Anna is an architecture student but she has never seen a building or read a book about architecture. Anna has learnt everything she knows about architecture through the medium of interpretive dance.

But Anna studies hard and, eventually, she knows almost everything there is to know about architecture and goes out into the world to see a building for the first time. When she sees the building, she learns one more fact about architecture: she learns what a building looks like.

Quite obviously, interpretive dance is a poor medium for learning architecture. It’s all much too floaty and you get no sense of the heft of a good solid building through dancing. If you want to learn architecture, you are better off learning from a book. But even a book can’t quite convey all of the facts: to get a complete understanding, you have to go out into the real world and look at actual buildings. You have to walk around them; you have to touch them and feel them.

Mary the Colour Scientist

Mary is a neuroscientist and she lives in a black-and-white room. She dresses in black and white and she has a black-and-white TV. Mary is one of the world’s foremost experts on colour vision and knows almost everything there is about it. One day, Mary leaves her room and for the first time, she sees a red, red rose and she learns a new piece of information: she learns what the colour red looks like.

Black-and-white TV is a poor medium for learning about colour. You can learn a lot but you can’t learn everything. You can get the gist of wavelengths, how we have three different kinds of receptors in our retinas and how colours are combined in the occipital lobe to form other colours. To learn everything there is to know about colour vision, you are better off with a colour TV. Black-and-white TV is just the wrong medium. It’s not possible to learn everything about colours on a black-and-white TV.

Frank the Philosopher

The philosophy world is divided over whether the world can be completely explained in physical terms or whether we need to introduce some new concept to explain things like the experience of roses that — according to some philosophers — is not physical. Descartes set the ball rolling on this latter view by suggesting that the mind exists independently of the body. In Descartes’ telling, the body is made of a material substance (material, physical — same difference) while the mind is made of some other, immaterial substance. Philosophers have argued ever since whether we need both to explain the world. Philosophers who think the world is entirely physical are known as physicalists while the other lot are called dualists.

Mary the Colour Scientist is a thought experiment invented by philosopher Frank Jackson. In Jackson’s original telling, Mary learns all of the physical information about colour in her room but when she steps out of her room and sees a rose for the first time, she learns something new. But, since Mary already knows all the physical information about colour, this new information must be non-physical and therefore physicalism is false.

Dualists like to assume that experiences are some special thing that can’t be explained in physical terms and the thought experiment is supposed to prove this by showing that the experience of red can’t be conveyed by a black-and-white TV. However, I don’t think it’s possible to learn all the physical information about colour through a black-and-white TV — it’s just not the right medium for the job (just as it’s not possible to learn all the information about architecture through interpretive dance). When Jackson says that Mary learns all the physical information about colour but not the experience of it, he is begging the question and assuming that experiences are not physical. If experiences are actually physical, Mary couldn’t have learned everything about colour inside the room — and she merely learned one more thing when she went outside.

The Surgeon Chops

Brain tumour patients often have surgery while they are awake (known as an awake craniotomy) so the surgeon can know which bits of brain are safe to chop. Once the surgeon has opened the patient’s skull, he will wake the patient up and then prod around inside his brain and have the patient report what he experiences.

Depending on where the surgeon prods, the patient might hear sounds or see colours or smell smells. A prod in the sensory region of the big toe will feel like an experience in the big toe. A physical prod on a neuron causes it to send a (physical) electrical signal down its (physical) axon which stimulates the (physical) synapses with a bunch of other (physical) neurons which creates the (physical) experience. It’s the same deal with sounds, colours and smells — you can make them happen by poking neurons in the brain. All these different sensory inputs — whether they come from the proper sense organ or from the surgeon’s prod — cause our brain’s model of the world to be updated and the model is shared with the rest of the brain. This is consciousness.

There’s more about awake surgery in this post:

Even without a surgeon poking around, a brain tumour might cause the patient to experience phantom smells or deja vu or hallucinations which are indistinguishable from the real experience. If a brain tumour or a brain surgeon can create experiences now, how long before a future colour scientist will be able to learn her experiences of the colour red by poking with a few electrodes rather than trying to get them from a black-and-white TV?