So far we’ve been looking primarily at the perception of information impinging on you from the outside world. But human experience involves more than that. You are a physical being, with a physical body that moves through space and interacts with the world around you, physically and in other ways. You assess situations, make choices, and carry out actions. Your experience encompasses all of those things — your body, your movement, and your interaction with the world. Any description of how you compose your experience must take those dimensions into account as well.
I’ll use the term somatic to refer to those aspects of experience that relate to physicality. The term comes from the Greek word soma, meaning body, in contrast to psyche, meaning mind. Its dictionary meaning is “relating to the body as distinct from the mind,” though a shading of its meaning in the direction of “relating to the experience of living in a body” has been coming into common use in recent years. That latter meaning is more in keeping with my use of the term.
Our previous approximation for the Perceptual Process model focused on information coming in from the outside. Let’s now add the somatic information flows within the body and from the body back to the outside world. In the schematic below, these flows are labeled motor stream, proprioceptive stream, and external effects.
The Perceptual Process Model (final approximation)
The motor stream
Your motor stream is made up of the motor commands that flow constantly from your central nervous system (CNS) to muscle fibers throughout your body, telling them when to contract, how much, and in what sequence. These commands control your conscious actions, such as reaching for a glass or walking across a room. They also control ongoing background activities such as breathing, keeping your balance, and maintaining your habitual level of background tension. Commands also flow to other physiological processes necessary for life, such as digestion, circulation, and hormonal activity. This total outflow of control information is represented by the curved arrow from ongoing experience to the body labeled the motor stream.
Your motor stream is a confluence of many different (and sometimes conflicting) motor control patterns. When you walk across a room drinking a glass of water, you control your walking, the movement of the glass to your mouth and the contractions in your throat necessary for swallowing, your breathing and its synchrony with your other activities, and whatever else you happen to be doing at the time. Ideally, the various elements that make up your motor stream would be coherent and in harmony. That is not always the case. When your intentions are in conflict — for example, when you have to do something that you don’t want to do — you may do it and resist it at the same time. You produce motor commands for both conflicting activities, and you feel “pulled” between the two of them. This type of conflict in the motor stream can make life feel difficult, and it is often the source of stress and fatigue. Much of the effort you feel when you are “working hard” comes from tension generated within your body by opposing motor commands in conflict with each other. We’ll consider these conflicts in more detail later, when we look at the process of motor control.
The exteroceptive stream
Earlier, we just considered one stream of incoming information and called it your perceptual stream. We’re now separating this incoming information into two distinct streams. One, which we’re calling your exteroceptive stream, comes from outside your body, and the other, coming from within, we’re calling your proprioceptive stream. Your overall perceptual stream is the confluence of these two streams.
The activity produced by your motor stream feeds back into your ongoing experience in two ways — through its results in the external world and through the changes it produces within your body. These results in the external world are indicated by the external effects arrow on the lower left. You throw a ball, for example, and it lands somewhere; you speak, and what you say affects your listeners; you walk across the room, and your location changes. You receive feedback about those results through your exteroceptive senses. You see where the ball lands, you see and hear the effects of your speech on your listeners, you sense your movement though the room visually and in other ways. This feedback becomes part of your exteroceptive stream.
The proprioceptive stream
The internal changes produced by your motor stream are constantly monitored by a wide range of proprioceptive sensors. These sensors measure and provide feedback about such things as muscle length and tension, joint position and movement. This information, together with balance information from the vestibular system and other information about internal processes such as digestion, body temperature, blood sugar and salinity levels, etc. makes up your proprioceptive stream.
You may not give much conscious attention to your proprioceptive stream. Indeed, it lies mostly unnoticed in the background. Yet proprioceptive information plays at least as big a role in your experience as does exteroceptive information, possibly even a bigger role. The total volume of proprioceptive information in your nervous system is probably greater than the volume of exteroceptive information.
Much of this proprioceptive information serves to keep things running smoothly in ways that hardly rise to consciousness — to regulate your breathing, or to keep you upright in the field of gravity, for example. It blends with your exteroceptive stream to shape your ongoing experience in ways you hardly notice. You experience your surroundings as a mixture of external sights, sounds, and smells, together with your internal sense of balance, movement, and body position in space. To pick up a glass of water and move it to your mouth to drink, you must integrate visual information (exteroceptive) about the position of the glass and the movements of your hands with kinesthetic information (proprioceptive) about those movements and the effort they require.
The terms exteroceptive and proprioceptive relate to sources of information, not to what that information is about. Both types of sources give you information about yourself as well as about the external world. Your experience draws on the integration of both sources. Reaching for a glass of water requires visual information about the relative positions of your hand and the glass, as well as kinesthetic awareness of your hand to guide your movements. When you touch an external object, your “sense of touch” involves the integration of tactile sensations from your contact with proprioceptive sensations about the way your body organizes itself in response to that contact — the amount of muscular effort you use to hold or press against the object, for example. Your sense of the vertical, of “which way is up,” comes from a mixture of visual information about horizontal and vertical surfaces in your environment, balance information from your vestibular system, and the pressure of your body against the surface supporting it — the ground, floor, chair, or whatever.
The exteroceptive senses of sight, hearing, smell, and taste have distinct localized sense organs. We think of them as conduits for information from those localized organs — though in actuality the images each “sense” provides can be affected by information from other sources. What you see (or hear, or smell, etc.) depends on context, and context is not determined by the information from that sense alone.
The situation with respect to proprioceptive senses is not so clear cut. Some writers identify a range different proprioceptive senses, though the number is variable and seems to depend on the writer’s particular interests. I prefer the idea of a single overall sense through which we interpret proprioceptive information, just as we interpret visual information through sight, and we can subdivide as needed to examine its components. The best term to describe that overall sense is <em>feeling</em>, and the sense organ for the <em>feeling-sense</em> is the body as a whole.
There are many subdivisions to the feeling-sense, of course. We “feel” physiological states such as hunger, thirst, or fatigue, sexual excitement, discomfort and pain, dizziness and disorientation. We “feel” temperature — both internal and external, and have “gut feelings,” which can convey a sense of rightness or wrongness as much as they convey physiological sensation. We “feel” body position and movement, effort, emotions of all kinds, and even textures or other characteristics of objects we touch. Some might see this diversity as arguing for a more differentiated taxonomy of feeling. I see the usage of the single term “feeling” to apply so broadly as recognition at some deep level of an underlying unity. That unity stems from the fact that everything we “feel” involves the interpretation of proprioceptive sensation — information coming from within the body.
Summarizing the Perceptual Process Model
The Perceptual Process model described above provides a good schematic representation of the basic information flows from which experience is composed. We can summarize those flows as follows. You are continuously inundated with streams of information from the external world, represented in the model as your exteroceptive stream, and from within your own body, represented by your proprioceptive stream. You filter this information through your perceptual lens, composing the perceptual images that comprise your current experience from a small portion of it. You respond to experience by sending a motor stream back to your body, to control muscular activity and other body processes. The effects of this motor stream are sensed and returned as part of your proprioceptive stream. All this takes place continuously, on a moment-to-moment basis.
Self-awareness practices like T’ai Chi and the Feldenkrais Method work by inserting new information into the proprioceptive stream that can be used by the perceptual lens to reshape the processes of perception and action. We don’t have the machinery in place yet to say more now about how that happens, but will develop that machinery as we go on.
Having laid out the basic information flows involved in composing experience, we’ll look next at two important processes we use to manage that information — awareness and attention. After that we’ll move on to consider the management of action, and the nature of the motor control processes through which we manifest our actions.