Here are the facts as we know them. This is a robotic buttocks created by the University of Electro-Communications in Tokyo to receive stimulation, and to respond via its artificial muscles to express the emotion it feels. What this will contribute to science is still unclear. Those are the facts.
That's not to say the makers of this robotic butt named Shiri — which means "buttocks" in Japanese — haven't tried to explain a reason for it's existence. A video demonstration says the robot ass project is to "advance the innovative use of robotic technology and its purpose," and "to raise the argument as to what perceptions will be manifested in the minds of people who communicate with Shiri."
I think we can pretty confidently say we know what the perceptions will be. If it bears repeating for clarity, we are talking about a robotic ass that trembles when it is smacked. If I were the university, I might consider asking for the funding money back: it will pay for itself, after all.
To be fair, the robot technology behind researcher Nobuhiro Takahashi's project seems solid. The robot butt certainly provides a variety of visible reactions to various stimuli, twitching to trembling in response. And, the video does take us through how the robot butt is constructed so the University can claim success on that count.
As for determining the perceptions of people interacting with it, I think it will depend entirely on the audience. If they test out the robot ass on student nurses armed with needles to practice their shot giving (picture robot bum clenching), that's one kind of input and response.
But, if they are looking for a bunch of random dudes to smack it (picture robot rear trembling — emotion unknown) as we see in the video, that's an entirely different set of input and response.
We may never fully understand the scientific implications of the robotic buttocks, but maybe that's not what's important here. The robo-butt could join the legion of Japanese inventions designed to bring us the feeling of humanity— well, without the humanity.