of millimeters across; in the dark, a set of dilator muscles laid out like bicycle spokes, which can expand the pupil up to 8 millimeters—approximately the diameter of a chickpea.

Cognitive and emotional events can also dictate pupil constriction and expansion, though such events occur on a smaller scale than the light reflex, causing changes generally less than half a millimeter. But that’s enough. By recording subjects’ eyes with infrared cameras and controlling for other factors that might affect pupil size, like brightness, color, and distance, scientists can use pupil movements as a proxy for other processes, like mental strain.

Princeton psychologist Daniel Kahneman showed several decades ago that pupil size increases in proportion to the difficulty of the task at hand. Calculate 9 times 13, and you pupils will dilate slightly. Try 29 times 13, and they will widen further and remain dilated until you reach the answer or stop trying. As Kahneman says in his recent book, Thinking Fast and Slow, he could divine when someone gave up on a multiplication problem simply by watching for pupil contraction during the experiment.

“The pupils reflect the extent of mental effort in an incredibly precise way,” Kahneman told the German news magazine Der Spiegel, adding, “I have never done any work in which the measurement is so precise.” When he instructed subjects to remember and recite a series of seven digits, their pupils grew steadily as the numbers were presented one-by-one and shrunk steadily as they unloaded the digits from memory.

Subsequent research found that the pupils of intelligent people (as defined by their SAT scores) dilated less in response to cognitive tasks compared to those of less intelligent participants, possibly indicating a more efficient use of brainpower. 

Scientists have since used pupillometry to assess everything from sleepiness to introversion, race bias,schizophrenia, sexual interest, moral judgment, autism, and depression. And while they haven’t been reading people’s thoughts per se, they’ve come pretty close.

“Pupil dilation can betray an individual’s decision before it is openly revealed,” concluded a 2010 study led by Wolfgang Einhäuser-Treyer, a neurophysicist at The Philipp University of Marburg in Germany. In the study, participants were told to press a button at any point during a 10 second interval, and their pupil size correlated with the timing of their decision. The dilation began about 1 second before they pressed the button and peaked 1 to 2 seconds after.

But are pupils informative outside the lab? Men’s Health Magazine says you can tell when it’s “time to make your move” by watching your date’s pupils, but some skepticism is warranted. “It is unclear to me to what extent this can be exploited in completely unrestrained settings,” Einhäuser-Treyer wrote in an email, pointing out that light conditions could easily interfere with attempts at interpersonal pupillometry.

Other efforts to exploit pupil dilations for purposes beyond scientific research have failed. During the Cold War, Canadian officials tried to develop a device they called the “fruit machine” to detect homosexuality among government employees by measuring how their pupils responded to racy images of women and men. The machine, which never worked, was to aid the government’s purge of gay men and lesbians from the civil service and thereby purportedly reduce their vulnerability to Soviet blackmail.

A pupil test for sexual orientation remains as unlikely as it was in the 1960s. Researchers at Cornell University recently showed that sexual orientation correlated with pupil dilation to erotic videos of their preferred gender, but the trend was only apparent when averaged across subjects, and only for male subjects. While pupillometry shows promise as a noninvasive measure of sexual response, they concluded, “not every participant’s sexual orientation was correctly classified” and “an observable amount of variability in pupil dilation was unrelated to the participant’s sexual orientation.”

Pupillometry also became popular in the advertising industry during the 1970s as a way to test consumers’ responses to television commercials, said Jagdish Sheth, a marketing professor at Emory University. But the practice was eventually abandoned. “There was no scientific way to establish whether it measured interest or anxiety,” Sheth said.

Indeed, pupillometry is limited in its ability to distinguish between the many types of cognitive and emotional processes that can affect pupil dilation. “All we can do is watch the change at the end,” Steinhauer said. “We can't monitor everything going into it.”

Still, he added, our eyes are easy to observe and provide a sensitive indicator of cognitive, emotional, and sensory response, making pupillometry a valuable tool for psychological research. “It's like having an electrode permanently implanted in the brain.”

This article is provided by Scienceline, a project of New York University's Science, Health and Environmental Reporting Program. 

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Seeing Isn’t Believing

How motion illusions trick the visual system, and what they can teach us about how our eyes and brains evolved.

© ISTOCK.COM/ATYPEEK

Animal vision has not evolved as one might think. In contrast to the invention of photography and film—which began with the first black-and-white daguerreotypes in 1839, then added color in 1861, and finally motion in 1891—motion perception in animals appears to have evolved long before color vision. Indeed, as vision researcher Gordon Walls declared in 1942, perceiving motion is one of the most ancient and primitive forms of vision.

