1. Self-Representation in Nervous Systems
Author(s): Patricia S. Churchland
Source: Science, New Series, Vol. 296, No. 5566 (Apr. 12, 2002), pp. 308-310
Published by: American Association for the Advancement of Science
Stable URL: http://www.jstor.org/stable/3076513
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2. REFLECTIONS ON SELF: IMMUNITY AND BEYOND
been noted by immunologistsgrapplingwith has undergonefrequentgene duplicationsand J. B. Nasrallah,Proc. Natl. Acad. Sci. U.SA. 88, 8816
the origin of adaptiveimmunity(1, 31), are a deletions during its evolution (33), and the (1991).
14. S. Takayamaet al., Proc. Natl. Acad. Sci. U.SA. 97,
consequenceof similarselective pressuresfor mating-type locus of Chlamydomonascon- 1920 (2000).
diversification co-evolutionof recognition
and tains a highly rearrangedregion that causes 15. S.-H. Shiu, A. B. Bleecker,Proc. Natl. Acad. Sci. U.SA.
functionsto retainaffinitybetween interaction suppressionof recombination over a 1-mega- 98, 10763 (2001).
16. A. L.Hughes, Cell. Mol. LifeSci. 56, 94 (1999).
partners. base chromosomalregion (36). 17. V. Vanoosthuyse, C. Miege, C. Dumas, J. M. Cock,
A hallmarkof these specific recognition Thus, in many respects, the challenges Plant Mol. Biol. 46, 17 (2001).
systems is that their genes are subject to facing researchin the crucifer SI system are 18. J. B. Nasrallah,Curr.Opin. Plant Biol. 3, 368 (2000).
19. J.-L.Giranton,C. Dumas, J. M. Cock, T. Gaude, Proc.
intense diversifyingselection. Largenumbers similar to those facing researchersof other Natl. Acad. Sci. U.SA. 97, 3759 (2000).
of alleles are commonly found, and extraor- recognition systems. Comparisons of these 20. D. Cabrillac, M. Cock, C. Dumas, T. Gaude, Nature
J.
dinarilyhigh levels of intraspecificpolymor- different systems should lead to insight into 410, 220 (2001).
21. S. L.Stone, M.Arnoldo,D. R.Goring,Science 26, 1729
phism are typically achieved, in some cases common selective pressures that drive the
(1999).
resulting from acceleratedrates of evolution diversification and co-evolution of self/non- 22. C. Azevedo, M.J. Santos-Rosa,K.Shirasu,TrendsPlant
(18, 32). Due to balancing selection, poly- self recognitiongenes and shape the structure Sci. 6, 354 (2001).
23. T. Nishio, M. Kusaba,Ann. Bot. 85 (Suppl. A), 141
morphismsin these genes can persist for long of their controlling loci.
(2000).
periods of time and often predate species 24. M. Watanabe et al., FEBS Lett. 473, 139 (2000).
diversification.Trans-speciespolymorphisms References and Notes 25. K. Hatakeyamaet al., PlantJ. 26, 69 (2001).
1. F. M. Burnet,Nature 232, 230 (1971). 26. M.Kusaba, C.-W.Tung,M.E.Nasrallah, B. Nasrallah,
J.
have been describedin the MHC (33) and in 2. D. De Nettancourt, Incompatibility Incongruity
and in Plant Physiol.128, 17 (2002).
SI systems (34), and in both cases, diver- Wild and Cultivated Plants (Springer-Verlag, Berlin, 27. M. K. Uyenoyama, Y. Zhang, E. Newbigin, Genetics
gence of some allelic lineages appears to 2001). 157, 1805 (2001).
3. J.J. Rudd, E.Franklin-Tong, Phytol.151, 7 (2001).
V. New 28. D. P. Matton et al., Plant Cell 11, 2087 (1999).
have occurredat least 20 million years ago. 4. K. Ida et al.,J. Mol. Biol. 314, 103 (2001). 29. D. Charlesworth,Curr.Biol. 10, R184 (2000).
Another emerging commonality between 5. I.S. Nou, M.Watanabe,A. Isogai,K.Hinata,Sex. Plant 30. A.J. Brown, A. Casselton,
L Trends Genet.17, 393 (2001).
recognitionloci is their structural
heteromor- Reprod.6, 79 (1993). 31. J. Klein,Natural Historyof the MajorHistocompati-
phism, which apparentlyreduces intralocus 6. C. R.Schopfer,M. E.Nasrallah,J. B. Nasrallah,Science bility Complex (Wiley, New York,1986).
