A&O – DEEP – PHYSIOLOGY – INPUT notes

ART AND ORGANISM


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PHYSIOLOGY

DEEP aspects of

INPUT NOTES

Sensation – Perception – Conception

STIMULI become SENSATIONS become PERCEPTIONS become CONCEPTIONS 

 

There is a flow of information through all organisms, but many (we in particular) are able to derive heuristics–ways of responding–by selectively representing the stimuli and currents they instantiate that are (or have been in our ancestral past) useful for conducting ourselves in the most adaptive manner–the manner best able to meet our biological needs.


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Sensations, our detection of stimuli that have impinged upon sense organs (both internal and external); Perceptions,the signals in the nervous system evoked by stimuli (the meaning of which is subject to past experience and expectation); and Conceptions, abstract ideas (that represent the essences of what they represent); all more-or-less grade into each other.

 

The intellectual life of man consists almost wholly in his substitution of a conceptual order for the perceptual order in which his experience originally comes.… Percepts and concepts interpenetrate and melt together, impregnate and fertilize each other. Neither, taken alone, knows reality in its completeness…. The world we practically live in is one in which it is impossible (except by theoretic retrospection) to disentangle the contributions of intellect from those of sense.  William James, Some Problems of Philosophy(1911: 51,52)

 

This weaving together of strands of information—like the warp and woof of a textile—creates a pattern –as the great neurophysiologist Charles Sherrington, put it, the brain is an “enchanted loom where millions of flashing shuttles weave a dissolving pattern.”


SO, who would you be if disconnected from your sensory input?  Floating in a vat (as in sensory deprivation experiments) 

While he was imprisoned in a castle, Avicenna wrote his famous “Floating Man” thought experiment to demonstrate human self-awareness and the substantiality of the soul. His “Floating Man” thought experiment tells its readers to imagine themselves suspended in the air, isolated from all sensations, which includes no sensory contact with even their own bodies. He argues that, in this scenario, one would still have self-consciousness. He thus concludes that the idea of the self is not logically dependent on any physical thing, and that the soul should not be seen in relative terms, but as a primary given, a substance. This argument was later refined and simplified by René Descartes in epistemic terms when he stated: “I can abstract from the supposition of all external things, but not from the supposition of my own consciousness.”[6]

 


The abstractions we live by must also be reconciled, shared elements found, and generalizations that enable predictions (about how best to behave) are then based on these shared elements.  There is a tolerance for degrees of imperfect mismatch (see notes on POETIC LICENSE and “zones (or range) of tolerance”in HOMEOSTASIS notes):  … Like harmony in music; there is a dark / Inscrutable workmanship that reconciles / Discordant elements, makes them cling together / In one society.William Wordsworth, The Prelude (1850)


 

ALL of this, of course, serves the overriding mandate of PHYSIOLOGY: “The stability of the internal medium is a primary condition for the freedom and independence of certain living bodies in relation to the environment surrounding them.”Claude Bernard, Leçons sur les Phénomènes de la Vie Communs, 1878-1879

 



 

 

INPUT

Review the interface between the organism and the external world –it’s senses.  Consider the terms “Umwelt” ( the subjective environment as perceived and impacted by an organism, presumably weighted according the importance of each sensory element to the organism’s survival) and “Umfeld” (the objective environment which encompasses and impacts all organisms in it’s realm). (These terms were developed by Jakob von Uexküll in his book Umwelt und Innnenwelt der Tiere (Environments and inner worlds of animals, published 1909) (see Andrian Kreye’s response to Edge.org’s query for 2012: WHAT IS YOUR FAVORITE DEEP, ELEGANT, OR BEAUTIFUL EXPLANATION?)   UMWELT (old web site unavailable)
  • SENSE ORGANS, sensations and perceptions.  are more-or-less highly developed cells that detect and transduce various forms of energy in the surrounding environment to a form that informs the organism about its various qualities.  Most are embedded on the surface of the organism but a few are deeper. Once a stimulus has evoked a sensation by its action on a receptor and enters the organism’s nervous system is can be called a percept. Clearly the, different sensations can evoke different perceptions depending on the nervous system that manages it: it is compared to other simultaneous percepts and with the organisms memory of all preceding percepts that the new one more-or-less resembles.  The nervous system then assigns relevance and distributes the information to the appropriate neural centers for further management.
  • Most SENSE ORGANS detect information about the external environment but some detect the qualities of the internal environment. [descriptive details about sensory apparatus]

