28/11/2011 by admin.

Synesthesia is a condition where attributes associated with one sense (say colour with sight) can be experienced in another inappropriate sense (say colour with the perception of musical notes). There are many kinds, and rare ones are still being discovered. There is no longer any question that these are ‘real’ perceptions and not hoaxes. Synesthesia seems to have its roots at the sensory level and is a bottom-up rather than top-down phenomenon. There is evidence for heightened sensory activity levels and of additional connectivity between sensory modalities. A lack of normal ‘pruning’ is one of the possible causes.

It is no longer a question that the condition is inherited – it is. But not the specific type of synesthesia. Rather the genetic tendency is for any one or more of 60 odd varieties. Brang and Ramachandran (see citation) discuss the possible reasons for this condition not to be eliminated during evolution. Perhaps it has no disadvantage; perhaps it is a side-effect of a useful gene(s); perhaps it is the extreme of a normal distribution that includes us all.

Another possible explanation is that synesthesia simply represents the tail end of a normal distribution of cross-modality interactions present in the general population. Partial evidence supporting this idea comes as sensory deprivation and deafferentation (i.e., loss of sensory input through the destruction of sensory nerve fibers) can lead to synesthetic-like experiences. For example, after early visual deprivation due to retinitis pigmentosa, touch stimuli can produce visual phosphenes, and after loss of tactile sensation from a thalamic lesion, sounds can elicit touch sensations . More remarkably, arm amputees experience touch in the phantom limb merely by watching another person’s hand being touched. Long-standing evidence has also demonstrated that hallucinogenic drugs can cause synesthesia-like experiences, suggesting the neural mechanism is present in all or many individuals but is merely suppressed. However, no research has yet established the relationship between these acquired forms to the genetic variant and whether the same neural mechanism is responsible for both.

And perhaps, synesthesia is actually advantageous. What are some possible plus points?

1. Synesthesia may assist creativity and metaphor – it is more frequent in creative people and is a little similar to metaphor.

2. It may assists memory – there is some evidence from savants.

3. There is enhanced sensory processing – such as finer discrimination of colours

These demonstrations of enhanced processing of sensory information suggest a provocative evolutionary hypothesis for synesthesia: synesthetic experiences may serve as cognitive and perceptual anchors to aid in the detection, processing, and retention of critical stimuli in the world; in terms of memory benefits, these links are akin to a method of loci association. In addition to facilitating processes in individual sensory modalities, synesthetes also show increased communication between the senses unrelated to their synesthetic experiences, suggesting that benefits from synesthesia generalize to other modalities as well, supporting their ability to process multisensory information. Furthermore, others have argued that synesthesia is the direct result of enhanced communication between the senses as a logical outgrowth of the cross-modality interactions present in all individuals.

The puzzle of how genetically, how physiologically, and why it is that synesthesia arises will be very illuminating to the questions of how qualia are bound to objects and why we have the vivid conscious experience that we have.

Brang, D., & Ramachandran, V. (2011). Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words? PLoS Biology, 9 (11) DOI: 10.1371/journal.pbio.1001205

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16/09/2011 by admin.

ScienceDaily has an item (here) reporting a paper by Damasio’s group, Seeing Touch is Correlated with Content-Specific Activity in Primary Somatosensory Cortex. They examined the touch equivalent of the mind’s eye.

“When asked to imagine the difference between touching a cold, slick piece of metal and the warm fur of a kitten, most people admit that they can literally ‘feel’ the two sensations in their ‘mind’s touch,’ ” said Meyer, the lead author of the study. “The same happened to our subjects when we showed them video clips of hands touching varied objects,” he said. “Our results show that ‘feeling with the mind’s touch’ activates the same parts of the brain that would respond to actual touch.”

Human brains capture and store physical sensations, and then replay them when prompted by viewing the corresponding visual image. “When you hold a thought in your mind about a particular object, that is not just mental fluff. It is rather a detailed memory file that is being revived in your brain,” Antonio Damasio said.

