When humans play dead

When a rabbit or other animal is trapped by a predator, it will freeze and assess the situation. It might then flee or attack, what we usually call the "fight or flight response". If that fails, a last-ditch defence mechanism is to go completely immobile, to play dead.

Researchers in Brazil now say that in times of grave danger, this same automatic last resort is also exhibited by humans and is experienced as a terrifying feeling of being "locked-in". The team led by Eliane Volchan performed what they describe as the first lab-study of "tonic immobility" in humans, and they argue that greater awareness of the response could help our understanding of people's reactions in real-life situations. For example, rape victims often experience shame after not resisting physically, and in some jurisdictions their passive response is interpreted as a sign of consent. Similarly, police officers and related professionals may be condemned for not reacting proactively in danger situations.

Volchan and her colleagues recruited 33 trauma survivors (15 women), including 18 with a dignosis of Post-Traumatic Stress Disorder (PTSD). They were asked to describe their ordeals in minute detail and these accounts were transformed into a 60-second audio narrative presented by a male voice in the second-person, present tense (e.g. "You are walking home and a man appears ..."). Each participant's account was played back to them over head-phones while they stood on a platform that records body sway. Their heart rate was also monitored and afterwards they were asked questions about how they felt as they listened to the recording.

The results provided physiological evidence of "tonic immobility" in humans. Participants who reported a strong sense of being paralysed, frozen, unable to move or scream, tended to show less body sway, higher heart rate and less heart rate variability. This was true across both PTSD and non-PTSD patients, but it was the PTSD patients who were more likely to report feelings of paralysis whilst listening to the recording of their ordeal.

"We succeeded in experimentally inducing tonic immobility in humans and recording its biological correlates, indicating that tonic immobility is preserved in humans as an involuntary defensive strategy to life-threatening events," the researchers said.

"Tonic immobility still remains largely unrecognized in humans," they added. "Thus, essential steps to alleviate entrapment symptoms, guilt and prejudice in the aftermath of tonic immobility are the recognition of tonic immobility and dissemination of this knowledge to the public."
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Volchan, E., Souza, G., Franklin, C., Norte, C., Rocha-Rego, V., Oliveira, J., David, I., Mendlowicz, M., Coutinho, E., Fiszman, A., Berger, W., Marques-Portella, C., and Figueira, I. (2011). Is there tonic immobility in humans? Biological evidence from victims of traumatic stress. Biological Psychology, 88 (1), 13-19 DOI: 10.1016/j.biopsycho.2011.06.002

Post written by Christian Jarrett for the BPS Research Digest.

How feeling socially connected can make strangers' hearts beat together

We find it easier to empathise with people who are socially and emotionally close to us, of course we do. Research has even shown how the sight of a loved one in pain triggers a kind of simulation of their agony in the pain network of our own brain. A new study builds on this, showing that superficial feelings of connectedness with a stranger are enough to lead to a mirroring of their emotions and even their heart rate.

In two studies, David Cwir and his collaborators had dozens of undergrads reveal their cultural interests and favourite places to visit. One to ten weeks later, for what they thought was a completely separate study, these same undergrads took part in what was described to them either as a personality and cognition experiment (study one) or an experiment on the physiological effects of exercise (study two).

The general format was the same for both studies: each participant was paired with another student who, unbeknown to them, was an accomplice working for the researchers. The proceedings kicked off casually enough with an experimenter asking the participant and the other student about themselves. Using the survey answers garnered weeks earlier, the researchers contrived things craftily so that the other student either did or didn't share the majority of the participant's own interests. This set-up was designed to provoke feelings of social connectedness with the other student. Based on later questions about how close they felt to the other student and how much they wanted to know them, the manipulation worked.

In the first study, the get-to-know you interview stage was followed by a random task allocation - either the participant would have to give a short presentation or the other student would. In truth, this was fixed and the other student had to do the talk. She acted out the process of preparing to give the talk, and showed every sign of being very stressed and anxious about it. The participants, meanwhile, answered a personality questionnaire, buried in which were questions about their current mood and emotions. The key finding here was that participants who'd been led to feel socially connected to their partner, reported mirroring her emotions - they felt more stressed than the participants who hadn't been prompted to feel socially connected. Empathy, it seems, had been stirred between strangers by the slightest of bonds.

