The Sensorimotor Theory

The sensorimotor approach is concerned with elucidating one particular aspect of the problem of consciousness, namely the problem of Phenomenal Consciousness or “feel”. Phenomenal Consciousness is the “what-it-is-like” or “phenomenality” associated with sensory stimulation or possibly with mental or bodily states. Contrary to what the philosopher Ned Block calls Access Consciousness, which seems amenable to analysis in scientific, or at least functional terms, phenomenal consciousness poses a problem for science because one cannot see how biological systems obeying known laws of physics could generate “feel”: feel seems to be something outside the realm of science (cf. the Explanatory Gap).

The sensorimotor approach takes the somewhat counterintuitive stance that the problem of feel can be solved by adopting the view that for a person to have a feel amounts to the person

  1. currently being engaged in exercising a certain sensorimotor skill, and
  2. attending to the fact that they are engaged in exercising that skill

A first example of how this skill-based approach can be applied concerns differences in sensory quality.

Differences in sensory quality

Classically an explanation for the fact that input in different sensory channels provokes different types of sensation is sought in the different cortical areas that are involved (cf. Neural Correlates of Consciousness). However this hypothesis leaves open the question of what exactly it is about these cortical areas or nerve channels that produces the particular sensations. Additional “linking hypotheses” always have to be made to justify, for example, why particular neurons or neural mechanisms should produce particular sensory qualities or why particular firing patterns should produce particular modulations in feel. But there would appear logically to be no way of making such a link in a scientifically testable fashion, since neural states are only physical characteristics of the firing patterns of neurons, and have no natural relation to facts of phenomenology. Thus it would seem that in general, the search for a neural explanation for sensory quality will logically always fail through lack of such a scientifically testable link. Appealing to mechanisms like Gamma oscillations or Reentrant processing or Quantum Theories of Consciousness or Microconsciousness in particular cortical areas only raises new questions about how exactly such mechanisms might provide the varieties of feel that accompany sensations.

On the other hand the appeal to skill provides a natural way of dealing with the question of why different sensations have different feels. If feeling involves attending to the fact that one is currently engaged in a particular mode of sensorimotor interaction with one’s environment, then the quality of a feel will be constituted by the particular laws that potentially govern the interaction. As an analogy one can take the feel of driving a Porsche as compared to driving a Volkswagen. The difference in feel is not “generated” anywhere in the brain, it is constituted precisely by the different things one can, do potentially (that is, one need not actually be doing them at any moment) when one drives these different cars. And now there is a way of making a link between the phenomenology and the objective, sensorimotor interaction, because to every aspect of the phenomenology of driving there corresponds an objective physical characteristic of the interaction one has with the car. For example, though it is difficult cognitively to precisely pinpoint what characterises the feel of Porsche driving, clearly epithets might be used such as “invigorating”, “light touch”, “responsiveness”, “sensitive steering”… Each such adjective obviously does not capture exactly the feel, but one has the conviction that anything that can be said about the feel of Porsche driving ultimately boils down to objective facts about the way the car behaves when one acts upon its controls. It is precisely and only the car’s potentialities under our control, the laws that govern our sensorimotor interaction with the car, which constitute the feel of Porsche driving.

The sensorimotor approach now applies this idea to all sensory feels. Thus, to understand the felt difference between different sensory modalities, the sensorimotor approach considers the example of seeing and hearing. Seeing is a form of interaction in which blinks, movements of the eyes, of the body and of outside objects provoke very particular types of change in sensory input. The laws governing these changes are quite different from the laws governing sensory input in the auditory modality. For example, when one sees, moving forward potentially produces an expanding flow-field on the retina, whereas when one hears, the change in sensory input is now mainly an increase in amplitude of the signal. The claim is now that the sum total of these differences constitute precisely what differentiates the sensations of seeing and hearing. (Note that in this explanation, the theory does not require continuous motor involvement. It suffices that the perceiver have sufficient information to know, implicitly, that if a movement were made, then particular sensorimotor laws would apply)

To understand the felt difference between red and pink, for example, the sensorimotor approach notes that when one moves a coloured piece of paper under different illuminants, or when one moves one’s eyes on or off the paper, there are precise laws that govern the changes in photon catches made by the three photoreceptor types that humans possess. In the case of red, for example, the changes in photon catches are confined to a single dimension of variation (Philipona & O’Regan, 2006), suggesting why red is in some sense a special colour as compared to, say, orange, where three dimensions of variation are observed. In general all differences in experience will, under the sensorimotor approach, correspond to differences in the sensorimotor dependencies (also called “sensorimotor contingencies”) governing interaction with sensory stimuli.