Even the humble housefly, which can only distinguish four to six different colors, is remarkably good at seeing motion. Try to swat a fly with your hand, and it will be gone long before you even get close. (The best way is to clap your hands above it so that it flies up between your hands. Wear gloves.) Oddly, however, while a fly is quick to register these fast movements, it cannot recognize slow movement at all. Move your hand very, very slowly toward a fly, and you can tap its back before it knows that you are there.

As good as animals are at detect­ing motion, they can also be fooled. Seeing the errors that a system makes can help us to understand how that system works nor­mally.

Much of the early research on motion perception was performed on insects,¹ but similar results have been found for a huge range of species, from fishes to birds to mammals. Frogs, which eat insects, respond to small, rapidly moving prey, as well as to overall dimming or darkening that likely signals an approaching predator, but they often ignore stationary objects, perhaps because they cannot see them.²

Mammals are likewise tuned in to motion. Although many people believe that it is the bright red color of the matador’s cape that enrages the bull, the popular TV program Mythbusters found that the color made no difference; it was the motion of the cape’s fabric that mattered. Red, blue, and white capes got equal, half-hearted attacks when they were motionless, but waving the capes elicited an aggressive charge. In fact, most mammals, including domestic and big cats, deer, cattle, and dogs, appear to be color-blind. Apes may have evolved color vision in order to find the ripe fruit among green leaves (see “The Rainbow Connection,” The Scientist, October 2014), but lions eat other mammals, most of which have evolved to match their surroundings, rendering color vision useless in finding prey. When a gazelle runs away, however, it becomes a strong stimulus for the lion’s keen motion vision. It’s no wonder that young deer will often freeze when they sense danger. Correspondingly, prey animals would find color vision of little use, but they are extremely good at seeing the motion of an approaching predator.

UNCOVERING STEALTH: Many animals are camouflaged to match their surroundings. Predator and prey animals thus rely heavily on motion to detect one another. A moving object pops out from the fixed background though a process called motion segmentation. Motion has broken the camouflage.

But as good as animals are at detecting motion, they can also be fooled. I study visual illusions of motion because seeing the errors that a system makes can help us to understand how that system works normally. Visual perception goes far beyond our retinal images, which provide only partial sensory information. We use our knowledge and expectations of the world to fill in the gaps, for instance, when an object is partly hidden. Ambiguous illusions that can be interpreted in two different ways, but not both ways at the same time, can also shed light on how we perceive the world around us.

Illusions of movement

Visual movement can be thought of as a change in brightness, or luminance, over space and time. A white spot that glides across a black screen shows real movement. If the same spot jumps back and forth between two positions, or makes a series of intermittent forward jumps, the brain can still perceive movement. Small, fast jumps give the smoothest impression of movement, but even large, slow jumps give a strong impression that the spot is, in fact, moving across the screen.

MINIMAL MOTION: The static oblique pairs of dots look random, but in fact are a minimum stimulus for seeing motion. Run your finger from left to right across the arrow at the bottom, following your finger with your eyes, and the dots will almost magically segregate and move up and down.

Why does the visual system treat this jumping dot as a single object in motion, instead of seeing one spot disappear while an unrelated spot appears nearby at the same instant? First, the brain usually treats “suspicious coincidences” as being more than coincidences: it is more likely that this is a single spot in motion rather than two separate events. Second, the visual system is tolerant of brief gaps in stimuli, filling in those gaps when necessary. This perception of apparent motion is, of course, the basis of the entire movie and TV industries, as viewers see a smooth motion picture when in reality they are simply watching a series of stationary stills.

We can pose a riddle to the visual system by presenting two apparent motions in opposite directions simultaneously. For example, an image of a white horse and an image of a black horse suddenly exchange positions. But you do not see each horse independently changing in color. Rather, you see the horses jumping from one location to the other. The coincidence is too great, and, instead of two independent events, the visual system economically infers a single event: the jumping horse.

CONTRAST DRIVES MOTION: In both panels, the jumping horses are identical, only the backgrounds differ. In the upper panel, the white horse has higher contrast against the dark background and appears to jump back and forth. In the lower panel, the black horse has higher contrast against the light background and appears to jump.

