1. Perception

Perception is that process by which objects in the objective world are represented by percepts in the subjective world of an individual.

The subjective domain is a point of view in which everything that exists is a reference to something (in addition to being something in and of itself). Your neurons may fire in the objective domain, but in the subjective domain, you have the experience of something (i.e. something referred to by those neurons). Although these descriptions refer to the same event, the language of the description is different: they differ in their point of view (i.e. their point of reference).

Ultimately, the perceiver, the perceived, and perception are all parts of the physical domain. At the physical end of perception are objects, and at the subjective end are percepts. In between these two endpoints, substantial transformation takes place: percepts and objects are very different from one another. This transformation is generally thought to be a passive process, such that phenomena from the world are conveyed relatively directly to an observer. However, there are a number of phenomena which demonstrate that it is also an active process: we influence our perception of the world. In cognitive science, cognitive influence on perception is called top-down , and the contribution of the senses is called bottom-up .

Percepts are caused, to some degree, by the objects that they reference.

Percepts of the subjective domain are caused by objects of the physical domain (objects are not the only cause, but they certainly play a causal role). In this way, information from the physical domain is represented in the subjective domain. As the subjective world has a limited capacity to represent all of the features of the objective world that it perceives, percepts represent a limited number of features of the physical world.

Although it is relatively clear that we perceive some small fraction of what there is to perceive, we have a tendency to believe that what we do perceive is relatively undistorted. While what we perceive is more or less consistent from moment to moment, it is not clear what it would mean to be entirely undistorted in this context. There seems to be an uneasy tension between the fact that we perceive electricity in the form of neuronal discharges, and at the same time the world does not appear like a lightning storm. Two of the primary requirements for the relations between the world and our perception of it is that they are consistent and isomorphic. Although our percepts of ‘green’ may have very little physical resemblance to the wavelength of light in the world, things in the world which are greenish are consistently perceived as greenish.[81]

The isomorphism between percepts and objects can be illustrated by considering a rainbow as it exists in reality and in our perception. The rainbow in reality reflects photons of varying wavelengths: the photons at the frequency which corresponds to ‘orange’ occur to the right of those photons with a ‘yellow’ wavelength and to the left of those photons with a ‘red’ wavelength. Regardless of the medium in which those colors are represented in our experience, this order is preserved: orange is to the left of red and to the right of yellow. This preservation of order is an isomorphic relationship between the structure of our brains and the structure of reality.

Percepts are caused, to some degree, by the mind in which they occur.

The role of our minds in both what is perceived and what is not perceived (through attention and inattention), not to mention how things are perceived, is often grossly underestimated. The eyes do not act as a mere window, letting information through without distortion. Further, the distortion that is introduced often goes unnoticed. To notice what you do not notice takes rather extraordinary investigation. As an example of how perception can be distorted without being cognizant of it, we will look at blind spots: literally, areas of the visual field that are not perceived.

In order to see one of your blind spots (or perhaps, in order to not see it), look at the following figure. Then, close one eye, and look at the dot on the same side as the closed eye. Then, move the book slowly towards, and then away from, your face. At a distance of approximately one foot, you will notice that the dot that you are not directly looking at has disappeared from your visual field.


These blind spots (there is one in each eye) are created by a small patch of missing retina: therefore, the area of the visual field which is mapped to this patch is not perceived. The optic nerve, which relays optical information to the back of the brain, connects to the retina a bit to the inside of the point directly behind the pupil, on the back of the eye. This creates a literal blind spot (i.e. a spot where there is no retina). Blind spots are odd things, since you do not perceive blind spots. To call them things at all is a bit problematic, since they are characterized by a lack of being present. If you pass a pen over the blind spot that you have identified in the experiment above, you will not see a hole in the pen; the missing part of the pen is continued by your mind. A blind spot is a hole that you do not see, and that you have no awareness of. This phenomena is massively exacerbated for people who have suffered certain brain traumas called hemifield neglect. In that disorder, an entire half of the person's body behaves like a blind spot: further, all of perception is affected, not just vision.[82]

The phenomena of blind spots might be characterized as a perceptual deficit, in that there is something wrong with, or missing from, the bottom-up pathways. But the top-down pathways are clearly also implicated in that they cover up the spot with a bit of hallucinated reality. As a result of this top-down influence, reality conforms to our understanding. For example, consider the following question:

What part of your mind are are you using?

