Roboticists often take their design cues from nature—humans in particular. Robots working on assembly lines or as surgeons feature long arms designed to manipulate tools, whether it’s a welding gun or laser scalpel. Other robots, designed as telepresence surrogates for remote office workers or aids for the elderly and disabled, come equipped with head-mounted cameras for eyes and wheels for upright motion to mimic human locomotion.

It’s tempting to think today’s robots are crude imitations of their human masters only because we lack the technology to make them more humanoid. Recent research, however, suggests some people actually prefer certain robots to look like, well, robots. The determining factor is largely the job the robot was built to perform. The Georgia Institute of Technology study confirmed that people tend to have an adverse reaction to robots whose appearance is close to—but not quite—human. This phenomenon is known as the “uncanny valley,” referring to the drop in comfort people feel when exposed to robots that try to accurately mimic humans but instead come across as creepy.

The Georgia Tech researchers’ main goal was to compare perceptions of robot faces that varied in terms of human likeness. To do this the researchers showed 64 people—half between the ages 65 to 75 and the rest 18 to 23—photographs of robots, humans, and mash-ups of robot and human faces.

Most older adults preferred a human appearance, with the mash-up being least popular. Younger adults’ preferences were more distributed across the three categories. For both age groups, appearance preferences depended on the robotic duty. “Robots are functional entities and therefore it is important to assess reactions to human-looking robots in the context of the task,” says Akanksha Prakash, the Georgia Tech School of Psychology graduate student who led the study.

Participants preferred a robotic face on machines that help with chores. But for decision-making tasks—such as investment advice—the younger adults in particular wanted a humanoid appearance, which they perceived as more intelligent, smarter or wiser than the other options.

There was less of a consensus for robots designed to perform personal care tasks such as bathing. Those who chose a human face did so because they associated the robot with human care—such as nursing—and trustworthy traits. Many others didn't want anything looking like a human to bathe them because of the private nature of the task, according to the researchers. In social tasks—playing a game or conversing—both age groups preferred a humanoid face.

In general, people either prefer a highly robotic or a highly humanoid appearance for their robot. “People who prefer a human-looking robot find the appearance—and hence the robot—more familiar and easy to relate with,” Prakash says. “They also believe that such a robot would be technologically more advanced and functionally more capable—at least as capable as humans are.”

Those who prefer robots to have a metallic sheen likewise have their reasons. “They want a technology”—in this case, a robot—“to be distinguishable from a human being,” Prakash says. “The closer the robot’s face resembles a human’s, the stronger the tendency to ascribe humanlike strengths and weaknesses [such as deceit] onto the robot.”

Prakash acknowledges that further research is needed to understand which robot characteristics stimulate empathy and which dip into the uncanny valley. Would a robot that can closely mimic a human gait and other movements create the same sense of revulsion as a humanoid robot whose face can’t quite form a realistic smile?

The researchers also point out that multipurpose robots pose design challenges and suggest that some sort of customizable appearance might be the best option.