PSYCH 4320 / COGST 4310 / BioNB 4330

Consciousness and Free Will

Theme II

  Week 4: being a vertebrate

Week 4: what is it like to be a bat vertebrate?

MacIver on neurophysiology vs. neuroethology

Neurophysiological approaches often implicitly suggest that many, perhaps most, components of the nervous system can be understood without examining an animal's larger context, be it behavioral, biomechanical, or evolutionary.

In contrast, neuroethologists believe that unless the larger context is understood — for example, by quantifying the profile of sen;ory signals that an animal is subject to in its habitat or by placing neural characters of related animals into phylogenetic trees ("neurocladistics") — many aspects of neural function will not be understood.

the Buena Vista Sensing Club

Sensory volumes of different active sensing animals.

  1. Bat echolocation beam; the illustrated range is the estimated detection range for small prey (mosquitoes) averaged across several bat species.
  2. Dolphin; the illustrated range is the estimated detection range for a prey-sized, water-filled sphere.
  3. Weakly electric fish; the illustrated range is the estimated detection range for small prey (water fleas).
  4. Rat whisker system.

buena vista and free will

From reactivity with a mala vista to planning with a buena vista. Control and planning in prey-capture behavior as a function of the ratio between the sensory volume (SV) and the stopping motor volume (MVstop) for two fictive animals: one (left) with the near unity ratio characteristic of many passive sensing animals that have poor acuity and active-sensing animals and another (right) with a large ratio to illustrate the rarer situation of long-range passive-sensing systems such as vision.

  1. With near-unity SV:MVstop ratios, search proceeds in a raster-sean-like fashion through the environment. If a prey is close enough to be within one of these search tracks, it is detected and possibly captured.
  2. With large SV:MVstop ratios, there is the possibility that multiple trajectories to a detected prey (dashed lines) can be assessed prior to action. After assessing multiple paths, one path is chosen (b1) that is longer than a path that may disclose the position of the predator to the prey too early (b2) or result in reaching an untraversable obstacle (b3).

Crazy Bob's Taxidermy and Pedicure

As you extend your sensory volume beyond the horizon of reactivity, you allow for more than simple reactive control strategies, such as braking or swerving. With a buena vista, you can look far ahead and execute long-duration plans such as multiple lane changes prior to an exit. [...] In less dynamic contexts, such as long-range navigation, and where perception is costly, guiding movement through internalized spatial maps may be more effective.

If, for example, that moose on the road in front of you is actually stuffed, and has been inconveniently installed in the center of the road, you could eventually learn to avoid it early on, on the basis of your recognition, say, that it is just past the hairpin turn before Crazy Bob's Taxidermy and Pedicure.

the consciousness connection

Bridgeman (1992) wrote, "Consciousness is the operation ofthe plan-executing mechanism, enabling behavior to be driven by plans rather than immediate environmental contingencies." Consciousness [...] is concerned with attention to intermediate-level representations that are useful for action. What I have presented here is a suggestion that planning, and perhaps therefore consciousness, was only necessary once perceptual systems delivered choices at such a distance that reactive (nonconscious) control schemes for action were no longer advantageous.

The lead-up to consciousness could therefore have been a gift of space wrought by passive teleceptive sensation in a niche where such acuity paid fitness dividends. The need to sequence behaviors over this space would then have given rise to executive control structures in the brain, including working memory and attention, for carrying out these sequences, in a case study of how "it is not the animal's brain that organizes its world, but the evolutionary ecology of the animal that organizes its brain.

Merker (2005)

Consciousness will be interpreted as a biological function evolved by mobile animals as a solution to neural logistics problems inherent in the control of orientation to their surroundings. The interpretation is motivated by the conspicuous absence from the contents of consciousness of two significant classes of information known to be present in brains, one on the afferent and the other on the efferent side of neural function.