But which horse jumps? The answer depends on the context. On a dark background, the white horse appears to jump back and forth; on a light background, the black horse appears to move. In other words, the horse with the higher contrast wins. This is because the strength of a motion signal in the brain of the observer is equal to the product of the contrast of each horse against the background color, a measure called motion energy.³ Interestingly, if contrast is held constant, the color of the horses makes no difference because color has little or no input into the motion pathways of the brain.⁴

Contrast can also explain why a black or white object on a background of the opposite color seems to move faster than a gray object on a gray background, and why cars appear to move more slowly in the fog. Indeed, we tend to judge motion not in absolute terms, but relative to the background: the perceived strength and speed of motion depend on the contrast of the moving object against its surroundings.⁵ In fact, a driver partly judges his own speed by the rate at which landmarks such as trees flash past him. In the fog, the trees appear slowed down, so he underestimates the speed of all cars, including his own, with potentially disastrous consequences.⁶

BABY STEPS: Two squares, one dark blue and one light yellow, move smoothly together at constant speed across a grey background. But when the background is changed to black and white vertical stripes, the motion seems to change as well. The little squares appear to hesitate and speed up in alternation, a little like the feet of a walking person (Anstis 2001, 2004: Howe et al. 2006).

Combining movement and changes in contrast results in an even more complex outcome. Suppose that a black spot on a medium-gray background makes a small jump to the right—a total distance much smaller than the diameter of the spot itself—and, at the same time, instantaneously changes to white. Instead of seeing a slight motion to the right, one sees something quite unexpected: the spot appears to move to theleft, toward the starting position and opposite to the physical displacement.

MOTION IN CONTEXT: A yellow bug and a red bug both fly around in perfect clockwise circles of the same size, though the red bug moves much more rapidly. When a background is added that also circles clockwise, the yellow bug’s orbit, which syncs up with the motion of the background, seems to shrink to about half the size of the red bug's orbit.

This effect, known as reverse phi, is particularly strong in peripheral vision: if someone fixes his gaze on a small stationary cross and observes the moving spot out of the corner of his eye, the backwards leap will be even more pronounced.^7,8 Once again, this phenomenon is consistent with the idea that perceived motion depends on motion energy, or the product of the contrasts of moving objects.³ If the spot makes a long series of jumps to the right, changing between black and white on each jump, one still sees steady motion to the left, but after a while the observer will recognize that, paradoxically, the spot is now farther to the right, demonstrating that position and motion are signaled independently.

RIGHT OR LEFT: The lion on the left moves to the right, then back to the left, in successive movie frames. Because the contrast is held constant, an observer accurately sees this movement. The lion on the right actually moves in the same direction, but since the lion on the right is alternately positive and negative, it seems to move in the opposite direction, as a result of a visual phenomenon known as reverse phi.

Why we are fooled

The phenomena described above are “low-level” illusions that are probably based on “bottom-up” sensory signals from brain cells in the visual system that are specialized to detect motion. Normally, sensory information agrees. If a cat is partly hidden behind a tree, for example, all the cues of color, shadows, and texture tell the same story—that the hidden part of the cat exists out of view behind the tree. The brain acts like a judge, confirming the same story as told by independent witnesses. The brain also strengthens this verdict with “top-down” information based upon prior learning: if the cat’s whiskers stick out on one side of the tree, and its tail on the other, the brain automatically “fills in” that there is a continuous cat partly hidden by the tree, not two unrelated cat bits. This interpolation process, called visual amodal completion, starts from a representation of the visible features of the stimulus in early visual cortex, probably an area called V1, and ends with a completed representation of the stimulus in the inferior temporal cortex.⁹ Jay Hegdé of the University of Minnesota and colleagues even found two regions in the object-processing pathways of the brain that actually responded more strongly to partly hidden objects than to complete ones.¹⁰

Visual object recognition thus involves two stages: a bottom-up inputting of perceptual information, and a top-down memory stage in which perceptual information is matched with an object’s stored representation. Tomoya Taminato of Tohoku University School of Medicine in Japan and colleagues last year presented volunteers with blurry pictures that gradually became sharper. Observers responded once when they could guess the identity of the object in the image, representing the perception stage, and a second time when they were certain of the identity, the memory stage. Their results attributed the perception stage to the right medial occipitotemporal region of the brain, and the memory stage to the posterior part of the rostral medial frontal cortex.¹¹

If a cat’s whiskers stick out on one side of the tree, and its tail on the other, the brain auto­matically “fills in” that there is a continu­ous cat partly hidden by the tree, not two unrelated cat bits.