286, 1697 (1999). 32. P. J. Ferris,C. Pavlovic,S. Fabry,U. W. Goodenough,
recombination events and preventsdisruption 7. H. Shiba et al., Plant Physiol. 125, 2095 (2001). Proc. Natl. Acad. Sci. U.S.A.94, 8634 (1997).
of the co-adaptedgene complex. The crucifer 8. T. Takasakiet al., Nature 403, 913 (2000). 33. J. Klein,A. Sato, S. Nagl, C. O'hUigin,Annu.Rev.Ecol.
S locus has been extensively restructured by 9. Y. Cui, Y.-M. Bi, N. Brugiere, M. Arnoldo, S. J. Syst. 29, 1 (1998).
Rothstein, Proc. Natl. Acad. Sci. U.S.A. 97, 3713 34. M. Uyenoyama, Genetics 139, 975 (1995).
expansion or contractionof the physical dis- (2000). 35. D. C. Boyes, M. E. Nasrallah,J. Vrebalov,J. B. Nasral-
tance between SRK and SCR, gene duplica- 10. A. P. Kachroo,C. R. Schopfer, M. E. Nasrallah,J. B. lah, Plant Cell 9, 237 (1997).
tion, as well as rearrangement these two
of Nasrallah,Science 293, 1824 (2001). 36. P. J. Ferris,E. V. Armbrust,U. W. Goodenough, Ge-
11. S. Takayamaet al., Nature 413, 534 (2001). netics 160, 181 (2002).
genes relative to each other and to flanking 12. M. Kusabaet al., Plant Cell 13, 627 (2001). 37. J. B. Nasrallah,data not shown.
markers(Fig. 1) (18, 35). Similarly,the MHC 13. J. C. Stein, B. Howlett, D. C. Boyes, M. E. Nasrallah, 38. Supportedby grants from the NIH, NSF,and USDA.
in Nervous
Self-Representation Systems
Patricia S. Churchland*
The brain's earliest self-representationalcapacities arose as evolution To identifythe phenomenonthat we want
and
found neuralnetworksolutions for coordinating regulatinginner-body explained,it is useful to startwith the idea that
signals, thereby improvingbehavioralstrategies. Additionalflexibility in one's self-concept a set of organizational
is tools
organizingcoherent behavioraloptions emerges from neuralmodels that for "coherencing" brain'splans, decisions,
the
represent some of the brain's inner states as states of its body, while and perceptions. Thus, if a brick falls on my
representingother signals as perceptions of the external world. Brains foot, I know the pain is mine. I know without
manipulate inner models to predict the distinct consequences in the pausingto figure it out that "this body is my
externalworldof distinct behavioral options. The self thus turns out to be own,"andthata decisionto fightrather thanflee
identifiablenot with a nonphysicalsoul, but ratherwith a set of repre- is a decision affectingmy body's painful en-
sentational capacities of the physicalbrain. counterwith the body of another.If I scold
myself aboutjaywalking,I know that it is me
What Is "the Self"? functions generally, including conscious talkingto myself. We know that if we fail to
Descartes proposed that the self is not iden- thoughtssuch as "I exist,"are activitiesof the plan for futurecontingencies, futureselves
our
tical with one's body, or indeed, with any physicalbrain(1, 2); (ii) aspectsof self-regula- may suffer,and we care now aboutthat future
physical thing. Instead,he famously conclud- tion (e.g., inhibitingsexual inclinations),and self. Sometimeswe use "myself"to mean"'my
ed that the essential self-the self one means self-cognition(e.g., knowing where I stand in body,"as when we say "I weighedmyself."By
when one thinks, "I exist"-is a nonphysical, my clan's dominancehierarchy), may be non- contrast,when we say "I deceivedmyself,"we
consciousthing. At this stage of scientificde- conscious(3); and (iii) as the Scottishphiloso- arenot referring ourphysicalbodies.We talk
to
velopment,the Cartesianapproachis unsatis- pher David Hume (1711-1776) realized,there of our social and our privateselves, of discov-
factory for three reasons: (i) psychological is in any case no introspective of
experience the ering and realizing ourselves, of self-control,
"self" as a distinctthing apartfrom the body self-improvement, self-denial(5).
