Abstract

A particular system of brain mechanisms, called the retinoid system, is proposed as the evolutionary adaptation responsible for the existence of subjectivity and our sense of being here in a surrounding 3D world. The structural and dynamic properties of the retinoid system successfully predict a novel conscious experience in which the brain constructs a vivid visual representation of an object moving in space without a corresponding image projected to the retinas. Implications of the retinoid system for human creativity and our scientific understanding of the universe are suggested.

KEY WORDS: consciousness, 3-D world, brain, retina, retinoid


1. INTRODUCTION

We are each born with a system of brain mechanisms that constitute the full scope of our entire phenomenal universe. The structure and dynamics of this crucial brain system actually construct the world of our experience. What we call consciousness is the presence of this world for us. Consciousness did not exist before a creature was able to represent something somewhere in a perspectival relationship to a fixed internal "point" of origin - a transformative evolutionary event that ushered in the dawn of the first-person perspective - subjectivity and consciousness. To this extraordinary biological development we owe the possibility of all of our past and present conceptions of everything that is in our cosmos. Here is the key question: What biological mechanism emerged that enabled subjectivity and set us on a path by which we can now engage in our present discourse about consciousness? My proposal is that a unique brain system with a particular kind of neuronal structure and dynamics - the retinoid system (Trehub 1977, 1991, 2007) -- is the essential generator of our conscious experience. The structural and dynamic properties of the retinoid system enable it to register and appropriately integrate disparate stimuli into an egocentric representation of one's volumetric surround - the world around us. This system of neuronal mechanisms composes an internal egocentric space that receives Input from all sensory modalities and, in recurrent fashion, projects its excitatory neuronal patterns back to each sensory modality. It organizes its multi-sensory features into a coherent global representation of 3D space. All the sensory features of objects and events in retinoid space are organized in proper spatiotemporal register, called feature binding. For example, if a red car were to travel from left to right in your field of view, the retinoid representation of its color would be contained within the contour of its shape, and both color and shape would move in concert left to right within your egocentrically organized retinoid space. Each sensory modality is served by a particular kind of neuronal mechanism called a synaptic matrix (Trehub 1991). The synaptic matrix is a self-organizing brain mechanism that has the capacity to learn and classify complex stimulus patterns, store them in long-term memory, and recall images of them in the absence of external stimulation. Synaptic matrices are specialized processors; each serves only one kind of sensory feature; e. g., for visual shape, for color, for motion, for taste, etc. It is the role of the retinoid system to integrate signals from these disparate sensory modalities, widely separated in the brain, into a single coherent representation of the surrounding world.

The rich content of our sense of the world around us is provided by reciprocal evocation among sensory images and their neuronal tokens embodied in the recurrent loops of the synaptic matrices in parallel coupling with the retinoid system. If we think in metaphorical terms of a theater of consciousness within the brain, then retinoid space would correspond to the bright stage of the "theater" on which we are a participant. This stage is our conscious content. The synaptic matrices in the various sensory modalities and the other cognitive mechanisms which categorize and evaluate the patterns of neuronal activity (the objects and events) presented on the retinoid "stage" would correspond to something like a critical observing audience in the dark (unconscious) part of the theater (Trehub 2007).

Most organisms on this earth are able to adapt reasonably well with nothing but mechanisms that we would relegate to the unconscious. They do not respond to an internal global represention of the world they live in. They have no such internal representation and respond instead only to those isolated stimuli that reach their sensory transducers. Other creatures, mankind in particular, respond to a phenomenal world full of events and contingencies that are far beyond what impacts the lower organisms. While the retinoid system is assumed to have first appeared in the brains of lower animals, its evolutionary development, together with the development of related cognitive brain mechanisms, peaked with the emergence of mankind.

Figure 1.  A. Non-conscious creatures. E1 and E2 are discrete events in the physical world. R1 and R2 are sensory transducers in the body that selectively respond to E1 and E2. R1 and R2 signal their response to unconscious processing mechanisms within the brain. These mechanisms then trigger adaptive actions. B. Conscious creatures. In addition to the mechanisms described in A, the brain of a conscious creature has a retinoid system that provides a holistic volumetric representation of a spatial surround from the privileged egocentric perspective of the self-locus -- the core self (I!). For example, in this case, there is a perspectival representation of E1 and E2 (shown as E1' and E2') within the creature's phenomenal world. Neuronal activity in retinoid space is the entire current content of conscious experience.

Notice in Fig. 1 that that there are neuronal pathways from the body's sensory receptors (R1and R2 in the diagram) to the brain's unconscious sensation to action processors, then from these neuronal mechanisms to the neuromuscular structures for overt action. It is assumed that all sentient and motile preconscious organisms have this kind of sensory-motor system. However, with the emergence of the retinoid system in the course of creature evolution, an entirely new kind of brain mechanism with new possibilities for adaptive action appeared in the world.

