Original Paper __________________________________________________________ Forma, 19, 25–37, 2004

The Variant and Invariant in Perception
Fumihiko TAYA 1,2 and Ken M OGI2*
1

Graduate School of Medicine, Osaka University, 2-2, Yamadagaoka, Suita, Osaka 565-0871, Japan
2
Sony Computer Science Laboratories,
Takanawa Muse Bldg. 3-14-13, Higashigotanda, Shinagawa-ku, Tokyo 144-0022, Japan*E-mail address: kenmogi@csl.sony.co.jp(Received February 1, 2004; Accepted March 15, 2004)

Keywords: Consciousness, Qualia, Subjectivity, Information Representation

Abstract. The recent advances in cognitive neuroscience have made it possible to study

the neural correlates of conscious experience in a systematic way. The first principles how
and why we have phenomenal experience at all, however, is at present not known. Here,citing some recent advances in cognitive neuroscience, we argue that the phenomenal
qualities (qualia) of subjective experience and the origin of subjectivity are tightly
coupled. We propose that in order to find the first principles behind subjective experience,
we need to tackle the yet-unknown principle in information representation in general, andin particular, the interplay between the variant and invariant in information representation.
The relevance of quantum mechanical formalism in this respect is discussed.

1. Introduction
Recent advances in neuroscience have opened several experimental and conceptual
tools in order to study the problem of consciousness in a scientific way. Most researchers
have attempted to find the neural correlates of consciousness (NCC), which is the minimal
set of neuronal events that give rise to a specific aspect of conscious percept.
The idea of the neural correlates of conscious percept is originally due to Francis Crickand Christ of Koch (CRICK and K OCH, 1995). They argued that an explicit representationin terms of neural activities is necessary for the subject to be aware of an object or event.
Here, an “explicit representation” refers to the multilevel, symbolic interpretation of some
aspects of the visual scene that is represented by a smallish group of neurons (CRICK and
KOCH , 1998). Taking the psychological and neurophysiological data into consideration,
they hypothesized that only the visual features represented by neurons with direct projections
to the prefrontal or premotor cortical areas are “explicit”. Those areas were assumed to benecessary for the planning and execution of voluntary actions, and were therefore considered
to correlate with awareness. They concluded that the neural activity in the primary visualcortex (V1) did not enter the visual awareness because it had no direct projection to thefrontal area.

25

26

F. TAYA and K. MOGICRICK and KOCH (2003) then went on to stress the importance of elucidating the neuralcorrelates of consciousness at least in one instance. They assumed that there was a basic
common mechanism under all different aspects of consciousness, so that if one could
understand the mechanism for one aspect of consciousness, we could understand all others.
Based on this assumption, they chose visual consciousness as the initial object to attempta scientific attack, because it appeared to be the most tractable. With the advent of themodern imaging techniques such as fMRI, MEG, optical recording, on top of the traditional
single unit recording, investigating the neural correlates of conscious percepts has become
one obvious and admittedly promising way of attacking the problem of consciousness.
However, as CHALMERS (1995) pointed out, the enigma of qualia is likely to remain
even if we have solved the mapping between neural activities and conscious percept as
CRICK and KOCH (1995, 1998, 2003) suggested. Here, the term “qualia” is used to refer tothe phenomenal aspect of consciousness. The problem of qualia has been regarded as the“hard problem”, which seems insusceptible to the standard methods of cognitive science(CHALMERS, 1996), and is central to the problem of subjectivity.
In this paper, we suggest that there are two distinct categories of qualia, i.e. the sensory
and intentional qualia. Based on neurophysiological evidences, we argue that these twodifferent categories of qualia correlate with different subsets of neural activities in thebrain. The distinction between sensory and intentional qualia leads to a useful streamliningof various neurophysiological data concerning the nature of the neural correlates ofconscious experience.
In order to tackle the relevance of qualia in considering the functional set-up of theneural network in the brain, we need to question the very framework of information
representation. Any system of information representation is composed of variant andinvariant elements. Investigations into the neural information representation havetraditionally focused on the variant in information representation, by investigating thechange of neuronal activities that correlate with a specific feature of the stimulus or aparticular aspect of the functionality of the brain. In order for such variations of neuralactivity to be functionally relevant, however, an invariant “framework” of representationmust exist, in which the variations count as coding of information, and thus become neuralcorrelates in the Crick and Koch paradigm. We argue that the origin of subjectivity isclosely related to this invariant framework in cortical information representation, providing
the prerequisite basis for neural correlates. We discuss how the phenomenally distinct
categories of qualia (i.e., the sensory and intentional qualia) originate from the cortical
network of subjectivity which functions as a framework of invariance in cortical information
representation. Finally, we discuss the possible relevance of the quantum formalism to thequestion of the variant and invariant in cortical information processing.
2. The Role of the Primary Visual Cortex in Visual Awareness
As Crick and Koch pointed out, at present the most robust experimental approach forstudying the nature of consciousness is to search for its neural correlate by means ofmeasurements of brain activities accompanied by a comparison with subjective reporting(both in humans and monkeys). For example, electrophysiological single unit recordingsin the behaving monkey’s brain observing perceptually ambiguous figures have been a