and
Philosophy Department0119, Universityof Califor- (4). Introspection,Hume concluded, reveals Thisremarkably diverserangeof uses of the
nia, San Diego, LaJolla,CA92093, USA. only a continuouslychanging flux of visual self-concept motivates recasting
problems about
*To whom correspondence should be addressed.E- perceptions,sounds, smells, emotions,memo- "the self" in terms of self-representational ca-
mail pschurchland@ucsd.edu ries, thoughts,feelings of fatigue,and so forth. pacitiesof thebrain.Doing so deflatesthe temp-
308 12 APRIL
2002 VOL296 SCIENCEwww.sciencemag.org

3. REFLECTIONS ON SELF: IMMUNITY AND BEYOND
tationto thinkof the self as a singular entityand hemisphereare disconnectedfromthose of its musculoskeletal structures the somaticsen-
via
encouragesthe idea that self-representing in- counterparthemisphere (21). This implied sory system; representing autobiographical
volves a pluralityof functions,each having a that the "unity of self," advertisedby some events via medialtemporallobe structures; de-
rangeof shades,levels, and degrees.Further, it philosophersas a "transcendental" necessity, ferring and
gratification controlling impulsesvia
broadensthe inquirybeyond humansto other was actually subjectto anatomicalmanipula- prefrontal andlimbicstructures; repre-
lobe and
species,suggestingthatvaryinglevels of coher- tion. The results implied that such unity and sentingthe sequenceof actionsto take next, as
encing operatein all nervous systems of any coherence as exist in one's self-conception well as representing where one is in space-time
significantcomplexity.The reformulation also depend not on transcendental necessity, andthe social order.
sets the stage for designingexperiments de- to whatever that might be, but on neuronal or- Studiesof humanpatientsreflectthe multi-
terminemore preciselythe types of self-repre- ganization. A recharacterization the phe-
of of
dimensionality self-representation show- by
sentations nervoussystemshave, how they are nomenonof unity of the self was consequent- ing thatparticular functionscan be spared when
connected one another, the nature their
to and of ly occasioned by the new empirical data. othersare impaired. example,a subclassof
For
neuralsubstrates (6). A standard principle, illustrated by the amnesic subjects with bilaterallesions in the
The expectation the brainandbehavior-
that split-brainresults, is that the definition of the hippocampal associatedcorticalstructures
and
al scienceswill eventually understand nature
the phenomenonto be explained coevolves with areunableto acquirenew knowledgeandhave
of self-representational capacitiesis not univer- experimentaldiscoveries. In the early stages lost essentially all autobiographical informa-
sally shared. Traditionalists prefer hive off the
to of the scientific attackon any problem,accu- tion. For example,the patientR.B. lives essen-
fundamental questions about the self or con- rate definition of the phenomenon is ham- tially within a moving 40-s time bin (3). Al-
sciousness as philosophicalin the "armchair- pered precisely because not enough is known thoughR.B. does sufferdiminishedself-under-
only"or "forever-beyond-science" senses of the to permitan accuratedefinition.A pragmatic standing, nevertheless
he retainsmanyelements
term (7). The dominantideology in academic strategy is to begin by studying those cases of normalself capacities,includingself-control
philosophy, functionalism,acknowledges the agreed to be obvious examples of the phe- in social situationsand the fluent and correct
relevance of the behavioralsciences, but dis- nomenon. Powered by this agreement,provi- use of "I." He also knows his currentbody
countsthe neurosciences largelyirrelevant
as to sional, rough characterizations can leverage configuration status,and he can engage in
and
making progress in understanding higher the the science's first stages, with refinementsin self-imagery,identify feelings such as happi-
functions (8). The functionalistrationalede- the phenomenon'sdefinition emerging as the ness, and show sympathywith the distressof
pends on an allegedly close analogy between surroundingfacts become clear. From a his- others. The existence of such amnesics is a
psychologicalprocesses and runningsoftware torical perspective, the interdependenceof to
counterexample the seemingly obvious hy-
on a computer.Accordingto the analogy,the definition and discovery typifies the transfor- pothesisthatone's self is constituted person-
by
brainis only the hardware which the cogni-
on mation of assorted problems of what was al narrative (9).
