Wednesday, 6 April 2011
Does bungee jumping freeze time?
That our subjective perception of time can vary is illustrated by the well worn proverb "Time flies when you are having fun". Some research psychologists specialise in how we perceive time, including a colleague two doors down the corridor from me at Keele, Professor John Wearden. Perhaps through conversations with John when we occasionally car share, I’ve long been intrigued by a paper he has talked about that apparently investigated whether a bungee jump slows down the subjective experience of time. I thought this paper would make for a perfect first “Cool Psychology” blog.
The idea behind the study was to investigate something that most people can relate to from their own experiences - the subjective feeling of time dramatically slowly during a potentially life-threatening emergency. Of course, it would be unethical to expose human volunteers to a true life-threatening emergency. So, very coolly, researchers from the University of Texas and Baylor College of Medicine had their participants do an activity sufficiently scary to feel life-threatening, without actually being too unsafe.
Although not an actual bungee jump as I think of it. In fact they did a 31m Suspended Catch Air Device (SCAD) jump at an installation at an amusement park in Dallas. This is a type of bungee jump that still involves a freefall vertical descent, but here the participants were harnessed to a platform during the drop, and they were caught in a giant safety net rather than bounced about on the end of an elastic rope. In case you were wondering, the edges of the net are connected to a giant inflatable tube. Presumably, the deformation of the tube is what cushions the fall.
There were two parts to the experiment. One part, the part I could remember, looked at 20 participants’ estimates of how long their jump lasted. Participants tended to overestimate the duration of their jump. On average, participants estimated that the jump lasted for 2.96 seconds, whereas the actual freefall duration was 2.49 seconds. This was consistent with the idea that time passes more slowly during a potentially life-threatening emergency. If you think about it, if a given time interval seemed to pass slowly, then you would estimate that it lasted for longer than if it seemed to pass relatively more quickly. An exciting prospect! All this is very cool science in my opinion, and this was all I really intended to talk about in the blog. However, there was a very clever second part to the study. Participants’ reports of time apparently slowing down that were made after doing the jump are one thing. However, a retrospective report is just that – a judgement made after the event. The scientists behind the paper intriguingly wanted to find out whether the participants experienced time slowing down during the actual jump itself.
To try and measure whether time slowed down for the participants during the jump, the researchers imaginatively made use of a perceptual phenomenon known as flicker fusion. Imagine a red 4 on a black background. Now imagine a black 4 on a red background. Now imagine a screen on which the red and black 4 are alternately displayed at a steady rate. You would see the 4 turn from red to black, red to black. Now imagine the alternating image display being sped up. For a while you would follow the 4 alternating between red and black, but above a certain threshold the red background of the black 4 would start to cancel out the red 4 (and vice versa) such that no digit would be discernable on the flickering display screen. In the experiment, different digits and flicker rates were used and participants asked to name the displayed digit. The flicker threshold at which each participant was just unable to identify the digit displayed was determined. For the record, this was 0.047 seconds on average in the daytime, and 0.033 seconds on average at night (some of the jumps were done in the evening).
Having done all this, the participants did the same SCAD jump with a small screen strapped to the wrist. The screen displayed red and black digits alternating at a rate that was slightly faster than their flicker threshold, that is, at a speed that made it slightly more difficult to discern the digit. Just one participant was unable to open her eyes at all to look at the screen during her jump (!!) and so her data was not used. However, the remaining 19 participants were much braver. They did manage to keep their eyes open so that they were able to report the digit they believed they saw displayed during their jump. If you have read up to here, then I hope that you will appreciate that if time does indeed subjectively slow down during a simulated life threatening emergency, then the accuracy with which the participants were able to discern these rapidly flickering digits should have been increased mid-jump. So – was there any evidence for this?
The answer, unfortunately, is no. Disappointingly for the theory, the participants were only able to report the flashing digit with around 30% accuracy during the jump, which was the same level of accuracy with which they were able to report the flashing digit in the control condition, on the ground. This counters the notion that time actually slows down in the midst of a potentially life or death emergency. With only the retrospective report data showing evidence of time distortion, the study findings instead suggest that the subjective feeling of time slowing down is some kind of perceptual illusion based on recall of the event afterwards.
Nevertheless, this was the coolest of cool psychology research on several counts. Employing a fairground ride as a stressor for psychology research purposes was cool (and has since been repeated). Finding that time seemed to slow down in retrospect was also cool, and using the flicker fusion phenomenon in this context was very cool. In fact, really, the only uncool thing was that they weren’t able to show that time was experienced more slowly during the jump. In relation to this I wonder why they used the slightly faster flicker rate during the jumps rather than the flicker threshold rate that they determined beforehand. I can’t help but think that in using the faster, and so harder to read rate, they may have dulled the sensitivity of the study to detect the slowed time effect they were looking for.
Finally, like most cool psychology research, this study was not funded by a mainstream research funding agency. The only acknowledgments are to two named individuals and the staff at the Zero Gravity amusement park in Dallas. The Cool Psychology blog salutes this collaboration between scientists and amusement park staff in producing such a thought provoking and cool piece of psychology research.
If you are interested, the full reference for the original research paper is:
Stetson C, Fiesta MP, Eagleman DM (2007) Does Time Really Slow Down during a Frightening Event? PLoS ONE 2(12): e1295. doi:10.1371/journal.pone.0001295
Richard Stephens, April 2011.
Thanks to Maria J Grant for proof reading and suggestions : )