But this isn’t always the case in reality. When it comes to a potentially painful experience, like having an operation, many people choose to get it over and done with rather than put it off.
In a 2013 paper published in PLOS Computational Biology, researchers from Imperial College London and University College London explore how this reluctance to wait for pain – a feeling commonly known as dread – changes depending on the timing of the painful event. The researchers wanted to know if dread is worse when pain is more delayed.
The study involved a series of experiments in which pain took the form of brief electric shocks to the back of the hand of 35 participants. Over the course of the experiments, participants could choose to receive shocks soon, or delay them by a certain amount of time, which could range from a few seconds to a quarter of an hour.
A minority chose to wait and receive the shocks further into the future. But 71% of participants opted to receive pain sooner, even if meant it would be worse, because, in half of the experiments, choosing earlier pain resulted in more shocks.
The researchers also compared the size of the delay and the probability a participant would choose the later shock. They found the relationship between the two was best described by what they called “exponential dread”: the bigger the delay, the more likely it was the person would opt for the earlier shock.
The shock experiments were relatively brief, so researchers also looked at what happens when people can delay a painful experience much further into the future. The participants were given a hypothetical scenario, in which they had to schedule an appointment for a painful dental procedure. They were told they could have the procedure “today”, or at a fixed later time. This time varied between participants: it could be 1, 5, 13, 32, 89 or 237 days.
Once again, the participants’ choices suggested dread increases exponentially as people approach a painful event:
These results build on previous work, such as a 2006 study which assumed people experienced constant amount of dread over time, rather than having dread increase with the size of the delay. There are, however, still some questions that remain unanswered.
First, how does dread scales with time? The researchers looked at events that occur over minutes and weeks, but can the same patterns be found at other timescales?
Second, what causes us to experience dread in the first place? The researchers suggest a couple of potential explanations. It might be that the brain processes designed to prepare us for a painful experience overrule other types of behaviour, even if this other behaviour could be beneficial. Alternatively, dread could be a form of “stimulus substitution”, whereby the anticipation of pain triggers the same responses that we experience during an actual pain event.
Even if the causes of dread remain elusive, understanding how people deal with the anticipation pain could help in a number of fields. In particular, it could be useful when assessing options about a potentially painful future event, whether that event is an electric shock, a medical procedure, or your girlfriend finding out you’ve eaten all the chocolates.
By Adam Kucharski, Research Fellow in Mathematical Epidemiology, London School of Hygiene & Tropical Medicine
This article was originally published on The Conversation. Read the original article.
Most cloud droplets need tiny airborne particles to act as “seeds” for their formation and growth. If a cloud has more of these seeds, and therefore more droplets, it will appear brighter and reflect away more sunlight from the Earth’s surface. This in turn can cool the climate. Therefore understanding the number and size of particles in the atmosphere is vital to predicting not only how bright and reflective the planet’s clouds are, but what global temperatures will be.
Today, around half of these particles come from natural sources. That includes dust from the ground, volcanoes, wildfires that make soot, or sea spray that evaporates midair leaving behind tiny specs of salt in the atmosphere.
Many airborne particles also result from us burning fossil fuels. This produces soot, but also sulphur dioxide gas which is made into sulphuric acid in the atmosphere. As well as causing acid rain, sulphuric acid molecules can stick together and grow into particles. Other molecules like ammonia often help glue the sulphuric acid molecules together, and overall this process forms around half of the cloud seeding particles in today’s atmosphere.
The CLOUD experiment at CERN also recently discovered that gases emitted by trees can stick together to make new seeds for clouds in the atmosphere – without needing any help from other pollutants as was previously thought. Scientists had thought that the cloud seeds needed sulphuric acid (often mixed with other compounds) or iodine molecules to stick together to initiate the process.
In our new follow-up study, published in PNAS, we worked with other CLOUD scientists to simulate this process in the atmosphere. Our work suggests that even today trees produce a large fraction of cloud seeds over the cleanest forested parts of the world.
Simulations of the atmosphere before fossil fuel burning started in earnest and the industrial revolution began (in climate science defined as the year 1750) predict fewer particles than are present today. With fewer particles the cleaner clouds would have reflected less of the sun’s energy and, perhaps counter-intuitively, they would have looked a bit greyer.
The ability of the gases from trees (terpenes) to make particles was first proposed back in 1960 to explain blue hazes seen over forests in remote areas. Many lab experiments have since confirmed terpenes can help form new particles, but until recently it was thought that other pollutants like sulphuric acid were required.
Much of the more recent progress in this area is thanks to the CLOUD experiment: a stainless steel cylinder, about three metres in diameter and three metres high. Gases are injected into the cylinder, where they react much as they would in the atmosphere and then stick together to make particles. State-of-the-art instruments count the gas molecules and particles in the chamber. We study how the number of new particles formed every second changes when we increase the amount of the sticky gases in the cylinder.
