Riggall said he isn't familiar with the design history behind the machines, but noted that new models aren't being designed now because optical scanning systems that use paper ballots are growing in popularity. More states are moving to optically scanned paper ballots because they offer a paper trail of every vote cast in case a recount is needed.
Since new touch-screen machines aren't being designed, no usability studies are being done to improve existing designs, he said.
Ken Fields, a spokesman for Election Systems & Software said in an e-mail reply that "certainly, the equipment is designed with voters in mind. I can assure you that in the national level certification process that's taken place before the equipment is ever used, there's great attention paid to the manner in which the technology is going to be used," he said.
ES&S' iVotronic touch-screen machines are designed to prominently display a voter's candidate choices so that they can be reviewed before the ballot is cast, he said. "If the iVotronic has captured what the voter did not intend to convey, but what the voter may have accidentally or inadvertently selected, then the voter is able to see the selection and easily change it if necessary. Every voter has multiple opportunities to see and validate the captured selection prior to casting a ballot."
Peter Lichtenheld, director of operations for vendor Hart InterCivic in Texas, said his company doesn't build or sell touch-screen machines because it felt that existing technologies weren't "up to snuff" when they were created. That could change, he said, because new touch-screen technologies like those used in Apple's iPod music players and iPhone, have shown maturity.
Hart's eSlate voting machines rely on a mechanical wheel that's used to select voting categories, and a button that makes a voter's selection.
When voters are given a chance to try various voting machines in government open houses, he said, the voters often prefer touch-screen devices because they are simple and have a familiar interface. The problem, he said, is that existing technologies are not as reliable as mechanical systems like those used in the eSlate.
"Have you ever used a signature pad" on an electronic check-out system in a retail store, he asked. "It looks nothing like your real signature 99 percent of the time. It looks like crap. That's why we don't use touch-screens."