Category Archives: motor control

Lingua Franca of the brain

Ezequiel Morsella has been kind enough to send me more information on the Passive Frame theory of consciousness. So here is another posting on ideas from that source.

From time to time I encounter notions of there being a ‘language of the brain’ or a brain coding system. Although I would not say that there was no extra language layer (who knows?), I have never seen the necessity for it. The idea seems a product of thinking of the brain in the context of software algorithms, digital transmission, information theory, universal Turing machines and the like rather than in biological cell to cell communication.

Look at forming and retrieving episodic memories: they are conscious experiences before they are stored and conscious experiences when they are retrieved. Awareness is in the form of consciousness and so is the access of various parts of the brain to information from other parts. We understand movement of ourselves and others in similar terms. The Passive Frame proponents talk of perception-like tokens - “they represent well-crafted representations occurring at a stage of processing between sensory analysis and motor programming” and are presumably accessible to both. Here we can have a lingua franca for sensory-motor interaction.

Of course for both sensory and motor processing we need a space and viewpoint for the perception-like tokens. This is often thought of as a stage or a sensorium, but I like to think of it as a model of the environment with the organism active in it. In this ‘space’ the objects we perceive can be placed and our actions can be simulated.

Passive Frame Theory

ScienceDaily has an item (here) on a paper by Morsella and others on the Passive Frame Theory of consciousness. This theory is one of my favorites!!

The passive frame presents information but does not create or act on that information. This consciousness is like an interpreter Morsella says, “the information we perceive in our consciousness is not created by conscious processes, nor is it reacted to by conscious processes. Consciousness is the middle-man, and it doesn’t do as much work as you think.” It is intuitive to think that consciousness is in control of the things it reports (actions, thoughts, feelings, perceptions). But really consciousness simply passively presents these things.

Morsella also says that consciousness is not a connected stream. “One thought doesn’t know about the other, they just often have access to and are acting upon the same unconscious information. You have one thought and then another, and you think that one thought leads to the next, but this doesn’t seem to be the way the process actually works.

This theory also puts action at a more central place in the function of consciousness than perception.

I do not have access to the original paper (Morsella, Godwin, Jantz, Krieger, Gazzaley; Homing in on Consciousness in the Nervous System: An Action-Based Synthesis; Behavioral and Brain Sciences 2015). But here is the abstract:

What is the primary function of consciousness in the nervous system? The answer to this question remains enigmatic, not so much because of a lack of relevant data, but because of the lack of a conceptual framework with which to interpret the data. To this end, we developed Passive Frame Theory, a internally-coherent framework that, from an action-based perspective, synthesizes empirically supported hypotheses from diverse fields of investigation. The theory proposes that the primary function of consciousness is well-circumscribed, serving the somatic nervous system. Inside this system, consciousness serves as a frame that constrains and directs skeletal muscle output, thereby yielding adaptive behavior. The mechanism by which consciousness achieves this is more counterintuitive, passive, and ‘low level’ than the kinds of functions that theorists have previously attributed to consciousness. Passive Frame Theory begins to illuminate (a) what consciousness contributes to nervous function, (b) how consciousness achieves this function, and (c) the neuroanatomical substrates of conscious processes. Our untraditional, action-based perspective focuses on olfaction instead of on vision and is descriptive (describing the products of nature as they evolved to be) rather than normative (construing processes in terms of how they should function). Passive Frame Theory begins to isolate the neuroanatomical, cognitive-mechanistic, and representational (e.g., conscious contents) processes associated with consciousness.



Why do coaches keep reminding golf and tennis athletes to concentrate on a good follow-through? It really should not matter that is done after the moment of contact with the ball. But it does. Howard and others show how, in a paper (citation below) on the effect of follow-through on learning and execution.

The details of motor control of an action (the details and timing of muscle commands) are held in memory as motor programs or motor memories. The appropriate motor memory must be learned and it must be retrieved from memory to be used. If we think of what happens just before and just after the important moment in an action, we have three things that can vary (lead-in - main-action - follow-through). Each different lead-in and each different follow-through would produce a different motor memory. So if there is only one lead-in and one follow-through there needs to be only one motor memory. All the practice in learning the skill can be concentrated in one motor memory. This results in faster, more accurate execution. If there are different actions near the main-action in time, those differences will give separate motor memories; and, if there are unrelated actions by in other parts of the body during the main-action, those too will give separate motor memories. The fewer similar motor memories the better.