The procedure was similar for the second study, but this time instead of preparing for a presentation, the other student was allocated the task of running on the spot vigorously for three minutes. This time, the sight of their partner running apparently caused the socially connected participants to experience increased heart rate and blood pressure, as compared with the participants who hadn't been prompted to feel socially connected. A weak bond had led the strangers' hearts to beat together.

'The present research suggests that psychologically, the self and the other can blur,' the researchers said. 'Even minimally instantiated social relationships can lead people to experience common psychological and physiological states. If brief social ties can have such effects, the degree to which individuals' psychological experiences arise in tandem with the psychological experiences of others may be more pervasive than now understood.'
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Cwir, D., Carr, P., Walton, G., and Spencer, S. (2011). Your heart makes my heart move: Cues of social connectedness cause shared emotions and physiological states among strangers. Journal of Experimental Social Psychology DOI: 10.1016/j.jesp.2011.01.009 [pdf via author website]

People who are more aware of their own heart-beat have superior time perception skills

What underlies our sense of time? A popular account claims an internal pacemaker emits regular pulses, which are detected by an accumulator. The amount of accumulated pulses represents the amount of time that's passed.

Trouble is, this is all very theoretical and no-one really knows how or where in the brain these functions are enacted. One suggestion is that the pulses are based on bodily feedback and in particular the heart-beat. Consistent with this is a recent brain imaging study that showed activity in the insular (a brain region associated with representing internal bodily states) rose linearly as people paid attention to time intervals (pdf). Now a behavioural study by Karin Meissner and Marc Wittmann has built on these findings by showing that people who are more sensitive to their own heart-beat are also better at judging time intervals.

Thirty-one participants listened to auditory tones of either 8, 14, or 20 seconds duration. After each one, they heard a second tone and had to press a button when they thought its duration matched the first. Counting was forbidden during the task and a secondary, number-based memory task helped enforce this rule. Heart-beat perception accuracy was measured separately and simply involved participants counting silently their own heart-beats over periods of 25, 35, 45 and 60 seconds.

The take away message is that the participants who were more in tune with their heart-beats also tended to perform better at the time estimation task. A further detail is that physiological measures taken during the encoding part of the task showed that as time went on, the participants' heart-rate slowed progressively, and their skin conductance (i.e. amount of sweat on the skin) reduced. Moreover, the rate of change in a participant's heart-rate (but not skin conductance) was linked with the accuracy of their subsequent time estimates.

'These results suggest that the processing of interoceptive signals [i.e. of internal bodily states] in the brain might contribute to our sense of time,' Meissner and Wittmann concluded.

The new findings add to past research showing that patients with cardiac arrhythmia are poorer than controls at time estimation tasks, and that drug-induced speeding or slowing of the autonomic nervous system (including heart-rate) affects people's under- or over-estimation of time intervals.
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Meissner, K., and Wittmann, M. (2011). Body signals, cardiac awareness, and the perception of time. Biological Psychology, 86 (3), 289-297 DOI: 10.1016/j.biopsycho.2011.01.001

New gadget provides fresh insight into goose-bumps

My most recent experience of goose-bumps (aka goose-flesh) was watching the latest episode of Being Human, the BBC's supernatural drama. This rather odd form of emotional reaction, in which a chill is felt and bumps form on the skin and the hairs stand erect, was noted by Darwin and has continued to intrigue scientists. Unfortunately, past research into 'piloerection' (to use its technical name) has been hampered by the lack of an objective measure.

Previous experiments relied on participants indicating when they were experiencing the feeling. This is problematic: the feeling might be illusory; participants' internally-focused vigilance creates an unnatural situation; and the act of indicating how one is feeling can interfere with other physiological measures taken at the same time. Now Mathias Benedek and Christian Kaernbach have taken a fresh look at goose-bumps using a new objective measure - a camera that records the skin of the forearm and uses an algorithm to detect the trade-mark pimpling and raising of the hairs.

Benedek and Kaernbach wired fifty undergrads (seven males) up to their new piece of kit. The students then listened to four music clips and four clips from films (each between 90 seconds and five minutes long). These were from a larger selection picked for their power to provoke goose-bumps. Examples included My Heart Will Go On, performed by Celine Dion; Only Time, performed by Enya; a scene from Armageddon (in which the astronaut says good-bye to his daughter before sacrificing his own life for the good of mankind); and a scene from Braveheart (featuring a stirring speech by William Wallace).