Ultimate causation.  The amount of neural tissue allocated for various senses is quite variable in different taxa, reflecting an organism’s evolutionary history.   (Compare differences in sensory cortices of different animals)

Developmental factors.  The amount of neural tissue allocated to a sensory modality also seems subject to needs experienced during development.  Review recent findings about Sensory Compensation .

notes:///852573D70000062B/F5B2CBF2A827C0198525624B00057D30/708A34B8D44EC4988525693C0042D0B9

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STIMULI:

  • Sign stimulus: Any stimulus that activates an innate releasing mechanism (IRM) responsible for evoking a fixed action pattern (FAP) or species-typical behavioral pattern. (This used to be called key stimulus recalling the idea of lock & key specificity)
  • Releaser: A sign stimulus emanating from a conspecific Examples: (a) Red spot on gull’s bill, (b) Lizard dewlap display.  There is likely congenital or rapidly learned (“imprinted”) sensory bias at work here.
  • Subliminal Stimulus:  perceived but doesn’t reach consciousness
  • Supernormal stimulus: A stimulus that produces a more vigorous response than the normal stimulus eliciting that particular response. For example, a female herring gull will brood a giant egg in preference to its own eggs, which are smaller. A supernormal stimulus is an exaggerated sign stimulus.  (in neurophysiology) A stimulus that is more intense than a normal stimulus and is capable of inducing a response in a nerve fibre during the relative refractory period)
  • Configurational stimulus: A stimulus, the effects of which are dependent upon relationships between its elements. Examples: (a) Hawk-Goose model or (b) human face

 

NO STIMULI

Stimuli, to the extent that our sensory apparatus can detect organizes the otherwise disorganized activity of receptive neurons into a path that conveys whatever is perceived with more or less fidelity (depending on development: experience, including expectations) represents the stimulus.  The intensity or duration of the stimulus may evoke only a subliminal[i] (nonconscious) response or proceed all the way to full awareness.

When a prospective recipient of a signal is biased or for any other reason a specific stimulus is particularly potent in evoking a response (something artists learn or intuit) it can be used to “control” the recipient.  In evolutionary biology, “sensory exploitation” describes ways organisms have evolved signals to take advantage of the recipient’s bias, particularly vividly manifest in courtship  (DEEP ethology link).   Are eyes powerful? Are the “eyes” of a peacock’s tail powerful stimuli for that reason?

 


Ganzfeld effect.  “The adepts of Pythagoras retreated to pitch-black caves to receive wisdom through their visions.”  … “Arctic explorers seeing nothing but featureless landscape of white snow for a long time also reported hallucinations and an altered state of mind.[8] (“…or perceptual deprivation) “is a phenomenon of perception caused by exposure to an unstructured, uniform stimulation field.[1] The effect is the result of the brain amplifying neural noise in order to look for the missing visual signals.[2] The noise is interpreted in the higher visual cortex, and gives rise to hallucinations.[3]

It has been most studied with vision by staring at an undifferentiated and uniform field of colour. The visual effect is described as the loss of vision as the brain cuts off the unchanging signal from the eyes. The result is “seeing black”,[4] an apparent sense of blindness. A flickering ganzfeld causes geometrical patterns and colors to appear, and this is the working principle for mind machines and the Dreamachine.[5]The ganzfeld effect can also elicit hallucinatory percepts in many people, in addition to an altered state of consciousness.

Ganzfeld induction in multiple senses is called multi-modal ganzfeld. This is usually done by wearing ganzfeld goggles in addition to headphones with a uniform stimulus.

A related effect is sensory deprivation, although in this case a stimulus is minimized rather than unstructured. Hallucinations that appear under prolonged sensory deprivation are similar to elementary percepts caused by luminous ganzfeld, and include transient sensations of light flashes or colours. Hallucinations caused by sensory deprivation can, like ganzfeld-induced hallucinations, turn into complex scenes.[5]”  –from Wikipedia on Ganzfeld Effect.  