Although we have shown that consistent follow-through leads to faster learning through selection of a single memory, this does not preclude other potential advantages of the follow-through, such as injury reduction or other biomechanical advantages … Our findings suggest that distinct follow-throughs associated with different motor skills, such as different tennis strokes, will help maintain these skills in separate motor memories, thereby protecting them from interference when learning other skills. Moreover, even for a single skill, maintaining a consistent follow-through will speed up learning. An intriguing question is why a particular follow-through might be preferred when learning a skill. Our results suggest that variability in the follow-through, which might arise from planning variability, motor noise, or other sources of variability, would lead to a reduction in the speed of skill acquisition. Therefore, it may be optimal to choose the follow-through for a skill that can be executed with the minimum variability.”

Here is the paper’s abstract: “In ball sports, we are taught to follow through, despite the inability of events after contact or release to influence the outcome. Here we show that the specific motor memory active at any given moment critically depends on the movement that will be made in the near future. We demonstrate that associating a different follow-through movement with two motor skills that normally interfere allows them to be learned simultaneously, suggesting that distinct future actions activate separate motor memories. This implies that when learning a skill, a variable follow-through would activate multiple motor memories across practice, whereas a consistent follow-through would activate a single motor memory, resulting in faster learning. We confirm this prediction and show that such follow-through effects influence adaptation over time periods associated with real-world skill learning. Overall, our results indicate that movements made in the immediate future influence the current active motor memory. This suggests that there is a critical time period both before and after the current movement that determines motor memory activation and controls learning.

Howard, I., Wolpert, D., & Franklin, D. (2015). The Value of the Follow-Through Derives from Motor Learning Depending on Future Actions Current Biology, 25 (3), 397-401 DOI: 10.1016/j.cub.2014.12.037

Fluid, flow, zone and zen

So we have conscious and unconscious, type 1 and type 2 cognitive processes, default and task related modes, fluid intelligence, being in the flow, being in the zone and the Zen mind. I am wondering which are really the same but just expressed in different semantic frameworks. What might actually be the same physical thing from a different view point. I suspect that these are all ways of expressing various aspects of how we use or fail to use unconscious cognition.

Here was an interesting Scientific American blog (here) by SB Kaufman last January, looking at the relationship between fluid reasoning and working memory. Fluid reasoning works across all domains of intelligence and uses very little prior knowledge, expertise or practice to build relationships, patterns and inferences. How much it depends on working memory is controlled by speed. If the fluid reasoning is done quickly, it requires good working memory; but it can be done slowly with less need for working memory. Is this the difference between quick and deep thinkers, both described as intelligent?

Fluid reasoning does not fit nicely with the two types of cognitive processes: type 1—intuitive, fast, automatic, unconscious, effortless, contextualized, error-prone, and type 2—reflective, slow, deliberate, cogitative, effortful, decontextualized, normatively correct. As type 2 is typified as using working memory and type 1 as not using it, there is an implication that when speed is required for fluid reasoning, more working memory is required and therefore the thinking is leaning towards type 2 processing which is the slower of the two. It is a bit of a paradox. Perhaps what sets apart fluid reasoning is the type of problem rather than the type of process. Maybe the two types of process are ends of a spectrum rather than some sort of opposites. Let’s imagine the reasoning as being little spurts of type 1 process feeding a type 2 use of working memory. This could be a spectrum: at one end continuous type 1 thinking with working memory and consciousness only being involved in the beginning and the end. The other end would be a continuous back and forth as working memory steps through a solution. Let’s imagine that there is little control of efficiency in the type 1 working. The unconscious does not necessarily stick to a plan, while the use of working memory almost dictates a step-wise method. Fluid problems which occur in areas with little expertise, knowledge and practice may tax the type 1 reasoning unless it is closely monitored and controlled with working memory. A ‘step-wise plan’ may restrict and slow down progress on a well-practiced task; not having such a plan, may overwhelm the process with irrelevant detail and slow down an unfamilar task. There may (for any situation) be an optimal amount of type 2 control of type 1 free-wheeling speed.