Some investigators have claimed that consciousness depends on particular kinds of quantum events in the brain's neuronal circuits. On the basis of our present understanding of quantum electrodynamics we should expect quantum events to be relevant to all biophysical processes at a fundamental level. However, I would argue that if particular kinds of quantum events are selectively determinate for conscious content, they must conform in some way to the structural and dynamic properties of the retinoid system. With a nod to the anthropic principle, I suggest that the entire conceptual edifice of modern science is a product of biology and is necessarily constrained by the conscious-cognitive structure and dynamics of the human brain. The cosmos as it is subjectively represented in the retinoid system of the human brain is the only cosmos we can think about.

2. Neuronal Activity in the Retinoid System Constitutes Our Phenomenal World.

A key feature of the representational space within the retinoid system is that it is organized around a fixed cluster of cells which constitute the neuronal origin - the 0,0,0 (X, Y, Z) coordinate -- of its 3D spatiotopic neuronal structure. All phenomenal representations are constituted by patterns of neuronal excitation on the Z-planes of retinoid space. I have proposed that the fixed spatial coordinate of origin in the Z-plane structure can be thought of as one's self-locus in one's phenomenal world, and I designate this central cluster of neurons as the core self (I!) (Trehub 1991, 2007).

Our consciousness is no more nor less than the current content of our phenomenal world, and on this I base my working definition of consciousness as follows:

      Consciousness is a transparent brain representation of the world from a privileged egocentric perspective.

Since, in this theoretical model, retinoid space is the space of all of our conscious experience, vision should be understood as only one of the sensory modalities that project content into our egocentrically organized phenomenal world. A blind person can have as keen a phenomenal sense of a surrounding volumetric space as a fully sighted person. All of our sensory modalities that serve both external and internal sensations can contribute to our phenomenal experience, as shown in Figure 1. The minimal neuronal structure and dynamics of the retinoid system and the nonconscious sensory and cognitive brain mechanisms, primarily with respect to the visual system, have been detailed in Trehub 1991. On the question of the retinoid system as the biophysical foundation of consciousness, we might ask: Is there a critical experiment that provides strong support to the theoretically formulated properties of the mechanisms in the retinoid system? The Seeing-more- than-is-there experiment described in the following section shows that there is such evidence.

3. Complementary Neuronal and Phenomenal Properties

In the development of the physical theory of light, the double-slit experiment was critical in demonstrating that light can be properly understood as both particle and wave. Similarly, I believe that a particular experiment - a variation of the seeing-more- than-is-there (SMTT) paradigm - is a critical experiment in demonstrating that consciousness can be properly understood as a complementary relationship between the activity of a specialized neuronal brain mechanism, having the neuronal structure and dynamics of the retinoid system, and our concurrent phenomenal experience.

Seeing-More-Than-is-There (SMTT)

If a narrow vertically oriented aperture in an otherwise occluding screen is fixated while a visual pattern is moved back and forth behind it, the entire pattern may be seen even though at any instant only a small fragment of the pattern is exposed within the aperture. This phenomenon of anorthoscopic perception was reported as long ago as 1862 by Zöllner. More recently, Parks (1965), McCloskey and Watkins (1978), and Shimojo and Richards (1986) have published work on this striking visual effect. McCloskey and Watkins introduced the term seeing-more-thanis-there to describe the phenomenon and I have adopted it in abbreviated form as SMTT. The following experiment was based on the SMTT paradigm (Trehub 1991).

Procedure:

1. Subjects sit in front of an opaque screen having a long vertical slit with a very narrow width, as an aperture in the middle of the screen. Directly behind the slit is a computer screen, on which any kind of figure can be displayed and set in motion. A triangular-shaped figure in a contour with a width much longer than its height is displayed on the computer. Subjects fixate the center of the aperture and report that they see two tiny line segements, one above the other on the vertical meridian. This perception corresponds to the actual stimulus falling on the retinas (the veridical optical projection of the state of the world as it appears to the observer).

2. The subject is given a control device which can set the triangle on the computer screen behind the aperture in horizontal reciprocating motion (horizontal oscillation) so that the triangle passes beyond the slit in a sequence of alternating directions. A clockwise turn of the controller increases the frequency of the horizontal oscillation. A counter-clockwise turn of the controller decreases the frequency of the oscillation. The subject starts the hidden triangle in motion and gradually increases its frequency of horizontal oscillation.

Results:

As soon as the figure is in motion, subjects report that they see, near the bottom of the slit, a tiny line segment which remains stable, and another line segment in vertical oscillation above it. As subjects continue to increase the frequency of horizontal oscillation of the almost completely occluded figure there is a profound change in their experience of the visual stimulus.

