An artificial arm programmed to work automatically disappointed some users in a study -- they said it was "too easy" -- U.S. researchers report.

University of Central Florida researchers thought the ease of using the program's automatic mode would be a huge hit, but they were surprised when most test participants preferred the manual mode-- which requires them to think several steps ahead and either physically type in instructions or verbally direct the arm with a series of precise commands -- a university release said.

"We focused so much on getting the technology right," Assistant Professor Aman Behal said. "We didn't expect this."

John Bricout, Behal's collaborator and associate dean at the University of Texas School of Social Work, said the study demonstrates how people want to be engaged -- but not overwhelmed -- by technology.

"If we're too challenged, we get angry and frustrated. But if we aren't challenged enough, we get bored," said Bricout, who has conducted extensive research on adapting technology for users with disabilities. "We all experience that. People with disabilities are no different."

The key is to design technology that can be individualized with ease, Behal said. Some patients will have more mobility than others, and they may prefer a design closer to the manual mode.

Though the automatic mode wasn't popular in the pilot study, it may be the best option for patients with more advanced disease and less mobility, he said.