People talking about ‘flow’ and ‘zone’ tend to acknowledge the similarity in the two concepts. But flow seems less concentrated and describes a way of living and especially working. While zone seems to describe short periods of more intense activity, as in a sport. This is almost the opposite of fluid reasoning in that neither flow nor zone can be achieved without first acquiring skill (expertise, knowledge and practice are basic). This seems to be type 1 processing at its best. In fact, one way to lose the zone is to try and think about or consciously control what you are doing. That is how to choke.

Mihály Csíkszentmihályi has documented flow for most of his career. His theory of Flow has three conditions for achieving the flow state: be involved in an activity with a clear set of goals and progress (direction and structure); have clear and immediate feedback to allow change and adjustment; have balance between the perceived challenges and perceived skills (confidence in one’s ability for the task). The person in flow is experiencing the present moment, a sense of control, a loss of sense of time and of self-consciousness, with a feeling of great reward and enjoyment. There is an automatic connection of action and perception and an effortless relaxation, but still a feeling of control.

Young and Pain have studied being ‘in the zone’. It is described as “a state in which an athlete performs to the best of his or her ability. It is a magical and…special place where performance is exceptional and consistent, automatic and flowing. An athlete is able to ignore all the pressures and let his or her body deliver the performance that has been learned so well. Competition is fun and exciting.” Athletes reporting on ‘in the zone’ moments report: “clear inner process”, “felt all together”, “awareness of power”, “clear focus”, “strong sense of self”, “free from outer restrictions”, “need to complete”, “absorption”, “intention”, “process ‘clicked’”, “personal understanding & expression”, “actions & thoughts spontaneous”, “event was practiced”, “performance”, “fulfillment”, “intrinsic reward”, “loss of self”, “spiritual”, “loss of time and space”, “unity of self and environment”, “enjoyed others”, “prior related involvement”, “fun”, “action or behavior”, “goals and structure”. Zone seems more intense and more identified with a very particular event than flow.

The hallmark of both flow and zone is that it appears to be the unconscious, fully equiped and practiced, in charge and doing the task well and effortlessly. The other thing to note is that the task mode is being used and not the default mode. Introspection, memory and imagination are taking second place.

The flow/zone way of acting is even more extreme in some Eastern religious exercises and also a few Western ones. The pinnacle of this is perhaps Zen states of mind. One in particular is like zone. “Mushin means “Without Mind” and it is very similar in practice to the Chinese Taoist principle of wei wuwei . Of all of the states of mind, I think not only is working toward mastery of mushin most important, it’s also the one most people have felt at some point in time. In sports circles, mushin is often referred to as “being in the zone”. Mushin is characterized by a mind that is completely empty of all thoughts and is existing purely in the current moment. A mind in mushin is free from worry, anger, ego, fear or any other emotions. It does not plan, it merely acts. If you’ve ever been playing a sport and you got so into it you stopped thinking about what you were doing and just played, you’ve experienced mushin.” I find the use of mind with this meaning misleading, but it is clear in the context that they are referring to just the conscious part of the mind when they use the word ‘mind’. It could be replaced with the word consciousness without changing the meaning.

In summary, unconscious control of tasks have been extremely well learned (the learning likely requires conscious thought) leads to states of mind that are valued, very skilled, without effort and agreeable. The default mode is suppressed and the self recedes in importance as do past and future because introspection, recall of past events and dreaming of future ones require the default mode. It is not an all or nothing thing but one of degree.

Fine control

My last blog on timing in some neurons in the cerebellum has started a string of thoughts. Here we have a part of the brain with an anatomy that is well mapped as opposed to many other parts. It has more neurons than the rest of the brain put together. It has grown relatively larger in human evolution then any other part of the brain. There are theories about how the system works, and yet, its actions are not understood in detail and new information on one of its important cell types was a surprise. (previous blog)

Abstract (Barton see citation below):