Visualizing motion is similarly subject to both bottom-up and top-down processes. Reverse phi, in which an object that changes contrast as it travels is viewed as moving in the reverse direction, is a bottom-up illusion that happens early in the brain’s visual processing pathway. Researchers have tracked the origin of this illusion to V1 cells, which in awake monkeys respond to the reverse phi illusion in the same way they respond to backwards-moving objects.¹² Meanwhile, top-down processes predict what objects these signals probably represent, based upon memory and previous learning. Object parsing, for example, is a process that guides perception by deciding what objects are likely to be present based upon prior knowledge of the world.¹³

Consider the closing blades of a pair of scissors. The intersection itself is not an object; only the blades are. This distinction is not lost on the visual system. Observers make 10 times the tracking errors—their eyes deviating from the target—when they attempt to follow a sliding rather than a rigid intersection.¹⁴ Although you can sense the movement of a sliding intersection, you do not interpret it as an object.

FOLLOW THE CENTER: In the top-left panel, a vertical bar and an overlapping horizontal bar both move in a clockwise circular path without rotating. Most observers correctly see each bar as moving clockwise, but falsely view the central intersection as going clockwise too. In fact, the intersection of the bars moves counterclockwise, as becomes apparent in the top-right panel, in which a red outline surrounds the bars.

This phenomenon stems from the fact that smooth eye movements require a smoothly moving target. Move your thumb from side to side in front of you and ask a friend to follow your thumb with his eyes. Watch his eyes and you will see them move smoothly from side to side. Now hold up both your thumbs a yard apart and ask him to move his eyes smoothly from one stationary thumb to the other. He cannot do it! You will see his eyes moving in a series of jerky eye movements called saccades. This shows that a moving object is necessary to drive smooth-pursuit eye movements.

Visual signals flow forward from the visual cortex at the back of the brain, then travel along the ventral stream for the decision about what objects are present, and also up along the dorsal stream to the medial temporal area, which analyzes motion. Finally, the nerve signals travel forward to the frontal eye fields that control eye movements. A sliding intersection is not parsed as a real object, and it cannot support smooth eye movements.

The visual system can also flip between local and global motions, but it cannot see both at once. The brain considers incompatible interpretations—Are there many small groups, or a few large groups?—and adopts them in alternation, but never both at the same time. The shape and spacing of spots on a screen, the duration and position of your fixations, and other factors can all influence which percept you see.

LOCAL OR GLOBAL: At first, viewers see pairs of spots, each pair rotating about their common center. But if you watch for a while, you will suddenly see it reorganize into two larger squares on top, or eight interdigitating octagons on the bottom. The visual system can alternate between either percept, but it cannot see both at once.

Motion can shift an object’s perceived position. If an image of an upright cross flashes briefly on a textured wheel that is rotating clockwise, the cross itself will appear to be tilted clockwise, and it sometimes even looks distorted. Notably, only the motion of the background that occurs after the flash can drag the cross along: motion beforehand has no effect.¹⁵

SPINNING BACKGROUND: Red and green crosses flashing in alternation look bent out of shape, with the right angles no longer looking like right angles. This is because the vertical arms of the crosses lie on the edge of a pie-shaped sector of the moving background, while the horizontal arms lie on the middle of a sector. The edge of a sector has more pulling power than the middle of a sector.

In sum, illusions teach us that perception goes far beyond the information picked up by our senses. Perception is an indirect, interpretive top-down process that is not driven simply by stimulus patterns, but is instead a dynamic, active search for the best interpretation of the available sensory data.
UNDERESTIMATING MOVEMENT: When it moves slowly, it is correctly seen as moving through 180°, from 12 o’clock to 6 o’clock. But at faster speeds, the length of its motion path is underestimated and it seems to move only from 1 o’clock to 5 o’clock. Spots that flash at its turnaround points simply provide milestones that mark this underestimation.

Stuart Anstis is a professor of psychology at the University of California, San Diego, and a visiting fellow at Pembroke College in Oxford, U.K. Working with international collaborators, he has published some 170 articles on visual perception.

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The dangers of working in an office

The office here at Medical News Today HQ is a pleasant place to work. It is a largely tranquil place (until somebody decides to use the shredder) where the tea is plentiful and occasionally a passing dog can be spotted through the window.

Posture is crucial to keeping healthy when working for long periods of time at a desk. This woman risks injuring her back and neck by hunching forward.