The study threw up a host of new findings. The film clips were a more reliable provoker of goose-bumps than the music clips (24 per cent vs. 11 per cent). The participants had heard of most of the music and film material, but there was a tendency for unfamiliar clips to have more goose-bump power. Overall it was fairly tricky to provoke goose-bumps, with only 40 per cent of the clips doing so. There was also a gender difference - none of the men experienced goose-bumps vs. 47 per cent of the women - but this has to be taken with caution because there were so few men in the sample.

Sometimes there was a mismatch between the objective measure of goose-bumps and participants' self-report. On 34 per cent of the occasions that their hairs stood on end, participants didn't report they had goose-bumps. Contrarily, on 11 per cent of trials, participants said they had goose-bumps when in fact they didn't. These data highlight the risks associated with relying on self-report.

From a theoretical perspective the most important findings relate to the physiological correlates of goose-bumps. One existing theory states that goose-bumps are a marker of peak arousal. The current study found that goose-bumps correlated with increased heart rate and blood pressure. On the other hand, breathing deepened during goose-bumps, and participants reported feeling more 'moved' when they had goose-bumps, not more aroused, neither of which is consistent with the peak arousal account.

Another hypothesis holds that goose-bumps are provoked by sadness, creating a cold sensation which promotes an evolutionary advantageous desire for social reunion. Benedek and Kaernbach said the increased heart rate, deep breathing (non-crying sadness has these effects too) and feeling of 'being moved' are consistent with this account. However, they also acknowledged that previous studies have found that goose-bumps are often pleasurable. Taken altogether, the researchers think goose-bumps probably reflect a distinct emotional state, a kind of awed mixture of fear and joy. In English and French we lack a dedicated word for this, but in German they have 'Rührung' and 'Ergriffenheit', which means something similar.

The researchers' conclusion is that given the low specificity of other physiological measures of emotion, measuring goose-bumps objectively could prove to be a useful new tool in the psychologist's armamentarium when studying emotional responses.
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Benedek M, and Kaernbach C (2011). Physiological correlates and emotional specificity of human piloerection. Biological psychology PMID: 21276827

Coffee helps women cope with stressful meetings but has the opposite effect on men

For men working together, stress plus coffee could be toxic

If a meeting becomes stressful, does it help, or make things worse, if team members drink lots of coffee? A study by Lindsay St. Claire and colleagues that set out to answer this question has uncovered an unexpected sex difference. For two men collaborating or negotiating under stressful circumstances, caffeine consumption was bad news, undermining their performance and confidence. By contrast, for pairs of women, drinking caffeine often had a beneficial effect on these same factors. The researchers can't be sure, but they think the differential effect of caffeine on men and women may have to do with the fact that women tend to respond to stress in a collaborative, mutually protective style (known as 'tend and befriend') whereas men usually exhibit a fight or flight response.

The study involved 64 male and female participants (coffee drinkers at the University of Bristol with an average age of 22) completing various construction puzzles, negotiation and collaborative memory tasks in same-sex pairs. They did this after drinking decaffeinated coffee, which either had or hadn't been spiked covertly with caffeine (the equivalent of about three cups' worth of coffee). Stress was elevated for some of the pairs by telling them they would shortly have to give a public presentation, and by warning them that their participation fee would be performance dependent.

How large were the caffeine effects? The men's memory performance under stressful conditions with caffeine was described by the researchers as 'greatly impaired' whereas caffeine didn't affect women in the same situation. For the construction puzzles, caffeine under high stress conditions led men to take an average of twenty seconds longer (compared with no caffeine) whereas it led women to solve the puzzles 100 seconds faster.

A short-coming, acknowledged by the researchers, was that there were overall few effects of stress on the participants' performance, no doubt in part because they'd been told they could bail out any time they liked (although none of them did). Further research is clearly need to replicate the findings and explore the possible underlying mechanisms. Such work is urgent, the researchers concluded, 'because many ... meetings, including those at which military and other decisions of great import are made, are likely to be male-dominated. Our research suggests that men's effectiveness is particularly likely to be compromised. Because caffeine is the most widely consumed drug in the world, it follows that the global implications are potentially staggering.'
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St. Claire, L., Hayward, R., and Rogers, P. (2010). Interactive Effects of Caffeine Consumption and Stressful Circumstances on Components of Stress: Caffeine Makes Men Less, But Women More Effective as Partners Under Stress. Journal of Applied Social Psychology, 40 (12), 3106-3129 DOI: 10.1111/j.1559-1816.2010.00693.x

Are you fluttering your eyelashes at me or just feeling creative?