Humans’ unique cognitive abilities are usually attributed to a greatly expanded neocortex, which has been described as “the crowning achievement of evolution and the biological substrate of human mental prowess”. The human cerebellum, however, contains four times more neurons than the neocortex and is attracting increasing attention for its wide range of cognitive functions. Using a method for detecting evolutionary rate changes along the branches of phylogenetic trees, we show that the cerebellum underwent rapid size increase throughout the evolution of apes, including humans, expanding significantly faster than predicted by the change in neocortex size. As a result, humans and other apes deviated significantly from the general evolutionary trend for neocortex and cerebellum to change in tandem, having significantly larger cerebella relative to neocortex size than other anthropoid primates. These results suggest that cerebellar specialization was a far more important component of human brain evolution than hitherto recognized and that technical intelligence was likely to have been at least as important as social intelligence in human cognitive evolution. Given the role of the cerebellum in sensory-motor control and in learning complex action sequences, cerebellar specialization is likely to have underpinned the evolution of humans’ advanced technological capacities, which in turn may have been a preadaptation for language.

This enlargement has been in the neocerebellum which is not primarily concerned with the fine tuning of movements of the whole body and limbs. What appears to have increased is: the ability to learn by being taught, imitating and practice; fine control of the hands as is needed for tool making; find control of the larynx as is needed for speaking; and it might said, fine control of any sequential process including language and some types of thought.

Wikipedia gives a summary of the neocerebral connections. “The lateral zone, which in humans is by far the largest part, constitutes the cerebrocerebellum, also known as neocerebellum. It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming cortico-ponto-cerebellar pathways), and sends output mainly to the ventrolateral thalamus (in turn connected to motor areas of the premotor cortex and primary motor area of the cerebral cortex) and to the red nucleus. There is disagreement about the best way to describe the functions of the lateral cerebellum: it is thought to be involved in planning movement that is about to occur, in evaluating sensory information for action, and in a number of purely cognitive functions as well, such as determining the verb which best fits with a certain noun (as in “sit” for “chair”).

A computing mechanism for fine control of a process using feedback from the environment has an almost universal usefulness. It does not initiate but controls an action. It evolved to give us balance and posture, to smooth our actions and make them more accurate, to move the eyes and give us a stationary vision from moving eyes, and to steer the eyes to points of attention. What we appear to have gained is extremely fine control of some muscles and the ability to use the same mechanisms for language, music and other forms of thought and social communication. It appears essential to supervised learning. And here is a biggy – it may be responsible for knitting together the fragments of memory and knowledge that produces imagination.

Barton, R., & Venditti, C. (2014). Rapid Evolution of the Cerebellum in Humans and Other Great Apes Current Biology DOI: 10.1016/j.cub.2014.08.056

A new feature of neurons

There are articles asking, “Are we ever going to understand the brain?” They imply that we have been studying the brain for long enough to be able to say how it works, if we are ever going to, and therefore hinting that it is a permanent mystery. But every week or so some new wrinkle on the brain’s nature comes to light. The brain is far more complicated and far less understood than many think.

Recently a paper appeared that pointed to a wholly new feature of neurons. (citation below) Johansson and his colleagues demonstrate a surprising feature of at least some neurons. They looked at a well known response. When a puff of air is directed at the eye, there is a blink. If this is done over and over with the same time interval between a signal and the puff, a reflex is formed so that the blink happens at just the right time to protect the eye from the puff. This is a standard conditioned reflex and we thought we understood conditioned reflexes. The researchers found that the learning of the time between signal and puff was not a function of a network of cells but an internal function of one type of cell. “The data strongly suggest that the main timing mechanism is within the Purkinje cell and that its nature is cellular rather than a network property. Parallel fiber input lacking any temporal pattern can elicit Purkinje cell responses timed to intervals at least as long as 300 ms. … In addition, the data show that a main part of the timing of the conditioned response relies on intrinsic cellular mechanisms rather than on a temporal pattern in the input signal. ” We have been modeling neurons as firing, or not, as a result of the strength of the signals at their synapses; and firing, if they do, immediately. Any timing effects were assumed to be produced by network structures. Neurons were modeled as very fancy switches but with no timing capabilities. Now understanding has changed. Large changes in understanding, like this one, happen regularly. We are a long way from understanding the mechanisms in the brain.

Here is the Significance and Abstract:

The standard view of neural signaling is that a neuron can influence its target cell by exciting or inhibiting it. An important aspect of the standard view is that learning consists of changing the efficacy of synapses, either strengthening (long-term potentiation) or weakening (long-term depression) them. In studying how cerebellar Purkinje cells change their responsiveness to a stimulus during learning of conditioned responses, we have found that these cells can learn the temporal relationship between two paired stimuli. The cells learn to respond at a particular time that reflects the time between the stimuli. This finding radically changes current views of both neural signaling and learning.

