01/12/2011 by admin.

We really do seem to be in direct contact with the world around us – we can reach out and touch it. But that directness is an illusion; there are many levels of manipulation between reality and our experience of it. Consciousness gives us this sense of presence right ‘here’. We are present in the world at the focal point of a 3 dimensional projection. It seems like we are born with this perspective at least in rudimentary form. It appears to be part of the structure of conscious awareness.

I feel that Metzinger’s descriptions of the nature of consciousness is the best available to date. Before dealing with more complex consciousness, he describes minimal consciousness or ’selfless snapshot consciousness’ which calls the presence of a world:

the most elementary form of conscious experience conceivable: The presence of a world. The phenomenal presence of a world is the activation of a coherent, global model of reality (Constraint 1 - globality) within a virtual window of presence (Constraint 2 - presentationality), a model that cannot be recognized as a model by the system generating it within itself (Constraint 3 - transparency). …If and only if a person is conscious, a world exists for her, and if and only if she is conscious, she can make the fact of actually living in a world available for herself, cognitively and as an agent.

There is an old joke (I will spare your the ethnic language, spoil the joke, but keep the logic): a man has one foot on the dock and one on a boat moving away from the dock, his friends yell “jump, jump”, and he cries “how can I jump when I have no place to stand”. Animals have to know where they are as well as where they are going in the same frame/map/picture/conscious experience. They have to stand ‘here’ or order to jump ‘there’. A world has to exist. But why does it have to have transparency? Metzinger again:

Transparency of internal data-structures is a great advantage for any biosystem having to operate with limited temporal and neural resources. Indeed, it minimizes computational load since it is synonymous to a missing of information on this level of processing: Our representational architecture only allows for a very limited introspective access to the real dynamics of the myriads of individual neural events out of which our phenomenal world finally emerges in a seemingly effortless manner. … Naïve realism hinders the system to lose contact (stops the system from losing contact) with external reality by (due to) getting lost in an introspective exploration of the underlying mechanisms.

Just as we can have a virtual ‘now’ when remembering the past or forecasting the future, we can also have a virtual ‘here’. Memories and imaginings have their own ‘here’s as well as their own ‘now’s. One of the most accessible places to see virtual ‘here’s is in the computer games industry. They work very hard to create a virual conscious ‘here’ using the minimum of code, gadgetry and expense. They can get people (who know throughout the experience that it is all smoke and mirrors) to really feel they are in the virtual world rather than the real one. It is similar to optical illusions where you know that the lines are the same length but you continue to see the illusion in spite of your knowledge.

What does it take to manipulate a person’s conscious ‘here’? Sanchez-vives and Slater reviewed a number of experiments investigating what is effective for virtual presence. (From presence to consciousness through virtual reality; Sanchez-Vives & Slater; Perspectives, Nature Reviews, Neuroscience April 2005)

The graphics frame-rate is positively correlated with reported presence, and the critical minimal frame-rate seems to be ~15 Hz…A lower latency between head movement and display update was also found to be associated… In addition, head tracking, stereopsis and geometric field of view are all associated with higher reported presence. ..Surprisingly, the evidence so far does not support the contention that visual realism is an important contributory factor to presence…In an experiment that exploited the pit room, the scene was displayed at various levels of realism (line drawings, without and with textures, and with photo-realism) in a between-groups design. Although all participants showed a significant increase in heart rate when they encountered the precipice, there were no significant differences in heart rate or reported presence between the different rendering conditions. .. Anecdotal reports indicate that sound has a highly significant impact on presence, and one study showed that spatialized sound was associated with higher reported presence than either no sound or non-spatialized sound…(touch is difficult to mimic but appears to have a definite effect)…One study showed that reported presence was increased when the body was represented by a complete (if crude) virtual body, compared with simple representation by a three-dimensional-arrow cursor. …It was noticed in early studies that many participants — especially those reporting a high degree of presence — were almost unable to move by button pressing, and repeatedly attempted to walk. To reduce the dissociation between proprioception and sensory data, an alternative approach was for subjects to ‘walk in place’ to simulate walking. Experimental results showed that, on average, the participants who moved through the environment using this method reported a significantly higher sense of presence than those who used the mouse-button method. … Other studies have shown a significant positive association between overall body mobilization and reported presence.

It looks as through ‘here’ requires that the timing of events is close, the visual and auditory space is believable and action/reaction/interaction works. It does not depend on believable detail of objects from sight, hearing or touch.