The Variant and Invariant in Perception

27

valuable source of information. In particular, binocular rivalry, where incongruent stimuli
from two eyes compete to emerge in the visual awareness, has been regarded as the mosteffective platform for studying the neural mechanism underlying visual awareness. Data on
the neural correlates of perceptual change in binocular rivalry provide a valuable source of
information on the neural correlates of conscious experience, where the percept changes
without a corresponding change in the physical stimuli.
We review now the experimental evidence of the neural correlates of visual awarenessas has been indicated by studies on binocular rivalry.
Signals from the right and left eye retina are conveyed through the LGN of thethalamus and then integrated in the primary visual cortex (V1). The activities of neurons
in area V1 are therefore the obvious candidate for the neural correlates of perceptual change
in binocular rivalry. However, there are apparently conflicting reports on the role of V1 inbinocular rivalry. Early studies on binocular rivalry have suggested that V1 is crucial in
inducing rivalry (B LAKE, 1989). POLONSKY and his colleagues (2000) measured BOLD
signals in early visual cortex while the subjects viewed rivalrous images with two different
contrasts presented dichoptically to each eye. They found that the activities in V1 changed
during binocular rivalry. These variations were about 55% as large as those induced by thealternating presentation of two monocular images without rivalry and roughly equal tothose observed in other visual areas (V2, V3, V3(a) and V4v). There are other evidencesthat support the view that area V1 plays a crucial role in the perceptual alternation inbinocular rivalry (TONONI et al., 1998; T ONG and ENGEL , 2001; LEE and BLAKE, 2002).
WILSON et al. (2001) reported that the speed of ocular dominance propagation as it ismapped onto the visual cortex depended on the eccentricity of the annual gratings,
indicating that the site of dominance wave propagation is retinotopically organized and has
a cortical magnification similar to V1.
On the other hand, there are reports which suggest that higher visual areas, rather thanV1, are the crucial correlates of perceptual change in binocular rivalry. Logothetis and hiscolleagues have suggested that the best correlation with the percept in the macaque visualsystem was found to be in the activities in the extrastriate cortex. They trained monkeys toreport which of the rivaling stimuli, i.e. gratings drifting in different directions (LOGOTHETIS
and S CHALL, 1989) or grating of different orientations (L EOPOLD and LOGOTHETIS, 1996)
was perceived. They found that ~35% of the recorded neural activity in area V5/MT and
38% of that in area V4, and about ~90% of that in STS and IT correlated with the monkeys’
reported percepts. On the other hand, only 20% of neurons in area V1 correlated with thereported percepts.
Other studies have also suggested that the extrastriate cortex was the site of rivalry.
TONG et al. (1998) showed by fMRI measurement of human brain that BOLD signals fromthe parahippocampal “place” area (PPA) and the fusiform “face” area (FFA) varied
reciprocally in magnitude during binocular rivalry. K OVACS et al. (1996) usedcomplementary patchworks of intermingled rivalrous images and found that perceptual
alternation occurs between coherent images rather than patchy images. This result suggested
that the competition among images in binocular rivalry is independent of the eye of origin,pushing the likely site of rivalry to higher stages of visual processing than V1. LOGOTHETIS
et al. (1996) also showed that the competition between two percepts was independent of theeyes. The subjects were presented with rivalrous stimuli which interchanged every 333 ms