An interesting point about the theory is the way it explains humans’ experience of a very rich and continually present visual world. Instead of supposing, as does the classic approach to vision, that this requires a continuous activation of a rich internal representation of the world (this, the theory claims, would be to make a vehicle-content confusion), the theory says that richness and continuity are due to the fact that a perceiver has immediate access, via a flick of attention or an eye movement, to any information about the outside world. The analogy is made of the light in the refrigerator: every time you open the fridge, the light is on, so you assume it is continually on. Similar arguments are put forward in the theory to explain the Filling In of the Blind Spot.

Why feels have a quality at all

Classically in the philosophy of phenomenal consciousness it is said that “there is something it is like” to have a sensory experience. One of the mysteries of phenomenal consciousness is considered to lie in explaining why the brain processes involved in sensory experiences give rise to this special quality — also referred to as “sensory presence” or “vividness” — while most other brain processes do not possess it.

The sensorimotor approach deals with this problem in the following way. If, as the approach claims, having a feel is precisely attending to the fact that one is engaged in exercising a sensorimotor skill, and if the quality of the feel is constituted by the laws of sensorimotor interaction that the skill involves, then by the very definition of feel, the feel must have a quality, namely the quality constituted by exercising the particular sensorimotor law involved…

Then, just as the sensorimotor approach invokes differences in skills to account for differences between sensations, the approach will also invoke differences in skills to account for the difference between experiences involved in perceptual acts and the experiences involved in “mental” activities like thinking, remembering or deciding. In particular, it is immediately clear that whereas perceptual acts invariably involve, at least potentially, changes caused by motor behavior, this is not true of “mental” activities. What we call sensory experience can always potentially (if not actually) be modified by a voluntary motion of the body: Sensory input to the eyes, ears, or any other sensory system is immediately changed in a systematic and lawful way by body motions. On the other hand, “mental” activities like thoughts, memories, and decisions, to the extent that these can be considered as skills, are not skills that intrinsically involve body motions. This then is what makes the skills constituting sensory experiences special as compared to other brain processes: they are by nature sensorimotor. Even if at any particular moment there need be no motion, they have what the sensorimotor approach calls “corporality” or “bodiliness”.

A second obvious characteristic that distinguishes the skills involved in sensory experience from those of mental functions is what is termed “alerting capacity” or “grabbiness”: this is the fact that sensory systems are genetically endowed with the capacity to deflect our cognitive processing. A loud noise or bright flash will automatically, incontrovertibly, attract our attention to the locus of the event. We are thus, in some sense, “cognitively at the mercy” of sensory input. This is not generally the case for mental activities. If a change occurs in the visual field, like a mouse flitting across the floor, one’s attention will immediately be caught by it. But if one forgets a word, one only discovers this if one actively tries to recover the word from memory. Memory, and in general other mental activities, possess no alerting capacity or grabbiness (an exception might however be, for example, obsessive thoughts).

Thus: a characterisation of the differences in skills associated with sensory acts, as compared to those involved in mental acts, reveals differences which naturally account for the difference in felt quality of sensations as compared to other mental processes. What has been called the “presence” of sensations seems precisely to consist in the fact that they are both under our control (in that we can modify sensory input by our bodily actions — they have corporality or bodiliness), and also not under our control (they can cause uncontrollable alerting reactions that interfere with our normal cognitive processing: alerting capacity or grabbiness). The sensorimotor approach suggests that this captures the idea of there being “something it is like” to feel, as opposed to other mental activities.


In the sensorimotor approach, appealing to skills is also taken to provide a natural way of accounting for the fact that sensations are personal and inaccessible to others.