Consciousness, it is here proposed, arose as a neural solution to a subdomain of this problem-space, namely as an interface between the spatial senses and the motor requirements of motivated behavior. The setting for this solution is the centralized organization of the brain characteristic of higher animals, including all vertebrates.

synthetic "reality space"

The solution, it is here proposed, is to make targets available for decision making by presenting them as part of a coherent and stable world-space synthesized from the various concatenated correction measures needed to remove the effects of self-motion from sensory information. On such a basis the spatial senses could be integrated within a common framework serving a number of decision processes. The solution amounts to giving decision mechanisms access to a synthetic ‘‘reality space’’.

A further reason now becomes apparent for the necessity to exclude from consciousness any sign of the transformations through which the stable panorama of the world is derived from the sense organs: the rich ‘‘reality space’’ of consciousness, crowded with objects and events, must be taken to be absolutely real, or the entire motivational underpinnings of behavior collapse. The credibility of that reality is a good reason not to let the trappings behind its surface show through, because life depends on taking its appearances seriously.

the defining trait of consciousness

The defining trait of consciousness is, in other words, not any special ‘‘feel’’ or other hypothetical qualitative marker of consciousness, but the simple fact of finding oneself in a world — any world — and ultimately, stripped to its minimal essentials, to be in the presence of any object whatsoever.

Nor is there, in principle, any particular level of complexity required of the world or object supplying the content of the conscious state: we can subtract one modality and channel capacity after another without for that reason altering the fact of consciousness itself.

the core control system of the upper brainstem

Parasaggital side view is shown below, and a crossection in the approximate plane marked by oblique arrows is shown above. Cellular territories included in the ‘‘core control system’’ are marked by oblique shading, except for the zona incerta (V) which is left unshaded for the sake of clarity. The separately marked caudal shaded territory represents the mesopontine ‘‘state control’’ nuclei. Systems described in the text are identified by the symbol marking sites of origin of their afferents and/or efferents. Open squares, the direct cortico-collicular projection ‘‘funnel’’ with a posterior cortex bias. Open triangles, the direct cortico-hypothalamic projection ‘‘funnel’’ with a frontal cortex bias. Open circles, the cortico-striato-pallido-nigral projection ‘‘funnel,’’ also with a frontal bias (though not identical to the cortico-hypothalamic one). Filled squares, finally, mark a small sample of zona incerta connective relations. Incertal cortical afference is dominated by but not restricted to the cingulate gyrus (indicated here by its location inside the dotted line demarcating ‘‘limbic’’ components of the telencephalon). Abbreviations: D, dorsal thalamus (dotted line encloses midline and intralaminar nuclei); V, ventral thalamus (zona incerta ventrally, thalamic reticular nucleus dorsally); H, hypothalamus; g, medial geniculate body (caudal extreme); lh, lateral hypothalamus; m, mammillary bodies; mrf, mesencephalic reticular formation; p, periaqueductal grey matter; r, red nucleus; sc, superior colliculus; sn, substantia nigra.

zona incerta

A sophisticated control system needs some means for resolving residual conflict among alternatives left unsettled by routine mechanisms because of stochastic happenstance in a complex multicomponent system or because of exceptional combinations of contingencies encountered in a lively and unpredictable world (e.g., simultaneous and equally attractive but incompatible choices).

Such a monitoring function may be performed by the anterior cingulate at the cortical level.

At the level of the core control system the zona incerta — whose most prominent source of cortical afference is the cingulate cortex — seems optimally placed to play such a role.

zona incerta (cont.)

Notice that the loss of such a function need not produce conspicuous behavioral symptoms. Since it deals preferentially with residual decision making, routine functions may run smoothly in its absence. Yet as a component of a mechanism of consciousness, such a function is likely to assume a peculiar status in the subjective life of a conscious being. As the final arbiter, by competitive interaction ‘‘within itself,’’ as it were, of conflicts not otherwise resolved, it may well be experienced as a nodal point of ‘‘active agency’’ within consciousness, thereby promoting an incipient sense of ‘‘unconstrained choice’’ or ‘‘free will.’’

Moreover, as a centrally connected monitor function it may supply consciousness with that subjective presence of a tacit ‘‘witness’’ to its contents which is at the heart of the very concept of consciousness (see Merker, 1997).

