Lecture 4: phenomenal Self; the details

— preamble

— the functional level

— the representational level

— the computational level

— the neurobiological level

— the phenomenological level

when did it happen?

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where does it happen?

in the late 1940s, Moruzzi and Magoun (1949) discovered that local stimulation of circumscribed cell groups in the pons and midbrain of experimental animals exerts a global activating influence on the cerebral cortex as well as on behavioral state, and that experimental lesions in these brainstem sites are capable of rendering animals somnolent and even comatose.

This came as a shock to the corticocentric perspective, and stimulated an avalanche of research on brainstem regulation of sleep and wakefulness and its relationship to the conscious state.

Merker (2007)

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it's not in the cortex...

... Key mechanisms of consciousness are implemented in the midbrain and basal diencephalon, while the telencephalon serves as a medium for the increasingly sophisticated elaboration of conscious contents.

[The superior colliculus] is the only site in the brain in which the spatial senses are topographically superposed in laminar fashion within a common, premotor, framework for multi-effector control of orienting (Merker 1980). Its functional role appears to center on convergent integration of diverse sources of information bearing on spatially triggered replacement of one behavioral target by another, and evidence is accumulating for a collicular role in target selection [lots of refs].

Merker (2007)

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what is it for? the functional level

The one functional need that any cognitive system must address is figuring out what to do next. In a routine situation, this task is essentially a matter of selection of:

Merker (2007):

"... Target selection is not independent of action selection, and neither of these is independent of motivational state (reflecting changing needs)..."

from which it follows that an optimal behavior planning mechanism would find

"some way of interfacing the three state spaces [action, target, and goal] — each multidimensional in its own right — within some common coordinate space."

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the representational level

The optimal control theorem of Conant and Ashby (1970) dictates the representational content of the common coordinate space posited by Merker (2007): a model of the world, which must include the embodied system itself, and which therefore functions as a "total flight simulator."

Individual states, which can be described as concrete realizations of points within this phenomenal space of possibility, are ... conscious experiences: transient, complex combinations of actual values in a very large number of dimensions. What William James described as the stream of consciousness under this description becomes a trajectory through this space.

Metzinger (2003)

The mind in a very clear computational sense consists of a trajectory through the phenomenal space.

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the computational level

The "neural analog reality simulation" that unfolds in the phenomenal space

[...] equips its bearers with veridical experience of an external world and their own tangible body maneuvering within it under the influence of feelings reflecting momentary needs, i.e., what we normally call reality. To this end it features an analog (spatial) mobile "body" (action domain) embedded within a movement-stabilized analog (spatial) "world" (target domain) via a shared spatial coordinate system, subject to bias from motivational variables, and supplying a premotor output for the control of the full species-specific orienting reflex.

Merker (2007)

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the computational level: coordination by mapping

Visual-motor control as a mapping between two representation spaces in an artificial crab-like creature (P. M. Churchland).

The function f that maps the visual space into the motor space is realized as a pattern of direct connections between spatially aligned sheets of "neurons" tuned to various combinations of gaze angles (upper sheet) and joint angles (lower sheet). Aligned maps of this kind are found in the superior colliculus.

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the neurobiological level: coordination as mapping

Some cells in the cat's superior colliculus respond to visual and tactile stimuli (Groh and Reiss, 2002). Once they are aligned, selection binds together perception, self-state, and action; there is the spotlight of attention, but nobody is (or needs to be) looking at what it illuminates.

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the neurobiological level: multimodal receptive fields

Receptive fields of multimodal cells in the superior colliculus of the barn owl are tuned to elevation and azimuth of the stimulus both in the visual and in the auditory modality (Knudsen et al., 2002).

This tuning is experience-dependent both in development and in adulthood.

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the neurobiological level: cross-modal effects

Left top: a monkey fixates one of three locations while listening to sounds from a movable speaker. Left middle: the firing of a neuron shows different dependencies on the speaker position (plotted along the abscissa) for the three different gaze directions. Left bottom: the firing rate profiles for the three gaze directions are revealed to be the same when plotted against "motor error" (the difference between speaker and gaze directions). Right top: computationally, this kind of response necessitates vector subtraction. Right bottom: a simple circuit capable of mapping the auditory target direction from head-centered to eye-centered coordinates.

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SC microstimulation studies in the bat

Doreen E. Valentine, Shiva R. Sinha, and Cynthia F. Moss

Orienting responses and vocalizations produced by microstimulation in the superior colliculus of the echolocating bat, Eptesicus fuscus

J Comp Physiol A (2002) 188: 89-108

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SC microstimulation studies in the bat

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SC microstimulation studies in the bat

Vocalizations evoked

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SC microstimulation studies in the bat

SC microstimulation sites and the effects observed

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the neurobiological level: the big picture

Schematic saggittal diagram depicting cortical convergence (in part via the basal ganglia) onto key structures in the region of the "synencephalic bottleneck" (marked by thick arrows in the main figure and by a black bar in the inset).

