1. Dimensions of the Subjective Universe

The most common partition of the subjective universe involves five external and several internal senses, which together form a nominal dimension.

Each of us perceives different things. We perceive objects which others do not (in virtue of being in different locations), we perceive the same things differently (in virtue of our perceptive and mental faculties), and we perceive different inner experiences (perception of various emotions, feelings, sensations, etc). Much of perception can be divided into modalities, such as the five external senses (smell, taste, touch, hearing, and sight) and a number of internal senses (mental, emotional, and various other senses). Perception, as the term is used in this book, covers both perception of external reality and perception of internal reality: things such as memories, perception of the thought process, emotions, etc.

The scope of the term perception as it used here is somewhat broader than its scope when used elsewhere, in that it includes sensation. In certain other contexts, perception often refers only to the level of mental awareness in which multiple sensory modalities are united; the level at which the smell of an apple and the sight of an apple come together to form the percept ‘apple’ , which is located somewhere in perceptual space. Although our use of the term perception includes the space in which percepts occur, it also includes the lower-level sensations. The difference between these is not relevant to our purposes here: what is relevant is the distinction between perception and conception. Although concepts can be perceived, they are also categorically different: they are referentially different.

In order to get a better understanding of subjective experience, it is useful to divide perception into parts. Perception is enabled by different modalities, namely the five external senses (smell, taste, touch, hearing, and sight) and several internal senses (which are categorized in various ways). We will refer to these types of perception as external perception and internal perception. External perception is the perception of things outside of the body, and internal perception is the perception of things originating within one's body (these are closely related to the notions of exteroception and interoception). To illustrate the matter graphically, we may divide subjective experience as follows:

Figure 5.1. Senses


The five external senses are well known: by comparison, the internal senses are poorly known, or at least poorly communicated. Although internal sensations may be well known to individuals, they are difficult to talk about: the language describing internal sensation is difficult to precisely define. Language develops best for phenomena that can be directly observed by multiple speakers, since in that context the correct or incorrect application of words can be verified easily. Hence, the categorization of internal perception presented here is very crude: it is divided into conception, various emotions, and bodily sensations. These terms should be understood as an exhaustive categorization of internal phenomena (i.e. they divide internal perception into three parts by definition ). For example, thought encompasses all rational mental events; emotion includes things like good and bad sensation, various kinds of pleasure and pain, and many others. Bodily perception (or bodily awareness) is therefore somewhat of a catch-all term: it encompasses proprioception, which means the perception of the location of one's body in space, as well as other internal percepts which are neither emotional nor conceptual.

Although the subjective universe has been divided here into eight parts, the most relevant division of the subjective universe in this book is perception/conception: hence, perception should be understood to contain external and most internal perception. Even emotions are viewed as things which are perceived, despite that the perception of them is phenomenally different than the perception of external phenomena.[53]

Precisely because the subjective domain does not present itself to multiple observers, it is difficult to arrive at a consensus opinion about just what we are referring to when we talk about our subjective experience. Perhaps one day a language of subjective experience will be developed which is highly correlated with the objective observation of physiological processes (i.e. a language that can be validated). In other words, physiological observation will serve as the basis for a language that describes our internal states (i.e. one which maps well onto our hormones, neurotransmitters, and various physiological structures).

The dimensionality and mapping of the various sensory modalities is sense-specific.

Experience is processed according to its modality: the dimensions of each modality differ from one another. Within each modality, sensation is mapped from the outside of the organism to the inside: this mapping is mediated by neurons. This mapping only preserves certain relations, and the mapping itself is quite complex.

One way in which this complexity manifests is that certain areas of the external world are represented with more cortical area than others, which leads to a greater sensitivity (or selectivity). For example, our sensitivity to sound at high or low frequencies is lower than our sensitivity at the center of the audible range. The visual field is more sensitive to the intensity of light at the periphery than at the center. The sensation of touch is more acute at the fingers than at the forearms. In fact, the input which is received from the fingers, in terms of cortical size, is disproportional to the input from the forearm. Hence, we literally perceive more of our fingers than we do of our forearms: even though fingers occupy a smaller amount of physical space, they appear to occupy a larger amount of perceptual space (based on the amount of cortex used to represent them).

This mapping of the body to the cortex (or surface) of the brain has been studied extensively. In doing so, it has been observed that this mapping varies somewhat across individuals. Further, the cortical area corresponding to various areas of your physical body can change over time. For example, if you take piano lessons, the size of the cortical area that is dedicated to your fingers will increase.