28

F. TAYA and K. MOGIwith each other and flickered at 18 Hz. The mean dominance time was 2,350 ms,
corresponding roughly to seven stimulus exchanges. This result, on the face of it, seems tosuggest that activities in V1 do not correlate with the perceptual change in binocular
rivalry.
3. The Sensory and Intentional in Perception
As summarized above, there are apparently conflicting reports on the involvement of
V1 in perceptual shifts in binocular rivalry. The question whether neural activities in V1
are crucial in the perceptual alternations in binocular rivalry, or the makeup of the neuralcorrelates of visual awareness in general, is interesting in terms of the argument by CRICK
and KOCH (1995).
Crick and Koch’s argument about the importance of direct connection to the prefrontal
areas and the exclusion of V1 from neural correlates of conscious perception carries someweight when one considers that visual information only makes sense when it is eventuallyreflected in the motor response.
However, neurophysiological evidences indicate that activities in V1 are necessary
for conscious visual perception, in a differential manner from the higher visual areas. In a
condition called blindsight, patients with V1 lesions retain residual visual functions while
reporting that they cannot see anything at the corresponding region of the visual field(WEISKRANTZ, 1997). When instructed to report under a two-alternative-forced-choice
condition, blindsight patients can discriminate the presence, location, orientation,
wavelength, and direction of motion of a visual stimulus well above the chance level. Theseobservations suggest that there are two distinct elements of visual perception, one tightly
coupled with our subjective sense of “seeing” something and the other coupled with theability to make appropriate motor responses. Blindsight conditions seem to suggest that
one is able to have the latter in the absence of the former.
By contrast, damages to any other cortical visual areas causes more restricted
impairments in visual perception, without a loss of the sense of being able to see. Lesions
in area V5/MT lead to the loss of motion perception (N EWSOME and PARE , 1988), whilelesions in the inferotemporal cortex (IT) lead to the impairment in face or object recognition(KOLB and WISHAW, 1985), without a loss in the sense of being able to see.
Considering these neurophysiological evidences, we suggest that the differential
contributions of V1 and higher visual areas to our conscious visual experience can bestreamlined by taking note of the fact that our visual percepts are composed of two
phenomenologically distinct elements, namely the sensory and intentional qualia. Here,sensory qualia refer to elements of visual percepts that correspond to color, shine,transparency, texture etc. that represent the stable qualities of object surfaces. On the other
hand, intentional qualia refer to the active interpretation of the visual scene, matched withthe representation of the outside world in terms of sensory qualia.
Kanizsa’s triangle (KANIZSA, 1976) consists of three black pacmans in a whitebackground (Fig. 1(a)). The completion of the edges of the illusory triangle is perceived interms of intentional qualia, not in terms of sensory qualia. You have a vague sense(intentional qualia) of the edges being completed, but not the sense of seeing an actual line
composed of distinct color (sensory qualia). In psychology, this particular nature of theThe Variant and Invariant in Perception

29

Fig. 1. Illusory triangle and real triangle. (a) The illusory edges in Kanizsa’s triangle are experienced asintentional qualia in an amodal completion. (b) The real edges in an actual triangle are experienced as
sensory qualia, i.e. lines composed of color distinct from the background.

triangle illusion is referred to as an “amodal” completion, as opposed to a “modal”
completion involving a change in the perceived color and/or luminance. Illusory perception
in general can be thought of as an instance where there is a discrepancy between sensory
and intentional qualia. In the case of a “real” triangle (Fig. 1(b)), there is no suchdiscrepancy.
Another instance where the distinction between the sensory and intentional qualia isuseful is the so-called “biological motion” stimulus, which is composed of a set of
appropriately coordinated moving point lights. When presented with a biological motion
captured from a walking person, subjects can perceive the stimulus as such, often finding
it possible to tell the sex, age, and other details of the walker (NERI et al., 1998). In termsof sensory qualia, only the point lights moving in the black background are experienced.
The “interpretation” of the point lights as a walking person is experienced as intentional
qualia, matched with the sensory qualia of lights on black.
Neurophysiological and lesion studies suggest that the sensory and intentional qualia
correlate with differential brain areas. Here, the word “correlate” is used in the sense thatwhen there is a change of neural activity in a particular brain area, there is a corresponding
change in the subjective percept. This statement does not necessarily mean that the neuralcorrelate of a particular conscious percept (qualia) is the sufficient condition for theparticular percept to occur.
We can almost certainly say that a particular neural correlate is a necessary condition
for a particular element of conscious perception. There is the theoretical possibility that
activities in other cortical areas can induce the same conscious percept. However, given theeconomy of cortical information representation, such a duplicative correlation is unlikely.
On the other hand, it is in general difficult to establish a sufficient condition for a particularelement of conscious perception to occur. We will come back to this point later.
With the above disclaimer in mind, evidences such as blindsight suggest that sensory
qualia correlate with neural activities in the early stages of visual processing, with theactivities of neurons in V1 required as a necessary element. Thus, activities in V1 count as

