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Chapter III. The Neurological Basis of Conscious Experience >> Evolution: from visual analysis to mental synthesis

Evolution: from visual analysis to mental synthesis

How did mental synthesis evolve during evolution? We can now answer this question on the neuronal level. As was described in the previous chapter, the brain first developed a greater propensity for visual analysis. While the right hemisphere remained holistic, encoding complete objects as one neuronal ensemble, the left hemisphere learned to automatically split the visual percept into smaller elements: each element encoded by its own neuronal ensemble (one neuronal ensemble for an eye, another neuronal ensemble for an ear, a third neuronal ensemble for a tail, and so on). The neuronal ensembles encoding object details were stored separately in memory and were matched directly to visual cues during the recognition process. This ability enabled hominids to identify predators faster when few visible details were available (for example, a leopard could be identified based solely on its tail visible above the grass). This new ability complemented a longer process of target identification by visual amodal completion (which remained a major means of identification by the holistic right hemisphere).

It can be safely assumed that visual analysis improved significantly in australopithecines (5 to 2.3 million years ago). However, visual analysis in australopithecines was probably automatic. Judging from the lack of manufactured stone tool artifacts, the australopithecines were probably not able to from a mental template. Neurologically, australopithecines probably had not acquired the ability to voluntarily shift neuronal ensembles out-of-phase with the attention rhythm in order to concentrate on one visual detail: they were not able to see a future chopper inside a cobble.

The next step in evolution enabled Homo habilis (2.4 million years ago) to have a mental template. Homo habilis was not only able to separate an object into several neuronal ensembles, he was also able to shift some ensembles out-of-phase with the attention rhythm voluntarily. The likely mechanism involved the development of the prefrontal cortex and its ability to change the timing of neuronal ensembles’ activity voluntarily. When looking at a natural cobble, the prefrontal cortex of the Homo habilis was able to identify the neuronal ensemble encoding a chopper (mental template for a chopper) and to shift the other neurons in the visual cortex (flakes) out-of-phase with the attention rhythm. Note that a complete cobble had already been registered by the hominid’s eyes and was represented in his visual cortex. When the hominid shifted the neurons encoding flakes out-of-phase with his attention rhythm, the parts of the visual cortex registering the flakes were de-synchronized, and therefore were no longer present in the hominid’s conscious experience. The neuronal ensemble encoding the chopper remained in-phase with the attention rhythm, which enabled the hominid to consciously experience the mental template of the chopper, that is, to “see” the chopper inside the cobble.

Judging by the rough shape of Oldowan choppers, the mental template in the mind of Homo habilis was most likely rough and unstable. However, the ability to form a mental template is indicative of significant development in the visual and prefrontal cortices. Improved visual analysis enabled Homo habilis to identify predators faster and from farther away. It also enabled the hominid to mass-manufacture sharp-edged choppers for protection, hunting, and butchering carcasses.

Based on the refined quality of Acheulean stone tools, it can be concluded that the visual and prefrontal cortices developed significantly in Homo ergaster and Homo erectus (2 million years ago). These hominids must have been capable of voluntarily dissecting the visual percept into fine details (a handaxe and small flakes). In order to form the mental template of the handaxe, their brain had to shift neurons that did not belong to the neuronal ensemble of the handaxe (neurons representing flakes) out-of-phase with the attention rhythm. The sophistication of Acheulean handaxes indicates that the hominid’s brain was able to form sharp and steady mental templates of handaxes. The hominids were not capable of synchronizing two neuronal ensembles with the attention rhythm (mental synthesis), but their processes of visual analysis and mental template formation (voluntary visual analysis) may have been as good as that in modern humans.

Homo ergaster and Homo erectus must have applied automated and voluntary visual analysis processes to multiple objects, not just to stone tools. When hominids hunted down an animal, their mind automatically dissected the animals into eyes, palms, body, tail, and so on (automated visual analysis). Further, Homo ergaster and Homo erectus were able to form a mental template of any part of an animal’s body (voluntary visual analysis). The ability of listeners to voluntarily form a mental template of nearly any object created an opportunity for development of a rich communication system. The hominids needed names for all the visual details they were able to imagine. This produced pressure on the speech apparatus. Skeletal remains indicate that Turkana boy (Homo ergaster who lived two million years ago) had a significantly more advanced vocal apparatus than a modern chimpanzee.

Where did evolution place the speech control centers? Transmission of information between departments in one hemisphere is faster than sending the information to another hemisphere via the corpus callosum (a bundle of about 250 million axons carrying information between hemispheres). It is not surprising that the speech control centers developed in the same hemisphere that performed automated visual analysis and formed mental templates: the left hemisphere. Two separate language areas developed in the cerebral cortex: one dedicated for speech analysis (Wernicke’s area) and another one for speech synthesis (Broca’s area).

Outfitted with voluntary mental analysis and enriched communication capabilities, Homo erectus and Neanderthals left Africa and colonized Asia and Europe. Their spread around the world is a tribute to their greatly advanced mental capacities. Their brain size increased dramatically to accommodate the neurons and interconnections necessary for advanced computations. In fact, the Neanderthal brain was bigger than the brain of modern humans.

The final step in the evolution of Homo was the acquisition of mental synthesis. About 100,000 years ago, the prefrontal cortex of Homo sapiens developed the capacity to synchronize several neuronal ensembles in one frame of consciousness. Note that Homo erectus and Neanderthals were only capable of forming a mental template by shifting cortical neurons that were not part of the neuronal ensemble out-of-phase with the attention rhythm. Hominids were only capable of “destructive interference”, but they were not yet capable of constructive mental synthesis. Homo erectus and Neanderthals were not capable of shifting two neuronal ensembles in-phase with the attention rhythm: their brain was not able to execute mental synthesis.

The speech apparatus as well as cortical areas responsible for speech analysis and speech synthesis were probably developed to a large extent in the ancestors of Homo sapiens, who communicated though a complex non-synthesizing language. In Homo sapiens, acquisition of mental synthesis was quickly followed by acquisition of a synthesizing language. It can be said with a high degree of certainty that by the time Homo sapiens left Africa 50,000 years ago, they had already acquired both mental synthesis and a synthesizing language.