Side B in the scheme refers to the non specific system (context) and concerns the Memory data based on the millenary dialectic between the natural selection founding the biologic evolutive structure and the material basis founding the dialectic-historical structure. This is exactly the dialectic explaining depth (3D).
Side A in the scheme is the specific system (content), it particularly concerns the visual input linked to the binocular Parallax and all the similar phenomena, including gestalt ones. All that would not give origin to the tridimensional anomaly if a disparity did not exist between the two systems, an incurable disparity at the basis of the symbolic-logical structure (Mathematics), and because of the erroneus space geometrical curvature.
As about the curvature, the brain is very helpful. One of its tasks is explaining why the image on the retina is bidimensional, since the image is projected onto a bent surface. "To be precise, there are two images, one for each eye: that is how nature allows to see the world in three dimensions"(1). Personally I think all that is not enough to INSTALL the whole tridimensional vision without the intervention of the impact of the STRUCTURAL DIALECTIC at the basis of reality: this is what does give foundation to tridimensionality. Naturally, an important role is carried out by the transversal function of gravitation implicit in light itself, a new element focused by Einstein when he modified the same law of gravitation.

EINSTEIN - MACH ISSUE (the problem of either the finite or the infinite space and of its curvature).
The main problem is still of perceptive nature; in this case, perception has to do with the anomaly concerning the tridimensional aspect of reality. Both Einstein and Mach rejected the idea of an ABSOLUTE SPACE-TIME- REFERENCE SYSTEM.
In contrast with the absolute space, Mach believes that it is the distribution of the matter in the universe to define the inertial systems.
The theory of General Relativity accepts this principle. In order to agree with Mach, Einstein chose in my opinion a contradictory solution of the universe. On the one hand, he convinced himself that the space should be FINITE because the distribution of MATTER was FINITE, but at the same time it was also BOUNDLESS. For that reason, he chose the solution of ELLIPTICAL and HYPERBOLICAL geometries, however a variation of Gauss's solutions. In other words, the SPACE CURVATURE was needed to remedy the perceptive error linked to TRIDIMENSIONALITY.
Scheme:

As I showed in the past, the conceptual confusions are partly found in the neuroperceptive system.(2)

Corrective space for the anomaly:

MONODIMENSIONAL LINE FOR METHODOLOGICAL PURPOSES
(representing an infinite full space in all directions and non-dimensional)

THE IMMOBILITY OF THE UNIVERSE: EINSTEIN'S COGNITIVE PERCEPTIVE ERROR
THE ISSUE OF EXPANSION AND OF CURVATURE

When the universe is declared not to be static but expanding (as largely demonstrated), the question is the influence of GRAVITY on the expansion and its slowing down due to gravity itself.
Since Einstein believed THE AVERAGE CURVATURE TO BE LINKED TO THE AVERAGE DENSITY, THEN GEOMETRY AND DESTINY OF THE COSMOS ARE LINKED TO EACH OTHER.
This can be stated in the numberless "partial curvatures" (as they are perceived because of the tridimensional anomaly), caused by the numberless big bangs and big crunches occurring on this FULL - INFINITE - NON-DIMENSIONAL SPACE, like Gauss's balloons (as they are perceived) that are born and then burst endlessly.

FUNDAMENTAL SCHEME OF ALL CURVATURES (Gauss):

TRANSPOSITION BY PARALLELISM (LEVI CIVITA)
It is a breakthrough, useful to go over the idea of curvature, but it is a failure at the same time: it does not rejecy the tridimensional coordinate system, instead it recognizes it as fundamental.
Levi Civita's scheme to represent the space allows to consider a variety like a collection of "small pieces of euclidean space oriented one to the other..."(3).

SCHEME:

The nature of parallel transposition is an attempt to solve the perceptive illusion of the space curvature due to the influence of gravity or else. Einstein was sure that gravity was not the cause of the space-time curvature but of the curvature itself.
Nowadays, after half a century's Neuroscience and Cognitive Psychology, we are able to state that gravity affects PERCEPTION. In this sense, GRAVITY is not the SPACE CURVATURE, but THE ILLUSION OF CURVATURE. What gets curved, in reality, is the light that the ILLUSORY IMAGE OF AN OBJECT IN THE SPACE brings with it, NOT THE OBJECT ITSELF.