30

F. TAYA and K. MOGI

neural correlates of sensory qualia. The absence of neural activities in V1 results in the lackof sensory qualia, and the loss of the subjective experience of seeing something. On theother hand, the intentional qualia are likely to arise from the cluster of neuronal activities
within the extrastriate cortex (i.e. V5/MT, MST and IT). The absence of sensory qualia inblindsight results in the loss of the subjective feeling of seeing something, while theresidual intentional qualia support the ability to make a correct guess of the nature of visual
stimuli presented. Thus, the phenomenal distinction between sensory and intentional
qualia can resolve the apparent discrepancy between the neuropsychological evidences
regarding blindsight and the Crick and Koch’s model of the neural correlate of visualawareness (CRICK and KOCH, 1995).
The distinction between sensory and intentional qualia can also remove the apparent
discrepancy among the studies on binocular rivalry. Variations in the neural activities
within the extrastriate cortex can be interpreted to correlate with the change in intentional
qualia (such as motion perception, object recognition etc.) occurring as a result of theocular dominance change. Ocular dominance itself is defined in terms of sensory qualia.
The variations in the neural activities in V1, on the other hand, can be interpreted tocorrelate with the corresponding change with sensory qualia, resulting in a change in oculardominance.
These arguments demonstrate that taking the phenomenology of visual perception
seriously can lead to a useful methodology of sorting out the implications of physiologicaldata.
4. Contextual Modulation and Perceptual Stability
The distinction between the sensory and intentional qualia is also useful in describing
how the stable and changeable elements of perception match to build an active and adaptive
perception.
In the perception of ambiguous figures (e.g., the Necker cube (Fig. 2(a)) or Rubin’svase (Fig. 2(b)), where more than one interpretation is possible, there is a transition
between the possible interpretations following a gamma distribution (FOX and H ERRMANN,
1967; LEVELT , 1967; WALKER, 1975; MURATA et al., 2003). Phenomenologically, such aperceptual shift is experienced as a change in the intentional qualia. The sensory qualia
representation of the figures, i.e. in terms of color, remains stable during the perceptualchange. Thus, the perception of ambiguous figures can be thought of as a matching process
between sensory and intentional qualia, representing the basic characteristics of the visual
scene and its dynamically constructed interpretation, respectively.
The importance of the matching between the sensory and intentional qualia inperception suggests a close interaction between the cortical areas that correlate with theseelements of perception. From this viewpoint, it is interesting to note that the activities in
V1 exhibit a high degree of contextual modulation.
Neurons in the primary visual cortex are activated by presentation of a stimulus to theirclassical receptive field (CRF). Stimulus presented outside the CRF does not induce anactivity. However, provided that there is a stimulus presented within the CRF, stimuli
presented in the surrounding non-CRF can modulate the activity of the target neuron(ALLMAN et al., 1985). This phenomenon is called a context-dependent modulation.

The Variant and Invariant in Perception

31

Fig. 2. Ambiguous figures with more than one plausible interpretations. (a) Necker cube. There are twoalternative interpretations of this line drawing, with different edges assigned as the forefront. The
alternations in interpretation are experienced as a change in intentional qualia, while the sensory qualia ofcolor remain constant. (b) Rubin’s base. This figure can be interpreted either as a vase or two human faces.
The alternations are experienced as a change in intentional qualia, and the sensory qualia of color do notchange.