Abbreviations: C, nucleus cuneiformis; H, hypothalamus (preoptic area included); M, mammillary bodies; MP, "mesopontine state control nuclei" (locus coeruleus, pedunculopontine and laterodorsal tegmental nuclei, and dorsal raphé); MR, midbrain reticular formation; N, substanta nigra; P, periaqueductal gray matter; Pt, pretectum; R, red nucleus; SC, superior colliculus; V, ventral tegmental area; Z, zona incerta.

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the neurobiological level: the big picture

The three principal domains of "world" (target selection), "body" (action selection), and "motivation" (needs) that must interact to optimize decision processes in real time, as implemented in the roof of the midbrain.

In the forebrain (incl. the cerebral cortex of mammals), the dorsolateral to ventromedial path from the surface of the colliculus to the midbrain aqueduct corresponds to a posterior to frontal to medial path in the cortex. In the reverse direction, and in functional terms, it reads "motivation", "action" and "world".

S, I and D: superficial, intermediate and deep layers of the superior colliculus, respectively. PAG: the periaqueductal gray matter surrounding the midbrain cerebral aquaduct. Bidirectional arrow aligned with the collicular lamina stand for compensatory coordinate transformations.

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Metzinger+Merker=!!

[...] our very body bears a tell-tale sign allowing us to recognize it as the product of a neural simulation. Vision differs topologically from somesthesis and audition by its limited angular subtense, particularly in animals with frontally directed eyes. The other two senses can be mapped in toto onto a spherical coordinate system for orienting, while vision is only partially thus mapped. This is not in itself a problem, but becomes one given that vision can be directed not only to the external world but to the body itself. This necessitates some kind of junction or transition between the distal visual world and the proximal visual body, and there a problem does arise.

Though as we have seen the ego-center is present in consciousness by implication only, its location can be determined empirically. It is single, and located behind the bridge of the nose inside our head. From there we appear to confront the visible world directly through an empty and single cyclopean aperture in the front of our head. Yet that is obviously a mere appearance, since if we were literally and actually located inside our heads we ought to see not the world but the anatomical tissues inside the front of our skulls when looking. The cyclopean aperture is a convenient neural fiction through which the distal visual world is "inserted" through a missing part of the proximal visual body, which is "without head" as it were or, more precisely, missing its upper face region. Somesthesis by contrast maintains unbroken continuity across this region. The empty opening through which we gaze out at the world betrays the simulated nature of the body and world that are given to us in consciousness.

Merker (2007)

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the neurobiological level: the big picture

Highly schematic depiction of the nested relation between ego-center, neural body and neural world constituting the analog neural simulation ("reality space").

Black depicts the physical universe, one part of which is the physical body (black oval), both of which are necessarily outside of consciousness. One part of the physical body is the physical brain (circle; shaded and unshaded). The heavy black line separating the reality space from other functional domains within the brain indicates the exclusion of those domains from consciousness (unshaded). Arrows mark interfaces across which neural information may pass without entering consciousness. The designation ego-center is a sensorimotor construct unrelated to the concept of self-consciousness.

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the phenomenological level

Human vision is phenomenally cyclopean because once the data streams from the two eyes get fused into a single representation they are no longer individually accessible.

To find out what the world looks like from my left eye, I must close my right eye; when both eyes are open, I cannot help seeing a single, integrated panorama (if I had impaired stereopsis due to amblyopia or some other condition, or if I were a rabbit, or a Pierson's puppeteer, things would look differently for me).

The visible world in the cyclopean panorama appears as if it is seen from a vantage point situated inside the skull, behind the bridge of the nose.

Of course, if the "I" (the phenomenal Self) were really where it seems to be, I would see nothing but bits of brain and bone. Instead, it looks like the entire front of my head is missing.

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the phenomenological level

My phenomenal world, which includes an image of my body, must therefore be a neural fiction perpetrated by the senses. It is presumably there for my own good (that is, for the greater good of my selfish genes), which is probably one reason why this illusion cannot be dispelled at will.

Part of the illusion would persist even if I were to shut the world out altogether, via total sensory deprivation. The part that persists is literally central to the illusion: it is the part at which all the sensory inputs seem to converge, and which is present at all times, because it is fed, in addition to the external senses, by a continuous internally generated somatic input. This is the phenomenal Self.