Human imagination is full of swarms of thoughts that we might want to organize and clump together and categorize as (mental) "images". If you take this line of reasoning too far, you might be tempted to believe (many folks such as Dennett have explained the naiveté displayed by this belief) that inside your brain somewhere there is a little TV screen which displays pictures for you. If you are a Functionalist, you might construct computational theories of thought in which algorithms compare these mental TV pictures pixel by pixel in order to match them to memories which are stored in memory, stored also as the same kind of digitally precise pictures you get on a TV screen. Biologists like Gerald Edelman have tried to explain that the neuronal mechanisms of brains can in no way produce such "picture-like" mental representations. Perception and memory are actively constructive processes, not at all like the passive image manipulators (photocopy machines, TV cameras) we are familiar with.

It is interesting that neurobiologists have found that the earliest stages of the visual system do convey "Xeroxed" copies of pictures to the brain. The eye IS like a TV camera and the retina faithfully (okay, so I'm ignoring the processing of the image that occurs in the layers of cells in the retina) transmits a 2D picture from the sheet of cells that is the retina on into the thalamus where the picture is reproduced several times in the activity pattern of additional sheets of cells. However, by the time sensory information reaches the cerebral cortex where it can participate in our conscious brain activity, the picture that was captured by the retina has been fragmented into many coded data channels and is no longer recognizable as a physically coherent picture.

The Functionalist will argue: "Okay, so the picture becomes scrambled or encoded within the contorted structure of the brain, but functionally there are still pictures there!" However, if we are to escape the lure of Platonism and the idea that language transmits information from person to person because there are universally identical thoughts (mental images that are digitally precise pictures) that are triggered in all brains by words like "red", then we need to say, "Okay, there is something in a mental image that is similar to a picture (this is a good first approximation), but there is also something in a mental image that goes beyond a picture." Each brain's "picture" of anyTHING will be unique since it is painted by the unique (but similar!) brain of each individual. Thus, we have private mental contents and words act as a type of publicly used triggering system that we can exchange in order to tickle each other's thoughts.

If we think about one computer "telling" another computer what a camera on a space ship has just "seen" on the back side of the Moon, then we think about a digital picture being transmitted from one computer to the other. Human Language does not transmit information in this way. A poet who views the back side of the Moon might compose a few verses that can be spoken and transmitted back to Earth where they will trigger a listener to paint a mental image of the backside of the Moon, but that image is composed of cobbled together fragments from the listener's life time of experiences. The poet and the listener each have a private mental "picture" of the Moon, not the digitally precise picture that is identical in the two computers.