Here is the abstract:

There is increasing evidence to suggest that primary sensory cortices can become active in the absence of external stimulation in their respective modalities. This occurs, for example, when stimuli processed via one sensory modality imply features characteristic of a different modality; for instance, visual stimuli that imply touch have been observed to activate the primary somatosensory cortex (SI). In the present study, we addressed the question of whether such cross-modal activations are content specific. To this end, we investigated neural activity in the primary somatosensory cortex of subjects who observed human hands engaged in the haptic exploration of different everyday objects. Using multivariate pattern analysis of functional magnetic resonance imaging data, we were able to predict, based exclusively on the activity pattern in SI, which of several objects a subject saw being explored. Along with previous studies that found similar evidence for other modalities, our results suggest that primary sensory cortices represent information relevant for their modality even when this information enters the brain via a different sensory system.

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16/04/2011 by admin.

We think of synaesthesia as an unusual sensory effect – the senses getting ‘mixed up’. But it may be more accurate to think of it as a ‘mix up’ in the binding of qualia to concepts. D. Nikolic, U. Jurgens, N. Rothen, B. Meier and A. Mroczko published a paper in Cortex, Swimming-style synesthesia (2011) that shows a clear concept component. I have not found free access to this paper but here is the abstract:

The traditional and predominant understanding of synesthesia is that a sensory input in one modality (inducer) elicits sensory experiences in another modality (concurrent). Recent evidence suggests an important role of semantic representations of inducers. We report here the cases of two synesthetes, experienced swimmers, for whom each swimming style evokes another synesthetic color. Importantly, synesthesia is evoked also in the absence of direct sensory stimulation, i.e. the proprioceptive inputs during swimming. To evoke synesthetic colors, it is sufficient to evoke the concept of a given swimming style e.g., by showing a photograph of a swimming person. A color-consistency test and a Stroop-type test indicated that the synesthesia is genuine. These findings imply that synesthetic inducers do not operate at a sensory level but instead, at the semantic level at which concepts are evoked. Hence, the inducers are not defined by the modality-dependent sensations but by the “ideas” activated by these sensations.

It would be interesting to find out if this effect is operating just at a semantic level or whether, as I suspect, it acts at a more general conceptual level. Can it happen with concepts that do not have associated name-words?

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13/04/2011 by admin.

Terhune, Cardena and Lindgren published a paper, Disruption of synaesthesia by posthypnotic suggestion: an ERP study, and this paper was discussed by Vaughan Bell in the blog Mind Hacks and in the Guardian newspaper. (here)

Abstract:

This study examined whether the behavioral and electrophysiological correlates of synaesthetic response conflict could be disrupted by posthypnotic suggestion. We recorded event-related brain potentials while a highly suggestible face-color synaesthete and matched controls viewed congruently and incongruently colored faces in a color-naming task. The synaesthete, but not the controls, displayed slower response times, and greater P1 and sustained N400 ERP components over frontal-midline electrodes for incongruent than congruent faces. The behavioral and N400 markers of response conflict, but not the P1, were abolished following a posthypnotic suggestion for the termination of the participant’s synaesthesia and reinstated following the cancellation of the suggestion. These findings demonstrate that the conscious experience of synaesthesia can be temporarily abolished by cognitive control.

In Bell’s discussion, he points out that this is very unexpected “it is equally new to science because no one had suspected that synaesthesia could be reversed.” The synaesthesic effect was being measured by the addition time it took to identify targets that were coloured differently than the colour that the synaesthesic gives them and by the neurological signs of conflict between the two colours (the Stroop effect). Hypnosis can reverse this by eliminating the synaesthesic colour. How?

