Those suffering from semantic dementia — usually the elderly — have brain damage such that objects and words mean something different to them than they do conventionally. For example, an old man in a video about my professor showed about semantic dementia kept identifying pictures of animals as a “little cat,” whether it was an antelope, a rat, etc. Then, when shown a picture of a tiger, he said, “That’s a dog.” The doctor asked, “Do dogs normally have orange stripes?” “Yes,” he said, “I saw one this morning walking down the street.”
It is hard for an undamaged brain to make sense of this. Are they simply forgetting the word for what they are trying to identify? No — they not only forget the word for something, but also forget the meaning of it. For example, if the old man just thought the word for a tiger was “dog,” he would not have stated that he saw one this morning walking down the street. They assign semantic information A to perceptual information B, rather than matching corresponding words/objects and meanings. It is as if the significances they have learned to assign to the world become detached from the very things they refer to.
To understand what it is like for them, I think of myself in dreams. Do you ever have a dream where what you normally perceive as A actually means B? For example, when you are in a strange and unfamiliar house, does it ever feel in the dream like it is “my house” or “my parents’ house” or even “school”? I once had a dream that took place on what I would normally identify as a farm, but the setting was so alienated from its original meaning that I interpreted it as a “Panic at the Disco concert.” This is what it is like to have semantic dementia (except that such patients are too old to know Panic at the Disco). You see one thing, but it means the other. Hence the word “semantic.”
I’m going to make a leap now to Ferdinand de Saussure and his famous assertion that “The connection between the signifier and the signified is arbitrary.” What a word or image symbolizes, in other words, is a function not of the word or image itself but of the language we have been taught. It is not to say that objects don’t lend themselves to certain interpretations. It is more likely that a chair would mean “something you sit on” than “something you row a boat with.” Even so, that sitting is a chair’s socially acceptable function must be learned. And the object itself certainly doesn’t suggest the sound “chair;” the sound is meaningless without attaching it to a thing in the world. Predictably, this Saussure’s theory has implications for feminist, racial, and queer theory: the things bodies symbolize to us (lower class, strangeness, otherness, sex, etc.) are not a function of the body itself but of the social meanings people have ascribed to them.
To make the final connection, I think that semantic dementia patients / dreamers who behave like them illustrate Saussure’s linguistic theory. The fact that different brain regions process meaning and perception shows that the meanings and symbolism we glean from people, places, things, etc. are not natural but learned. The fact that semantic dementia patients don’t struggle with verbs or abstract nouns supports this statement: Their representation is semantic rather than perceptual, so losing the ability to connect perception with meaning doesn’t pose a problem. Situations in which the connection between the semantics and the perception is lost, such as with most nouns, make it clear that the thing and the meaning we ascribe to it are two separate things.
P.S. The tendency to imbue objects with fixed meaning is less engrained in children and artists. They can see something and creatively look at what the possibilities are for its use, whereas ordinary people more often have what psychologists call “functional fixedness”: the attitude that if this is what I see, this is what it means and this is how it is used.