On the idyllic surface, it seems as though it would be a perfectly safe and healthy place to work. There are certainly no obvious hazards of the kind that are commonplace on construction sites or in factories, and many office workers enjoy the benefits of rigid working days, rather than having their body clocks thrown by changing shift patterns.

But offices are not without their hazards, even if these are not as overt as those in other environments. One significant problem comes from being sat at a desk for most of the day. A recent study has suggested that the amount of time spent sitting each day is associated with a higher risk of various diseases.

According to the US Bureau of Labor Statistics (BLS), around 21,638,470 people are employed in jobs defined as office and administrative support occupations. However, this figure does not include other occupations, such as management roles, business and financial operations occupations or computer occupations that are also likely to be based in office environments.

In this Spotlight, we investigate what the health-conscious office worker needs to be wary of if they are going to complete their 9-5 with both body and mind intact, and if there are any ways for them to maintain peak fitness during their employment.

Chained to your desk

As mentioned above, sitting for long periods of time every day is bad for your health. While sitting reduces the amount of time individuals can spend exercising, researchers have demonstrated that prolonged sitting time is associated with poor health outcomes regardless of the amount of physical activity performed.

Although sitting at a desk is a seemingly simple task, it is an easy one for people to do wrong. Workers often complain of sore wrists and pain in the back and neck, and this will frequently be due to the way they position their body while working.

If an individual is sitting or typing in an unhealthy way, it is likely that they will be putting strain on their body for most of their working day. That is a lot of strain for a body to take over the course of a week. Unsurprisingly, back pain is one of the most common reasons for employees missing work and is the second most common reason for visits to the doctor.

The American Chiropractic Association (ACA) state that back pain can be caused by poor posture, obesity and psychological stress among other factors, all of which can easily come into play in an office environment if work is tense and not allowing for employees to take leave from their desks.

Good posture at the desk is the first step to be taken in protecting your health when working in the office. This can be achieved with efficient office ergonomics. Making sure that all objects that will be needed are situated close by reduces excessive stretching.

When sitting in front of a computer, the body should be positioned centrally to the monitor and keyboard. You should sit up straight with feet rested flat on the floor. If this is not possible, a footrest should be used. Thighs should ideally be horizontal with the knees and level with the hips.

The forearms should also be level or tilted up slightly. When typing, wrists should be in a straight and natural position. Using a wrist rest can reduce stress on the wrists and help prevent specific awkward positioning.

There are a number of common posture mistakes that can be made when sitting and can easily become part of a routine if not addressed:

• Slouching - this position places a lot of pressure on the lower back, damaging the ligaments, joints and soft tissue in this area and can lead to hunching
• Sitting cross-legged - this position tucks in the hip, making it difficult to sit up straight and leading to slouching. Sitting cross-legged can also lead to muscle imbalances in the hips that cause pain and stiffness
• Hunching forward - can lead to a tight chest and weak upper back, potentially leading to the development of a rounded upper back that is susceptible to pain and stiffness
• Poking the chin forward - sometimes a symptom of a hunched back or sitting too low as an attempt to compensate for excess downward pressure, this can lead to muscle weakness around the neck
• Phone cradling - employees that have to use a phone frequently may hold their phone handset between their ear and shoulder in order to leave their hands free to operate a computer or write. This can weaken the neck muscles and lead to muscle imbalances that cause headaches.

Office workers are advised to get up and move around whenever they can. The nature of many office jobs, however, usually results in long periods of sitting down. If you are going to be sitting down at a desk for any length of time, it is a good idea to get the basics right.

"The number one thing that gets people into trouble as far as a downgrade in their health is their posture," says Luis Feigenbaum, a director of sports physical therapy at the University of Miami's Miller School of Medicine, in conversation withABC News.

Computers: one-eyed monsters of the office

These days, most people sitting at a desk will have a computer sitting right in front of them. Although they make a lot of jobs easier, they also make keeping healthy in the office a lot harder.

Many office workers will be familiar with computers, and using them properly is important for keeping healthy.

Firstly, where a computer and its related hardware are positioned can drastically influence posture. The height of a computer monitor will affect the height of an office chair - a monitor should be positioned directly in front of the user, about an arm's length away, with the top of the screen just below eye level.

As well as posture, using a computer can wear down other parts of the body that are directly using it, namely the eyes and the wrists.

