As the bottom-up engineer has seen, throughout the evolution of species, increases in the mobility of organisms and increases in the sophistication of the neural apparatus go hand-in-hand.
It was the increasing mobility in primordial metazoans which prompted the compound eye, which led to an increasingly mobile primordial vertebrate and the adaptations of the vertebrate eye. We then saw the evolution leading to terrestrial locomotion in the primordial tetrapod, which led to a more sophisticated neural system and the adaptations of our primordial mammals.
This dialog is in agreement with the hypothesis that it was the traumatic global ecological changes following the K-Pg asteroid event that forced Nature to evolve neural structures which could assimilate adaptive behaviors within the life-time of an organism, organisms having phylogenetic adaptations for an environment which no longer existed, and the adaptations of post K-Pg event organisms have brought the discourse to our primordial cognitive mammal. And it is at this point that adaptations in the mobility of our primordial mammal will “drive” the next epochal evolutions in the neural sophistication of mammalian species.
For tens of millions of years following the K-Pg asteroid event, our primordial mammals flourished, claiming larger areas of habitation as their terrestrial locomotion became more specialized, which created selective pressures for many mammalian species to rise above the increasingly hostile ground environment, and move into that next frontier of terrestrial life: Arboreal habitation.
Much like the dawn of the Devonian period witnessed the evolution of free swimming pelagic organisms, as they rose up from the increasingly crowded and dangerous bottom of coastal shallows, arboreal mammals began a significant branch of terrestrial species.
Life above ground for our primordial mammals will require some not so subtle changes to the limbs and especially the “feet”, which were formerly specialized for terrestrial walking and running but will now require adaptations for climbing and most importantly, grasping tree branches. And just as terrestrial locomotion prompted changes in the visual and haptic senses of the primordial tetrapod, arboreal life will also call for visual and haptic senses of a more focused nature.
As the splayed digits of terrestrial mammals changed from their function of distributing weight over uneven surfaces to grasping tree branches, the limbs in arboreal mammals would undergo adaptations to provide increased balance control over terrestrial speed. And besides the vegetative adaptations required by a change in diet, these conformal alterations would not require much more neural sophistication on the part of evolving species until a particular seminal situation arose in some species. There would come a time when some species would be attracted to certain arboreal objects which could not be had by merely climbing out on a tree branch. There would come a time in some species where one of the forelimbs would release its grasp on a tree branch or trunk and reach out to grasp something other than another supporting branch. And as this act would provide the species with some survival advantage, selective pressures would prod Nature into adaptations developing limbs which manipulate the arboreal environment around the mammal in addition to navigating through it.
Now, for sure, our primordial mammals have been engineering alterations to their environment for hundreds of millions of years. As nocturnal animals, they have been burrowing habitats and forming nests since the Mesozoic period. But none of these behaviors required specialized adaptations of the limbs or sophistications of the neural system beyond phylogenetic mechanisms. In contrast, the manipulation of an arboreal environment will require a prehensile hand, and more importantly, a neural sophistication that can change its behavioral perspective from broad allocentric movements to target centered movements.
Although this change in perspective might sound like just a simple change in the scale of spaces encompassing the activity between the two movements, it is not so neuro-scientifically simple. There are two distinct centers of neural activity required when an animal reaches for a specific target in its visual environment. There is the neural center tied to the preparation and organization of the movement itself, and there must be some neural control that is tied to the target location independent of the movement itself. Unlike the egocentric or even allocentric movement of the whole body in a mammals world, reaching and grasping in an arboreal environment is an activity with movements toward a target that are uncoupled in both time and space.
Reaching and grasping in an arboreal environment is an orchestra requiring a different conductor than the ground based animal, that can maneuver the body close enough to a desired target to place it into a common egocentric frame of reference encompassing the eyes, body and the extending limb. Perhaps the semantic abstractions developing in the PFC can span the disconnect in separate egocentric and target frames of reference directing a singular movement sequence, but these aerial acrobatics will also require a visual apparatus with an acuity extending outside the range of the primordial mammals’ vergence imaging capability. And perhaps the survival value of this ability provided the selection pressures for the evolution of foveal vision in some species of mammals we call the primates.
From the standpoint of the sensory area of the cortex that conducts primary visual processing, foveal vision would not be regarded by many neuroanatomists as a separate vision process, but, indeed, if one looks at the lateral geniculate nucleus in the thalamus of mammals, (the area of the thalamus on which the optic retinal ganglion afferents terminate), one finds six distinct layers of differentiated terminations in human and simian primates, where only three distinct layers terminate in non-foveal mammals. This is emphasized by the fact that approximately half of the ganglionic fibers in the optic tract for human and simian primates carry signaling from the central 5 degrees of the retina, while the remaining half carry signaling from the rest of the retina. And the occipital region of human cortex which represents the retinotopically 5 degrees of central vision is supplied with a dual blood supply, whereas the remaining occipital cortex is supplied from a single artery. And among other particulars, there is a neuroanatomical distinction between the input from the central and peripheral visual field to the inferior temporal cortex, which results in a foveal bias in the occipito-temporal association mapping.