So what does consciousness give us for an advantage when it gives us a ‘here’? The picture still seems very vague to me, with no clear substantial functions for ‘here’ and yet I am sure there is a function. Possibly it provides a place in consciousness to house the ’self’, a window on the world, and a place to stand while interacting with the world, an anchor for the mechanism of space/place/navigation. I have the feeling that there is something I am missing. But for now I will assume that we cannot be acting in the world unless we have a location in the structure of conscious awareness of the world.

There is more to come. Previous posts in this series:

Possible functions of consciousness 1 - leading edge of memory

Possible functions of consciousness 2 – gate to meaning

Possible functions of consciousness 3 – working memory

Possible functions of consciousness 4 – place to imagine

Possible functions of consciousness 5 – create ‘now’

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26/08/2011 by admin.

ScienceDaily has a item (here), R.Hayman, M.Verriotis, A.Jovalekic, A.Fenton, K.Jeffery (2011) Nature Neuroscience, Anisotropic encoding of three-dimensional space by place cells and grid cells, about the coding of vertical position.

Animal’s brains are only roughly aware of how high-up they are in space, meaning that in terms of altitude the brain’s ‘map’ of space is surprisingly flat, according to new research….The study looked at two types of cells known to be involved in the brain’s representation of space: grid cells, which measure distance, and place cells, which indicate location. Scientists found that only place cells were sensitive to the animal moving upwards in altitude, and even then only weakly so… “This finding is surprising and it has implications for situations in which people have to move freely in all three dimensions — divers, pilots and astronauts for example. It also raises the question — if our map of space is flat, then how do we navigate through complex environments so effectively?”… It seems as if grid cells do not “know” how high they are…. Place cells, found in the hippocampus itself, produce single activity hotspots in the environment and seem to function to encode specific places. These neurons were only weakly sensitive to height too — but they did show some responsiveness, suggesting they received information about height from some other, possibly non-specific, source.

So, there is a lot more to learn about navigation!

Here is the abstract:

The subjective sense of space may result in part from the combined activity of place cells in the hippocampus and grid cells in posterior cortical regions such as the entorhinal cortex and pre- and parasubiculum. In horizontal planar environments, place cells provide focal positional information, whereas grid cells supply odometric (distance measuring) information. How these cells operate in three dimensions is unknown, even though the real world is three-dimensional. We investigated this issue in rats exploring two different kinds of apparatus: a climbing wall (the pegboard) and a helix. Place and grid cell firing fields had normal horizontal characteristics but were elongated vertically, with grid fields forming stripes. It seems that grid cell odometry (and be implication path integration) is impaired or absent in the vertical domain, at least when the rat itself remains horizontal. These finding suggest that the mammalian encoding of three-dimensional space is anisotropic.

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27/06/2011 by admin.

Is our experience of space embodied? Do we learn that the world is three dimensional or is this something we cannot escape because of how our bodies are made? It is embodied by three lines of reasoning: (1) our bodies contain the nature of our space (2) we know space at too early an age to have learnt it from experience (3) our use of spatial metaphors imply an automatic use of our understanding of space.

Physical bodies:

Our sense of movement/acceleration of the head comes from the semi-circular channels of the ear. The three sensors are at right angles to each other like the x,y,z of a three-dimensional graph. They sense any movement as a combination of movement in three directions. That dictates 3-D space.

During embryo development, starting at (or shortly after) the single fertilized egg, development proceeds with differences between ventral and dorsal, rostral and caudial, dextral and sinistral. The chemical signals and gradients that steer development determine what will become up and down, front and back, left and right and where all the tissues will fit in that framework.

The brain, not just the human but all vertebrate brains, have a spatial centre which contains specialized neurons to represent place and space. They include place neurons, grid neurons, border neurons, heading neurons. Vision, hearing and touch cooperate in our representation of space in this internal mapping system. When we loss our place on this internal map, they feel a very particular emotion, the feeling of being lost. This system is central to episodic memory.

So given our bodies, it would be next to impossible to avoid an embodied spatial cognition.

Innate knowledge:

Now there are methods of questioning very young babies about what they know by following their gaze; they look longer at things and events they find unusual or less predictable than they do with the ordinary. This type of investigation can be done with babies that are only a few months old.

