2. Parts of the Subjective Universe

All of our experience comes to us through our external and internal senses.

There is no way for us to perceive beyond the boundaries of our perception: to become aware of objects or concepts, they must be perceived. Although this is to some extent tautologous, it is worthwhile to consider that from the subjective point of view, objective reality is contained entirely in subjective experience, or the subjective universe.

The parts of the subjective universe are called percepts. Percepts are both things that we perceive as well as objects, in that our perception is mediated by the neurons of the brain. Of course, if a neurosurgeon were to look at the neurons responsible for our percepts, the neurons would not look to the neurosurgeon as they do to us. The electrical activity of the neurons firing are all that we have ever perceived, and for us, they do not fire randomly but in concert with the external world. In fact, from our perceptual point of view, they are the external world: we have a context for the neuronal activity that makes it meaningful. From the doctor's point of view, there is no such correlation: the doctor observes a small set of meaningless impulses.[57]

Percepts are formed of both objects and concepts.

To form percepts that correspond to objects is just to perceive things. This act is so commonplace that we often forget that the objects are much richer in detail than the limited aspects of them that we perceive: we have an exaggerated expectation that things exist in the world in approximately the way that they appear to us. For example, when the early psychologists began looking inside peoples' heads (literally), they did not find internal mechanisms that looked like things in the external world: they found things of a very different nature. For example, when a person sees red things, red things do not appear in that person's head. On the one hand this is not surprising: to achieve this would be a rather remarkable feat of engineering. However, if the thing is not red in the brain, then what is it that is responsible for the subjective experience of red?

Although “red in reality” and “red in the brain” are quite different things, the perceptual mapping between these two is consistent: red things in reality produce a consistent effect in the brain, whatever effect that happens to be. This mapping also preserves several relationships between things in each domain: for vision, spatial relationships are preserved. So even though objects and percepts are quite different things, they have similar relationships to other things in their respective domains.[58]

As an example of the percept-object correspondence, imagine an apple as it is represented in both the physical universe and the perceptual universe. In the objective world, an enduring apple object can be seen as a collection of many instantaneous events. In the subjective world, an enduring apple concept can similarly be seen as a collection of many instantaneous events. For our concept of the “apple” to correspond to the apple object means that the apple events correspond to ‘apple’ percepts which are grouped together by an “apple” concept.

Our ‘apple’ percepts are very limited representations of the apple events; there are numerous properties of the object which are not represented. Of those features that are apparent, percepts are regarded to be very direct : they are expected to suffer from very little subjective distortion, and reflect reality as would a mirror.[59]

If a given percept corresponds well to a given object, we say that percept is valid; in other words, we correctly perceive the object. This contrasts with invalid percepts, such as hallucinations, for which there are no corresponding objects. Even if we hold that an apple does not exist in the world as a single object (i.e. any more than its two two half-apple parts), we still have a valid basis for calling the object an apple as opposed to an orange. In other words, even if our concepts do not physically resemble percepts, there are still reasons to apply the label “apple” as opposed to the label “orange” .

Just as percepts can be of objects, they can also be of concepts (i.e. we can perceive concepts). Perceiving concepts, however, is a delicate art: it is all too easy to conceive of concepts, since that is most often their intended use: and that interferes with the perception of concepts. An example of forming percepts of symbols without additionally forming concepts that correspond to them occurs when listening to speakers of a language with which we are not familiar. In that case, although we are aware of the auditory sensations of the words (such as the pitch, volume, and timbre), we do not understand the meaning of the words.

Listening to speakers of a foreign language is by no means the only example of perceiving without conceiving: even in our native language, there are times when we listen to someone without understanding what they are saying. To some extent, our faculties of perception and cognition present us with a choice: perception of a thing and conception of that thing destructively interfere. The trade off between perception and conception applies not just to other people's speech, but to our own thought: to some extent, it is possible to be either perceivers or conceivers of our own thought process.

Perception is perception of change.

All perception happens in the present. To some extent, this statement is tautologous due to the use of the present tense, which for most people implies existence at only a single point in time. The present is often conceived of as an interval of time so short that no change can take place. However, the present has also been called the specious present , in order to convey that it exists for a short duration of time (as opposed to existing at only a single instant).