In today’s atmosphere, there is so much sulphuric acid around that it is difficult to measure how much anything else contributes to forming new particles, and so to the clouds. However our new simulation using the CLOUD results shows that terpenes were very important in the cleaner atmosphere of a few hundred years ago. Computer modelling suggests that estimates of particle concentrations in the cleaner pre-industrial atmosphere should be increased, while our estimates of today’s concentrations are mostly unchanged.
It’s hard to make accurate predictions at this early stage as not all of the complicated chemical processes are understood. However, the new results may be important because more particles in the atmosphere mean more reflective clouds and a cooler climate.
Over the past century, cooling due to increasing numbers of particles in the atmosphere has offset, or masked, some of the warming due to increasing carbon dioxide levels. Our simulations suggest that this extra cooling might not have been as strong as previously thought.
There have recently been concerns that as we collectively improve air quality across the world, by emitting fewer particles into the atmosphere, we will also be reducing the capacity of particles to act as cloud seeds and have a cooling effect.
While our simulations remain quite uncertain, the potential importance of this new process suggests that as we reduce pollution from combustion and other sources, natural compounds could once again become more important. By helping to replace cloud seeds from air pollution, trees may be able to help us limit global temperature rises.
By Hamish Gordon, Research Fellow in Amospheric Science, University of Leeds and Cat Scott, Research Fellow in Atmospheric Science, University of Leeds
This article was originally published on The Conversation. Read the original article.
In UK data that I was involved in collecting around a decade ago, a representative sample of adults by age, sex and geography said they slept for an average of seven hours and three minutes a day. This suggested that over half of the population slept between five hours 30 minutes and eight hours 35 minutes; and about three-quarters slept between five and nine and a half hours per night.
The problem with these general figures, just like the mythical eight hours a night, is that things get more complicated when we ask people how much they sleep on rest or work days, and what age they are. People sleep longer on rest days than on work days by an average of about 20 minutes, and this is true of all age groups until retirement (see figure below). And although the graph does not show it, reported sleep duration also depends on gender. In middle age, for example, women report sleeping longer than men.
Work day and rest day sleep by age group
So are we sleeping less than we did? The graph above suggests this is probably the case on an individual level – by about 20 to 30 minutes per decade. But these data refer to different people at different ages rather than the same people when they were younger and older.
A small number of studies which have used similar methods over time show small increases or small decreases of a few minutes per night over several decades in different countries across the world. But there is absolutely no good evidence that sleep durations are shortening dramatically in the UK or elsewhere.
A fascinating study from last year looked at the sleep patters of tribes-people in Tanzania, Namibia and Bolivia. It measured their actual sleep – as opposed to self-reports – and found they averaged between five hours 40 minutes and seven hours six minutes a night. In other words, many of them seem to be sleeping less than those in the fast-paced 24-7 UK. This again suggests that modern lifestyles are depriving people of less sleep than you might have expected.
Incidentally, another study reported sleep data earlier this year from 8,000 users of an iPhone sleep app around the world. It showed that the average length of a night’s sleep was around seven hours 50 minutes.
The UK, Germany, Norway, Spain, the US and Mexico were all very close to this average. Australia, New Zealand, the Netherlands and France reported longer sleep, while Brazil and Japan were below average. Unfortunately, the numbers in age groups in different countries wasn’t controlled. The data are therefore unlikely to be representative of the countries concerned or directly comparable with each other, and so need a large pinch of salt.
From the information above, it might mean that our intuition is simply wrong about glorious night times past. Or maybe the real question is different: whether we are sleeping less than we need. We know from laboratory studies in which people can have nearly unlimited sleep that they quickly satiate: that is, they reach a point where the amount they sleep stabilises.
This suggests that if we were getting enough sleep on weekdays, we would not sleep more on rest days. For individuals, a large difference in sleep on rest days and work days is a useful indicator of unmet need for sleep. For the UK as a whole, the gap between work and rest days suggests that people maybe are sleeping less than they need – at least those of school or working age.
We don’t know much about how this gap has changed over the years, though there are some fascinating data from South Korea taken from regular surveys between 1981 and 2005. Weekday sleep didn’t change over the period, though Saturday sleep increased by 13 minutes and Sunday sleep by 24 minutes per night.
I suspect we would see something similar if we looked for the same phenomenon in other countries. What is probably happening is that the rising demands of the working week are increasing the amount of sleep we need. If so, having less time available on weeknights might mean we can only meet this increased need for sleep on the weekend – if at all. Time with family, exercising and other demands on our lives outside work probably allow us all less scope than we would like.
So are we sleeping less? No. But we may be sleeping less well than we need to.
By John Groeger, Professor of Psychology, School of Life Sciences, University of Hull
This article was originally published on The Conversation. Read the original article.
