The Human Eye: an intelligent optical sensor

A brief synopsis of the book entitled “The Human Eye: an intelligent optical sensor (The inverted human retina: a diffractive-optical correlator)”.

The interpretation of early human vision up today is based on a camera-like optical hardware design in the eye and on a stepwise and hierarchically layered neuronal software processing along the central visual pathway (retina, CGL and V1) and in other cortical visual centers. The hardware in the eye in this interpretation consists of a geometrical-optical lens-pupil system imaging the visible onto a flat CCD-like photoreceptor matrix with monotonously distributed photoreceptors (RGB-cones in daylight and rods in scotopic vision). The 3rd dimension of the visible in monocular vision is lost from the very start on. All structuring and intelligent processing of visual information is attributed to the neuronal software: the figure-ground separation, the spatial frequency filtering, the centering of an object as a whole, the reconstruction of the 3rd dimension, the RGB-chromatic adaptation to illuminants to reach color constancy, the (log-)polar coding for object classification or identification etc.

Contrary to this classical camera-like interpretation of early human vision a revolutionary new insight into the optical visual processing becomes available with the supplementary addition of the micro- and nano-structured diffractive interference-optical hardware in aperture and image space of the human eye and the interpretation of its intelligent functionalities in vision, supported also by the hardware-structure of the central visual pathway between the eye and the cortical visual center V1. In Chapters I – VIII the main interdisciplinary aspects of this new interpretation of the optical hardware are described, showing that the ‘inverted’ human retina has a key-function in an eye’s cortical design and that the grating- and space-grating based diffractive Fresnel-interference optics assume intelligent functions: the spatial frequency filtering, the figure-ground separation and the dealing with the 3rd dimension, the space-grating diffractive-optical RGB-transformation, the processing of chromatic adaptation to illuminants, the centering of an object as a whole, the (log-)polar coding for object classification or identification etc.; the eye through modern micro- and nano-optics is given back a great part of the intelligent functionalities up today exclusively attributed to the neuronal software processing.

Chapter I: The prenatal development of the eyes and the central visual pathway.

During the 9 months before birth a cortical cellular layer is invaginated into the optic cup of the eye and develops the three nuclear layers in the ‘inverted’ human retina, the biaxial structure of the inner eye, the bipolar centering at the Papilla and the Fovea, the centripetal optic nerve running out of the eye and at least the photoreceptor array of cones and rods behind the retina. The construction of the ‘inverted’ human retina is analyzed in details and interpreted as a targeted cortical design of the hardware in the eye and a revolutionary step in the design of the hardware in vision. The central visual pathway with its optical nerve crossing on its way to CGL and V1 (cortical visual centers) dissects the image of the fixated object into quadrants, relates them to the body’s orthogonal coordinate system and after layer-by-layer information processing converges the visual data in binocular fusion at V1.

Chapter II: Diffraction and Interference of light; Information in diffraction images.

The three nuclear layers of the inverted retina are interpreted as diffractive-optical cellular gratings producing Fresnel-diffraction images in reciprocal grating space, therefore guaranteeing local information about seen objects. This is in contrast to Fraunhofer-diffraction in the far-field of optical gratings offering global information about visible scenes.

Chapter III: The spatial frequency filtering of the grating-optical correlator in the eye.

The inner nuclear layer INL of the inverted retina is interpreted as a spatial frequency filter, based on the histological distribution of ganglion cell bodies in retinal zones. It guarantees the visual acuity data with high spatial frequencies in central retinal zones and with low spatial frequencies in peripheral zones.

Chapter IV: The monocular 3D-depth map in the eye.

The grating-optical correlator of the inverted retina with the combined INL outer and MNL middle nuclear layers provides monocular 3D-depth information about object space. The geometrical optical system furnishes object-specific image planes and the Fresnel diffraction optics miniaturizes the optical range map available in reciprocal space, provided by ‘phase retrieval’-processing in Fresnel-space.

Chapter V: Spectral RGB-processing in the space-grating of the human eye.

The ONL outer nuclear layer with the hexagonally densest packed cell bodies of the photoreceptors is interpreted as a three-dimensional space-grating optically transforming incoming light into three RGB-diffraction orders with peaks at 559, 537 and 447nm corresponding to the peaks of the spectral sensitivity curves of the photo pigments in photopic vision and to the peak at 512nm in scotopic vision. The von-Laue- and the reciprocal von-Laue-Equation well-known from Crystal-Optics mathematically describe the light-double-cone transformations in the visible spectrum.

Chapter VI: Space-gratings in aperture and image space of the eye: RGB-color vision, color constancy, opponent colors, Purkinje-shift and Bezold-Brücke-Phenomenon.

The diffractive-optical RGB-transformation explains results obtained by E. Land’s Retinex experiments (the relation of local RGB-data to the global RGB-data of the overall illumination) and allows a new interpretation and better understanding of visual phenomena like paradoxically colored shadows in twilight, adaptation to colored lights and color constancy, the adaptive Purkinje-shift between photopic and scotopic vision and the relation of brightness and color in the Bezold-Brücke phenomenon.

Chapter VII: The grating-optical layer-by-layer pre-processing of the visible in global and local optical columns.

The diffractive-optical image preprocessing in the inverted human retina clearly structures image space into ‘global’ optical columns processing a seen object as a whole, and in ‘local’ optical metapixels enclosing all optically transmitted information about local aspects of seen objects (brightness, RGB-color, distance of objects, oriented form and texture structures etc.). It also allows establishing a new correlation of the optical multilayer-preprocessing of images in the inverted retina with the well documented multilayer data processing in associative layers of the retina, in CGL and in V1.

Chapter VIII: The (log-) polar pre-processing for object classification and identification in vision.

In the grating-optical structure of the inverted retina each visible object is analyzed at its image position by the object-specific local centering and (log-) polar coding in the hexagonal net in its scale-, orientation- and shift-invariant features. The optical (log-) polar coding helpfully prepares classification and identification of objects, to answer to the question about WHAT an object represents generically or specifically.

In summary the diffractive-optical and interdisciplinary approach to the human eye illustrates with the diffractive-optical layer-by-layer processing in nuclear retinal layers, the hardware structure of the ‘inverted’ retina and of the central visual pathway with its neuronal layer-by-layer processing, how intelligent functionalities can be guaranteed in early vision, too often and too quickly in science up today attributed to the cortex. This research was supported during 12 years by the R&D-Ministry of the German Government.

Appendix: Prevention of Myopia: the eye ought to exercise the use of the 3rd dimension of the visible at an early age.

In a practical application it is shown how myopia in early childhood could be avoided by regular active focusing of visible objects at different distances in the three-dimensional world. Scientists have proven that the daily time of reading, the distance of the text and intensive near-work facilitate the progression of myopia. Children who spend more time in the fresh air will develop myopia less often or will see it progress more slowly. But the presented optical analysis of the development of the rest state of accommodation in vision shows that life in fresh air is not sufficient but must be complemented by active focusing as it is given at football games or walking through forests etc.
A brief synopsis of the book entitled “The Human Eye: an intelligent optical sensor (The inverted human retina: a diffractive-optical correlator)”.