LIGHT: ELECTROMAGNETICAL RADIATION AND PERCEPTIVE CONNECTION BRIDGE
BETWEEN GRAVITY AND ELECTROMAGNETISM.

Maxwell realised that electromagnetic radiations and light move at the same speed (300,000 Kms per second), hence he derived that light itself is a sort of electromagnetic radiation. That was then confirmed by Hertz, too.
In Rods, and precisely in the retina photoreceptors, occurs the perceptive synthesis between the structural system (non-specific system B) and what is part of the vision mechanisms (non-specific system A); the gravity system affects both systems.
As Roberto Casati states, referring to Gary Marcus. "the retina has its receptors internally and not externally, therefore the connections with the optic nerve have to pass in front and filter the light, as if a camera had its cables in front of the objective (and the result is the blind spot, by which the brain remedies afterwards with a software erasing it and filling it with a colour coming near the colour detected aound the spot). Only a drunk could have designed a similar eye."(4)
The patched consciousness, as Casati calls it, is an original anomaly at the foundations of tridimensional vision which, as I explained, depends on the specific system of consciousness, but is consolidated in its stable structure by the non-specific system. That is the reason why receptors are turned towards inside.
A similar eye was not designed by a drunk, but perhaps by the early developed civilizations, which designed consciousness as self-defence, not from nature, but from their own structures on which they were founded.(5)
SYMMETRY AS A RESULT OF THE ANOMALY MADE CONCRETE IN THE SYMBOLIC LANGUAGE AT THE BASIS OF THE MATHEMATICAL STRUCTURE.

The dichotomy highlighted by Matteo Blanco as BI-LOGICAL(6) is not sufficient to explain SYMMETRY, the fundamental structure of Mathematics. As I realized some time ago, not only does the SYMMETRY - ASYMMETRY dichotomy exist, but also the ones inside symmetry itself. We can state it is the synthesis between unconsciousness and consciousness, performed through a connection of concepts (syllogism), as a result of the alignment of Mental Objects deriving from sublimation. The fundamental structure of set theory(7) is obtained thanks to these concepts and the proper mediations.

SYMMETRY - CONSERVATION OF PHYSICAL LAWS.

Mental Objects are already aligned in a syllogistic way according to the non-accidental psychoanalytic mechanism of SUBLIMATION. As explained(8), this mechanism uses the symbolic synthesis to link two realities which are contradictory. The symbolic language in this sense is conservative and that involves stability of laws in theoretical Physics. Einstein also believed it, as Edelman says, "Einstein was the first person to understand how important the invariance of Physics was, and therefore their symmetry. Actually, the theory of relativity can be considered as a system useful to find out the conditions of absolute invariance!"(9).

Notes:

1 Keith Devli,, "L'istinto matematico", Raffaello Cortina Editore, 2007, Milan, (page 104) or a longer dissertation in Steven Pinker, "Come funziona la mente", Ed. Mondadori, Milan, 2000.
2 "Le scienze web news", Bertagnolio.
3 U.T.E.T. Encyclopedia, reprint La Repubblica, page 348, volume 14, part I, "Geometry", Umberto Buttazzini.
4 Roberto Casati, from "Klun: The Haphazard Construction of the Human Mind" by Gary Marcus. In "Il Sole 24 ore",
Sunday insert 11 May 2008, N. 129.
5 3D is a weapon of defence allowing the structurale perception of reality (with the help of gravity) an immanent character and a dualistic structure of the world. (see studies in "Le scienze web news").
6 Ignacio Matteo Blanco, "L'inconscio come insiemi infiniti, saggio sulla bi-logica", Ed, Einaudi, 2000 Turino.
Introduction by Pietro Bodei.
7 "Simmetria, asimmetria, dicotomia non superabile attraverso la Bi-logica...", Bertagnolio in "Le scienze web news".
8 see scheme "Logical-symbolic thought", Bertagnolio "Le scienze web news".
9 G. M. Edelman, "Sulla Materia della mente", Ed. Adelphi 1995 (2), Milan; page 314.