The world as we perceive it is not the world as it is; the act of perception is often, if not always, a process to which we contribute. We filter what we perceive, and make it comprehensible to ourselves. Through this process of comprehension, our perception of reality is altered to a nontrivial extent. This alteration is not necessarily a bad thing, but it is unfortunate that we forget that we have altered it. To return to the question preceding this paragraph, we note that most people who read the sentence for the first time believe that it is identical to the following sentence: “What part of your mind are you using?” . It is not: the sentence at the top of the page does not make sense, as it is not syntactically well-formed. However, most of us make it make sense ; we alter it to conform to our expectations and understanding. This alteration is sometimes helpful, precisely because it helps us to understand: extraneous features are eliminated. It is also somewhat detrimental, because it limits our views of reality: it makes us less able to see what we do not understand.

The notion of playing a creative role in what we perceive can be disturbing, although it clearly appears to be true. Dreaming and hallucinations are rather extreme (and interesting) examples of this phenomena: they show that no external cause is necessary for perception. Often, there is no apparent external basis for dreaming about a particular thing at the moment of the dream. The dream of an apple arises without an apple. Of course, this does not contradict the usual case in which the percept of ‘apple’ arises when a physical apple is present. However, if the percept can occur without the presentation of the object, the causal relationship between these two things becomes less direct (or more tenuous) than we might otherwise have thought. If percepts do not necessarily depend on objects, we are led toward a somewhat unsettling observation: we have no way to tell if we are dreaming or not. This thought led Confucius to make the following famous statement:

Once I, Chuang Chou, dreamed that I was a butterfly and was happy as a butterfly. I was conscious that I was quite pleased with myself, but I did not know that I was Chou. Suddenly I awoke, and there I was, visibly Chou. I do not know whether it was Chou dreaming that he was a butterfly or the butterfly dreaming that it was Chou.[83]

In dreams, we perceive our environment as clearly as if we were awake. This seems to indicate that perception, even when we are awake, is very indirect; in some sense, we live in a perceptual world, where percepts bear little (intrinsic) resemblance to objects. God only knows what actual objects look like: our percepts are to some extent created within the confines of our own heads.[84] Although this realization may initially feel alarming, remember that there is most often a valid, consistent isomorphism between objects and percepts: percepts almost always refer to objects. So even if we are in some sense hallucinating, we can take comfort in the fact that we are more or less hallucinating correctly .

The relative contributions from bottom-up and top-down perception are hard to determine. Perhaps our concepts have a relatively small top-down role in perception when compared to the bottom-up role of objects. Even in that case, however, they retain an influential role in guiding attention to what is perceived. Our concepts direct our attention to some things and not others, and therefore we perceive some things and not others. So even if cognition does not strongly influence the way we perceive, it still strongly influences what we perceive.[85]

Given that reality seems to conform to our understanding, we might ask if this is beneficial: do we want reality to conform to our understanding? On one hand, this is beneficial. If we conceive of something as a dangerous snake, even when it is not a snake, this tendency to misconceive things might keep us alive in the event that we see an actual snake. On the other hand, if the world always conformed to our understanding, our understanding would not grow: we would always recognize only those things with which we were already familiar. If we do not perceive anything which we do not already understand, this overuse of the sense-making part of our mind would prevent learning. Although it seems paradoxical, there is a sense in which greater understanding can be achieved by (temporarily) not-understanding.[86]



[81] Brightness, as another example, is a monotonically increasing function in each universe. The study of these mappings between the objective and the subjective, in which various relations are preserved, is known as psychophysics.

[82] Agnosias and aphasias have been popularized by Oliver Sacks in the book The Man Who Mistook his Wife for a Hat .

[83] A Source Book in Chinese Philosophy, Translated and Compiled by Wing-Tsit Chan, Princeton University Press, 1963

[84] Of course, to presume looking also presumes the act of perception, so perhaps the notion of looking like something in reality , or in a non-subjective sense, is completely meaningless.

[85] If you are not convinced, I highly recommend watching the video about basketball on the following page: http://www.cognitivesettheory.com/links

[86] Of course, we presume that people will do something useful with the leftover cognitive resources like put more energy into perception. Withholding rational thought, if it does not entail something else, is probably not any better than going to sleep.