We tend to perceive things that change: things that do not change are forgotten, even at a basic perceptual level. For example, if we eat sweet things all the time, then we adapt to this sweet baseline; it requires increasingly sweet stimuli to trigger the same sensation of sweetness. This acclimatization (or habituation) happens at the neural level, across all sensory modalities. Our perceptual functions are detectors of change: if the objects that we perceive do not change (relative to some baseline), then the percepts tend to disappear as our neurons grow accustomed to the stimulus.[60]

Vision is a particularly interesting modality for the study of habituation, since there is a physiological compensation for the habituation of the neurons: eye saccades. If you look at your environment without moving your eyeballs, your visual receptors habituate to it fairly quickly, and you will not see anything. We are prevented from encountering this situation in practice by eye saccades. Eye saccades are small, ubiquitous eye movements which provide the visual neurons with novel input by moving the eyes rapidly back and forth. Hence, each neuron sees change even in an unmoving scene: saccades generate change for our receptors to witness. We don't see the world similarly jerking about, because our higher-order perceptual processes counteract for the movement of the eyes.[61]

Awareness may be restricted to parts of certain dimensions.

Attention is an operation which restricts the domain of perception. The technical definition of the term attention is somewhat ambiguous (although it is better defined than the term consciousness). The term attention is used here to mean the restriction of perception, from an awareness of everything to an awareness of something . It is analogous to putting blinders on a horse: although it causes them to be less distracted, they are literally perceiving less. Visually, attention is related to the selection of a visual area. Linguistically, it is related to defining a universe of discourse. Mereologically, it is related to the selection of a universe from which parts are chosen. Although all of these mechanisms are not necessarily the same, the effects are similar.

The perceptual creation of a part out of a larger whole is analogous to the separation of a figure and its ground. The figure/ground dichotomy is borrowed from Gestalt psychology. In that system, the figure is the thing toward which attention is directed; it is more salient than the ground (and perhaps more important). When figure and ground are created, therefore, the figure comes to the forefront: this is similar to the part/complement relationship.[62]

Attention is a mechanism which can be arbitrarily directed: hence, it can be arbitrarily complicated. However, there are a number of basic perceptual principles which guide attention. Several of these have been formulated into what are called Gestalt laws, or grouping principles.[63] Some of the most common Gestalt laws are:

  • Law of Closure: Percepts which are similar to percepts that have been seen previously are completed (i.e. the differences between the current and the remembered percept are ignored).

  • Law of Similarity: Similar percepts (e.g. in terms of color, size, and various other properties) are grouped together.

  • Law of Proximity: Contiguous and continuous things are seen as the same thing.

  • Law of Common Fate: Things moving in the same direction are perceived as the same thing (unfortunately, this is hard to represent in non-moving media).

[57] Perceptual mappings near the exterior of the nervous system will have a close accord with the external world. For example, the optic nerve projects the visual field to our brains with such fidelity that if the neurosurgeon were to see the pattern of neural activity on the back of our brains, they could determine what we were observing. For example, in an experiment in which an fMRI scanned the back of the occipital lobe as the subject looked at various words (where the visual field is projected by the optical nerve), the words that the subject is looking at are clearly legible (i.e. the are projected onto the back of the brain with good fidelity). Yoichi Miyawaki et al, Visual Image Reconstruction from Human Brain Activity using a Combination of Multiscale Local Image Decoders, Neuron, December 10 2008

[58] The relationship between “red in reality” and “red in the brain” is known in philosophical circles as the problem of qualia .

[59] Upon a little reflection, the notion that perception reflects reality without distortion is a bit preposterous. Reality is relayed to us through electrical impulses, but the world consists of things which look different than lightning storms. There certainly is a mapping between these different domains, but they remain very different domains. Although we tend to agree with each other about what we observe, that does not make what we each observe identical to objects themselves.

[60] Is it meaningful to say that all perception is the perception of change? This speculation corresponds to the fact that the objects that we perceive are not objects without a duration, but rather objects-undergoing-change. Mathematically, this amounts to saying that we perceive object differences (i.e. finite differences) rather than objects themselves.

[61] Another example of the mind's ability to adapt to changes in perception is its ability to remap distorted perceptual fields. Examples of this come from experiments in which subjects were forced to wear glasses that turned their worlds upside-down. It takes subjects only a few days to adjust to this change; in fact, taking off the glasses at the end of the experiment feels strange. These experiments were first conducted by George Stratton in the 1890s.

[62] It is not necessary to pay attention to the figure and neglect the ground, although we often do just that. This is not surprising, though, given that some increased level of relevance was what directed us to create the separation in the first place. To indicate the importance of both parts (i.e. the figure and the ground without that figure), and to underscore the fact that it is not possible to create just one part out of a larger whole, we emphasize the division between a part and its complement.

[63] Similar rules were formulated by Aristotle in terms of the associations between objects. However, since relations between objects often define the objects themselves, there is a large amount of overlap. Aristotle proposed the following four laws that influence whether things are associated:

  • The law of contiguity: things which are close together in space and time.

  • The law of frequency: things which co-occur, or happen at the same time.

  • The law of similarity: things which are similar, or close together on some dimension.

  • The law of contrast: things which are dissimilar, or far apart on some dimension.