To return to the topic of this section, an approximate (and certainly incomplete) attempt at characterizing the dimensions of the different external modalities is shown in the following table:

In the table above, most of the dimensions enumerated in the column on the right are merely illustrative, and somewhat arbitrary. The analysis of taste however, and in particular the taste receptor corresponding to the flavor umami , is the result of research by the scientist Kikunae Ikeda in 1908. There are five different known types of taste receptors (the neurons which are responsible for the detection of sensory events). In addition to the fact that taste is located in the mouth, each of those types of receptors can be represented as a dimension.

Since we experience such a plethora of tastes, the relative paucity of types of taste receptors may be surprising. Part of this can be explained by the fact that most foods we eat also have a distinctive mouth feel and a different smell (the sensation of smell is heavily intertwined with taste). It should be noted that it does not take very many orthogonal dimensions to produce a dense quantification of phenomena: adding new dimensions to existing spaces increases the size of these spaces exponentially. In particular, adding a novel dimension to a space multiplies the size of that space by the number of divisions that occur in the new dimension. For example, if we perceptually discriminate twenty different intervals along each of the five dimensions of taste (which grossly underestimates our capacity), then we would be capable of 205 possible perceptions, or over three million different tastes.[54]

Some of the features (or dimensions) in the table above may be the result of aggregating smaller-scale features. For example, rough and smooth may be aggregates of lower-level physical sensations: a single perceptual point may be incapable of being either rough or smooth on its own. This table represents a list of those dimensions of perception that are truly external, or those that come from outside of the organism (perceptions which are aggregates of other perceptions are regarded as internal). For example, this is the reason that depth is not listed as a dimension of vision: we have determined the dimensionality of visual sensation by measuring close to the eyeballs , and monocular vision does not produce the phenomenon of depth (at least without a number of simplifying assumptions). It is only when further along the neural pathways deeper in the brain that we find the input from each eye is combined, and a disparity map is formed to determine the distance of a given object. The bottom line is that the dimensions of perception are significantly different when determined proximal to the organs of perception as opposed to when they determined are observed further inside the brain. In this example, the dimensionality of vision increases as we follow perception from external sensation inwards.

Internal perception is responsible for like and dislike.

There are a large number of internal senses for which language is rather poorly developed. For example, if I say that I am feeling a little “zippy” today, you may not know exactly what I mean by this: you cannot directly perceive the subjective experiences that coincide with my feeling of “zippiness” . The situation is different for the perception of external things: if we both perceive the same object, then we do not need to rely on symbolic communication to learn the conceptual mapping. This is one of the issues that makes the determination of exactly which emotions exist (and the dimensionality of each) a difficult topic.

There are a number of basic internal percepts, which are categorized as feelings or emotions. Many of these emotions are bound up with concepts: for example, we like certain things and dislike other things. Liking conceptual things (i.e. having a positive valuation for certain concepts) entails that we have learned an association between some enjoyable perception (pleasure) and that conceptual thing (e.g. the concept of an apple). Similarly, disliking something may have its root in experienced pain. The sensations of liking and disliking clearly have a dimension of intensity, and probably several others, but a vague characterization is suitable here.[55]

If like and dislike are perceived, instead of conceived, then they occur in a perceptual space. If I am eating ice cream, that perceptual space is easy to localize: there is some sweetness in my mouth. Coupled with this sweetness is the perceptual (visceral) like of ‘ice cream’ : although it may later be responsible for transferring a positive valuation to the concept of “ice cream” , it is initially perceptual goodness. That perceptual goodness is not always easy to localize. For example, if you flirt with someone, it may be difficult to precisely localize the good feeling associated with that flirtation. On the other hand, this feeling certainly goes beyond purely conceptual happiness.

Although we claim that all percepts can be found within a perceptual space, they may not have a precise locality (perhaps this is related to the non-local effects of hormones and neurotransmitters). Even if internal senses are ultimately localizable, this location is often amorphous or hard to determine. For many people, however, internal perceptions are associated with particular areas of the body. Fear, for example, may occur in the belly; stress may occur in the shoulders. Although cognitive events may remain difficult to localize, most feelings are at least partially localizable, especially if we do not get too caught up in them.[56]

[53] Although perception is a bit of an awkward word choice, the alternative of inventing a new word that denotes all experienced phenomena other than concepts seems worse. The fact that no such word already exists might be regarded as evidence that terminology in the subjective domain tends to be poorly developed.

[54] Because of this combinatorial explosion, modeling systems with many dimensions is a problem referred to in engineering circles as the curse of dimensionality (of course, this dimensionality is not a curse when it is time for dessert).

[55] The dichotomy of like/dislike is potentially coincident with those of pleasure/pain, happiness/sadness, attraction/aversion, want/don't-want, or desire/repulsion. These dichotomies all have slightly different meanings to different people, and we really intend a bit of all of them when we are talking about like/dislike.

[56] In fact, whole systems have been developed with the aim of localizing various bodily energies, the most famous of which is probably the Indian chakra system.