An intriguing new study has found that the rate at which students blink (as measured over six minutes using electrodes placed near the eyes) is associated with both their divergent and convergent creativity scores, but not their intelligence. Divergent creativity was measured with the 'alternate uses task', which required the students to come up with as many original uses for a brick, shoe and newspaper as possible. Lower and higher eye blink rate was associated with poorer performance, whilst medium eye blink rate was associated with superior performance at this task.

Convergent creativity was tapped with the 'remote associates test', which required the students to identify the one word that matched three other words (e.g. for 'time', 'hair' and 'stretch' the answer would be 'long'). In this case, eye blink rate was negatively related with divergent creativity - the less a student blinked the better they tended to do at this task.

Why should eye blink rate be associated with creativity? The study authors Soghra Chermahini and Bernhard Hommel explained that eye blink rate is a marker for dopamine activity and in turn, dopamine has previously been linked with creativity.

The researchers pointed to evidence showing, for example, that patients diagnosed with schizophrenia, which is associated with excess dopamine, tend to have high eye blink rates. Patients with Parkinson's, by contrast, which is associated with reduced dopamine, show low eye blink rates. They also highlighted past research linking dopamine with creativity. For example, there's evidence that positive mood - which is related to dopamine levels - can enhance creativity, although the results in this area have been extremely inconsistent.

Chermahihin and Hommel said their research adds to the literature by showing that the dopamine-creativity link is far from straight-forward. There was a negative linear relationship with convergent thinking but a positive, inverted U-shaped relationship with divergent thinking. This could help explain the inconsistent research findings linking mood with creativity, as they explained:

'Participants with a relatively low level of dopaminergic functioning would be likely to benefit from better mood, whereas people with a relatively high level of dopaminergic functioning, such as individuals scoring high in psychoticism, would actually be expected to suffer from better mood. Depending on which part of the distribution happens to be more strongly represented in a given sample, the corresponding study may find a positive, negative, or no relationship between mood and the given performance measure.'

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Chermahini, S., & Hommel, B. (2010). The (b)link between creativity and dopamine: Spontaneous eye blink rates predict and dissociate divergent and convergent thinking. Cognition, 115 (3), 458-465 DOI: 10.1016/j.cognition.2010.03.007

How to nap

Even naps as short as ten minutes have been shown to provide psychological benefits in terms of reduced fatigue and improved concentration (pdf). But would-be nappers face some strategic decisions, most obviously - does it matter whether I nap in my chair or ought I try to find somewhere to lie down? And then ... if remaining seated, is it okay to lean forwards and rest my head on a desk?

When it comes to napping while leaning back in a chair or car seat, past research has shown that the further you can lean back, the better, at least in terms of subjective fatigue and reaction times. Now Dayong Zhao and colleagues have addressed the leaning forward issue, comparing lying-down napping and leaning-forward napping, and they've found that the former is the most effective, but that the leaning-forward variety still has clear benefits compared with no nap at all.

Thirty undergrads, all regular nappers, had electrodes attached to their heads before lunch. Then they performed an 'oddball' auditory task in which they had to listen to a string of tones and listen out for the occasional one of a different pitch. Next they had lunch before splitting into three groups: one group enjoyed a twenty minute nap lying down; another enjoyed a twenty-minute nap leaning forwards onto a desk (plus pillow for comfort); the final group just spent the same time sitting quietly.

After this, all the participants performed a repeat of the oddball task whilst having their brainwaves recorded via electroencephalography. Zhao's team were particularly interested in the size and delay of the P300 - a brainwave measure of cognitive alertness.

Participants in both of the napping conditions showed benefits compared with their peers who'd been denied a nap. The nappers, leaning and lying, reported being in a better mood and feeling less sleepy and they performed better at the oddball task. When it came to the brainwave recordings, however, the leaning-forward nappers, unlike the lying-down nappers, showed no difference from the control group. Uniquely, the lying-down nappers showed an increased P300 amplitude, perhaps indicating increased cortical arousal on their part.

The message it seems is clear. A post-luncheon nap is beneficial to your mental functioning even if you're forced to rest your head on your desk. However, if you can find somewhere to lie down properly, then do, because the benefits of the nap will be that much greater.
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Zhao, D., Zhang, Q., Fu, M., Tang, Y., & Zhao, Y. (2010). Effects of physical positions on sleep architectures and post-nap functions among habitual nappers. Biological Psychology, 83 (3), 207-213 DOI: 10.1016/j.biopsycho.2009.12.008