tive softwarehappensto run (9). The brainis originally "pure"philosophy (e.g., the nature Schizophrenia, known to involve decreased
thus deemeda mereimplementation the soft-
of of fire, space, matter, life, the cosmos) into prefrontal activityand increased striatal
activity
ware. The corollaryis that understanding the problems of the experimentalsciences (2, 6). (23), presentsa different dimensionof self-dys-
hardware therefore
is unimportant, andlarge,
by function. Duringa floridepisode,a schizophren-
in figuring the software.
out Thoughthe analogy Self-Representational Capacities ic mayhavegood autobiographical memory,but
between cognitive functionsand runningsoft- In the brain, some networksare involved in sufferdeep confusionaboutself/nonselfbound-
ware is not close but feeble, and though the representing things in the externalworld, such aries, e.g., respondingto a tactile stimulusby
corollaryfails to follow, functionalism retains as the face of GrouchoMarxor a loomingbus. claimingthatthe sensationbelongsto someone
considerable popularity beyond the bordersof Other networksrepresentstates of the body, else or thatit exists somewhereoutsideof him.
neuroscience (10). such as its postureor its need for water.Some Auditoryhallucinations, often considereddiag-
Mysticismand functionalism notwithstand- networks operate on other representations, nostic of schizophrenia, exemplify integrative
ing, questions about self-representation are yielding meta-representations as knowing
such failure.The "voices"appearto be the patients'
steadily shiftinginto the provinceof the brain that my need to flee is more urgentthan my own thoughtsor innerspeech,but they are not
and cognitive sciences. This shift is part of a need for water,knowingthatJohndislikesme, and
represented, thus not recognized,as such
generaltrendenabledby the scientificadvances or remembering John hit me. Neural net-
that (24, 25). The anestheticketamine and drugs
in the 20th centuryat all levels of brainorgani- works engagedin integrating such meta-repre- such as LSD can triggersimilarphenomena.
zationfromsynapsesto systems.Theseadvanc- sentations probably ones mostrelevant
are the to A patient with lesions in right parietal
es, alongwith improvements technology,
in data questionsaboutself-representation. cortex, resulting in loss of sensation and
analysis, and computationalmodeling, have Self-representations be widely distrib-
may movement on the left side of the body, may
meant that virtuallyall topics concerningthe utedacrossbrainstructures, coordinated on
only firmlydeny thather left limbs are in fact hers.
mind are now vigorouslyexploredat the inter- an "as-needed" basis, and arranged a loose
in On occasion, a patient with limb denial will
face of neuroscience, cognitivescience,andphi- and loopy hierarchy.We see the slow emer- use the normal right arm to try to throw the
losophy.Thishas been the fortune, example,
for gence and elaborationof self-representational paralyzedleft leg out of the bed, insisting it is
of colorperception (11), autobiographical mem- in
capacities children (22), andthe tragicfading alien. Despite suffering compromised body-
ory (12, 13), the emotions(3, 14-16), decision- of these capacitiesin patientswith dementia. the
representation, patients may nevertheless
making(3, 12, 14, 17, 18), sleep and dreaming Despite largegaps in ourknowledge,humanas have normal autobiographical memory as
(19), and consciousness(6, 12, 15, 20). well as animalstudieshave made it possibleto well as other self-representationalfunctions
As in any science, some discoveries force begin to distinguish differenttypes of self-rep- such as knowing whether they feel bored or
a more enlightened articulationof the very resentational functions,and in some instances, hungry. Patients with lesions in the anterior
questions themselves. For example, the split- to identify,albeit in generalterms,theirneural cingulate region may exhibit alien hand syn-
brain studies revealed that interrupting infor- dependencies. drome.In these cases, the contralesionalhand
mation flow between the two hemispheresby Self-representational capacitiesincluderep- will sometimes behave as though it is inde-
surgical section of the cerebralcommissures resenting the internalmilieu and viscera via pendentlycontrolled.Patientswith alien hand
gives rise to striking disconnection effects; chemicaland neuralpathwaysaimedlargelyat syndromesometimes controltheir embarrass-
that is, the perceptions and decisions of one the brainstemand hypothalamus; representing ing alien hand with verbal commands.
www.sciencemag.org SCIENCE VOL296 12 APRIL
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4. REFLECTIONS ON SELF: IMMUNITY AND BEYOND
Self-regulatingfunctions can also be se- answer to this question: What motor com- ordinate female but not the dominant male.
