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Seeing in the Dark

Find a space with total darkness and slowly move your hand from side to side in front of your face. What do you see?

If the answer is a shadowy shape moving past, you are probably not imagining things. With the help of computerized eye trackers, a new cognitive science study finds that at least 50 percent of people can see the movement of their own hand even in the absence of all light.

"Seeing in total darkness? According to the current understanding of natural vision, that just doesn’t happen," says Duje Tadin, a professor of brain and cognitive sciences at the University of Rochester who led the investigation. "But this research shows that our own movements transmit sensory signals that also can create real visual perceptions in the brain, even in the complete absence of optical input."

Through five separate experiments involving 129 individuals, the authors found that this eerie ability to see our hand in the dark suggests that our brain combines information from different senses to create our perceptions. The ability also “underscores that what we normally perceive of as sight is really as much a function of our brains as our eyes,” says first author Kevin Dieter, a post-doctoral fellow in psychology at Vanderbilt University.

The study seems to confirm anecdotal reports that spelunkers in lightless caves often are able to see their hands. In other words, the “spelunker illusion,” as one blogger dubbed it, is likely not an illusion after all.

For most people, this ability to see self-motion in darkness probably is learned, the authors conclude. “We get such reliable exposure to the sight of our own hand moving that our brains learn to predict the expected moving image even without actual visual input,” says Dieter.

Tadin, Dieter, and their team from the University of Rochester and Vanderbilt University reported their findings online October 30 in Psychological Science, the flagship journal of the Association for Psychological Science.

Although seeing one’s hand move in the dark may seem simple, the experimental challenge in this study was to measure objectively a perception that is, at its core, subjective. That hurdle at first stumped Tadin and his postdoctoral advisor at Vanderbilt Randolph Blake after they initially stumbled upon the puzzling observation in 2005. “While the phenomenon looked real to us, how could we determine if other people were really seeing their own moving hand rather than just telling us what they thought we wanted to hear?” asks Blake, the Centennial Professor of Psychology at Vanderbilt and a co-author on the paper.

Years later, Dieter, at the time a doctoral student working in Tadin’s Rochester lab, helped devise several experiments to probe the sight-without-light mystery. For starters, the researchers set up false expectations. In one scenario, they led subjects to expect to see “motion under low lighting conditions” with blindfolds that appeared to have tiny holes in them. In a second set up, the same participants had similar blindfolds without the “holes” and were led to believe they would see nothing. In both set ups, the blindfolds were, in fact, equally effective at blocking out all light. A third experiment consisted of the experimenter waving his hand in front of the blindfolded subject. Ultimately, participants were fitted with a computerized eye tracker in total darkness to confirm whether self-reported perceptions of movement lined up with objective measures.

In addition to testing typical subjects, the team also recruited people who experience a blending of their senses in daily life. Known as synesthetes, these individuals may, for example, see colors when they hear music or even taste sounds. This study focused on grapheme-color synesthetes, individuals who always see numbers or letters in specific colors.

The researchers enlisted individuals from Rochester, Nashville, Fenton, Michigan, and Seoul, South Korea, but, in a lucky coincidence, one synesthete could not have been closer. At the time, Lindsay Bronnenkant was working as a lab technician for co-author David Knill, a professor of brain and cognitive sciences at Rochester.

"As a child, I just assumed that everybody associated colors with letters," says the 2010 Rochester graduate who majored in brain and cognitive sciences. For Bronnenkant, "A is always yellow, but Y is an oranger yellow." B is navy, C burnt orange, and so on. She thought of these associations as normal, "like when you smell apple pie and you think of grandma." She doesn’t remember a time when she did not see numbers and letters in color, but she does wonder if the particular colors she associates with numbers derived from the billiard balls her family had going up. When she donned the blindfold and waved her hand in the experiment, "what I saw was a blur. It was very dim, but it was almost like I was looking at a light source."

Bronnenkant was not atypical in that respect. Across all types of participants, about half detected the motion of their own hand and they did so consistently, despite the expectations created with the faux holes. And very few subjects saw motion when the experimenter waved his hand, underscoring the importance of self-motion in this visual experience. As measured by the eye tracker, subjects who reported seeing motion were also able to smoothly track the motion of their hand in darkness more accurately than those who reported no visual sensation—46 percent versus 20 percent of the time.

Reports of the strength of visual images varied widely among participants, but synesthetes were strikingly better at not just seeing movement, but also experiencing clear visual form. As an extreme example in the eye tracking experiment, one synesthete exhibited near perfect smooth eye movement—95 percent accuracy—as she followed her hand in darkness. In other words, she could track her hand in total darkness as well as if the lights were on.

"You can’t just imagine a target and get smooth eye movement," explains Knill. "If there is no moving target, your eye movements will be noticeably jerky."