The standard view of the mechanisms underlying learning is that they involve strengthening or weakening synaptic connections. Learned response timing is thought to combine such plasticity with temporally patterned inputs to the neuron. We show here that a cerebellar Purkinje cell in a ferret can learn to respond to a specific input with a temporal pattern of activity consisting of temporally specific increases and decreases in firing over hundreds of milliseconds without a temporally patterned input. Training Purkinje cells with direct stimulation of immediate afferents, the parallel fibers, and pharmacological blocking of interneurons shows that the timing mechanism is intrinsic to the cell itself. Purkinje cells can learn to respond not only with increased or decreased firing but also with an adaptively timed activity pattern.

Johansson, F., Jirenhed, D., Rasmussen, A., Zucca, R., & Hesslow, G. (2014). Memory trace and timing mechanism localized to cerebellar Purkinje cells Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1415371111


What is in a smile?


We distinguish genuine from fake smiles, even though we appreciate the polite sort of fake smile in many cases. I have thought it was a settled matter. Smiles are marked by the raising of the corners of the mouth and pulling them back. A broad smile (fake or real) opens the mouth by lowering the jaw. But only authentic smiles are marked by crow’s feet at the corners of the eyes. This is the Duchenne marker. Would you believe that it is just not that simple? The smile is a dynamic thing and research has mostly used static pictures to investigate smiles. A recent paper by Korb (citation below) examines dynamic smiles. Here is the abstract:

The mechanisms through which people perceive different types of smiles and judge their authenticity remain unclear. Here, 19 different types of smiles were created based on the Facial Action Coding System (FACS), using highly controlled, dynamic avatar faces. Participants observed short videos of smiles while their facial mimicry was measured with electromyography (EMG) over four facial muscles. Smile authenticity was judged after each trial. Avatar attractiveness was judged once in response to each avatar’s neutral face. Results suggest that, in contrast to most earlier work using static pictures as stimuli, participants relied less on the Duchenne marker (the presence of crow’s feet wrinkles around the eyes) in their judgments of authenticity. Furthermore, mimicry of smiles occurred in the Zygomaticus Major (smile muscle - positive), Orbicularis Oculi (Duchenne muscle - positive), and Corrugator muscles (frown muscle - negative). Consistent with theories of embodied cognition, activity in these muscles predicted authenticity judgments, suggesting that facial mimicry influences the perception of smiles. However, no significant mediation effect of facial mimicry was found. Avatar attractiveness did not predict authenticity judgments or mimicry patterns.”

In these experiments stronger smiles were found both more realistic and more authentic. This did not depend as much as previously thought on the eyes. The smile muscle action, the opening of the mouth and the lack of a frown in the brow were as important as the Duchenne marker. The subjects showed electrical activity in the muscles of their own faces mimicking the video being shown and whether the subject found the smile genuine could be predicted from this mimicry. The most clear mimicry was the combination of smile muscle and frown muscles. These two are correlated: in a smile the Zygomaticus is activated and the Corrugator is relaxed, while the opposite happens in a frown. The Masseter (jaw) muscle did not show mimicry. Since this is different from findings on static smiles, the question is raised whether smiles are judged by a different pathway when they are dynamic.

Embodiment theories propose that facial mimicry is a low-level motor process that can generate or modify emotional processes via facial feedback. However, other scholars favor the view that facial expressions are the downstream reflection of an internally generated emotion, and therefore play at best a minor role at a later stage of the emotion generation process. The main critique of the embodiment view is based on the observation that, in addition to their well-documented role in facial mimicry, the Zygomaticus and Corrugator muscles respond, respectively, to positive and negative emotional stimuli not containing facial expressions. However, the Orbicularis Oculi muscle is not clearly associated with positive or negative emotions and contracts, for example, during smiling (producing crow’s feet) as well as during a startle reflex in response to a sudden loud noise.”

This points to a low-level motor process because the Duchenne marker is mimicked in the Orbicularis muscle even though it is not actually a diagnostic for a smile. (It can occur in other situations and can be missing in some smiles.) It is more likely that the identification of a smile is due to mimicry than that mimicry is due to the identification of a smile. The authors suggest that this should be further investigated.