This trait (hypnotisability) is usually described as “suggestibility” but it is nothing to do with gullibility or being easily led. People susceptible to hypnosis are not more naive, trusting or credulous than anyone else, but they do have the capacity to allow seemingly involuntary changes to their mind and body. The key phrase here is that they “have the capacity to allow” because hypnosis cannot be used to force someone against their will…

When a suggestion is successful, the experience of it seeming to “happen on its own” is key and this is exactly what neuroscientists have been working with – by suggesting temporary changes to the mind that we wouldn’t necessarily be able to trigger on our own. In the case of the two experiments that managed to temporarily “switch off” the Stroop effect in highly hypnotisable people, the suggestion was that the words appeared as “meaningless symbols”. This avoided a clash between the colour and the word because the text suddenly appeared to be gibberish…

Neuroscientists Amir Raz and Jason Buhle suggest hypnosis is really when we allow suggestions to take over from our normally self-directed control of attention that deals with mental self-management, allowing science an exciting tool to “get under the hood” of the conscious mind.

If you find hypnosis intriguing then you will find Bell’s article very interesting, as I did.

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10/04/2011 by admin.

Vision is so important to humans that it is difficult to imagine how we can produce a conscious model of the world without it. And what is done with the third of the cortex that is involved in vision when it is idle. Kupers and others (see citation) have been comparing fMRI scans using congenitally blind, blind that were once sighted, sighted and blindfolded sighted individuals.

How do individuals who never had any visual experience since birth form a conscious representation of a world that they have never seen? How do their brains behave? What happens to vision-devoted brain structures in individuals who are born deprived of sight or who lose vision at different ages? To what extent is visual experience truly necessary for the brain to develop its functional architecture? What does the study of blind individuals teach us about the functional organization of the sighted brain in physiological conditions?

It is known that the cortex has capacity for plasticity and reorganization when input from a sense is lost. Other senses will use the spare cortical areas. Studies have shown that there are changes in the grey matter, the white matter under it, and the cell metabolism during this reorganization. In the blind, the occipital cortex (visual cortex) becomes involved in other senses and in a variety of cognitive functions including: lexical, semantic, phonological, attention, verbal memory, working memory.

A part of the cortex (extrastriate ventrotemporal cortex) is concerned with recognizing objects, a function that is very important to acquiring knowledge of the external world. Different categories of object give specific activity patterns in this region, termed object-form-topology. This processing relies heavily on vision. But blindfolded people who recognize an object from feel show very similar patterns to those that occur when they use sight. The patterns are supramodal – they do not depend on any particular sense.

The findings in the congenitally blind subjects are important also because they indicate that the development of topographically organized, category-related representations in the extrastriate visual cortex does not require visual experience. Experience with objects acquired through other sensory modalities appears to be sufficient to support the development of these patterns. Thus, at least to some extent, the visual cortex does not require vision to develop its functional architecture that makes it possible to acquire knowledge of the external world.

So the ventral ‘what’ pathway can process without vision. What about the dorsal ‘where’ pathway? Is spatial processing possible without vision? Yes, the dorsal pathway can use senses other than sight and does not require visual experience to develop. We process motion per se.

Both optic and tactile motion provide information about object form, position, orientation, consistency and movement, and also about the position and movement of the self in the environment.

And when they looked at mirror neurons, they found the same condition. Vision is not necessary for the development of a functional efficient mirror neuron system. This suggests that abstract representation of actions is also not tied to any particular sense.

The main hypothesis that we have put forward here is that the development of consciousness in the absence of vision is made possible through the supramodal nature of functional cortical organization. The more abstract representation of the concepts of objects, space, motion, gestures, and actions – in one term, awareness of the external world – is associated with regional brain activation patterns that are essentially similar in sighted and congenitally blind individuals. The morphological and/or functional differences that exist between the sighted and the blind brain are the consequence of the cross-modal plastic reorganization that mostly affects that part of the cortex that is not multimodal in nature.

What about the experience that results from the reorganization in the blind? It appears that the type of qualia is connected to the source of the input not the region that processes it.

The results of these TMS studies constitute the first direct demonstration that the subjective experience of activity in the visual cortex after sensory remapping is tactile, not visual. These findings provide new insights into the long-established scientific debate on cortical dominance or deference. What is the experience of a subject in whom areas of cortex receive input from sensory sources not normally projecting to those areas? Our studies suggest that the qualitative character of the subject’s experience is not determined by the area of cortex that is active (cortical dominance), but by the source of input to it (cortical deference). Our results are in line with evidence that sensory cortical areas receive input from multiple sensory modalities early in development.

