The Case for Paying Attention

Can we be aware without actually paying attention? In other words, can our brains somehow imbibe visual information from the outside world without any conscious effort on our part? It would certainly be nice if that were the case.


As it happens, the necessity of visual attention for visual awareness is a steady debate in the study of consciousness. The can-we-or-can’t-we camps have gone back and forth for over a decade. I’d love to be in the “we can” group—it would make my life a whole lot easier—but unfortunately for me (and for those who’ve long argued for the possibility of awareness without attention), it now seems like the central piece of evidence for that viewpoint is being put into question.

Do we need to pay attention to perceive natural scenes?

Up to now, it has been generally accepted that natural scenes don’t suffer in the same way as other objects from so-called inattentional blindness, whereby if you only focus on one element in a scene, the other elements disappear (perhaps the most famous example of the phenomenon is the invisible gorilla). But a recent series of studies casts doubt on that assertion, suggesting that even such scenes require us to actively pay attention: if we are busy doing something else, we will remain largely unaware of the details and may even fail to realize we’ve seen something to begin with.

In one study, researchers used a multiple-object tracking task that forced participants to keep their eyes on a series of discs as they moved across a changing checkerboard, while in another, they asked their subjects to pay attention to a stream of letter and digits—presented against the same checkerboard background—and count how many times a given digit appeared. In both experiments, a visual scene (beach, building, highway, indoor, and mountain in the first task and animals or vehicles in the second) would flash on the screen during the fifth trial, and participants would then be asked to answer some basic questions about the scene.

What happened next counteracts the results of many a prior experiment: in the first case, fully 64% of participants experienced full inattentional blindness and only 18% detected the visual scene immediately—as compared to 96% in a condition where the task was reversed, so that observing the background became the main goal. In the second case—an easier task—50% experienced full inattentional blindness and only 23% could identify the category of the scene right away, in contrast to the 93% who could accurately do so in the reverse condition.

Attention is necessary for awareness—and it is a limited resource

It thus seems that we can’t actually be aware unless we pay attention. True, natural scene awareness is perhaps one of the most automatic and streamlined processes in visual perception—hence the prior results that suggested it might be possible without attention—but if our attention is truly taxed, in a more difficult task than has traditionally been used, we lose even that rapid and basic ability. Yes, awareness may require only minimal attention; but it does require some attention. Nothing happens quite automatically. As the authors put it, “Although there is good reason to believe in attention without awareness, there is no evidence of awareness without attention.” It’s just not that simple. We can be paying attention even though we’re not completely aware of doing so—but we can’t be aware of something if we’re not paying attention to it.

As we multitask more and more and have ever-increasing demands on our attentional streams, such research is increasingly pertinent. For, it goes to the heart of a crucial notion: the limited nature of attention. We only have so much to spare, and each additional element requires some part of a very finite resource. Each new piece comes at a cost.

When it comes right down to it, there is no such thing as free attention; it all has to come from somewhere. And every time we place an additional demand on our attentional resources—be it by tracking discs or checking our email or following five media streams at once—we limit the awareness that surrounds any one aspect and our ability to deal with it in an engaged, mindful, and productive manner. 

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[photo credit: Shutterstock.com]

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New research establishes an unexpected connection.

Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

Image source: Vaccaro et al, 2020/Harvard Medical School
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We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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