lectively impaired.Lesions in prefrontalcor- mand should be issued to get my arm to Infant human development studies and non-
tex, especially in the ventromedial region, contact the plum? Taking the command-pro- human primate studies support these hy-
have been followed by significantchanges in posal, the forwardmodel calculates the error potheses (28, 29).
self-control, and particularlyin the capacity by runningthe command on a neuronalem- Whetherneuroscience can build on these
to inhibit unwise impulses, despite normal ulator,and the inverse model respondsto the foundationsto discover full and detailed ex-
functioning of many other self-representa- errorsignal with an upgradedcommand.Em- planations of all self-representationalphe-
tional capacities. Personality changes com- ulation is faster and safer than real-world nomena remains to be seen. Still, unpredict-
monly occur with prefrontaldamage. Hither- feedback. Assuming the forwardand inverse ability obscures the destiny of essentially all
to quiet and self-controlled, a person with models are also capable of learning, this or- neurobiologicalpuzzles, includingnoncogni-
lesions in the ventromedialregion of frontal ganizationcan be very efficient in acquiringa tive functions such as thermoregulation. An
cortex is apt to be more reckless in decision- wide range of sensorimotorskills. With suf- abiding challenge in neuroscience is to dis-
making, impairedin impulse control, and so- ficient access to background knowledge, goal cover the basic principlesgoverningthe inte-
cially insensitive (3, 17, 18). priorities, and current sensory information, gration of information at various levels of
emulatorscan compute accuratesolutions to brainorganizationand at various time scales.
Evolutionof Self-Representational complex motor problems. This challenge is not confined to the neuro-
Capacities Rudimentary neuronalemulators,ground- science of self-representation, but confronts
The most fundamental the self-representa- ed in the basic coordinatingand self-regulat-
of neuroscience generally.
tional capacitiesprobablyarose as evolution ing functions,can in turnbe upgradedto yield
stumbledon solutions for coordinating inner- fancier inner models of planning. Emulators References and Notes
body signals to generate survival-appropriate can facilitate making an appropriatemove- 1. P. M. Churchland,Matter and Consciousness (MIT
Press,Cambridge,MA,ed. 2, 1988).
innerregulation. The basic coordination prob- ment after the target has become invisible, 2. P. S. Churchland, Neurophilosophy(MITPress, Cam-
lems for all animalsderivefromthe problemof perhapsbecause the prey is in a cavity or the bridge, MA, 1986).
whatto do next. Pain signalsshouldbe coordi- predator is sneaking up on the prey. More 3. A. R. Damasio, Descartes' Error (Grossett/Putnam,
New York,1994).
nated with withdrawal,not with approach. generally, with appropriateconnectivity, an 4. D. Hume,A Treatiseof HumanNature (1739); modern
with
Thirstsignalsshouldbe coordinated water- emulator could run off-line to plan for the edition by L. A. Selby-Bigge, Ed. (Clarendon Press,
seeking,not with fleeing,unlessa present threat long-term future, thus deploying extended Oxford, 1888).
functions and body-image manipulation.Additional modi- 5. G. Lakoff,M. Johnson, Philosophyin the Flesh (Basic
takeshigherpriority. Homeostatic
Books, New York,1999).
the abilityto switchbetweenthe different inter- fication permits off-line emulation of cogni- 6. P. S. Churchland, Brain-Wise: Studiesin Neurophiloso-
nal configuration fight and flight from that tive states. For example, when planning the
for phy (MITPress, Cambridge,MA,in press).
needed for rest and digest requirecoordinated details of a raid, one may imagine oneself in
7. See the essays by Z. Vendlerand by C. McGinn, The
Mind-BodyProblem:A Guide to the CurrentDebate,
controlof heart,lungs, viscera,liver, and adre- feeling anxiety while stalking the enemy R. Warner,T. Szubka,Eds. (Blackwell,Oxford, 1994).
nal medulla.Body-statesignalshave to be inte- camp, assessing the attentivenessof the camp 8. J. A. Fodor,Synthese28, 97 (1974). Forcriticism this
of
grated, options evaluated,and choices made, guards,formulatingspecific intentionsto out- view, see P. S. Churchland, J. Sejnowski, Compu-
T. The
tationalBrain(MIT Press,Cambridge, 1992).