Kupers, R., Pietrini, P., Ricciardi, E., & Ptito, M. (2011). The Nature of Consciousness in the Visually Deprived Brain Frontiers in Psychology, 2 DOI: 10.3389/fpsyg.2011.00019

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04/04/2011 by admin.

I have often wondered about how we recognize faces. We are so very good at recognition and so bad at describing faces in words. One person will say big nose, freckles, oval shape – and this is correct – but it is of no help to someone else in forming an image of the face. The way faces are recognized rarely rises to consciousness and therefore to useful for verbal description.

The current theory is that we build up by experience an ‘average face’. We then compare faces we encounter to this average face. It can be thought of as a mathematical ’space’, a multi-dimensional face-space. The distance from the average corresponds to the amount of difference the face is from the average and the direction from the average face corresponds to the way/s the face differs from the average. So there is a center with arrows going out various distances in various directions to each known face.

This makes certain things clearer.

First, this is probably the reason that a person who has encountered only a few people from another racial group, has difficulty identifying people of that group. People are left stammering that all Chinese people look alike, knowing how stupid this sounds. They do not have a good average face for the unfamiliar group and therefore have difficulty establishing the differences between any face and the average.

Second, we use the average face as a sign post for beauty. The closer a face is to our average, the more attractive it is.

Third, the closer a face is to the average, the faster we recognize that it is a face. But knowing that a object is a face, the farther it is from average, the faster it is recognized as a particular face. These results depend on the density of faces in the face-space: high near the average and low far from the average.

Fourth, caricatures are recognized as the target although they are actually very, very different from the target face. But a good caricature is on the near exact direction from the average but just a much farther distance away then the target face. It is like following our imaginary arrow to the particular faces and then carrying on in the same direction for some distance.

Fifth, another interesting effect is archetypes. We can think of face-space having places (other than the average) of unusual high density of encountered faces surrounded by low density areas. Some particular face near the center of such a clump could come to stand for this type of face.

Sixth, this explains why we can sometimes hardly notice such prominent changes as new glasses, loss of a mustache etc. These are just not dimensions/directions in the face-space so they are not used to recognize faces.

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11/03/2011 by admin.

I have found another Edge answer that is very interesting (here). Donald Hoffman, author of Visual Intelligence, describes a metaphor for sensory qualia – a computer desktop.

Our perceptions are neither true nor false. Instead, our perceptions of space and time and objects, the fragrance of a rose, the tartness of a lemon, are all a part of our “sensory desktop,” which functions much like a computer desktop.

I have encountered people who judge our senses by how accurate they are. They are not happy with the lack of a one-to-one mapping between wave length of light and the perception of colour. The illusions that fool us are treated as mistakes. This all is interpreted as sloppiness in biological systems. But really, the purpose of our perceptions is not accuracy but usefulness.

Graphical desktops for personal computers have existed for about three decades. Yet they are now such an integral part of daily life that we might easily overlook a useful concept that they embody. A graphical desktop is a guide to adaptive behavior. Computers are notoriously complex devices, more complex than most of us care to learn. The colors, shapes and locations of icons on a desktop shield us from the computer’s complexity, and yet they allow us to harness its power by appropriately informing our behaviors, such as mouse movements and button clicks, that open, delete and otherwise manipulate files. In this way, a graphical desktop is a guide to adaptive behavior.

Graphical desktops thus make it easier to grasp the nontrivial difference between utility and truth. Utility drives evolution by natural selection. Grasping the distinction between utility and truth is therefore critical to understanding a major force that shapes our bodies, minds and sensory experiences.