Interesting account of figure/ground phenomea when an object is introduced to a ganzfeld.


HALLUCINATIONS?   “The brain doesn’t seem to tolerate inactivity,” said the late neurologist Oliver Sacks when I spoke to him about this in 2014. “The brain seems to respond to diminished sensory input by creating autonomous sensations of its own choosing.” This was noted soon after the second world war, he said, when it was discovered that high-flying aviators in featureless skies and truck drivers on long, empty roads were prone to hallucinations.

Now researchers believe these unreal experiences provide a glimpse into the way our brains stitch together our perception of reality. Although bombarded by thousands of sensations every second, the brain rarely stops providing you with a steady stream of consciousness. When you blink, your world doesn’t disappear. Nor do you notice the hum of traffic outside or the tightness of your socks. Well, you didn’t until they were mentioned. Processing all of those things all the time would be a very inefficient way to run a brain (see “Out of touch“)[ii]. Instead, it takes a few shortcuts.”  –(Thompson 2016 in New Scientist) (Archive copy

 

SO, hallucinations are not rare in everyday life and the ordinarily hidden processes that provide these mental experiences overlap considerably with other aspects of perception.   Still, unusual circumstances affect these processes in ways that invite the scrutiny of clinicians and reveal elements of the underlying processes in normal conscious life: read Seven Rare Syndromes.  For example, look at a clinical summary of causes of “Alice in Wonderland” syndrome leading to macrosomatognosia (Blom 2016).  

Less rare is Charles Bonnet Syndrome. The experience of complex visual hallucinations in a person with partial or severe blindness.  With a growing scotoma (spot on retina that is not functioning) the gap in vision is filled in with images–sometimes patterns, sometimes a specific face (Also known as “Visual release hallucinations”)


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Hallucinations, particularly those that fill in sensory gaps with other content, are exemplars of an overarching principle that seems to act at all levels of organization of cognition:  We need COHERENCE to function and often–arguably always–have imperfect information.  so, 

WE TELL THE BEST STORY WE CAN WITH THE BEST FACTS AVAILABLE.

We may or may not have the luxury of review and revision … as in the gradual improvement of scientific hypotheses, approaching the best possible story by successive approximations: a dominant concern of artists and scientists.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Enotopic Phenomena, Phosphenes. Phosphenes are a form of “entopic” phenomenon.  (see Suzanne Carr’s review) The experience of light in one’s closed eyes can take a variety of forms (indexed by early psychophysicists in the 19th century).  I see reticulated patterns or balls of light that expand and contract.    It is an interesting area because the diversity of entopic phenomena underscore the diversity of ways of perceiving in different individuals.   “The most common phosphenes are pressure phosphenes, caused by rubbing the closed eyes. They have been known since antiquity, and described by the Greeks.[6] The pressure mechanically stimulates the cells of the retina.”  Presumably, the pressure activates the same cells in the visual pathway that are stimulated by light (retinal ganglion cells).  Hermann von Helmholtz and others have published drawings of their pressure phosphenes. One example of a pressure phosphene is demonstrated by gently pressing the side of one’s eye and observing a colored ring of light on the opposite side, as detailed by Isaac Newton.

Another common phosphene is “seeing stars”, from a sneeze, laughter, a heavy and deep cough, blowing of the nose, a blow on the head or low blood pressure (such as on standing up too quickly or prior to fainting). It is possible these involve some mechanical stimulation of the retina, but they may also involve mechanical and metabolic (such as from low oxygenation or lack of glucose) stimulation of neurons of the visual cortex or of other parts of the visual system.

Less commonly, phosphenes can also be caused by some diseases of the retina and nerves, such as multiple sclerosis. The British National Formulary lists phosphenes as an occasional side effect of at least one anti-anginal medication .”  (from Wikipedia on Phosphenes

(sometimes known as the prisoner’s cinema.  Miners trapped by accidents in mines frequently reported hallucinations, visions and seeing ghosts when they were in the pitch dark for days.)

