Does my bum look big in this?

I love the Wii Fit. I smile every time I power it up. I get up extra early every morning to use it. In just a few weeks it has become an unmissable part of my life. And here's the weird thing: I am beginning to treat it like a real person! How can this be?

The Wii Fit has a Body Test function that measures your body's performance including your weight. If (perish the thought!) your weight has increased since your last Test, the Wii asks you to give a reason for the gain. It then gives some helpful advice on how to keep your weight under control.

So the other day I was in a great restaurant having a wonderful meal and drinking some lovely wine (and not in moderation) when....

....I caught myself thinking "what am I going to tell the Wii?" How was I going to explain my inevitable weight gain?

So what on earth is going on here? Why do I care what a piece software thinks of me? Can a Wii have a personality?

I think there is something very, very special about the user interface of the Wii. It is not simply the accelerometer-based Wii remote that you use to interact with the games. That's pretty cool and revolutionary I agree. It's the personality that really intrigues me. Let's investigate why.

My first clue is the way that the Wii Balance Board and the Wii Remote sense and respond to my body movements. If I start to wobble during yoga or let my arm drop during a fitness exercise, the Wii lets me know and gives me encouragement: "don't give up", or "your leg is unsteady". If I am doing well it praises me: "your balance is terrific". Of course the voice is pre-recorded but it is the timing that is so perfect and makes it so effective. Even though I know this is a machine, I feel good when am praised and I try harder when I am encouraged. It is AS IF the machine can see me.

When you first set up the Wii Fit, you choose a personal trainer, either an athletic woman or a muscular man. The trainers are reasonably lifelike, unlike the bobblehead-like Mii characters that are used in the other Nintendo games. When they speak they use arm gestures. They address you directly. They talk you through the exercises and it is their voice that praises or encourages you. The combination of the sensors and the avatars makes the interaction even more PERSONAL.

The Wii is UNPREDICTABLE. Every so often, the trainer changes. "Sorry", they say, "your usual trainer isn't available so I'll be doing your training today. Hope you don't mind". Occasionally the trainer yawns and admits they had a late night last night. I have tried to detect a pattern but I cannot. Either these actions are truly random or the algorithm is based on some non-obvious variables.

And then there's the FUN details. When you power up and stand on the Balance Board, it gives a sort of surprised squeal. It's an unnecessary feature but it never fails to make me smile. Your Mii character on the start-up screens matches your Body Mass Index; being (a little!) overweight, my Mii is decidedly podgy which makes my kids laugh every time they see it.There are all the usual PERSONALIZATION features you would expect too. It also has a many-layered reward structure that unlocks new exercises and levels. Body Performance is measured by your Wii Fit Age, much like Brain Age.

A dictionary definition of personality reads: "the complex of all the attributes--behavioral, temperamental, emotional and mental--that characterize a unique individual".

I think the personality of the Wii Fit comes from the complex of interactions with me the user. There is a physical interaction as it responds to my movements. There is an emotional interaction as it praises or encourages me at exactly the moment I need it. There is a mental interaction as you try to improve your scores in the exercises. The unpredictable and fun elements make it seem almost temperamental.

In short, the combination of hardware and software engages me in a complex way using multiple senses. It responds to me.

I think the Wii and the Wii Fit can teach us a lot about how to engage the user, in particular the way that the hardware and software both contribute to the user experience. I suspect that in a few years time we will look back and see the Wii and the accelerometer that makes it possible as a huge milestone in human-computer interaction.

And finally I hear that the new version of the Wii Fit will give you fashion advice based on your body shape...does my bum look big in this?