They gave them distinct personalities. It was an experiment: would humans react to the robots differently based on how they carried themselves? They tried out two different personalities on each robot. One version was extraverted; the robot would speak loudly and quickly, use more animated hand gestures, and start conversations instead of waiting to be spoken to. The other personality was more reserved, speaking much more slowly and quietly, moving around less, and letting the user initiate communication.
What the researchers found, as they described in a recently published paper, was a striking difference between the two. When it came to the nurse robot, people preferred and trusted it more when its personality was outgoing and assertive. What people wanted in a security guard was exactly the opposite: the livelier, extraverted version clearly rubbed people the wrong way. Not only were they less confident in its abilities, and dubious that it would keep them away from danger, they simply liked it less overall.
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What researchers are finding is that it’s not enough for a machine to have an agreeable personality—it needs the right personality. A robot designed to serve as a motivational exercise coach, for instance, might benefit from being more intense than a teacher-robot that plays chess with kids. A museum tour guide robot might need to be less indulgent than a personal assistant robot that’s supposed to help out around the house.
A growing body of research is starting to reveal what works and what doesn’t. And although building truly human-like robots will probably remain technologically impossible for a long time to come, researchers say that imbuing machines with personalities we can understand doesn’t require them to be “human-like” at all. To hear them describe the future is to imagine a world—one coming soon—in which we interact and even form long-term relationships with socially gifted devices that are designed to communicate with us on our terms. And what the ideal machine personalities turn out to be may expose needs and prejudices that we’re not even aware we have.

More here. How many of our personality preferences for robots will we inherit from the human analogues we're most familiar with? We may wish for a robot personal trainer to be tough, forceful, while we may prefer a calm, almost flat affect from our robot therapist.

Regardless, I'm excited to see the first generation of robots or AI's with personality roll out to the world. It feels like one of the most likely vectors of delight in user experience design when it comes to AI.