Charles Bonnet Syndrome. The experience of complex visual hallucinations in a person with partial or severe blindness. (Also known as “Visual release hallucinations”)

 

 

 


Signals that feed information into a site (such as a coordinated group of neurons) are eften termed AFFERENT, those that leave a site are EFFERENT.   REAFFERENCE is a more recent term to represent stimuli that are generated by our own bodies —  for example, The component of sensory input an animal receives as a consequence of its own movements. (Thus, in the case of movement of the limbs, reafference is the proprioceptive or visual sensation that arises as a direct consequence of the motor act. “process of relaying messages from limbic system via entorhinal cortex to sensory cortices, in parallel with limbic commands to motor systems, serving (1) to compensate in advance for changes in sensory input accompanying actions, and (2) to sustain states of expectancy and attention.” — from Freeman, Societies of Brains)

 

EMBODIED COGNITION –stimuli generated by our body (either as a result of changes coordinated by levels of neural organization beneath the brain (such as spinal reflexes or collateral or epiphenomenal changes accompanying autonomic or motor adjustments programmed to maintain homeostasis) interact with the nervous system at multiple levels of organization and able to profoundly affect cognition.  For example, acute or chronic changes in any of the various hormones associated with stress levels can affect perception: the same stimulus can be perceived differently in a body enduring or preparing to cope with a challenge to homeostasis: body temperature, muscle tension, etc.  Sensory acuity is famously affected by stress.

 

Take a look at Samuel McNerney’s Scientific American blog entry on November 4, 2011, “Why You Are Not Your Brain”


 

The MEANING of STIMULI changes over time.  “The aspects of things that are most important for us are hidden because of their simplicity and familiarity. (One is unable to notice something – because it is always before one’s eyes.) The real foundations of his enquiry do not strike a man at all. Unless that fact has at some time struck him. – And this means: we fail to be struck by what, once seen, is most striking and most powerful.” (Wittgenstein, Philosophical Investigations, 1953, No. 129)

 

DEVELOPMENT.

 

DEVELOPMENT of PERCEPTION:  Aslin and Smith (1998) conducted a “selective review of perceptual development [and highlighted] three different structural levels: sensory primitives, perceptual representations, and higher-order operations. Each of these levels appears to undergo considerable development. Moreover, both within- and between-level developments appear to influence the emergence and form of perceptual abilities. [more]

 

 


 

THE INTEGRATION OF INPUT

Sensations become percepts when they are integrated with other sensations, past experiences, and expectations (time past, present, and future).  

 

SENSATION. The detection of stimuli produced by environment by of more-or-less specialized organs: The ability to detect other stimuli beyond those governed by these most broadly recognized senses also exists, and these sensory modalities include temperature (thermoception), kinesthetic sense (proprioception), pain (nociception), balance (equilibrioception), vibration (mechanoreception), and various internal stimuli (e.g. the different chemoreceptors for detecting salt and carbon dioxide concentrations in the blood). (Wikipedia)

  • SENSE ORGANS are more-or-less highly developed cells that detect and transduce various forms of energy in the surrounding environment to a form that the organism is prepared to detect and manage and informs the organism about its various qualities.  Most are embedded on the surface of the organism but a few are deeper.

 

all our lonely little brains, isolated in their skull, separated from the world … but knowing it as best it can through the thin, fragile, detectors of environmental energy we call sense organs

  • EXTEROCEPTION: perception of stimuli originating in the environment outside the body: “Sight (vision), hearing (audition), taste (gustation), smell (olfaction), and touch (somatosensation) are the five traditionally recognized senses.  Somatosensation is also known as a kind of interoception since many receptors are within the body.
  • INTEROCEPTION: perception of stimuli originating in the body
    • Somatosensory
    • pain, tactile
    • Proprioception (joint and body position transmitted by (e.g.) muscle spindles and Golgi tendon organs; read notes)   

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TACTILE. To translate touch, the brain can quickly rearrange its sense of the body.  Is this an example of a general principle of neurosensory integration? : The “links between different bodily senses show that the brain constantly updates its internal map, and they shed light on the dynamic and flexible nature of the body map that is used to interpret each new perception.” (de Vignemont et al. (2005) Bodily illusions modulate tactile perception.  Current Biology  15:1286-1290,)

 


ARTISTS tend to specialize in particular modalities informed by theoretical and intuitive understanding of cognition and the ways they and their public will respond.