The reason is that while we have mastery of our sensorimotor skills, the mastery we have is implicit: we do not have cognitive access to each and every muscular contraction or change in sensory input that occurs. Indeed muscular contractions and sensory inputs are not in themselves things that can be sensed. Only skills themselves can be attended to, and even there we do not have complete access to all the characteristics of skills. The situation is like tying your shoelaces: you know that you are tying your shoelaces, but you cannot say exactly how you are doing it, exactly what are the positions of your fingers, exactly what are the muscle movements involved. You may attend to different ways of tying your shoelaces, like differences occurring when the shoelaces are of different rigidity, length, thickness, etc., but though you can identify that there are these differences, and that these differences provide different “feels” to the shoelace tying action, you cannot describe in detail what these differences consist in.

Similar considerations then apply to sensory feels: the sensorimotor dependencies involved in seeing are even less accessible to you than the intricacies of shoelace tying: you know that moving your eyes provokes changes in the information available to you, but you do not know in detail the changes in optic flow that are produced on your retina. You have a notion that when you move colored surfaces under different lights, changes occur that depend on the particular surface reflectances, but the precise laws that govern those changes are not cognitively accessible to you. Nevertheless, the brain can distinguish between the different laws governing interaction with coloured surfaces, and can classify the associated surfaces as corresponding to different colours — just as you can recognize the feel of driving different cars without being able to cognitively pinpoint what causes these differences. Furthermore the brain structures the similarities and differences between the colour-interactions in ways that correspond to the dimensions of brightness, hue and saturation, and this structure determines the the structure of the classifications and colour differences to which we have cognitive access.

How feel is generated by the brain

This question is eluded in the sensorimotor approach, in the sense that it is considered not to be an appropriate question to ask about feel. The sensorimotor approach considers that the idea that feel might be generated in the brain is a category error similar to the error of thinking that something about the shape of a word might generate its meaning. The idea is that if we think properly about feel, then we realize that feel is not an “essence” that can be generated: we have a feel when we attend to the fact that we are interacting with our environment in a particular skillful mode. The quality of the feel is constituted by the characteristics of the mode of interaction. Why do we feel the feels ourselves? Because we as cognitive entities with “selves”, attend to the fact that we are exercising the associated skill.

Attention, Access Consciousness

Whereas the essential ingredient of the sensorimotor approach is the appeal to skill — since this provides the basis for an explanation for experienced differences in feel — the theory also stipulates that to experience a feel, one must attend to the skill that one is exercising. Thus simple sensorimotor automata, like for example thermostats, missile guidance systems and perhaps insects, cannot have feels: it is not sufficient for a system to be exercising a sensorimotor skill, it must in addition have sufficient cognitive capabilities to attend to the sensorimotor contingencies involved. However it is claimed that this appeal to attention does not necessitate any scientifically mysterious mechanisms: attention is a notion already widely used in psychology, where it is considered difficult, but not in any way “magical” or impossible to implement or understand scientifically.

To the extent that the sensorimotor approach makes use of the notion of attention, it bears resemblance to theories of consciousness such as the Global Workspace Theory. Such theories are probably able to provide an acceptable explication of Access Consciousness. However it is the addition, in the sensorimotor approach, of the notion of skill which provides the essential element that allows the sensorimotor theory to go further than Access Consciousness, and provide insights into what has been considered beyond the reach of functional accounts, namely Phenomenal Consciousness.

The essential role of skill in the theory

The reason that invoking skill in the theory provides help in explaining phenomenal consciousness is that differences and similarities between skills are objective facts about an organism’s interaction with the world. Since in the theory the quality of experience is taken to be constituted by the exercise of skills, differences and similarities between qualities are describable in terms of these objective differences in skillful modes of interaction. Making the connection between skill and feel is now easy to do because sensorimotor laws are both describable in terms of objective facts about the perceptible world, and they also have a natural correspondence with what people generally agree characterises sensory feels as compared to other mental phenomena, in particular their perceptual “presence”.

