We humans have a visual bias. Experiments have demonstrated our preference for sight, but there is no need for experiments. “The proof of the pudding is in the eating,” not the tasting, but “Seeing is believing,” they say. Whenever we want to illustrate something, well, we illustrate it. Our language and culture reify vision. Even our metaphysical discussions are rife with visual references: consider Mary the color scientist, spectrum inversions, and Gettier problems.
Our belief in seeing privileges our sense of sight relative to our other senses, and we are likely to take its instruction more seriously. We wave off any perceptual conundrums arising from our other senses as foibles of inferior organs. But we should take our nonvisual phenomena more seriously, for they have lessons for us if we do.
Those lessons start at the bottom, with our sense of smell. Though it is our crudest sense, and arguably the one sensory modality that we could most do without, the structure of smell has weighty implications. Olfactory neurons each bear a single kind of receptor. The odors we experience are mediated by activation of a set of receptors entirely. The number and distribution of that activation determines everything about a smell: its intensity, favorability, and motivational power. An odor is something which can be described, but not named. There is no equivalent to “red” in our odor palette. However, there are good and bad smells, and as with moral qualities (supposedly), smells are intrinsically motivating on the basis of their goodness and badness.
That motivational power lies in the smell itself. A chemical in a test tube which smells like a steaming pile, produces the same revulsion as the smell of a steaming pile itself. It is tempting to say that the odor of the chemical in the test tube is just an olfactory misrepresentation of crap. The common scent is supposed to smell just as it does, though. The smell is a conjunction linking an aversive mood, and things to be avoided. The smell and the mood are about a broad landscape, stretching over memory, history coded in our genetics and cultural instruction, all mediated by a particular pattern of receptor activation.
A similar sort of two-directional representation occurs in our auditory experience. The organ which generates auditory nerve signals, the cochlea, is tuned to the range of the human voice. The structures at the auditory end of the line are primed to respond directly to voices and music, and indirectly, to stimulate an emotional response to voices and music. As with smell, when hearing evokes a mood, it builds a memory of itself and its circumstances on a broad and sturdy base. A good framework improves the recollection’s relevance, and therefore its odds of survival. Here is another temptation. Fans of evolutionary psychology and divine teleology may see the beginnings of a good story in this structure. But those sorts of stories are unnecessary, and far beyond the point, which is: our hearing shapes the map of our experience in terms of words and music, as much as it recognizes musical and linguistic experiences.
The other senses break down the uni-directionality of representation, but even further, they blur the internal/external division itself. Taste receptors give us the sensations of sweet, salt, sour, bitter, and umami. Our conscious experience of taste locates those sensations on the tongue. But there are taste receptors for bitter and sweet in the pharynx, and sweet taste receptors throughout the intestinal tract. Those sweet receptors attach to neurons which do not reside in the central nervous system, but instead, lie in the intestinal tract itself, and the pancreas. Though these sense organs have no direct connections to the central nervous system, they still contribute to conscious experience. They simply do so via the adjacent somatosensory system.
Our somatic senses are a bit of a jumble. As a whole, they are the thing that represents our status. Though there are a few specialized sense organs in the system, it mostly relies on bare nerve endings and chemical signals built in to the tissues surrounding the nerve endings. This sense tells us where our limbs are, and what each appendage is doing. The somatosensory system lets us know when our gallbladder is on the fritz, and, indirectly, when we are hungry or full..
Though they are rarely the center of our conscious attention, our somatosensory experiences are always present in our conscious states. If I interrupt Dr. Penrose’s visualization of a 5 dimensional object, he will immediately be able to tell me whether he is standing or sitting, feeling hungry, feeling warm or cold, fit or tired. Somatosensory experience serves as the shade tree, grass, and sky in the painting of our phenomenal picnic.
Of all the senses, our somatic sense most effectively dissolves the boundary between what is internal and what is external. Because, our hunger is apparently our hunger. Our cold is our cold. These are things that seem to incorrigibly belong to us, just like our thoughts or our moods.
The thought that any of these things belong to us is a bit off anyway. Words and music, hunger, thought, and mood are constituents, but there is no separable “us” to which they may belong. We come by this error regarding identity via our most favored sense. Because we rely so heavily on vision, we confer an unmerited degree of independence to our visual experiences. We conceive of sight as purely received information, which given the limitations of the medium, naïvely represents an unconditioned reality. The plain truth gets transmitted through our optic nerves, into the dark room behind our eyes for the viewing pleasure of a little man in front of his little screen – the real us. Visual realism leads to other mistakes in its turn, regarding what is real and what is not. We begin to believe that numbers may be real because our eyes see objects as very discrete. Geometric shapes may seem real because we are able to depict them visually. A separate observer made up a separate stuff must sit behind our eyes to validate the reality of our visions. Our other senses beg to differ. They give as good as they get. Their contributions to our experience only make sense in reference to our global experience itself and do not rest on some outer, hard surface. Our world may be a ship sustained by the tension of its own spars, but it works for us – better than a brittle realism would.