An aside about ART informed by the diversity of senses and their integration:  read about gesamtkunstwerk (read on)


 

 INPUT  Taken together, 

Review the interface between the organism and the external world –its senses.  Review the idea of UMWELT

 

 

 

 

 

 

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SELECTED INPUT LINKS

 

 

 

 

 

 

 

 

 

 

 

 

 

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THE SYSTEMS VIEW

see Wikipedia on SYSTEMS BIOLOGY

and DYNAMICAL SYSTEMS

in A&O I emphasize the flow of information within and between our competencies for sensation, perception, conception, and adaptive action

| INPUT | INTEGRATION | OUTPUT |

 

Representing and interpreting the multiple streams of information that flow through organisms is a “systems view” — typically, specific streams of input evoke varying amounts of arousal or receive differing amounts of attention.  They are integrated with ongoing competitive streams or past experiences, and thereby affect the selection of one of an assortment of possible outcomes. 

We associate input with the senses, integration with the central nervous system, and output with the muscles, but there is more . . .

These will each and cumulatively be subject to the constraints of evolution (what equipment has the organism been provided with),   the changes that occur during development, the stimuli in the environment that affect the organism at a specific moment, and the physiology of how this information is received (input), processed (integrated), and acted upon (output)

This is all designed to help the organism maximize its fitness — ability to survive and thrive.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

“The senses cannot think.  The understanding cannot see.” (Kant) so what is the relationship of INPUT to INTEGRATION?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Jan 15, 2013.   Confidence in the validity of causal relationships can be hugely comforting: in order to function we must commit to actions based on imperfect information … so we do the best we can.  I find great comfort in believing there is an order to the phenomena that underlie my thoughts and I’m disposed to finding connections in the mechanisms of the brain.  I search for clues … evidence … and I hope I’m wary enough to remember that all clues are fragmentary. And may even be wrong.   Gary Marcus recent essay,  “Neuroscience Fiction,”  in the New Yorker (Dec 2, 2012) helps with that. “It’s a must read.”  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DEEP AESTHETICS

  • INPUT: “Patterns of anatomical connections in the visual cortex form the structural basis for segregating features of the visual image into separate cortical areas and for communication between these areas at all levels to produce a coherent percept. Such multi-stage integration may be a common strategy throughout the cortex for producing complex behaviour” — read Semir Zeki’s essay, “Art and the Brain,” in Daedalus (127(2):71-103)  Zeki, Semir. “Art and the Brain.” Daedalus, vol. 127, no. 2, 1998, pp. 71–103. JSTOR, www.jstor.org/stable/20027491 .
  • INPUT from the environment that passes the gateway of the senses leads to percepts – BUT not all PERCEPTS originate in the environment:  For example,  PHOSPHENES: Luminous impressions produced through excitation of the retina by some cause other than the impingement upon it of rays of light, as by pressure upon the eyeball when the lids are closed.  [more]
  • INTEGRATION: All senses converge eventually, but the first wave of interpretation involves the development of privileged pathways which tend to project to the parts of the sensory cortex that best interprets them … but sometimes other areas are influenced: For example, read about Synesthesia [more
  • OUTPUT: What is the origin of the aesthetic or artistic impulse? (DEVELOPMENT);  What contexts enable or empower the phenomenon of aesthetic expression? (ECOLOGY);  What are the evolutionary roots of this phenomenon … ancestors and descendants, how does it “jump generations”?? (EVOLUTION);  and what is the “proximate causation” of the aesthetic expression? its path from mental process to externalizing (PHYSIOLOGY)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

stochastic resonance

 

Background noise can facilitate the detection of a weak signal!

or

“Is this why the brain has so many neurons?”

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“stochastic resonance” is the ability of noise to enhance the detection of weak signals

 

“It is now well known that noise can enhance the response of the nonlinear system to weak signals, via a mechanism known as stochastic resonance (SR) [1]. This concept has proposed a general mechanism for weak signal transmission in a variety of neuronal systems, possibly including the brain. In fact, previous experimental results have reported that the sensitivity of sensory neuron to weak signals can be optimized by adding noise [2]. Furthermore, several recent studies have shown that the higher central nervous system can actually utilize the noise enhanced sensory information; it enhances the human tactile sensation [3], the human visual perception [4], or the animal feeding behavior [5]. Whether these functional improvements would be caused by the enhanced sensory afferents at the receptor level or by the effects of noise in the central nervous system is, however, still unknown.