The modulation by stimuli presented to areas surrounding the CRF tends to work in
a suppressive manner. WALKER et al. (2000) examined the context-dependent modulationin the cat’s striate cortex. They found that for over half of the cells, the effect of stimulationin the surround of the CRF is to suppress activity by at least 10%.
It is known that the effect of the surround suppression is strongest when the propertyof stimulus presented to the surround of the CRF is similar to that of stimulus inside the
CRF. When a vertical grating is presented within the CRF, the presentation of a verticalgrating in the surrounds (Fig. 3(b)) induces a strong suppression, sometimes eliminating
the target neuron’s activity altogether. On the other hand, presentation of a horizontal
grating in the surrounds (Fig. 3(a)) results in a weak suppression effect.
Context-dependent modulation of neural activities may play significant roles in object
perception. LAMME (1995) suggested that the figure-ground segregation was the key
functionality of the context-dependent modulation. In this experiment, recordings weremade from awake, behaving macaque monkeys while the animals were viewing texture
stimuli. Neural responses in V1 were significantly larger for the figure part of stimulus thanfor the ground part, consistent with the idea that the one of the functions of contextual
modulation in V1 is to separate the figure from ground.
The contextual modulations in the primary visual cortex pose an interesting question
regarding the neural correlates of sensory and intentional qualia, and the interaction
between these areas underlying the dynamical matching in perception. The contextual
modulation is likely to reflect some aspects of the dynamic interpretation of the scene by
the visual cortex. While such a dynamical change is expected for a neural correlate ofintentional qualia, there is an apparent discrepancy between the fact that neurons in V1

32

F. TAYA and K. MOGI

Fig. 3. Stimuli inducing differential contextual modulation in the neural activities in the primary visual cortex.
(a) Vertical grating in horizontal grating background. (b) Vertical grating in vertical grating background.

exhibit contextual modulation and the idea that activities in V1 are neural correlates of
sensory qualia.
As is obvious when looking at Figs. 3(a) and (b), our perception of the vertical gratingin the center is remarkably stable in terms of sensory qualia (i.e. color). The major
perceptual difference between Fig. 3(a) and Fig. 3(b) is to be found in the intentional qualia
accompanying the subjective feeling whether the central circular region “pops out” or not.
These observations suggest the need to build a more sophisticated model of the neuralcorrelates of conscious visual percepts, beyond that of simple one to one mapping. Whileintentional qualia mainly correlate with the activities of neurons in higher visual areas,secondary correlates might be found in the contextually modulated neural activities in V1.
Neural correlates of sensory qualia, which definitely include activities of neurons in V1 asevidenced by blindsight data, need to be defined in terms of some invariant properties ofneural activities which remain stable despite the extensive contextual modulation found in
V1. The interplay between the neural correlates of sensory and intentional qualia
encompassing both V1 and higher visual areas in this respect is likely to be central to theprocess in which the brain actively represents and constructs an interpretation of theoutside world.
5. The Variant and Invariant in Information Representation
Based on the neurophyiological review above, we now attempt to consider the
essential requirements for a model of neural information representation and subjectivity,
centered around, but not limited to, the neural correlates of conscious perception.
In CRICK and KOCH (1995), the basic idea behind the formulation of neural correlateof conscious experience is that certain aspects of cortical neural activity co-varies with thatof the phenomenal elements in conscious experience. There are some possible complicationsin the concept of co-variance due to nature of correspondence between physical time (inThe Variant and Invariant in Perception

33

which neural activities are embedded) and the psychological time (MOGI, 1999). However,within the specious moment of ~100 ms, it is not unreasonable to assume that we can
empirically establish a correspondence between neural activities and elements of conscious
perception in the conventionally accepted sense of a “neural correlate”.
As discussed previously, a neural correlate in the conventional sense only means thata certain neural activity is a necessary condition so that the subject experiences a certain
aspect of conscious perception. In considering the sufficient condition, one of the essential
factors is the neural origin of subjectivity. At the core of the subjectivity enigma, there isa general and even functionally conceptualizable question regarding information
representation in a system, conscious or otherwise.
The idea of the covariance of physical activity and information contents is an implicit
assumption behind any conventional model of information representation. For example,
when some bits in computer are said to represent numbers, what is implied is that the system
is configured in such a way that the bits change in a way consistent with the semantics ofthe number. Information representation in this sense is primarily concerned with what is
explicitly variant in the physical system. The neural correlate idea has inherited theessential framework from this conventional assumption behind information representation.
Empirical evidences based on single unit recording, fMRI, MEG etc. are all concerned withthis explicit covariance.
In any system configured to represent and handle certain information, the explicitly
variant parameters need to be complimented with an implicit, invariant structure thatmakes it possible to encode, store, and read the information in such a system. In otherwords, in order for certain parameters that co-vary with the information to continue torepresent the same information, certain aspects of the system structure need to remain
invariant.
Let us assume that a system in question is composed of N variables. Out of N, E
variables would explicitly co-vary with the information represented within the system,
while I variables remain stable, to make it possible that the E variables explicitly represent
the relevant information, where E + I = N. In conventional theories of information
representation, upon which the neural correlate idea is based, attention is directed only
towards the explicitly variant part. It is the usually unquestioned implicit part, however,upon which the framework of information representation in general and the origin of
subjectivity in the case of the conscious brain depends.
An interesting empirical question to ask is how much of a population of neurons in thebrain actually sustains stable activity no matter what the brain is explicitly processing interms of sensory, motor, emotional or other types of information. This population of stably
firing neurons is conjectured to function as the neural correlates of the frame-of-reference/subjectivity structure in the context of which the explicitly varying populations of neurons
are given their specific functionality and become neural correlates of conscious experiencein the phenomenological context.
The conventional idea of the neural correlates of conscious experience has centeredon the variant elements, effectively assuming that I = 0 or otherwise ignoring theseelements. The invariant variables sustaining the frame-of-reference/subjectivity structure
can be thought of invariant neural correlates, as opposed to the conventional variant neuralcorrelates of conscious perception.