In contrast, if the onus of explanation in explaining feel is put on neural states, as is done in the classical “neural correlate” approach to phenomenal consciousness, then there is no natural way of making the connection between similarities and differences of feel and similarities and differences in the neural states. Even something so simple as supposing that somewhere in the brain there is a location where increased neural firing should cause increased intensity of feel would require providing an explanation for that particular choice of link between feel and neural activity.

Proponents and opponents

The sensorimotor approach, as set out originally by O’Regan & Noë (2001a,b) and more recently by O’Regan, Myin & Noë (2006), has also been called the enactive approach (Noë, 2005). The notion of enaction involves the idea that one can only adequately describe the functioning of the mind in the context of a system with a body acting and sensing in its environment.

But often the notion of enaction is additionally associated with dynamical systems, and with the idea that reentrant processing, chaos and complexity in neural systems might be the key to consciousness. This would be contrary to the sensorimotor approach, which considers that if one thinks carefully about consciousness and feel, one realizes that no appeal to such mechanisms can help to understand why feels feel the way they do.

The sensorimotor approach is sometimes compared to Gibson’s ecological approach to perception, with both approaches emphasizing the role of action and sensorimotor dependencies in perception and both approaches rejecting some senses of the notion of “internal representation”. But the two approaches have very different agendas, with the sensorimotor approach being aimed at solving a problem that Gibson was not concerned with, namely the problem of the origin and nature of phenomenal experience.

There are points of similarity between the sensorimotor approach and aspects of the thinking of French philosopher Maurice Merleau-Ponty, who also wanted to replace the picture of perception as a primarily internal event (involving an iconic replica in the case of vision), with a conception of vision as an active, and further-action-oriented, exploration of the environment. Some of the metaphors used by Merleau-Ponty, such as seeing as having a visual ‘grasp’ on the world, and the analogy between touch and vision anticipate aspects of the sensorimotor theory. On the other hand there are clearly points of dissimilarity: the idea that ‘cognitive access’ is required for consciousness would be rejected by Merleau-Ponty as a piece of ‘intellectualist thinking’ about the mind.

The sensorimotor approach is sometimes labelled as being behaviourist: A relation to behaviorism might lie in the fact that the theory makes use of the concept of skills, which are sensorimotor dispositions. However, to the extent that the theory invokes cognitive capacities and attention, it is not behaviourist in the psychological tradition.

A different link to behaviourism (and to functionalism, and to Dennett’s heterophenomenology) might be the attitude of the theory to qualia: the theory rules out qualia if they are meant to be in principle unobservable and in principle unrelated to behaviour. On the other hand if qualia are considered to be the phenomenal experiences that are involved in sensation and perception, then far from eliminating qualia (cf Eliminativism), the theory attempts to explain why they are the way they are. Here the theory claims that compared to other functional approaches, the appeal to skill provides an advantage in accounting for the phenomenology of sensory experience: the quality of sensation is an objective fact about the way an agent interacts with its environment. For this reason there is also a link with Externalism.

The sensorimotor approach invokes a two-level mechanism to explain phenomenal consciousness: (1): attention to (2): the exercise of a skill. If attending to something can be considered to be a form of cognitive access to that thing, the theory might be considered to be related to the higher order thought theory of consciousness: it could be said that under the sensorimotor approach, having a feel is: having a higher order thought about the fact of exercising a skill. But the main ingredient of the theory are the skills themselves, since their similarities and differences allow similarities and differences in phenomenal experience (including the difference between feel and no feel) to be explained in a natural way.

An important aspect of the sensorimotor approach is its emphasis on empirical evidence. The original experiments on change blindness were motivated by the sensorimotor approach, which is also compatible with the phenomenon of inattentional blindness. The approach finds support in empirical results concerning the possiblity of sensory substitution, and concerning expected changes in phenomenal experience caused by sensorimotor adaptation in touch, as found in the rubber hand illusion and the success of mirror therapy in reducing phantom limb pain. A sensorimotor approach to understanding tetrachromacy and the phenomenal structure of colour space (cf. Philipona & O’Regan, in press) as well as predictions concerning eye movement contingent modifications of colour sensation (cf Bompas & O’Regan, in press) have also proven successful.