Here is part of the discussion in Spelk & Kinzler, Core knowledge (2007):

The last system (previous pages dealt with the others) of core knowledge captures the geometry of the environment: the distance, angle, and sense relations among extended surfaces in the surrounding layout. This system fails to represent non-geometric properties of the layout such as surface color or odor, and it fails under some conditions to capture geometric properties of movable objects. When young children or non-human animals are disoriented, they reorient themselves in accord with layout geometry. Children fail, in contrast, to orient themselves in accord with the geometry of an array of objects, and they fail to use the geometry of an array to locate an object when they are oriented and the array moves. Under some circumstances, children and animals who are disoriented fail to locate objects in relation to distinctive landmark objects and surfaces, such as a colored wall. When disoriented children and animals do use landmarks, their search appears to depend on two distinct processes: a reorientation process that is sensitive only to geometry and an associative process that links local regions of the layout to specific objects…This research suggests that the human mind is not a single, general-purpose device that adapts itself to whatever structures and challenges the environment affords. Humans learn some things readily, and others with greater difficulty, by exercising more specific cognitive systems with signature properties and limits. The human mind also does not appear to be a ‘massively modular’ collection of hundreds or thousands of special-purpose cognitive devices. Rather, the mind appears to be built on a small number of core systems, including the four systems just described. (object, agent and number preceded geometry/place in this description)

Here is the abstract from Regolin, Ruganil, Stancher and Vallortigara (2011) Spontaneous discrimination of possible and impossible objects (think Escher drawings) by newly hatched chicks:

Four-month-old infants can integrate local cues provided by two-dimensional pictures and interpret global inconsistencies in structural information to discriminate between possible and impossible objects. This leaves unanswered the issue of the relative contribution of maturation of biologically predisposed mechanisms and of experience with real objects, to the development of this capability. Here we show that, after exposure to objects in which junctions providing cues to global structure were occluded, day-old chicks selectively approach the two-dimensional image that depicted the possible rather than the impossible version of a three-dimensional object, after restoration of the junctions. Even more impressively, completely naive newly hatched chicks showed spontaneous preferences towards approaching two-dimensional depictions of structurally possible rather than impossible objects. These findings suggest that the vertebrate brain can be biologically predisposed towards approaching a two-dimensional image representing a view of a structurally possible three-dimensional object.

Here is the abstract from Izard, Pica, Spelke and Dehaene (2011), Flexible intuitions of Euclidean geometry in an Amazonian indegene group:

Kant argued that Euclidean geometry is synthesized on the basis of an a priori intuition of space. This proposal inspired much behavioral research probing whether spatial navigation in humans and animals conforms to the predictions of Euclidean geometry. However, Euclidean geometry also includes concepts that transcend the perceptible, such as objects that are infinitely small or infinitely large, or statements of necessity and impossibility. We tested the hypothesis that certain aspects of nonperceptible Euclidian geometry map onto intuitions of space that are present in all humans, even in the absence of formal mathematical education. Our tests probed intuitions of points, lines, and surfaces in participants from an indigene group in the Amazon, the Mundurucu, as well as adults and age-matched children controls from the United States and France and younger US children without education in geometry. The responses of Mundurucu adults and children converged with that of mathematically educated adults and children and revealed an intuitive understanding of essential properties of Euclidean geometry. For instance, on a surface described to them as perfectly planar, the Mundurucu’s estimations of the internal angles of triangles added up to ∼180 degrees, and when asked explicitly, they stated that there exists one single parallel line to any given line through a given point. These intuitions were also partially in place in the group of younger US participants. We conclude that, during childhood, humans develop geometrical intuitions that spontaneously accord with the principles of Euclidean geometry, even in the absence of training in mathematics.

Babies and some animals also can follow another’s gaze. This takes a facility with modeling 3-D space. There does not appear to be time for infants to learn about the nature of space from their own experience. A baby would need some framework in order to start learning about the world as quickly as they do.

Root of metaphor:

Finally space is at the root of a great many linguistic metaphors. We use our comfortable knowledge of space in order to understand other things by analogy. Time for instance is often expressed as a space metaphor by almost everyone no matter their language or culture.

We look forward to the future and back to the past. We go straight for the goal or we take a corner in our life. Today I am up for the challenge, tomorrow I may be down. I can rise to the top or get stuck at the bottom of the ladder. She went under under the anesthetic but he got high on the drug. Examples of spatial metaphors can go on for pages and pages but I will resist.

What ubiquitous metaphors (such as the spatial group) tell us is that we have an embodied area of cognition that is so firmly grounded and can be used to visualize, understand, express, and communicate other less grounded areas.

Even though Physics may convince us that there is actually a four dimension, or even eleven and a half, we cannot escape our experience of three dimensions. Our representation of space is embodied.

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