The world shifts to the right when you’re sleepy

When you’re drowsy, new research shows that what’s happening on your left often sounds to you as though it’s happening on your right. Perhaps that’s why it can be so tricky to land a punch on the alarm clock in the morning!

Corinne Bareham and her team asked 26 healthy volunteers (17 women; all right-handers) to relax in a comfortable reclining chair, to close their eyes, and listen to a series of tones. The tones occurred either on the left or right side of space, some further from the centre than others.

After each tone, the participants pressed a button to indicate whether they thought it had originated on the left or right side of space. While this was going on, the researchers recorded the participants’ surface brain activity using EEG (electroencephalography). This provided an objective marker of their sleepiness.

The task may appear easy, but when the participants were sleepy, they mislocated nearly 25 per cent of left-sided tones to the right. This compares to an error rate of under 14 per cent when they were alert. “A participant was 17 times more likely to show a right-ward shift with drowsiness … than a leftward shift, or no shift,” the researchers said. In contrast, the participants were slightly more accurate at locating right-hand tones when sleepy compared with when alert.

The finding that tiredness triggers a shift in attention to the right-side of space is not new – researchers have shown this before. However, past demonstrations of the phenomenon have used visual stimuli. This study is novel because of its use of auditory tones and because of the highly accurate measurements of participants’ alertness.

Research on this topic has clinical relevance. The drowsiness-induced attentional shift towards the right side of space is similar to a phenomenon known as “spatial neglect” that’s observed in patients who have suffered right-hemisphere brain damage. People with left-sided brain damage show the opposite pattern – they tend to ignore the right-hand side of space. However, right-hemisphere brain damage leads to more prolonged and profound spatial neglect than left-sided damage, and this new study offers a clue as to why.

One explanation for spatial neglect following left or right-sided brain damage is that the two hemispheres of the brain are usually in competition, so that when one is damaged, balance is lost, and attention is skewed towards the same side of space as the brain damage. However, people with right-sided brain damage suffer twice, because damage to the right hemisphere is known to induce sleepiness, which – as this study shows – also leads to a skewing of attention to the right side of space.

In the researchers’ words, patients with right-hemisphere damage are “doubly compromised” – by the loss of hemispheric balance, and by the effects of drowsiness. The good news is that this insight offers an avenue for treating patients with right-sided brain damage. “The results here confirm that the maintenance of alertness should be …[an] important therapeutic target,” the researchers said.

  ResearchBlogging.orgBareham, C., Manly, T., Pustovaya, O., Scott, S., & Bekinschtein, T. (2014). Losing the left side of the world: Rightward shift in human spatial attention with sleep onset Scientific Reports, 4 DOI: 10.1038/srep05092

–further reading–
Hemispheric bias shifts with tiredness
Space is compressed by a fast turn of your head
Novelty seekers are biased to the right

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

11 thoughts on “The world shifts to the right when you’re sleepy”

  1. I'm wondering how the initial ratings for the boys and girls were given. If the girls were evaluated on their competition versus only other girls then would the ratings still be accurate? If the ratings were given by compartmentalised girlvgirl and boyvboy data, that wouldn't create a standardised rating. The difference in results would only be a difference in the average skill between boys and girls. Also since boys and girls develop at different rates, the test would do well to compare older boys and girls. However the idea that women naturally feel pressure against men could still have merit if you found girls and boys of similar skills, though that seems impossible if you rate their skills in separate tournaments. Also don't boys feel similar pressure when facing a girl to live up to stereotypes? How about you rate them together when boys and girls compete together through double blind experiments then conduct the same experiment having them play together knowing each other's genders. This experiment seems rather poorly thought out and proves very little.

  2. What about left-handers? Does this study replicate results with them? Numbers/ tested subjects seem statistically invalid.

  3. Why does “Numbers/ tested subjects seem statistically invalid”? Could you justify/elaborate?

  4. Yeah,I totally don't understand the numbers. You had 17 women. All of them were right handed. You had 26 participants. Was the data from the other nine thrown out? were they all men? Were they right handed, left handed or ambidextrous? Wht woukd you give us that information but not the rest?

  5. 9 men 17 women seems a bit unequal but what really bothers me is that they were all right handed and the test involves pushing a button, left or right. It makes sense that as they are tired, they will push with their dominant hand on the closest button or on the dominant side regardless of the aural input. I'd like to see left handed people in the study. Do the results still replicate? Until then, I feel the conclusion would be invalid.

  6. I think you have to read the paper again along with the supp info, all the responses to your criticisms are actually there (except the lefties). But I respond to you point by point anyway, there is a single subject graph showing that 21 of 26 participants showed the bias, and stats for that. those not showing the bias were 2 men and three women, so no much problem in that, besides we have a higher sample of this and replicates beautifully. The test involves pushing two button, some pushed with the left hand, some with the right and some with both hands. Again, no differences there, it is unlikely that it is a hand performing-the-task thing. If fact they mislocate sounds on the left saying they come from the right side of space, regardless of gender o hand used to push the button. And the effect is there no matter how you define drowsiness (by EEG, by sleep scale, by RTs). It is a very strong effect! The point is that there is a bias on these subjects. Yes there are all right handers and handedness is a factor that we report in the paper coming out soon (is under review). But regardless of that the effect is there and it is likely that your spatial attention representation shifts even if you still consider the results invalid. IN fact I do not think you can call them invalid, you are entitled to remain unconvinced but the experimental design are valid, the data clear and sound and the results convergent. So maybe you mean that our conclusions are invalid. Last point, all your concerns were raised by reviewers last year in a more elegant manner and answered with new analyses also in a more elegant manner!

  7. Of course, if I were writing a formal peer review, my response might have been more elegant; however, this was informal commentary based solely on the information presented in the article and not on the paper still under review, which I obviously have yet to read. As my points were raised by others who have read this paper, I feel that, whether elegantly stated or not, they were still valid. You are, of course, free to disagree.

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