This discrepancy creates sex differences in how well VR works, because, as boyd discovered, men are ‘significantly more likely’ to rely on motion parallax for depth perception, while women rely on shape-from-shading. 3D environments are literally sending out information signals that benefit male over female depth perception. The question is: would we be so behind on recreating shape-from-shading if we had been testing 3D VR on equal numbers of men and women from the start?
Tom Stoffregen, professor of kinesiology at the University of Minnesota, has an entirely different theory for why women experience more motion sickness than men. The classic theories, he says, are ‘focused almost entirely on sensory stimulation’. The idea is that what you feel in your inner ear doesn’t match up with what you see with your eyes. And ‘that’s true,’ says Stoffregen, ‘but it’s not the only thing that changes. The big thing that traditional theories have not talked about,’ he says, ‘is changes in what you need to do to control your body.’
In the normal course of your day, your body is constantly making micro-adjustments in order to keep you stable. When you stand, when you sit, when you walk. But when you’re in a moving environment – say a car, or a ship – what you have to do to remain stable changes because your body is being destabilised. So, says Stoffregen, ‘You are being physically required to move in a different way and you haven’t learnt how to do it yet.’ And like cars and ships, he says, VR destabilises the body. Hence the motion sickness.
The VR industry has so far shown little interest in Stoffregen’s research. ‘They understand that it’s a serious problem,’ but they’re going the wrong way about fixing it, he says. ‘The people who design VR think it’s just an object that you put in front of your eyes, and the idea that it would have anything to do with anything other than your eyes is incoherent to them.’ But, he says, VR developers have to understand that they’re doing more than ‘simply placing screens in front of people’s eyes. Whether they like it or and whether they know it or not.’
VR developers also have to start collecting data systematically – and separating it by sex. ‘Most of the data on motion sickness in VR are anecdotal,’ explains Stoffregen, ‘and they come from the people who are working in these companies just using the systems themselves or trying them out at computer technology conferences or whatever. So they’re completely unsystematic – and most of these people are men.’
One of the most convincing aspects of Stoffregen’s theory is how it finally explains why I get car sick in every seat other than the driving seat: it’s all about control. When you’re walking, you are in control of your movements. You know what’s coming. On a ship, or in a car, someone else is in control – unless you’re the driver. ‘The driver knows what the motion of the car is going to be and so the driver is able to stabilise his or herself in what we call an anticipatory fashion,’ explains Stoffregen, ‘whereas the passenger cannot know in quantitative detail what the car is going to be doing. And so their control of their own body must be compensatory. And anticipatory control is just better than compensatory control. You know, that ain’t no rocket science.’
But where does the sex difference come in? ‘Everybody who studies motion sickness has known that women are more susceptible than men basically forever,’ says Stoffregen. ‘It’s just an utterly uncontroversial fact. It’s just there. But, and he includes himself in this group, ‘very few people did any research on it or made any effort to try and figure that out.’ Plus ça change.
But in 2010, Stoffregen made a discovery. ‘I was sort of fooling around in the literature and I came across some results that I didn’t know about,’ and which showed that there are sex differences in body sway. ‘These are small subtle differences. You can’t just watch somebody and see them, but in terms of the subtle quantitative details of how the body moves back and forth, there are in fact reliable sex differences. And as soon as I saw this, I mean, I’m talking the minute that I saw this I knew that oh, OK, now I have something to say about the sex difference in motion sickness. Because my whole story about motion sickness is that it’s related to the control of the body.’ Since then, Stoffregen has also discovered evidence that ‘women’s postural sway changes across the menstrual cycle’. And this is significant because ‘a woman’s susceptibility to motion sickness changes across the menstrual cycle. And those two things link up, believe it or not.’
A considerable gender data gap remains. We don’t yet know exactly how and when women’s body-sway changes. But as a woman who suffers from extreme car sickness, I am excited and enraged by Stoffregen’s findings, particularly because of how it ties into another gender data gap I’ve been looking into: car design.
When you’re sitting down, you’re still swaying. ‘If you’re sitting on a stool then you’re swaying around your hips,’ explains Stofcegen. ‘If your chair has a back, then your head is swaying on your neck. The only way to really get rid of that is to have a headrest and to use it,’ he adds. And I feel like one of those cartoon light bulbs has just gone off in my head. What if the headrest is at the wrong height, at the wrong angle, and the wrong shape to accommodate your body? Could women’s increased propensity to motion sickness in cars be exacerbated by cars being designed around the male body, I ask. ‘I think that’s quite possible, sure,’ Stoffregen replies. ‘The quality of the stabilisation, if it’s the wrong height or whatever . . . what you’re telling me is new to me,
