"When he's tired, he curls up to sleep, and sometimes he comes up to see what we're doing. When Mother calls out, 'Hey, Hachikins!' he hears, and moves his head so prettily. I know I shouldn't, but sometimes, when we've been eating together, I've put a bit of food in his mouth."
But Hachibe has no mouth and no digestive system - no orifices of any kind. His ears are tiny microphones concealed inside his sleek silver head. His paws are articulated plastic, and his eyes are miniaturised video-cameras that glow behind a curved Perspex screen. Hachibe is an Aibo, or Artificial Intelligence roBOt, a computerised dog released, in limited numbers and at enormous expense, by the Sony Corporation. He has no fur, no smell and no warmth, but for Mrs Yamada - who, as a child, had an early and traumatic experience with a hamster - this is his great attraction. "I actually hate dogs and cats," she admits, as the little bundle of joy himself head-butts the wall a few feet away. "In fact I can't stand being near any live, furry animal, and Mother's the same way. So we don't think of him as a robot. For people like us, this is a real dog."
This week, if you like your pets cool and metallic, you too can purchase an Aibo - for the first time, through the company's website (www.world.sony.com/aibo), Sony is accepting orders from Europe, as well as the US and Japan, for the second generation of robot pets. Even at 2,400 euros - about pounds 1,530 - each, the 10,000 units for sale are likely to be ordered several times over, and there is little doubt where most of them will end up. When the first 5,000 Aibo went on sale last summer it took four days to sell out in America. In Tokyo, they were cleaned out in 20 minutes. For the Aibo is just the visible tip of a potentially enormous new field of personal robots - robots designed to assist, entertain, communicate with and maybe even to love human beings. The leading researchers, the designers and the keenest consumers of this new technology are in Japan, the global centre of robot civilisation.
Robots in their more functional forms are in use everywhere, from the giant industrial limbs that assemble cars to the Nasa planetary rover that collected samples from the surface of Mars. Japan still has a higher ratio of industrial robots to human beings than any other country in the world, although since its economy began to decline the lead has been slipping. But nowhere is there greater interest in what may soon be the most interesting and lucrative area of robotics research - human and animal-like robots, capable of interacting directly with people and expressing something very like emotion.
"The Eighties was the age of personal computers," said Toshitada Doi, the inventor of the Aibo, at the launch of the latest model last week. "The Nineties is the age of the Internet. But the 21st century will be the age of digital creatures."
The first walking humanoid robot, the Wabot, which could move one leg every 45 seconds, lurched out of Tokyo's Waseda University in 1974. Ten years later the piano-playing Wabot 2 made robotic and musical history by performing Bach's "Air on a G-String" with the NHK Symphony Orchestra; as the robot sat at the keyboard his circuitry and memory chips occupied an entire room at the back of the concert hall. As the new model of the Aibo was tottering through his paces for the press last week, the latest in robotic innovation was on display on the other side of Tokyo, at the International Robot Exhibition. There were vigilant guard robots, looking like benign Daleks without the death-ray, and industrious cleaner robots, designed to scrub and vacuum. There were "welfare" robots aimed at the elderly and disabled, moving platforms with robot arms that can fetch and carry household or objects, or scoop up food from a plate and lift it to the mouth. And then there were those robots which, in the short to medium term, stand to make the most money of all - the "entertainment" robots.
Omron and Panasonic are both planning to put on to the market furry robot cats that will respond to being stroked, and even chat about the morning's news. NEC is developing mobile robots that can recognise faces, receive e-mail and, best of all, read it aloud to their owners. But surging ahead is the Aibo, which can walk, respond to colours, play football and express six different "moods", from happiness to anger - and which matures and develops depending on how it is treated.
"If we stroke his head, Aibo considers that he is being praised, and he is happy," says Sony's Mr Doi. "If we tap his head, he feels scolded. If no one reacts to him, his mood will go down. If he's treated with love, and he's continually happy, then he will learn a lot quickly. If he feels blue, then this will not happen."
"Europeans would look at this and think it's a very nice machine," says Pierre Blazevic, of the Laboratoire de Robotiques de Paris, who has designed football-playing software for the Aibo. "Admiration is one thing, but this emotional relationship between humans and machines is strange, I think. People in Japan have more feeling for machines." Partly, this may have to do with the country's ancient tradition of animist religion, in which animate and inanimate objects such as rocks, trees and mountains are endowed with personality and intelligence. "Many Japanese do not have a clear idea of God, but it is very easy to believe that an object has mind or soul," says Dr Tetsuya Ogata, of Waseda University. "It is easy for Japanese to regard machines as their friends."