Nevertheless, the hypothesis that facial mimicry mediates the effect of smile characteristics on rated authenticity remains the most parsimonious one based on the fact that 1) facial mimicry is a costly behavior for the organism, 2) participants spontaneously mimicked the perceived smiles, and 3) this mimicry predicted ratings of authenticity. Importantly, the reverse hypothesis, i.e. that perceived authenticity may have caused participants’ facial reactions, seems less likely based on the finding that participants’ Orbicularis Oculi muscle was most activated in response to two types of smiles that contained the highest degree of the corresponding (marker), but resulted in very different ratings of authenticity.”

I hope that researchers will follow up on the idea that static and dynamic images of smiles are processed differently. Would there be clues in the order and timing of a smile unfolding that would point to its authenticity? If fake and genuine smiles are produced by different mechanisms then perhaps they would by quite different in their dynamics. Using avatars is a neat way to vary the dynamics of the muscle movements.

Korb, S., With, S., Niedenthal, P., Kaiser, S., & Grandjean, D. (2014). The Perception and Mimicry of Facial Movements Predict Judgments of Smile Authenticity PLoS ONE, 9 (6) DOI: 10.1371/journal.pone.0099194

What is conscious intent anyway?

A recent paper (citation below) reports that conscious intent precedes motor preparation activity, and not that motor preparation is well underway before consciousness registers intent. Here is Zschorlich and Köhling conclusion:

Motor intention (intention in action) describes a process of motor preparation without executing an overt movement. In our study, we explored the link between motor intention in the movement preparatory phase and the motor outcome. The experiments present evidence that the excitability of the agonistic motor system is significantly enhanced when subjects develop an intention to move. The opposite was true for the antagonistic movement direction and muscles. The results presented indicate

that the excitatory cortico-spinal drive is enhanced during directed motor intention. The data shows that movement intention induced during the enhancement of the cortico-spinal pathway was significantly greater than in the no-intention condition, which argues for the movement-specific modulation of cortico-spinal excitability. The results support the hypothesis that conscious intention to move induces the enhancement of target-specific motor circuits prior to overt movement execution.

But Neuroskeptic in a recent blog (here) casts doubt on the finding:

The authors, Zschorlich and Köhling of the University of Rostock, Germany, are weighing into a long-standing debate in philosophy, psychology, and neuroscience, concerning the role of consciousness in controlling our actions. To simplify, one school of thought holds that (at least some of the time), our intentions or plans control our actions. Many people would say that this is what common sense teaches us as well. But there’s an alternative view, in which our consciously-experienced intentions are not causes of our actions but are actually products of them, being generated after the action has already begun. This view is certainly counterintuitive, and many find it disturbing as it seems to undermine ‘free will’. That’s the background. Zschorlich and Köhling say that they’ve demonstrated that conscious intentions do exist, prior to motor actions, and that these intentions are accompanied by particular changes in brain activity. They claim to have done this using transcranial magnetic stimulation (TMS), a way of causing a localized modulation of brain electrical activity….As far as I can see, volunteers could simply have been pressing the TMS button and then moving their wrist of their own accord. Ironically, they might not have consciously intended to do this; they might have really believed that their movements were being externally triggered (by the TMS) even though they themselves were generating them. This can happen: it’s called the ideomotor phenomenon, and is probably the explanation for why people believe in ‘dowsing’ amongst other things.”

Neuroskeptic points out that this possibility could be tested by simply having some of the TMS events be fakes – ie there would be no TMS field on some occasions but the participants would not know this. Either the real and fake TMS events would give the same result (an ideomotor indication) or they would give different results (ideomotor improbable). This was not done.