These characteristics would amount, in other words, to a subjective sense of self, not in the sense of a self-image—which is a content of consciousness—but in the sense of the nodal monitoring function presupposed by all contents of consciousness. It would be that ‘‘for which’’ these contents are present as seen, felt, and heard objects, a role essential for the ‘‘unity of consciousness.’’ It was called the ‘‘synthetic unity of apperception’’ by Kant, the ‘‘pure subject of knowing’’ by Schopenhauer, the saksin (‘‘witness’’) in Vedanta philosophy, and the ‘‘seeing’’ as opposed to ‘‘seen’’ part of the totality of consciousness in the Alayavijnana doctrine of Mahayana Buddhism (see Merker, 1997, and references therein).

absence epilepsy

When Penfield and Jasper (1954) formulated their hypothesis of a subcortical ‘‘centrencephalic system’’ responsible for the highest integrative (conscious) functions of the brain, one of their reasons was that the ‘‘absence seizures’’ of epilepsy seemed ‘‘generalized from the start,’’ and specifically compromized the highest, conscious, functions of the brain’s operations.

Spells of absence epilepsy, on the other hand, compromize consciousness specifically without inducing sleep or coma (Stefan & Snead, 1997). The zona incerta is directly connected with key upper brainstem structures implicated in various aspects of the physiology of generalized seizures: substantia nigra (Deransart, Le-Pham, Hirsch, Marescaux, & Depaulis, 2001), dorsal midbrain (Shehab, Simkins, Dean, & Redgrave, 1995), and thalamus (Danober, Deransart, Depaulis, Vergnes, & Marescaux, 1998, & references therein; Seidenbecher & Pape, 2001).

before moving on to Merker (2007): revisiting the relevant levels of explanation

Merker (2007): preliminaries

"To the extent that any percept, simple or sophisticated, is experienced, it is conscious, and similarly for any feeling, even if vague, or any impulse to action, however inchoate.


"Consciousness may be regarded most simply as the 'medium' of any and all possible experience."

[...] Additional awareness, in reflective consciousness or self-consciousness, is one of many contents of consciousness available to creatures with sophisticated cognitive capacities. However, even in their case, it is present only intermittently, in a kind of time-sharing with more immediate, unreflective experience. To dwell in the latter is not to fall unconscious, but to be UNSELFCONSCIOUSLY CONSCIOUS. Reflective awareness is thus more akin to a luxury of consciousness on the part of certain bigbrained species, and not its defining property.

the functional level: what is it for?

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:

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

From this 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.

The ethological insight, that animal behavior rests upon a foundation of diverse goal functions that sometimes entail incompatible tasks or behaviors requiring sequencing / selection, entered the so-called behavior-based approach to ROBOTICS under the name “ACTION SELECTION”. [See also COMPETITIVE QUEUING.]

the functional level: but why does it require awareness?

Why can't we have action selection without (at least occasional) awareness?

Because evolution.

Without experiencing the world, why care about it? And if you don't care, how can you be motivated?

[Note that motivation is tricky only if it needs to be structured and sustained in the long run (compare MacIver's Buena Vista insight); for immediate reflex action, no special motivation is needed.]

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 Geometric Theory that we'll discuss in weeks 8 and 9 holds that the mind consists of a trajectory through a properly structured phenomenal space.]

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. [Cf. a diver's experience with cleaner wrasse. ]

Merker (2007)

the computational level: coordination by mapping [Computing the Mind, p.422]

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.

[This story leaves out the critical question of HOW to exert dynamic control and support planning in this architecture... Hint: zona incerta.]

the neurobiological level: what does it take?

"A conscious mode of functioning is dependent upon quite specific neural arrangements creating interfaces of particular kinds between specific domains of neural function, rather than a result of a general increase in informational capacity or complexity achieved by expansion of a structural substrate which below a certain size does not support consciousness. Thus, what disqualifies the medusa nerve net in this regard is not its simplicity, but its lack of specific structural arrangements required to support conscious function."

the neurobiological level: (in vertebrates) where does it happen?