 (VOLUME 85, NUMBER 17 PHYSICAL REVIEW LETTERS 23 OCTOBER 2000: “Functional Stochastic Resonance in the Human Brain:Noise Induced Sensitization of Baroreflex System” by  Ichiro Hidaka, Daichi Nozaki, and Yoshiharu Yamamoto)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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A&O students:  DO YOU HAVE SYNESTHESIA?

Research the term and describe how is can be viewed from the perspectives of DEVELOPMENT and PHYSIOLOGY.   e-mail a summary of your work: put “synesthesia” in the subject line   brief explanation  You might be sensing the world in very different way that they person next to you.   GOING FURTHER: Check out the theory that we might we all have been born with synesthesia?  IF SO, have we then gradually sorted out the sensory pathways according to the predominating neurodevelopmental program … or not?  Do you have any synesthetic tendencies? How would you know?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In the last decade, interdisciplinary researchers such as Ramachandran, Sacks, and Zeki have laid the foundations for

NEUROAESTHETICS

& see also, NEUROAESTHETICS, a must-visit page

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DIGGING DEEPER:

Visit the PBS Series “The Secret Life of the Brain”

RESOURCES:

http://www.lehman.cuny.edu/courses/arh141/links.html

Glossary of terms in A&O

 

 

 


[i]Subliminal stimuli (/sʌbˈlɪmᵻnəl/; literally “below threshold”), contrary to supraliminal stimuli or “above threshold”, are any sensory stimuli below an individual’s threshold for conscious perception.[1] A recent review of functional magnetic resonance imaging (fMRI) studies shows that subliminal stimuli activate specific regions of the brain despite participants being unaware.[2] Visual stimuli may be quickly flashed before an individual can process them, or flashed and then masked, thereby interrupting the processing. Audio stimuli may be played below audible volumes or masked by other stimuli.” (Wikipedia on subliminal)

 

[ii] Out of touch (from New Scientist). 

 

You are constantly hallucinating. If and when failing senses turn down the dial on your vision or hearing, your brain fills in the missing pieces to keep the world around you in line with expectations. When this model diverges too far from reality, you get hallucinations. Studying the phenomenon has revealed just how much of the world our brain is constantly making up.

 

But not all your senses work this way. In fact, the opposite seems to be true of touch. Your skin, after all, is never short of sensory input: from the chair under you to the tag in your sweater.

 

Reverse hallucinations

To cope with this onslaught while still being able to guard against real threats, your brain has a formula to decide which require attention. Touches that are rapid – 250 milliseconds apart or less – are dismissed, so away go the chair and the sweater tag. Your tactile brain is in the grip of a constant “reverse hallucination”. It feels nothing even though there is actually a lot going on.

 

For most people, anyway. Research is revealing that people with schizophrenia can’t do this reverse hallucination trick. John Foxe at the University of Rochester in New York got 30 participants to wear a bracelet that vibrated at various intervals. Foxe expected that the brain’s response to the stimuli would be large at first and then taper off, obeying the standard formula. But people with schizophrenia were still aware of the vibrations long after the rest had become inured. They were feeling things that, to everyone else, were no longer there.

 

Such finding are causing some to re-examine schizophrenia, not as a condition of impaired cognition but as a sensory disorder. Impaired sensory processing plays a far larger role than anyone thought, Foxe says.

 

The findings also imply that the brains of people with schizophrenia aren’t that different from other people’s brains. “The brain likes a world that makes sense, so it tends to make up stories to explain weird experiences,” says Dan Javitt, a psychiatrist at Columbia University in New York. That goes some way to explaining why case studies of tactile hallucinations in people without schizophrenia so often involve insects. Many of these cases start when someone has been taking a non-prescribed stimulant, which may disrupt the brain’s ability to turn off the sensory input. Then they explain the new tactile hyper-awareness using a familiar culprit.

 

While tactile hallucinations are less common than their auditory or visual cousins, they are fundamentally a similar mechanism: the brain decides what you will see, feel and hear irrespective of what’s happening around you. Carrie Arnold