I had a problem with this paper before I read Neuroskeptic’s useful suggestion. And I have had the same problem with many other papers. In the second paragraph of the introduction they say, “The central question of how the conscious motor intention is connected to complex motor programs still remains unclear. ” I have, always have had, a difficulty with what ‘conscious motor intention’ is supposed to mean. It very obviously does not happen to me. I am conscious, I act, I have intentions – all well and good. But the intentions I am conscious of come fully formed, they ‘pop’ from nowhere (ie they are formed unconsciously). So conscious motor intention can mean one of a number of things: an intention made by some conscious process (never happened to me nor have I found an actual description of how it happened to someone else), an intention that is not made by any sort of process at all and is then rendered conscious (very unbelievable mechanics), or an intention that is made by an unconscious process and is then rendered conscious (a reasonable idea, not a counterintuitive one to me, that the Zschorlich paper purports to disprove). My complaint is that Zschorlich et al have not put forward an alternative that can be believed. Nor have others. It could not be simpler – if I am not conscious of an actual process then it is not a conscious process. This is an old problem for me and one of the reasons I have taken such an interest in consciousness.

Zschorlich VR, & Köhling R (2013). How thoughts give rise to action - conscious motor intention increases the excitability of target-specific motor circuits. PloS one, 8 (12) PMID: 24386291

Unconscious vision

Milner (see citation below) reviews the evidence that the visual-motor control is not conscious.


Visual perception starts at the back of the optical lobe and moves forward in the cortex as processing proceeds. There are two tracks along which visual perception proceeds, called the dorsal stream and the ventral stream. The two streams have few interconnections. The dorsal stream runs from the primary visual cortex to the superior occipito-parietal cortex near the top the the head. The ventral stream runs from the primary visual cortex to the inferior occipito-temporal cortex at the side of the head. Their functions, as far as is known, differ. “The dorsal stream’s principal role is to provide real-time ‘bottom-up’ visual guidance of our movements online. In contrast, the ventral stream, in conjunction with top-down information from visual and semantic memory, provides perceptual representations that can serve recognition, visual thought, planning and memory offline… we have proposed that the visual products of dorsal stream1 processing are not available to conscious awareness—that they exist only as evanescent raw materials to provide the unconscious moment-to-moment sensory calibration of our movements.


The researchers used three methods in their studies: patients with lesions in their visual system, patients suffering from visual extinction, and fMRI experiments.


One patient had part of their ventral streams destroyed – they could reach and grasp objects that they were not conscious of. The opposite was true of other patients with damage to their dorsal streams – they had difficulties grasping objects that they were consciously aware of.


Visual extinction is a form of spatial neglect. The patient fails to detect a stimulus presented on the side of space opposite the brain damage when and only when there is simultaneously a stimulus on the good side. By carefully arranging an experimental setup, a patient with visual extinction took account of an obstacle that they were not conscious of when reaching for an object. Avoiding an obstacle depends of the dorsal stream because patients with damage to the dorsal stream did not adjust their reaching movements in the presence of obstacles.


There is visual feedback during reaching. “Under normal viewing conditions, the brain continuously registers the visual locations of both the reaching hand and the target, incorporating these two visual elements within a single ‘loop’ that operates like a servomechanism to progressively reduce their mutual separation in space (the ‘error signal’) as the movement unfolds. When the need to use such visual feedback is increased by the occasional introduction of unnoticed perturbations in the location of the target during the course of a reach, a healthy subject will make the necessary adjustments to the parameters of his or her movement quite seamlessly. ..In contrast, a patient with damage to the dorsal


stream was quite unable to take such target changes on board: she first had to complete the reach towards the original location, before then making a post hoc switch to the new target location…It thus


seems very likely that the ability to exploit the error signal between hand and target during reaching is dependent on the integrity of the dorsal stream.


The phenomenon of binocular rivalry where the subject has different images projected to the two retinas and is alternatively conscious of one or the other image has been studied with fMRI. It is possible to see which image is conscious by the activity in the ventral stream. But the dorsal stream is able to act on information even if it is not being processed by the ventral stream and therefore not consciously available.


The authors do point out that they are not saying that the dorsal stream plays no role in conscious perception. It may for example have some control over attention.


In the conclusion, they say “according to the model, such ventral-stream processing plays no causal role in the real-time visual guidance of the action, despite our strong intuitive inclination to believe otherwise (what Clark calls ‘the assumption of experienced-based control’). According to the Milner & Goodale model, that real-time guidance is provided through continuous visual monitoring by the dorsal stream of those very same visual inputs that we experience by courtesy of our ventral stream.

A.D. Milner (2012). Is visual processing in the dorsal stream accessible to consciousness? Proc R Soc B, 2289-2298 DOI: 10.1098/rspb.2011.2663