The link with synesthesia suggests that our human ability to see self-motion is based on neural connections between the senses, says Knill. “We know that sensory cross talk underlies synesthesia. But seeing color with numbers is probably just the tip of the iceberg; synesthesia may involve many areas of atypical brain processing.”

Does that mean that most humans are preprogrammed to see themselves in the dark? Not likely, says Tadin. “Innate or experience? I’m pretty sure it’s experience,” he concludes. “Our brains are remarkably good at finding such reliable patterns. The brain is there to pick up patterns—visual, auditory, thinking, movement. And this is one association that is so highly repeatable that it is logical our brains picked up on it and exploited it.”

Whether hardwired or learned, Bronnenkant finds the cross talk between her senses a potent reminder of the underlying interconnectivity of nature. “It’s almost a spiritual thing,” she says. “Sometimes, yeah, I think to myself, ‘I just got this sense from a billiard ball,’ but other times I think that being able to cross modalities actually reflects how unified the world is. We think of math and chemistry and art as different fields, but really they are facets of the same world; they are just ways of looking at the world through different lenses.”


Chronic ankle instability alters central organization of movement.

Haas CJ, Bishop MD, Doidge D, Wikstrom EA. Am J Sports Med 2010 Apr;38(4):829-34.

Epub 2010 Feb 5.

Department of Applied Physiology and Kinesiology,University of Florida, Gainesville, Florida, USA.


This article focuses on altered proprioception. Proprioception (or Kinesthesis) is our ability to orient our body or a body part in space.  Poor proprioception can result in balance and coordination difficulties as well as being a risk factor for injury. Think about people with syphillis, who lose all afferent information from a joint coming in through the dorsal root ganglia. This ultimately leads to a wide based ataxic gait (due to a loss of position and tactile sense) and joint destruction (due to loss of position sense and lack of pain perception). The same consequences can occur, albeit on a smaller scale, when we have diminished proprioception from a joint or its associated muscle spindles.


Proprioception is subserved by both cutaneous receptors in the skin (pacinian coprpuscles, Ruffini endings, etc.), joint mechanoreceptors (types I,II,III and IV) and from muscle spindles (nuclear bag and nuclear chain fibers) . It is both conscious and unconscious and travels in two pathways in the nervous system.


Conscious proprioception arises from the peripheral mechanoreceptors in the skin and joints and travels in the dorsal column system to ultimately end in the thalamus, where the information is relayed to the cortex and cerebellum.

Unconscious proprioception arises from joint mechanoreceptors and muscle spindles and travels in the spino-cerebellr pathways to end in the midline vermis and flocculonodular lobes of the cerebellum. This unconscious information is then relayed from the cerebellum to the red nucleus to the thalamus and back to the cortex, to get integrated with the conscious proprioceptive information.


Information from both systems (both separate and combined; the nervous system loves redundancy) is then sent down the spinal cord to effect some response in the periphery. As you can see, there is a constant feed back loop between the proprioceptors, the cerebellum and the cerebral cortex. This is what allow us to be balanced and coordinated in our movements and actions.


Chronic ankle instability is merely a more serious form of dysfunction on the continuum of ankle pathomechanics. It refers to subjects with both coronal and saggital plane stability problems due to altered proprioception. This results in a loss of fine motor coordination of the foot (ie foot intrinsics) and a recruitment of larger motor units about the joint (peroneus longus,  flexor and extensor digitorum longus, tibialis posterior and anterior, etc) . This is equivalent to writing a letter with a pencil taped to your wrist, rather than in your fingers.


This study looked at plantar pressure changes (actually it measured the amount of deviation in forward/backward and side to side motions, which are corrective motions by the CNS due to a loss of fine motor control). As expected, they were greater in the group with ankle instability, particularly when they led with that foot (ie the impaired foot). Thus they lacked the skill necessary to perform the task and developed another movement or recruitment pattern to compensate.


This would be an excellent example of restoring function (ie skill)  for rehab, rather than just increasing strength. If fine motor control is not mastered 1st and you do not change the central pattern, you are carving a turnip with a chainsaw.

We are…. The Gait Guys

I’ve been thinking a lot about digital art and its capabilities in comparison with those of traditional arts. Discussions with my professors have triggered a lot of back and forth in my head about what makes digital art limited when it is against traditional, and this is the best answer I’ve been given:

Digital art is analytical art.

That’s a little vague, and at first I didn’t believe it, but it makes sense. When one works in traditional media, there is kinesthesis, or a sense of the body being used, becoming the instrument that makes art. You “perform” the artwork with your whole being, especially on a large scale, and it taps nicely into that left side of the mind that can be so important for an artist. (That’s not to say you can’t be analytical with paint or a pencil; you can definitely work small and get the same effect.)

When you work with a tablet or mouse, however, studies show greater activity in the right side, that side that’s all about logic and reason, and this has a lot to do with that loss of kinesthesis. The limited scale makes your mind think and analyze, and never tap into that valuable subconscious state. Art becomes math, and with it you achieve something very different.