… We must take our sensory experiences seriously, but not literally. This is one place where the concept of a sensory desktop is helpful. We take the icons on a graphical desktop seriously; we won’t, for instance, carelessly drag an icon to the trash, for fear of losing a valuable file. But we don’t take the colors, shapes or locations of the icons literally. They are not there to resemble the truth. They are there to facilitate useful behaviors.

This is useful to keep in mind then thinking about just how personal our personal conscious experience is. Of course we know that we can’t actually know whether your red is the same as my red. But we know that we have a map of our retinas in our thalamus and another in the cortex at the back of our heads. There may be others too. These maps are linked with nerves so that the same points on the maps communicate with one another. A place on the retina has a corresponding place in the thalamus map and the cortex map. This is accomplished by a combination of genetically produced developmental chemicals and ordinary experiences of the world environment. There is no reason for either identical or for significantly different results from this developmental program. Similarly we have the same chemicals in our retina to respond to colours etc. So the answer to whether your red is the same as mine is probably – not identical but extremely similar. Further, it hardly matters because the reason for the red or any other shade is to inform and guide our behaviour – the system has evolved to give us ‘adaptive behaviour’. Qualia have evolved to contrast what needs to be separated, to notice what needs to be noticed, to be attracted or alarmed as appropriate and they seem to do a good job of it.

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18/02/2011 by admin.

My intuition was very wrong. I thought that the greyness of depression was part of a change in the process of constructing consciousness that reduced the vividness of experience. A recent post in Discovery Magazine by E. Strickland (here) points to two papers which put the dulling of experience near the sense organ level rather than the consciousness level.

Here is a bit from the abstracts of these papers:

Biol Psychiatry. 2010 Jul 15;68(2):205-8. Epub 2010 Mar 31 “Seeing gray when feeling blue? Depression can be measured in the eye of the diseased” Bubl, Kern, Ebert, Bach, Tebartz van Elst.

Everyday language relates depressed mood to visual phenomena. Previous studies point to a reduced sensitivity of subjective contrast perception in depressed patients. One way to assess visual contrast perception in an objective way at the level of the retina is to measure the pattern electroretinogram (PERG). To find an objective correlate of reduced contrast perception, we measured the PERG in healthy control subjects and unmedicated and medicated patients with depression…Unmedicated and medicated depressed patients displayed dramatically lower retinal contrast gain. We found a strong and significant correlation between contrast gain and severity of depression. This marker distinguishes most patients on a single-case basis from control subjects. A receiver operating characteristic analysis revealed a specificity of 92.5% and a sensitivity of 77.5% for classifying the participants correctly.

And doi:10.1016/j.neuroscience.2010.05.012 “Reduced olfactory bulb volume and olfactory sensitivity in patients with acute major depression” Negoias, Croy, Gerber, Puschmann, Petrowski, Joraschky, Hummel.

The purpose of this study was to assess olfactory function and olfactory bulb volume in patients with acute major depression in comparison to a normal population. Twenty-one patients diagnosed with acute major depressive disorder and 21 healthy controls matched by age, sex and smoking behavior participated in this study. Olfactory function was assessed in a lateralized fashion using measures of odor threshold, discrimination and identification. Olfactory bulb volumes were calculated by manual segmentation of acquired T2-weighted coronal slices according to a standardized protocol. Patients with acute major depressive disorder showed significantly lower olfactory sensitivity and smaller olfactory bulb volumes. Additionally, a significant negative correlation between olfactory bulb volume and depression scores was detected. Their results provide the first evidence, to our knowledge, of decreased olfactory bulb volume in patients with acute major depression. These results might be related to reduced neurogenesis in major depression that could be reflected also at the level of the olfactory bulb.

It is a good thing to have my intuitions shown to be very wrong every now and then. Keeps me honest and on my toes. I will have to be careful about thinking that one of the minor reasons for consciousness is to supply vividness to our experiences – to engage and entertain us. Forget that idea unless there is some evidence for it.

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05/12/2010 by admin.

The OnTheHuman site has an article by J. Prinz (here). I certainly like his approach and find his arguments very convincing.