But where the bottom-up engineer should consider foveal vision as a separate vision “channel”, without regard to any neuro-anatomical considerations, is in its functional treatment. Although it neurologically relies on the retinotopic maps developed in the optokinetic/vergence imaging process, its neurologic implementation requires cognitive intentionality.
From a physiological perspective, the central 5 degrees of human and some primate vision systems behave as an “optical zoom” mechanism, and like a pair of binoculars, foveal vision has to be “aimed” by an intentional mechanism. In Discussion 10G, the dialog introduced the neural implementation of spatial invariance as a domain transformation, and in Discussion 10H, this domain transformation was further refined in its definition to be a function of translational invariance in retinotopic transformations. This was because a true spatial invariant operation would require a function to spatially scale the retinotopic map to an absolute scale.
With this in mind, the bottom-up engineer should consider foveal vision as a vision system separate in its abstract functionality from the optokinetic/vergence image maps of the primordial primates’ occipital cortex. Foveal vision provides for the capacity for fine distinctions and discriminations in perceptions, in addition to the retinotopic scale imagery of vergence vision, a capacity needed to develop absolute scales in retinotopic imagery.
It is separate functionally because it requires the mechanical cooperation of the eyes, head and neck to optically fixate the foveal spot of the retina onto a particular target in the animals’ visual field. Although this is also a step in vergence imaging, the functional separation is further emphasized by the implication that, once fixated, there is a phasic process needed to “fuse together” the higher resolution foveal map with the retinotopic resolution of the vergence image, (A phasic process very similar to the 3-D phasic fusion which develops vergence images themselves), and this fused foveal image, which is essentially a re-scaling of the fused vergence image, is then associated with the environmentally ambiguous semantic “things”, those ghostly, purely temporal invariants of semantic maps alluded to in the previous discussion, forming Natures’ first neurological constructions of true objectifications in the environment of the cognitive organism, a cognitive objectification apart from the infinite complexity of its background.
Perhaps this explains the perceptual disintegration that occurs when lesions of the occipito-parietal region creates an inability to fuze objects separately focused on (a circle with a dot in its center, for example) into a visually integral structure.
Since it was the PFC which had to direct the eyes, head and neck toward the point of fixation, foveal imaging is an intentional process, separate from the optical redirection processes of the attention mechanism, and its semantic abstraction occurs in the PFC as well.
Because the foveal image was abstracted from semantic maps having a temporal dimension, demarcated by the emotive swings in the animals’ activity, the abstraction carries with it an attached emotive motivational significance as well as its objective perceptual form as an entity in the environment. This complexity in abstraction should not be surprising to the bottom-up engineer because, in mammals, and especially humans and the primates, the complexity of cerebral pyramidal cells increases from posterior to anterior brain regions as the degree of time and space coupling in processes increasingly disintegrates.
And because the foveal image is a product of the intentional fixation of the animals optical apparatus, the overall process of foveal imaging creates anticipatory structures in the PFC as well, structures which permit the temporal uncoupling of the processes in the PFC to extend to a certain extent into the future, as far as the valence of the attached emotive motivational significance can hold the animals attention.
But this is enough for the PFC, with the enlistment of the cerebellum, to evolve behaviors which demonstrate the production and execution of primal anticipatory schemata alluded to at the end of Discussion 5. These primal anticipatory structures are not yet quite as sophisticated as those elusive human anticipatory schemata in Discussion 5, because the anticipatory structures of primates, although extending into the future in their temporal uncoupling, cannot extend into the future in a spatially uncoupled manner as well, for the reason that the spatial coupling of the foveal image of the primordial primate is bound by the currently attached motivational significance of that objectifications’ semantic.
Uncoupling of both the temporal and spatial processes extending into the future, in an organic, anticipatory manner, would define “rationality”, and to accomplish this, Nature would need to evolve the ability for the PFC to attach the emotive motivational significance to an objectification in a temporary fashion, or perhaps with an artificial salience, and not as just the mere by-product of the foveal imaging process. So the first glimmering projection of time in the processes of the PFC would require some adaptations to the nascent foveal imaging process, and rationality would have to wait until primordial Man leaves the primates in their arboreal habitation and returns to life on the grassy savannah.
GO TO NEXT DISCUSSION
GO TO TOP OF DISCUSSION
Copyright © 2019 All rights reserved