But it may also turn out to be a far-sighted necessity. With the world's longest life expectancy, and one of its lowest birth rates, Japanese society is ageing at a rapid rate. With more and more old and very old people and fewer and fewer young folk to support and look after them, they are going to need all the help they can get.
Robot visionaries foresee computerised nurses who will monitor a patient's health, dispense medication and raise the alarm where necessary, and robot companions who will provide a simulation of human contact to people living alone. Of the 5,000 Aibo sold in the first batch, a number were purchased by old people's homes and hospitals, as well as by people such as the Yamadas, slightly lonely people perhaps, living in small apartments, who dislike animals but love pets.
"The possibilities are almost endless - it's just a matter of thinking of them," says Hugo de Garis, an Australian specialist in artificial intelligence who works at Japan's Advanced Telecommunications Research Institute (ATR).
"Robot pets will be the first application, then things like household robots and cleaning robots. There'll be guiding robots for showing people around places such as museums. Imagine something like the Star Trek computer, which you can ask a question in English and get an answer back. Then sex robots, of course - a huge market." At the moment, the imaginary applications still outstrip the technology but, assuming that computers continue to get faster, bigger and cheaper, it is only a matter of time before we see them all.
Of all Japan's adventures in artificial intelligence, none is more ambitious than the work being conducted by Professor de Garis, at ATR's gleaming headquarters near the ancient capital, Kyoto. For the last six years he has been working on the creation of what his Japanese bosses call Robokoneko - Robokitten. The animal itself is still a year or two away from existing in physical form, though the drawings and animations show a creature not unlike the Aibo - a cute, articulated quadruped complete with tail, paws and whiskers.
But, assuming she eventually makes it off the computer screen, Robokitten will be a great robotic leap forward, as superior to the Sony creature as a mammal is to an insect.
The truth is that, for all his cuteness, the artificial intelligence incorporated in the Aibo is extremely basic, no more impressive than that of a rather naive ant. Robokitten, by contrast, will have the brain of, well, a kitten - a huge advance in robotic terms.
The key to all this lies inside a curved grey box in de Garis's laboratory, which will be connected to Robokitty by wireless remote control - the CAM Brain Machine (CBM), potentially the most powerful electronic brain in the world.
"It will run, jump, play with its tail, get bored, have moods of its own," says Professor de Garis.
"The kitten robot is purely a means to show off the capacities of the artificial brain. The aim is to get people to look at it and say, 'Oh my God. There is a brain in there'." But having described the creature he aims to create, Professor de Garis raises the alarm.
Once it is possible to create a kitten-sized brain, that is likely to lead fairly quickly to the ability to make a human-sized one, and then to brains far bigger, quicker and more sophisticated than our own. Within 30 to 50 years, say Professor de Garis and a small but convinced band of fellow-scientists, robots will have outstripped human beings. In other words, we shall no longer be the dominant species on Earth. And here things become scary.
"I have two major life goals," the Professor declares. "One - to build artificial brains. Two - to raise the alarm on a possible gigadeath artilect war."
"Artilect" is short for artificial intellect, the Professor's name for the "God-like, massively intelligent machines" that will emerge from the researches of people like himself. As a lengthy treatise on his web- site warns: "Asteroid-sized, self- assembling, nanoteched, one bit per atom, reversible, heatless, 3D, quantum-computing artilects could have intelligences literally trillions of trillions of trillions of times the human level."
Human beings would be to the artilects about as significant as amoebas are to humans.
To say that Professor de Garis's scenario is speculation is to put it mildly, but he appears genuinely terrified by his own prediction.
"This what keeps me awake at night," he says in his laboratory, glancing around for any eavesdroppers who may be spying on our conversation.
"I see this inevitable conflict on a subject more important than any other in history: species survival. If in my eighties I end up being called the father of artificial brains, that would be a source of great pride. But if people point the finger and say 'that's the future father of gigadeath', well, that terrifies me."
In any case, there is no going back. Little Hachibe is out of his box; artificial intelligence is under way, and it has far too much potential for the world to ignore it.
Will the robot dog be remembered as a dream-maker, the first step into the brave robot age? Or as the advance agent of the artilects, a yapping omen of human destruction?