Gabe Newell told the New York Times "Zero percent of people get motion sick" when they use SteamVR tech. In his frank speech at the conference, Mr. Carmack did not sugarcoat his explanation for why Oculus has moved slowly to ship a public version of its virtual reality technology. Personally I have an oculus as well, and can't play longer than 5 minutes before I get sick to my stomach.

It is well known that virtual reality headsets can cause motion sickness and eyestrain in people who use them, though the severity varies by person, the type of game being played and the length of time a game is played. 

Oculus and other companies are still making technical modifications to their products to avoid those effects. They are encouraging game developers to avoid creating virtual environments that tend to cause nausea, like roller coaster rides. Mr. Carmack said Oculus would still allow virtual reality games that could make people uncomfortable into the online store for its headset, but it will label them as such. 

In the meantime, they are keeping access to the products limited. Oculus has released a version of its headset that connects to PCs for developers only. Gear VR, the mobile phone headset Samsung makes, has been on sale since late last year, but only in limited quantities and without broad distribution in wireless stores and other retail locations. 

In explaining why Oculus has gone slow, Mr. Carmack described what he called a "nightmare scenario" that has worried him and other Oculus executives. "People like the demo, they take it home, and they start throwing up," he said. 

At least one company, Valve, believes it has solved the discomfort problem with headsets. In an interview at the developer conference, Gabe Newell, the president and co-founder of Valve, said he, too, had reacted badly to most headset demonstrations, describing them as the "world's best motion sickness inducers." 

Mr. Newell said the company had worked hard on its virtual reality technology to eliminate the discomfort, saying that "zero percent of people get motion sick" when they try its system. Part of its solution is a motion tracking system that uses lasers to accurately reproduce a person’s real-world movements in the virtual world. Mr. Newell said Valve would offer the tracking system, called Lighthouse, free to hardware manufacturers. 

During a 15-minute demonstration of the Valve headset, it caused no discomfort for a reporter. In one segment of the demonstration, a colossal whale comes precariously close to the viewer, who is standing on the prow of a wrecked ship.