At an oscillation of ~ 2 cycles/sec (~ 250 ms/sweep), subjects report that they suddenly see a complete triangle moving horizontally back and forth instead of the vertically oscillating line segment they had previously seen. This perception of a complete triangle in horizontal motion is strikingly different from the tiny line segment oscillating up and down above a fixed line segment which is the real visual stimulus on the retinas.

As subjects increase the frequency of oscillation of the hidden figure, they observe that the length of the base of the perceived triangle decreases while its height remains constant. Using the rate controller, the subject reports that he can enlarge or reduce the base of the triangle he sees, by turning the knob counterclockwise (slower) or clockwise (faster).

3. The experimenter asks the subject to adjust the base of the perceived triangle so that the length of its base appears equal to its height.

Results: As the experimenter varies the actual height of the hidden triangle, subjects successfully vary its oscillation rate to maintain approximate base-height equality, i. e. lowering its rate as its height increases, and increasing its rate as its height decreases.

This experiment demonstrates that the human brain has internal mechanisms that can construct accurate analog representations of the external world. Notice that when the hidden figure oscillated at less than 2 cycles/sec, the observer experienced an event (the vertically oscillating line segment) that corresponded to the visible event on the plane of the opaque screen. But when the hidden figure oscillated at a rate greater than 2 cycles/sec., the observer experienced an internally constructed event (the horizontally oscillating triangle) that corresponded to the almost totally occluded event behind the screen. The experiment also demonstrates that the human brain has internal mechanisms that can accurately track relational properties of the external world in an analog fashion. Notice that the observer was able to maintain an approximately fixed one-to-one ratio of height to width of the perceived triangle as the height of the hidden triangle was independently varied by the experimenter.

These and other empirical findings obtained by this experimental paradigm were predicted by the neuronal structure and dynamics of a putative brain system (the retinoid system) that was originally proposed to explain our basic phenomenal experience and adaptive behavior in 3D egocentric space (Trehub, 1991). It seems to me that these experimental findings provide conclusive evidence that the human brain does indeed construct phenomenal representations of the external world and that the detailed neuronal properties of the retinoid system can account for our conscious content.

4. The Heuristic Self-Locus (I!*)

The ability to move excitation from the source point of the self-locus (I!) to selected regions within the depth (Z-planes) of retinoid space also provides an important means of selective attention. The projection of neuronal excitation from the excitatory source of the core self to a target of interest in 3D retinoid space constitutes a selective shift of attention which is realized by an excursion of the heuristic self-locus (I!*; see Fig. 2). Neurons in regions of a retinoid that are stimulated by the added local excitation of a heuristic self-locus excursion are preferentially primed and marked relative to othercells in retinoid space. Cells in a primed region respond more quickly and vigorously than those in unprimed regions.

Figure 2. Excursions of the heuristic self-locus (I!*) are the biophysical equivalent of selective attention. In this example, attention (I!*) is directed at a square, a triangle, and an oval in the phenomenal world of retinoid space (egocentrically arranged with respect to the core self (I!).

An important feature of the heuristic self-locus is its property of inducing excitatory traces or patterns of cellular activity in accordance with its movement through retinoid space. We can think of these excitatory images as similar to the patterns drawn by a stylus on a display board. These self-locus traces might represent unimpeded travel routes between regions of interest, they might represent barriers to be avoided, or they might be retinoid images of our own imaginative construction serving us as cognitive maps or internal sketches to be used for many different purposes.

5. Creativity

The capability for invention, trivial and great, is arguably the most consequential characteristic that distinguishes humans from all other creatures. Our cognitive brain is especially endowed with neuronal mechanisms that can model within their biological structures all conceivable worlds as well as the world that we directly perceive or know to exist. External expressions of an unbounded diversity of brain-created models constitute the arts and sciences and all the artifacts and enterprises of human society (Trehub, 1991).

Our retinoid system together with a specialized preconscious brain mechanism for learning, long-term memory, and imaging, which I call a synaptic matrix, make creative modeling possible. A detailed description of the basic neuronal design of the synaptic matrix, as well as the structure and dynamics of the retinoid system, is given in Trehub 1991 (The Cognitive Brain). Synaptic matrices in all of our sensory modalities serve learning, memory, recognition, recall, and imaging of sensory features and events, while the retinoid system receives feedback signals from the imaging matrix of each modality to organize a coherent global layout of objects and events in our egocentrically organized retinoid space.

Figure 3. The self system (Trehub 2007). Neurons at the self-locus anchor the I-token (I!) to the retinoid origin of egocentric space. I! has reciprocal synaptic links to sensory and cognitive processes. Damage to the neuronal mechanisms below the dotted line results in cognitive impairment. Interruption of the synaptic link between the neurons at the origin of retinoid space (the self locus) and I! results in loss of consciousness.