"[...] 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)

the neurobiological level: it's not in the cortex...

A system can be "anatomically subcortical but functionally supra-cortical." Thus, the fact that the motor cortex maintains direct connections with brainstem and spinal motoneurons by no means implies that it ever is in sole command of behavior. At every level of its descending innervation of motoneuron pools it is only one of many inputs determining final outcomes. [...] When an act of deliberate effort (say driven by prefrontal executive systems) is successful in overriding or inhibiting a given behavioral tendency, the cortex is in command of behavior, temporarily exercising determining control over its course. The fact that such effort does not always succeed (say in the face of sufficient magnitudes of fear, hunger, or pain) means that the frontal executive can be overridden by more primitive mechanisms. When a subcortical source prevails in such competitive interactions, an anatomically subcortical system has exercised supra-cortical functional control over behavior.

the neurobiological level: 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].

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. [Recall the wrasse.]

Any sensory modality used in phasic orienting behavior appears to receive obligatory representation in the colliculus. Besides the major spatial senses of VISION, AUDITION, and SOMESTHESIS, they include PAIN and exotic senses such as INFRARED, ELECTROCEPTIVE, MAGNETIC, and ECHOLOCATION systems, depending on species.

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.

the neurobiological level: cross-modal effects

Top: a monkey fixates one of three locations while listening to sounds from a movable speaker.

Middle: the firing of a neuron shows different dependencies on the speaker position (plotted along the abscissa) for the three different gaze directions.

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).

the neurobiological level: cross-modal effects

Top: computationally, this kind of response necessitates vector subtraction.

Bottom: a simple circuit capable of mapping the auditory target direction from head-centered to eye-centered coordinates.

["The head-centered auditory map projects to the intermediate unit with graded synaptic weights. The eye position signal is subtracted at an inhibitory synapse. The resulting rate code for the target’s location with respect to the eyes is converted into a place code for auditory space in an eye-centered frame of reference through graded thresholds and inhibitory interneurons."]

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

SC microstimulation studies in the bat

SC microstimulation studies in the bat

Vocalizations evoked

SC microstimulation studies in the bat

SC microstimulation sites and the effects observed

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. 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. PAG: the periaqueductal gray matter surrounding the midbrain cerebral aqueduct. Bidirectional arrow aligned with the collicular lamina denotes compensatory coordinate transformations.

the neurobiological level: the big picture


the neurobiological level: the big picture

Sagittal diagram of cortical convergence (in part via the basal ganglia) onto key structures in 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.

the neurobiological level: the big picture — zona incerta

[...] Zona incerta [...] is a mammalian derivative of the ventral thalamus and has emerged from obscurity only recently (Mitrofanis 2005).

Collicular input to the higher-order nuclei is excitatory, whereas their incertal input is inhibitory. This implies dynamic competition between colliculus and zona incerta for influence over the two principal thalamic dependencies of the prefrontal and the posterior parietal cortex. In this competition the inhibitory incertal element stands under cingulate cortex influence and is also in a position to inhibit the colliculus directly and with topographic specificity.

The zona incerta is monosynaptically (and often reciprocally and bilaterally) connected with on the order of 50 separate structures along the entire length of the neuraxis from spinal cord to olfactory bulb.

Internally, the zona incerta features profuse mutual connectivity in a setting of cytoarchitectonic and cytological heterogeneity in which GABAergic cells are prominent. A combination of reciprocal external connectivity with internal mutual inhibition is the theoretically optimal solution for implementing global competitive interaction among structures separated by long distances.

Nothing would be more elegant than to entrust the final arbitration of “what to do next” to a self-inhibitory “winner-take-all” or other decision network (Richards et al. 2006) lodged at the origin of the coordinate system that controls the orienting movements which execute that decision once made. As a primary perspectival viewpoint charged with changing motives, it would possess the essential attributes of a self.


[...] 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.

Merker (2007)

Metzinger+Merker=!! (cont.) [PHENOMENOLOGY!!]

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)

from the functional to the phenomenological 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 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.

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, 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.