34

F. TAYA and K. MOGI

Invariant Neural Correlates

intentional qualia

sensory qualia

Variant Neural Correlates

Fig. 4. The variant and invariant in the neural correlates of subjective experience. In order for the degrees of
freedom that co-vary with information represented in the brain to be functional, we need a set of variables
that remains stable during the processing of information. These invariant degrees of freedom are expected
to form a second class of neural correlates, namely the invariant neural correlates of conscious experience,
which gives rise to the subjectivity structure. The phenomenally distinct sensory and intentional qualia arelikely to arise from the interface between the variant and invariant neural correlates. The known locus of theneural activities that generate sensory and intentional qualia, along with other neurophysiological evidences,suggest that the invariant neural correlates are centered in the prefrontal region, whereas the variant neuralcorrelates are distributed over the sensory cortex.

Figure 4 shows a scheme for the interaction between the variant and invariant neuralcorrelates. The sensory and intentional qualia are conjectured to correspond to theprojection from the variant to invariant elements, and from the invariant to variant
elements, respectively. Evidence which show that sensory and intentional qualia in vision
correlate mainly with neural activities in V1 and higher visual areas, respectively, alongwith other neurophysiological evidences, suggest that the invariant neural correlates are
centered around the prefrontal cortex, while the variant neural correlates are distributed
over the entire sensory cortex. These interpretations are consistent with the idea that theinvariant neural correlates are central to the neural mechanism of subjectivity, usuallyconsidered to be seated in the prefrontal cortex.
6. Possible Relevance of Quantum Formalism
Now we consider the broader implications of the necessity of the invariant neuralcorrelates of conscious experience.
There is an apparent non-locality in the correspondence between neural activities inthe brain and the elements of conscious perception. In visual awareness (CRICK and KOCH,
1995, 1998, 2003), the “self” is able to access and integrate the massively parallel
distribution of visual sensory qualia in the visual field. Even in the absence of specific andexplicit interpretation in terms of objects, the self is able to hold an awareness of the visual
scene. For this, the brain must somehow conduct property binding (TREISMAN , 1996),
binding features whose neural correlates are distributed over spatially distributed areas in
the physical brain. Although the explicit interpretation of the visual scene by the putting
together of various parts that constitute an object exhibits serial (one at a time) nature (partThe Variant and Invariant in Perception