MA,
since the organismneeds to act as a coherent fox wary guards,and so on. Like body-image 9. D. C. Dennett, ConsciousnessExplained(LittleBrown,
whole, not as a group of independent systems manipulation used in planninga climb, this is Boston, 1991).
with competinginterests. mind-imagemanipulationused in planninga 10. S. Pinker,How the Mind Works(Norton, New York,
1997).
complex, extended me-them encounter(27). 11. S. E. Palmer, Vision Science (MITPress, Cambridge,
The Neural Platform MA, 1999).
The most basic level of innercoordination and Consciousness and 12. A. R. Damasio, The Feeling of What Happens (Har-
Self-Representation court Brace,New York,1999).
regulationoccurs in the brainstem,anchoring 13. L. R. Squire, E. R. Kandel, Memory: From Mind to
whatDamasiorefersto as "theprotoself"(12). An appealing hypothesis defended by Molecules (Freeman,New York,1999).
In vertebrates, brainstem-hypothalamic
the axis Damasio (12) is that the self/nonself distinc- 14. J. Le Doux, The EmotionalBrain(Simon & Schuster,
New York,1996).
is the site of convergenceof signals from the tion, though originally designed to support 15. R. R. Llinas, of the Vortex(MIT
I Press,Cambridge,MA
viscera,internal milieu,andthe somaticsensory coherencing, is ultimately responsible for 2001).
system.Also locatedin the brainstem nuclei
are consciousness. According to this view, a 16. J. Panksepp, Affective Neuroscience (Oxford Univ.
thatregulatevital functions,sleep-wakefulness brain whose wiring enables it to distinguish Press, New York,1998).
17. S. W. Anderson al., NatureNeurosci.2, 1032 (1999).
et
cycles, arousal, attention,and the emotions. between inner-worldrepresentations out-
and 18. A. Becharaet al., Science 275, 1293 (1997).
This level of integration,sharedacross many er-worldrepresentations to build a meta-
and 19. A. R. Hobson, Sleep (Freeman,New York,1989).
20. F. Crick, C. Koch, in Problems in Systems Neuro-
species, is the nonconscious neurobiological representationalmodel of the relation be-
science, J. L.van Hemmen, T. J. Sejnowski,Eds. (Ox-
platform higherlevels of self-representation.
for tween outer and inner entities is a brain ford Univ. Press, Oxford, in press).
Other, more complicatedand flexible as- enjoying some degree of consciousness. 21. R. W. Sperry,Science 217, 1223 (1982).
pects of the self demandgreatercomputational Thus, such a system could representthe rela- 22. S. Harter,The Constructionof the Self: A Develop-
mental Perspective (Guilford,New York,1999).
resources.Wolpert(26) and Grush(27) have tion between the thistle and itself as "that 23. A. Meyer-Lindenberg al., Nature Neurosci. 5, 267
et
proposedthat increasedaccuracyin planning (outer) thing causes me (inner) pain." Con- (2002).
and execution of movement in space-timeis ceivably, as wiring modifications enable in- 24. C. D. Frith.TheCognitiveNeuroscienceof Schizophre-
nia (Eribaum, Hillsdale,NJ, 1992).
achieved by cortical models of the body in creasinglysophisticatedsimulationand delib- 25. G. L.Stephens, G. Graham,WhenSelf-Consciousness
relationto its environment. Roughly, a some- eration, the self-representationalapparatus Breaks(MITPress,Cambridge,MA,2000).
what sloppy inversemodel is connectedto an becomes correspondingly more elaborate, 26. D. M. Wolpert et al., Science 269, 1880 (1995).
27. R. Grush,Philos. Psychol. 10, 5 (1997).
error-predicting forwardmodel, and the two and therewith the self/not-self apparatus. 28. A. N. Schore,Affect Regulationand the Originof the
convergeon a good answerto the problemof On this hypothesis, the degrees or levels of Self (Eribaum, Hillsdale,NJ, 1994).
how to move a many-limbed body in just the conscious awareness are upgraded in tan- 29. M.Tomasello,J. Call,PrimateCognition(OxfordUniv.
dem with the self-representational up- Press, New York,1997).
rightway at just the righttime. M.
30. Specialthanks to P. M. Churchland, Churchland, A.
If, for example, the goal is to reach a grades. Thus, chimpanzees, but not frogs, Churchland, Cohen, F. Crick,A. Damasio, D. Eagle-
J.
plum, the inverse model gives a first-pass know whether they can be seen by a sub- man, and R. Grush.
310 12 APRIL
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