Forget the laptop and look the world in the face...

Tonight there will be a gala at the National Portrait Gallery and it has made me think of all the faces one sees in London. The city, like the gallery, is famous for faces. And it has struck me forcibly, during nine months as chairman of the gala's organising committee, what a fantastic resource for the imagination these faces are - a resource, I might add, which is completely free.

The imagination, it seems to me, has become a bit neglected in the current passion for action at all costs, and the encouragement towards the particular, and peculiar, kind of logic that technology demands. This imbalance is - if human happiness is what you're after - a pity.

The imagination, if fed properly, is what stimulates us and enriches us and enables us to be mentally self-sufficient not to need perpetual external stimulus. It is the element in the human psyche that hopes and dreams, that remains curious and interested, that give us insight into other lives and thus allows us to join fully in the human dance. It is what encourages us to see what might be possible - and even computers didn't come into being without that.

Unless you are an ultra-geek, the kind of person for whom only diagrams and statistics have reality, faces are a powerful stimulus to the imagination. It's quite difficult to look at another human face without your mind ambling off into a whole list of questions as you attempt to fill in the landscape behind the features you are staring at. A Tube journey, for example, can be a vivid period of imaginative activity if you look at a few faces, rather than the floor.

The word "activity" is crucial. Our contemporary lives, in front of screens of one kind or another - however inventive - are alarmingly passive. They also have a kind of fake engagement to them - as every human engagement must when the physical presence is withheld - or can, as with modern celebrity photography, be subtly adjusted to conform to a bland, if beautiful stereotype. If we're not careful, we'll soon believe that air-brushing isn't really a lie.

But - and it's a big and exciting but - there is no need to live exclusively at the dictation of technology, nor without exercising that part of our minds that means we aren't afraid of being left with no diversion from the insides of our own heads. It isn't The Answer, of course, but it's a start, a pointer, a way of re-learning a proper inner life, and all it requires of you is that you go and look at some portraits, pictures of real flawed people, painted by real flawed people, to be looked at, and wondered about, by real flawed people.

You can start by wondering what kept Henry VIII obsessed with getting Anne Boleyn into bed for seven long years. You can go on to wonder why JK Rowling looks so intensely private, even withdrawn. You can look at faces who never gave a stuff about being known outside their own villages. You can see the faces that made our past, shaped our culture and fashion our present. You can see sportsmen and poets (you will expect Seamus Heaney to speak to you, so approachable is his portrait) and soldiers and gardeners and kings and queens and children and rock stars and suffragettes and doctors and beggars and captains of industry. You can, as a bonus from this week, see the lovely portraits John Constable painted to fund all those landscapes - "Painting," he said memorably, "is for me but another word for feeling."

And I defy you to emerge from an encounter with all those eloquently painted faces, without feeling that something rather unexercised in you has responded with sheer relief.

The National Portrait Gallery is holding a charity auction tonight in aid of its education outreach programmes , selling postcards by leading British artists.