Previously learned images and layouts can be recalled from the preconscious cognitive mechanisms, then decomposed and recomposed by the neuronal mechanisms of the retinoid system to form novel images or models. The content of retinoid space may consist of such imaginative constructions as well as the veridical makeup of a current environment. External expressions of novel phenomenal objects and events in retinoid space comprise our creative productions.

The conscious brain constructs the world of our experience by inserting and arranging on the Z-planes of retinoid space selected patterns of exteroceptive and interoceptive sensory patterns together with images recalled from the memory stores of synaptic matrices. The retinoid mechanisms are able to create phenomenal representations of novel objects and events by parsing objects or their parts in existing representations and rearranging these excitatory neuronal patterns in new combinations projected into retinoid space. The analytic mechanisms of the cognitive brain (shown below the dotted line in Fig. 3) can then evaluate the novel retinoid images in terms of their practical or theoretical utility. These putative brain mechanisms have been described in detail (Trehub 1991).

On the basis of Fig. 3, we can say that damage to any of the mechanisms below the dotted line would result in cognitive impairment with a sparing of consciousness. But if the synaptic link between the self-locus cells in the retinoid's Z-plane and its neuronal token (I!) below the dotted line were broken or damaged we would expect a loss of consciousness. Taking this into account, we might conjecture that the reason a sharp blow to the head can cause a loss of consciousness is precisely because the jolt can effectively interrupt synaptic communication between the self-locus neurons in the retinoid structure and I!, which is in an excitatory feedback loop with the retinoid's self locus (the core self), and which provides a gateway to the rest of the cognitive system.

6. Discussion

Can the retinoid model answer the daunting questions that have long perplexed the search for a scientific understanding of consciousness? An important consideration in making an assessment is whether the theoretical model enables the scientific community to perform reasonable empirical tests of its implications. In this respect, I have suggested that a science of consciousness requires the adoption of a bridging principle between the first-person subjective description of conscious content and a third-person objective description of conscious content (Pereira Jr, A. et al 2010). To this end, I have proposed the following principle:

For any instance of conscious content there is a corresponding analog in the biophysical state of the brain.

The objective, then, is to formulate brain mechanisms that can generate proper analogs of conscious content. Application of this bridging principle led to successful predictions about subjects' conscious experiences in the SMTT experiment on the basis of the detailed structure and dynamics of the retinoid system. It should be added that there are many more previously puzzling subjective phenomena that are straightforwardly explained by the causal properties of the retinoid system, among them, the moon illusion, size constancy, and motion after-effects (see Trehub 1991, pp. 89-93 and pp. 239-255). A positive aspect of the retinoid theory, beside its explicit account of subjectivity and phenomenal consciousness, is its ability to explain human creativity on the basis of the normal operation of plausible brain mechanisms. This, together with the well founded supposition that the retinoid structure of the brain is an advanced evolutionary adaptation, adds credence to the theoretical model. Moreover, the implications of the retinoid model for understanding the source of our scientific concepts lends substance to the weak version of the anthropic principle (Barrow and Tipler 1986). In addition to extending the retinoid model and further testing its implications, one would want to see others pursue the scientific challenge of formulating an alternative testable model that can do a better job of explaining subjectivity and the brain mechanisms that present us with our phenomenal world.

7. Conclusion

Our phenomenal world, the world of everyday experience, the world in which we try to thrive and probe for understanding, is an amazing product of biological evolution. The big questions that science now tries to answer could not be posed before the evolutionary emergence of the brain's retinoid system. It is this biological system which gives us subjectivity -- a sense of a self centered in a surrounding universe.

References

Barrow, J. D. and Tipler, F. J. (1986). The Anthropic Cosmological Principle. Oxford University Press.

McCloskey, M. and Watkins, J. W. (1978). The seeing-more-than-is-there phenomenon: Implications for the locus of iconic storage. Journal of Experimental Psychology: Human Perception and Performance 4: 553-564.

Parks, T. (1965). Post-retinal visual storage. American Journal of Psychology 78: 145-147.

Pereira Jr., A., Edwards, J. C. W., Lehmann, D., Nunn, C., Trehub, A., and Velmans, M. (2010). Understanding Consciousness: A Collaborative Attempt to Elucidate Contemporary Theories. Journal of Consciousness Studies 17: 213-219.

Shimojo, S. and Richards, W. (1986). Seeing shapes that are almost totally occluded: A new look at Park's camel. Perception and Psychophysics 39: 418-426.

Trehub, A. (1977). Neuronal models for cognitive processes: Networks for learning, perception, and imagination. Journal of Theoretical Biology 65: 141-169.

Trehub, A. (1991). The Cognitive Brain. MIT Press.

Trehub. A. (2007). Space, self, and the theater of consciousness. Consciousness and Cognition 16: 310-330.

Zollner, F. (1862). Uber einer neuer Art anorthoscopischer Zerrbilder. Annalen der Physik und Chemie 27: 477-484.