To avoid eye strain, both the computer monitor and the office lighting need to be addressed. The screen should be adjusted so that its brightness and contrast levels suit the lighting conditions in the room, which should not be too bright.

Screen glare is a major cause of eyestrain and can be reduced by ensuring that monitors are not positioned opposite windows where possible. If situated close to a window, use shades and blinds to reduce the amount of light that falls on the monitor.

If the font size of text being read on a computer is too small it can lead to eyestrain as well as harming posture, as a worker may be inclined to hunch forward to read text more closely. Increasing font size or zooming in on a page that is being read protects employees from this risk.

Typing is a repetitive action that puts the hands and wrists under great pressure. If performed forcefully enough and for long enough periods of time, it can lead to disabling pain. In office workers, it can lead to repetitive strain injuries, whereby the tissue surrounding the joints becomes inflamed or stress fractures develop.

Wrist injuries through typing can be prevented or at least reduced by maintaining a good typing posture. As mentioned earlier, wrists should be kept in a relaxed, natural position. Foam or gel wrist supports can provide extra protection.

One of the key messages when it comes to using computers in the office is how important it is to take regular breaks. The US Occupational Safety and Health Administration (OSHA) recommend that workers take a 10 minute break for every hour spent on a computer, allowing the body to recover and reducing the risk of strain.

These breaks can include working on other tasks that do not involve using a computer. They also represent an opportunity for employees to get out of the sitting position. Alternatively, if employees have the freedom to do so, breaks could involve seeking sustenance to refuel their bodies.

Here be vending machines

The office environment is often full of temptation when it comes to eating healthily. Many offices are home to vending machines filled with sugary drinks and fatty snacks that sing out to workers eager to get a quick energy boost.

Bringing a packed lunch from home is good for both your health and your wallet.

A desire for this kind of unhealthy food is increased if an individual hasn't eaten properly in the morning or obtained enough sleep the night before. Finding time for both sleep and breakfast helps reduce the lure of unhealthy food throughout the working day.

Bringing a lunch and snacks to work also helps keep office workers away from vending machines and restaurants, as well as saving them money. Snacking is fine if it is done healthily, and while vending machines are unlikely to stock fruit, vegetables, hummus and seeds, workers can bring these in themselves.

"It's really important to eat at least every four hours," Beth Thayer tells ABC. "You need to make sure you're setting some time aside to make sure you're getting food in."

Thayer, a registered dietitian and spokesperson for the American Dietetic Association, recommends packaging and preparing your own meals. "Small bags of nuts or snack mix you make yourself, or a small bag of fruit like apples or grapes," she suggested. "Fruit works well for people who drive a lot."

Eating is a great opportunity for workers to escape from their workstations, but few take advantage of it. According to a survey conducted by the American Dietetic Association in 2011, 62% of Americans eat lunch at their desks.

As well as preventing workers from getting away from work and keeping them sitting down in the same place, eating at the desk can lead to a build-up of bacteria if the correct hygiene precautions are not taken.

"We need to wash our hands and clean up the area after we eat at our desks," Thayer warns. "Don't let desks become places for bacterial growth."

Leaving the desk for a break allows workers to regroup and collect themselves away from their work. Doing this can be particularly important in mentally demanding roles. Taking a proper break can help reduce stress levels that can be responsible for a wide range of health problems.

How to improve your fitness at work

Although the office can often be a comfortable place to work, it is important that workers do not allow unhealthy practices to become comfortable and routine. Remaining sedentary, using office equipment incorrectly and eating unhealthily can eventually lead to debilitating health problems that could stop individuals from working altogether.

Thankfully, office work also provides a number of options for keeping fit, and if these are incorporated into a working routine then there is no reason why working in an office should condemn employees to a life of ill health.

• Travel to work by walking or biking. Get off public transport a stop earlier than normal or park your car further away from the office
• Stand instead of sitting when working as much as possible. Find as many excuses to get out of your chair as possible
• Spend time during breaks to go for a brisk walk or do some stretching to keep the muscles loose and strong.

On the surface, working in an office appears to be a simple form of employment. While that may be true in comparison with some other jobs, it is important that office workers do not get complacent and sit idly as their health runs away from them.

Dr. Timothy Church, from the Preventive Medicine Laboratory at Pennington Biomedical Research Center, Louisiana State University, told MNT that the biggest risk to the health of office workers is the sedentary lifestyle.

"The answer is getting active," he said. "Get up at least every 45 minutes and obtain at least 7,000 steps per day."

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