âas Gary Marcus and Jeremy Freeman note in their Preface to The Future of the Brain, '[a]t present, neuroscience is a collection of facts, still awaiting an overarching theory’â?. This in a review of the “Attention Schema Theory of subjective awareness” (FKA “…theory of consciousness”) advanced by Michael Graziano (Associate Prof. of psych and neuroscience at Princeton) in his book titled Consciousness and the social brain.Â
A brief popular article by Graziano illustrates how neuroscience facts are construed so as to be consistent with open-loop assumptions. The pitch is to explain the evolution of consciousness in terms of the successive emergence of three major parts of brain anatomy in the course of evolution from the neural net of the hydra, to the tectum of vertebrates, to the cortex mammals (the wulst of birds, reptiles, and some other critters).
Selective signal enhancement is described in terms very like the pandemonium architecture proposed by Oliver Selfridge in the late 1950s to account for pattern recognition. Different signals of the same sort compete and the strongest signal ‘wins’. (If it doesn’t provide input needed for a controlled perception at a higher level, it is suppressed and the next-strongest ‘wins’, explaining sudden flips of misperception to ‘correct’ perception.) But Graziano’s discussion confounds this with the many-one reduction of complexity that is inherent in the perceptual hierarchy, such that hundreds of signals at level n-1 may synapse together in the input function for one signal at level n. (A notable example is the series of transformations in the retina between sensory input and signals in the optic nerve.) This mechanism has been well studied in the hydra, and is understood to persist in higher organisms.
The tectum accounts for the orienting response and what Graziano calls overt attention: the dedication of sensory organs (eyes, ears, skin sensors) to selected parts of the available environmental input. The explanation is classic CogPsych:
To control the head and the eyes efficiently, it constructs something called an internal model, a feature well known to engineers. An internal model is a simulation that keeps track of whatever is being controlled and allows for predictions and planning. The tectumâs internal model is a set of information encoded in the complex pattern of activity of the neurons. That information simulates the current state of the eyes, head, and other major body parts, making predictions about how these body parts will move next and about the consequences of their movement. For example, if you move your eyes to the right, the visual world should shift across your retinas to the left in a predictable way. The tectum compares the predicted visual signals to the actual visual input, to make sure that your movements are going as planned. These computations are extraordinarily complex and yet well worth the extra energy for the benefit to movement control. In fish and amphibians, the tectum is the pinnacle of sophistication and the largest part of the brain. A frog has a pretty good simulation of itself.
On analogy to this explanation of the tectum, Graziano attributes to the wulst/cortex the creation of a cognitive map of cognition itself. “[T]he cortex must model something much more abstract. According to the AST [Graziano’s Attention Schema Theory), it does so by constructing an attention schema-a coonstantly updated set of information that describes what covert attention is doing moment-by-moment and what its consequences are.” This is posited to account for what he calls covert attention: “the virtual movement of deep processing from one [perceptual] item to another”.
So yes, âneuroscience is a collection of facts, still awaiting an overarching theoryâ?.
And as Bakker observes in the review from which I took that quote, Graziano’s “subjective awareness, far from being a property perceived, is actually a [putative!] neural construct, a tool the human brain uses to understand and manipulate both other brains and itself.” In other words, it isn’t about awareness at all.
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/Bruce