35

binding, TREISMAN, 1996), the massively parallel nature of visual awareness in terms of
sensory qualia in particular indicates that the brain must somehow integrate information
represented by neurons non-locally.
The apparent non-locality of the mapping between the activities in the physical brain
and the elements of conscious perception has led some authors to suggest the involvementof quantum dynamics (JIBU and YASUE, 1995; BERNROIDER , 1998). The EPR type
entanglement (EINSTEIN et al., 1935), if it exists in the brain, could be a physical correlateof such a non-locality. Some authors have suggested that quantum processes in the
microtubules could provide the basis for conscious perception (HAMEROFF, 1994; HAMEROFF
and PENROSE, 1995).
Some authors have pointed out that conditions in the brain, such as a high temperatureand the involvement of many degrees of freedom, make it unlikely that a quantum
mechanical effect is involved in the physical correlates of consciousness (G RUSH and
CHURCHLAND, 1995; TEGMARK, 2000).
The juries are still out. Although the opponents to quantum involvement in conscious
processes appear to have a more solid reasoning at present, the remarkably integrated
parallelism exhibited in visual awareness alone seems to justify a search for a radically new
way of thinking, quantum or non-quantum, to come to the gist of the physical (neural orotherwise) correlates of conscious experience.
Here, we suggest that quantum processes might be involved in the implicit, invariant
nature of information processing in the brain, supporting in some essential manner thecomputations conducted by the explicitly varying neural activities.
Given the reality of biological neural networks, it is reasonable to assume that therelevant degrees of freedom involved in the information processing in the brain, as
reflected in our conscious experience, is that of neural firings (B ARLOW, 1972). Quantum
processes in the brain, if they are relevant, are unlikely to correlate in a direct and explicit
manner with the change in elements of conscious perception.
However, there is a possibility that quantum mechanical processes contribute to thenature of conscious experience by providing a basis for frame-of-reference/subjectivity as
the invariant neural correlates discussed above. An intriguing possibility is that quantum
processes influence the subjectively unique nature of each sensory quale, so that theredness of red has this particular feeling, while the transition between a particular quale toanother correlates with the neural activities in the brain, which are macroscopic phenomena
well above the quantum limit.
In this respect, it is interesting to note that a solution for the still enigmatic quantum
measurement problem (P ENROSE, 1989) likely involves a fundamental relation between theinvariant and variant in the description of a physical process, where the macroscopic
functions as a invariant frame-of-reference for the microscopic quantum wave function.
7. Conclusion
In this paper, we have argued that it is important to consider the invariant as well as
variant parameters in a model of the neural correlates of conscious perception in order toexplore the nature of the correspondence between the physical processes in the brain andthe phenomenal properties of our conscious experience. We suggest that the implicit

36

F. TAYA and K. MOGI

assumption behind the conventional treatment of information focused only on explicitly
varying variables must be questioned. Through a new look on the relation between thevariant and invariant, we might be able to come to a deeper understanding of the mind-brain
problem and the foundations of the information representation and processing at the sametime.
We thank Yoshihide Tamori and Gustav Bernroider for helpful discussions in formulatingsome of the ideas in this paper. One of the authors (Fumihiko Taya) thanks Toshio Yanagida forcontinuous inspiration and guidance.
REFERENCES
ALLMAN , J., MIEZIN , F. and M CGUINNESS , E. (1985) Stimulus specific responses from beyond the classicalreceptive field: Neurophysiological mechanisms for local-global comparisons in visual neurons, Annu. Rev.
Neurosci., 8, 407–430.
B ARLOW, H. (1972) Single units and sensation: A neuron doctrine for perceptual psychology?, Perception, 1,
371–394.
B ERNROIDER, G. (1998) Quantum-neurodynamics and the relation to conscious experience, ARGESIM Rep., 10(ISBN 3-901608-10-9), Tu-Vienna, Austria.
B LAKE, R. (1989) A neural theory of binocular rivalry, Psycho. Rev., 96, 145–167.
C HALMERS , D. (1995) Facing up to the problem of consciousness, J. Consciousness Studies, 2, 200–219.
C HALMERS , D. (1996) The Conscious Mind, Oxford University Press.
C RICK, F. and KOCH , C. (1995) Are we aware of neural activity in primary visual cortex?, Nature, 375, 121–123.
C RICK, F. and KOCH , C. (1998) Consciousness and neuroscience, Cereb. Cortex, 8, 97–107.
C RICK, F. and KOCH , C. (2003) A framework for consciousness, Nat. Neurosci., 6, 119–126.
E INSTEIN , A., PODOLSKY , B. and R OSEN, N. (1935) Can quantum-mechanical description of physical reality beconsidered complete?, Phys. Rev., 47, 777–780.
F OX, R. and HERRMANN J. (1967) Stochastic properties of binocular rivalry alternation, Percep. Psychophys.,2, 432–436.
GRUSH , R. and CHURCHLAND , P. S. (1995) Gaps in Penrose’s toilings, J. Consciousness Studies, 2(1), 10–29.
HAMEROFF , S. R. (1994) Quantum coherence in microtubules: A neural basis for emergent consciousness?, J.
Consciousness Studies, 1(1), 91–118.
HAMEROFF , S. R. and PENROSE , R. (1995) Orchestrated reduction of quantum coherence in brain microtubules:
A model for consciousness, Neural Network World, 5(5), 793–804.
J IBU , M. and YASUE, K. (1995) Quantum Brain Dynamics and Consciousness, John Benjamins.
KANIZSA , G. (1976) Subjective contours, Sci Am. Apr., 234(4), 48–52.
KOLB , B. and WISHAW , I. Q. (1985) Fundamentals of Human Neuropsychology, 2nd Ed., Freeman, New York.
KOVACS , I., PAPATHOMAS , V., Y ANG, M. and FEHER, A. (1996) When the brain changes its mind: interoculargrouping during binocular rivalry, Proc. Natl. Acad. Sci. USA, 93, 15508–15511.
L AMME , V. A. (1995) The neurophysiology of figure-ground segregation in primary visual cortex, J. Neurosci.,
15, 1605–1615.
L EE, S. H. and B LAKE, R. (2002) V1 activity is reduced during binocular rivalry, J. VIS., 2(9), 618–626.
L EOPOLD, D. A. and L OGOTHETIS, N. K. (1996) Activity changes in early visual cortex reflect monkeys’ percepts
during binocular rivalry, Nature, 379, 549–553.
L EVELT , W. J. (1967) Note on the distribution of dominance times in bonicular rivalry, Bri. J. Psychol., 58, 143–
145.
L OGOTHETIS, N. K. and SCHALL , J. D. (1989) Neuronal correlates of subjective visual perception, Science, 245,
761–763.
L OGOTHETIS, N. K., L EOPOLD, D. A. and SHEINBERG , D. L. (1996) What is rivalling during binocular rivalry?,
Nature, 380, 621–624.
M OGI, K. (1999) Response selectivity, neuron doctrine, and Mach’s principle, in Understanding Representationin the Cognitive Sciences (eds. A. Riegler and M. Peschl), pp. 127–134, Plenum Press, New York.