We … ask which of our psychological states can be conscious. Answers to this question range from boney to bulgy. At one extreme, there are those who say consciousness is limited to sensations; in the case of vision, that would mean we consciously experience sensory features such as shapes, colors, and motion, but nothing else. This is called conservatism (Bayne), exclusivism (Siewert), or restrictivism (Prinz). On the other extreme, there are those who say that cognitive states, such as concepts and thoughts, can be consciously experienced, and that such experiences cannot be reduced to associated sensory qualities; there is “cognitive phenomenology.” This is called liberalism, inclusivism, or expansionism. If defenders of these bulgy theories are right, we might expect to find neural correlates of consciousness in the most advanced parts of our brain. …

Not only do I think consciousness is restricted to the senses; I think it arises at a relatively early level of sensory processing. Consider vision. According to mainstream models in neuroscience, vision is hierarchically organized. Let’s consider where in that hierarchy consciousness arises. … I think consciousness arises at the intermediate level. We experience the world as a collection of bounded objects from a particular point of view, not as disconnected, edged, or viewpoint invariant abstractions. … I think this is true in other senses as well. For example, when we listen to a sentence, the words and phrases bind together as coherent wholes (unlike low-level hearing), and we retain specific information such as accent, pitch, gender, and volume (unlike high-level hearing). Across the senses, the intermediate-level is the only level at which perception is conscious. …

Expansionists say we can be conscious of concepts and thoughts, and that such experiences outstrip anything going on at the intermediate-level of perception. … Associative visual agnosia … cannot recognize objects, but they seem to see them. When presented with an object, they can accurately describe or even draw its shape, but they can’t say what it is. Bayne thinks their experiences are incomplete. He thinks knowing the identity of an object changes our experience of it. This is intuitively plausible. … Instead, we can suppose that our top-down knowledge of the meaning changes how we parse the image. … imaginatively impose a new orientation; we segment figure and ground; and we generate emotions and verbal labels, which we experience consciously along with the image; these are just further sensory states—bodily feelings in the case of emotions, and auditory images in the case of words. I think features of this kind can also explain what is missing in agnosia. Without meaning, images can be hard to parse, and associated images and behaviors do not come to mind.

Another argument comes from Charles Siewert. He focuses on our experience of language. Sometimes, when hearing sentences, we undergo a change in phenomenology, and that change occurs as a result of a change in our cognitive interpretation of the meanings of the words. … Phenomenology also changes when we repeat a word until it becomes meaningless, or when we learn the meaning of a word in a foreign language. In all these cases, we experience the same words across two different conditions, but our experience shifts, suggesting that assignment of meaning is adding something above and beyond the sound of the words. … But there are many sensory changes that take place as a result of sentence comprehension. First, we form sensory imagery. … Second, comprehension effects parsing. … Third, comprehension entails knowing how to go on in a conversation … Fourth, meaning effect emotions. …

The third argument I will consider comes from David Pitt. He begins with the observation that we often know what we are thinking, and we can distinguish one thought from another. This knowledge seems to be immediate, not inferential, which suggests we know what we are thinking by directly experiencing the cognitive phenomenology of our thoughts. The most obvious reply is that knowledge of what we are thinking is based on verbal imagery. … I think this is a kind of illusion. We erroneously believe that we are directly aware of the contents of our thoughts when we hear sentences in the mind’s ear. This belief stems from two things. First, we often use verbal imagery as a vehicle for thinking …Second, when contemplating a word that we understand, we can effortlessly call up related words or imagery, which gives us the impression that we have a direct apprehension of the meaning of that word. Our fluency makes us mistake awareness of a word for awareness of what it represents. …

Putting these points together, I think restrictivsts should admit that thinking has an impact on phenomenology, but that impact can be captured by appeal to sensory imagery including images of words, emotions, and visual images of what our thoughts represent. Expansionists must find a case where cognition has an impact on experience, without causing a concomitant change in our sensory states. That’s a tall order.