The problem I have is that traditional art lends itself to the left brain, but can still tap into the right brain. But digital art can tap into the right brain, but cannot tap into the left brain.

How do you make digital art kinesthetic? How do you perform with a computer? I feel like there has to be a way.

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Kaleidesthesis Smoke & Water | June ‘12
This is an experiment creating a kaleidoscope effect and utilising the theories of synesthesia and kinesthesis. 

Let us first reduce spatio-temporality (temporality as simultaneity and successivity) to the spatio-temporality of this pure life-world

Let us first reduce spatio-temporality (temporality as simultaneity and successivity) to the spatio-temporality of this pure life-world, the real world in the prescientific sense. Taken in this way it is the universal form of the real world in and through which everything real in the life-world is formally determined. But do souls have spatio-temporality in the true sense, in existence in this form, as do bodies? It has always been noted that psychic being in and for itself has no spatial extension and no location. This denial of the spatiality of the psychic was obviously oriented around the actual content of experience, [though] without a radical distinction between life-world and scientifically thought world. But can world-time (the form of successivity) be separated from spatiality? Is it not, as full space-time, the proper essential form of mere bodies, in which form the souls take part only indirectly? All objects in the world are in essence “embodied,” and for that very reason all “take part” in the space-time of bodies - “indirectly,” then, in respect to what is not bodily about them. This applies to spiritual objects of every sort, primarily to souls, but also to spiritual objects of every other sort (such as art works, technical constructions, etc.). According to what gives them spiritual signification, they are “embodied” through the way in which they “have” bodily character. In an inauthentic way they are here or there and are coextended with their bodies. Equally indirectly they have past being and future being in the space-time of bodies. Everyone experiences the embodiment of souls in original fashion only in his own case. What properly and essentially makes up the character of a living body I experience only in my own living body, namely, in my constant and immediate holding sway [over my surroundings] through this physical body alone. Only it is given to me originally and meaningfully as “organ” and as articulated into particular organs; each of its bodily members has its own features, such that I can hold sway immediately through it in a particular way - seeing with the eyes, touching with the fingers, etc. - that is, such that I can hold sway in a particular perception in just the ways peculiar to these functions. Obviously it is only in this way that I have perceptions and, beyond this, other experiences of objects in the world. All other types of holding-sway, and in general all relatedness of the ego to the world, are mediated through this. Through bodily “holding sway” in the form of striking, lifting, resisting, and the like, I act as ego across distances, primarily on the corporeal aspects of objects in the world. It is only my being - as ego, as holding sway, that I actually experience as itself, in its own essence; and each person experiences only his own. All such holding-sway occurs in modes of “movement,” but the “I move” in holding-sway (I move my hands, touching or pushing something) is not in itself the spatial movement of a physical body, which as such could be perceived by everyone. My body - in particular, say, the bodily part “hand” - moves in space; [but] the activity of holding sway, “kinesthesis,” which is embodied together with the body’s movement, is not itself in space as a spatial movement but is only indirectly co-localised in that movement. Only through my own originally experienced holding sway, which is the sole original experience of living - bodiliness as such, can I understand another physical body as a living body in which another “I” is embodied and holds sway; this again, then, is a mediation, but one of a quite different sort from the mediation of inauthentic localisation upon which it is founded. Only in this way do other ego-subjects firmly belong to “their” bodies for me and are localised here or there in space-time; that is, they are inauthentically inexistent in this form of bodies, whereas they themselves, and thus souls in general, considered purely in terms of their own essence, have no existence at all in this form. Furthermore, causality too - if we remain within the life-world, which originally grounds ontic meaning - has in principle quite a different meaning depending on whether we are speaking of natural causality or of “causality” among psychic events or between the corporeal and the psychic. A body is what it is as this determined body, as a substrate of “causal” properties which is, in its own essence, spatio-temporally localised. Thus if one takes away causality, the body loses its ontic meaning as body, its identifiability and distingtuishability as a physical individual. The ego, however, is “this one” and has individuality in and through itself; it does not have individuality through causality. To be sure, because of the character of the physical living body, the ego can become distinguishable by any other ego and thus by everyone in respect to its position in the space of physical bodies, a position which is inauthentic and which it owes to its physical, living body. But its distingtuishability and identifiability in space for everyone, with all the psychophysically conditioned factors that enter in here, make not the slightest contribution to its being as ens per se. As such it already has, in itself, its uniqueness. For the ego, space and time are not principles of individuation; it knows no natural causality, the latter being, in accord with its meaning, inseparable from spatio-temporality. Its effectiveness is its holding-sway-as-ego; this occurs immediately through its kinesthesis, as holding-sway in its living body, and only mediately (since the latter is also a physical body) extends to other physical bodies.

Edmund Husserl, The Crisis of European Sciences and Transcendental Phenomenology