The Variant and Invariant in Perception

37

M URATA, T., M ATSUI, N., M IYAUCHI, S., KAKITA , Y. and YANAGIDA , T. (2003) Discrete stochastic process
underlying perceptual rivalry, Neuroreport, 14(10), 1347–1352.
NERI , P., MORRONE, M. C. and B URR, D. C. (1998) Seeing biological motion, Nature, 395, 894–896.
NEWSOME , W. T. and PARE, E. B. (1988) A selective impairment of motion perception following lesions of the
middle temporal visual area (MT), J. Neurosci., 8(6), 2201–2211.
OOI , T. L. and HE , Z. J. (1999) Binocular rivalry and visual awareness: the role of attention, Perception, 28, 551–
574.
P ENROSE, R. (1989) The Emperor’s New Mind, Oxford University Press.
P OLONSKY, A., B LAKE, R., B RAUN, J. and HEEGER , D. (2000) Neuronal activity in human primary visual cortex
correlates with perception during binocular rivalry, Nature Neurosci., 3, 1153–1159.
T EGMARK, M. (2000) The importance of quantum decoherence in brain processes, Physical Review E, 61, 4194–
4200.
T ONG , F. and ENGEL, S. (2001) Interocular rivalry revealed in the cortical blind-spot representation, Nature, 411,
195–199.
T ONG , F., NAKAYAMA , K., VAUGHAN, J. T. and KANWISHER , N. (1998) Binocular rivalry and visual awarenessin human extrastriate cortex, Neuron, 21, 753–759.
T ONONI , G., SRINVVASAN, R., R USSELL, D. P. and E DELMAN, G. M. (1998) Investigating neural correlates ofconscious perception by frequency-tagged neuromagnetic responses, Proc. Natl. Acad. Sci. USA, 95, 3198–
3201.
T REISMAN , A. (1996) The binding problem, Current Opinion in Neurobiology, 6, 171–178.
W ALKER , G. A., O HZAWA, I. and F REEMAN, R. D. (2000) Suppression outside the classical cortical receptive
field, VIS. Neurosci., 17, 369–379.
W ALKER , P. (1975) Stochastic properties of binocular rivalry alternations, Percept. Psychophys., 18, 467–473.
W EISKRANTZ , L. (1997) Consciousness Lost and Found, Oxford University Press.
W ILSON, H. R., B LAKE, R. and LEE, S. H. (2001) Dynamics of travelling waves in visual perception, Nature, 412,
907–910.