At this point the dispute between restrictivists and expansionists often collapses into a clash on introspective intuitions. … By way of conclusion, I will try to break this stalemate by sketching five reasons for thinking restrictivism is preferable even if introspection does not settle the debate.

Next comes the arguments for excluding cognitive phenomenology.

1. To make a convincing case for cognitive phenomenology, expansionists should find a case where the only difference between two phenomenologically distinct cases is a cognitive difference. But so far, no clear, uncontroversial case has been identified.

2. The second argument points to the fact that alleged cognitive qualities differ profoundly from sensory qualities in that the latter can be isolated in imagination. … If other qualia can be isolated, why not cognitive qualia?

3. Third, it is nearly axiomatic in psychology that we have poor access to cognitive processes. … The only processes we ever seem to experience consciously are those that we have translated, with great distortion, into verbal narratives.

4. A fourth argument follows on this one. The incessant use of inner speech is puzzling if we have conscious access to our thoughts. Why bother putting all this into words when thinking to ourselves without any plans for communication? …

5. Finally, expansionism seems to dash hopes for a unified theory of consciousness. … But there is little reason to think a single mechanism could explain how both perception and thought can be conscious, if cognitive phenomenology is not reducible to perception. This is especially clear if the mechanism is attention. There is no empirical evidence for the view that we can attend to our thoughts. There are no clear cognitive analogues of pop-out, cuing, resolution enhancement, fading, multi-object monitoring, or inhibition of return. Thoughts can direct attention, but we can’t attend to them. Or rather, thoughts become objects of attention only when they are converted into images, words, and emotions. Expansionists might say that thought and sensations attain consciousness in different ways, but, if so, why think that the term “consciousness” has the same meaning when talking about thoughts, if it does not refer to the same mechanism?

This fits with the idea that only what enters the cortex through the thalamus, can be involved in the thalamo-cortical loops that synchronize their firing during the conscious experience. This category is sensory input (except the bulk of smell) and input about movement and emotion input via the basal ganglia.

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21/10/2010 by admin.

Perception of shapes is possible by touch and by sight. Kim and Zatorre have been using a coding of shape information into sound information to examine the nature of shape perception. They use boards with 2D drawings on them have textured surfaces giving visual and tactile targets. These are coded to give matching ’soundscapes’ where one dimension is coded by frequency and the other by stereo panning. With current and previous experiments, they show that subjects can be trained to identify both visual and tactile targets from soundscapes. Further subjects trained to match sound and touch can do the matching of sight and sound without further training.

Here is the abstract:

Shape is an inherent property of objects existing in both vision and touch but not audition. Can shape then be represented by sound artificially? It has previously been shown that sound can convey visual information by means of image-to-sound coding, by whether sound can code tactile information is not clear. Blindfolded sighted individuals were trained to recognize tactile spatial information using sounds mapped from abstract shapes. After training, subjects were able to match auditory input to novel auditory-tactile pairings. Furthermore, they showed complete transfer to novel visual shapes, despite the fact that training did not involve any visual exposure. In addition, we found enhanced tactile acuity specific to the training stimuli. The present study demonstrates that as long as tactile space is coded in a systematic way, shape can be conveyed via a medium that is not spatial, suggesting a metamodal representation.

Not mentioned in the abstract is their theory of what these experiments say about the perception of shapes.

This transfer of crossmodal learning further supports our hypothesis that shape can be represented at a highly abstract level in a form independent of the sensory modality in which it is learned. This amodal, abstract representation of shape is closely associated with the findings of human imaging studies that identified the lateral occipital region as a common brain region involved in shape recognition by both vision and touch and by audition using the same type of sound transformation used in the current study.

It is interesting to think of shape perception as a link between two aspect of perception: the housing of our perceptions in a three dimensional space and the separation of our perceptions into distinct objects. Both of these seem hardwired and at the foundation of the form our conscious awareness takes.

Kim, J., & Zatorre, R. (2010). Can you hear shapes you touch? Experimental Brain Research, 202 (4), 747-754 DOI: 10.1007/s00221-010-2178-6

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