Modeling, Localization and the Explanation of ... - Steven W. Horst

Modeling, Localization and the Explanation of Phenomenal Properties: Philosophy and the Cognitive Sciences at the Beginning of the Millennium Author(s): Steven Horst Source: Synthese, Vol. 147, No. 3, Neuroscience and Its Philosophy (Dec., 2005), pp. 477-513 Published by: Springer Stable URL: http://www.jstor.org/stable/20118671 Accessed: 03/11/2009 16:11 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=springer. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].

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STEVEN HORST

LOCALIZATION AND THE EXPLANATION MODELING, OF PHENOMENAL PROPERTIES: PHILOSOPHY AND THE COGNITIVE SCIENCES AT THE BEGINNING OF THE MILLENNIUM

Case

ABSTRACT. human nitive

sciences.

philosophy not

in the psychophysics,

studies

are

vision

presented These studies

of mind:

as

an

also

example yield

the explanatory

of

important

and

modeling

"hands-on" results

of

localization of

philosophy for familiar

the

cog in

problems

gap surrounding phenomenological

feels is

to of investigations the science is able However, by the kinds surveyed. some as sorts the of such human color facts, space explain phenomenological why or why takes the form is a phenomenologically of the Munsell color there solid, a phenomenologically-pure but not pure orange. yellow closed

1. INTRODUCTION:

Future allels

historians between

philosophers ing of new tury, upon were upon form

the

PHILOSOPHY OF COGNITION THE MILLENIUM of philosophy 20th century

were much

engaged

scientific

the most deduction

may and with

developments. influential philosophical and

AT THE TURN

OF

see important very well par the 17th.1 In both centuries, the philosophical At the midpoint view

of

science

understand of

each

cen

was modeled

in logic or mathematics; and there no measure in small motivated ambitions, of all knowledge in the for a unification

construction

grand philosophical a prioristic grounds,

of something like a single axiomatic-deductive system. And were on two the end of the these ambitions century, challenged by as a in of in result of) actual sci fronts, part (and important spite entific

progress.

20th

century

their

apparent distinctive

most

semantic

On

the one

17th century and rationalist hand, both models of for science became problematic positivist as to incorporate unsuitedness the things we count about

normativity.

ourselves: And

on

consciousness, the other hand,

freedom, moral actual scientific

and pro

gress often took forms that looked significantly unlike the kind of Synthese (2005) 147: 477-513 DOI 10.1007/s 11229-005-8365-5

?

Springer 2005

STEVEN HORST

478

or by Car and Hobbbes, system envisioned by Descartes and In the 17th and the late into nap 18th, Newton's century Nagel. overthrow of contact mechanism remark and his cryptic "hypothe deductive

ses non jingo" on the question of the nature to an even broader led many of his admirers tionist

of a view

in favor

program

laws

trail

blazed

in concentrating found strategies comparatively to force them

by

of

the history

force gravitational of the reduc rejection

of science

that describe

that concentrated upon the phenomena and are use causes. In for hidden seeking

quantitative finding and control without ful for prediction the late 20th century, "naturalistic" philosophers the

of

upon describing in a number of

of

science

movement

science the actual

followed

in the

1960s

of

variety explanatory a number of sciences, particularly recent entries in the life sciences, rather than trying into a preconceived framework from logic imported

and mathematics. We "decade

are now of

as in a period that has variously been heralded or of neuroscience". While the brain" writers "century

the as

to become friend John Locke "Newtons aspired early as Newton's a of mind Newtonian of the mind" science upon by producing prin can seriously it is really only much more that anyone recently ciples, even the beginnings to successfully of such laying down lay claim a project. of cognition have recently made The sciences rapid gains a and number the of fronts: functional anatomy along physiology with like the study of brains of the brain, beginning investigations in the 19th century and up through of trauma patients by Broca of neu the more studies modern fine-grained imaging techniques; at both roanatomy, and of the connections

the

function and anatomy, single-cell networks of cells; the collection and from the of psychophysical data stemming level

rigorous systematization works and Fechner; of Weber and computational mathematical an exaggeration and damental

to say

unifying is credited with

of

between

and

the development

of

specialized It would be

modeling techniques. has yet made the kinds of fun that anyone in the that sciences cognitive breakthroughs

at least be at in mechanics. But we might a point in with that of and celestial mechanics physics comparable the early 17th century. an exciting and a trying time to be a It is, as a result, both It is trying and excit of mind/psychology/neuroscience. philosopher

Newton

to keep up of the daunting task of trying ing, not only because new and brain, but also discoveries about mind of with the wealth because

the

explosion

of

knowledge

in

the

sciences

of

cognition

PHILOSOPHY AND THE COGNITIVE SCIENCES raises

nature

the very

about

questions

of

479

the philosopher's

in

role

the mind.

understanding One question

that looms of large is that of how the philosophy the cognitive sciences should be in dialog with the actual sciences on the one hand, and with more and main themselves traditional stream in and epistemology metaphysics, philosophical problems own view is like Levine's gap on the other. My (1983) explanatory

every effort to be in significant dialog with both. to it is be hand, important guided by our best under mind of what of and brain actually look like, standing explanations such as that they should and not by some armchair look notion, we in an axiomatic like mathematical deductions Moreover, system. that

it should make

the one

On

to developments in philosophy elsewhere of sci or are to of the sciences similar differ cognition such as physics, and biology. But sciences chemistry

be attentive

should ence

to see how

ent

from

on

the other

other

are comparatively the cognitive sciences hand, young The dominant with immature. para physics, compared quite an I was in the space of years or decades. (When changes

and, digm

there was

no support available for research in to for So will need modeling, example.) philosophers take a long-term rather than assume that the latest big perspective news will have lasting we status. Moreover, until proven otherwise,

undergraduate, neural network

would

do well

as Descartes'

to think "real

almost

that

such long-lived philosophical problems, between mind and body, Levine's "hard problem and Chalmers' of consciousness", distinction"

"explanatory gap" have some real and

may

2. THREE APPROACHES

Clark

has

Glymour

(1998) Mind

intellectual

lasting

TO THE PHILOSOPHY COGNITION in a

out,

pointed

in a Physical World, to

tend

chology/neuroscience

bite.

review

OF MIND

of

into

two

camps.

of mind/psy One

which he locates Kim's book) prefers to treatmetaphysical about

the mind

in isolation

(to which he himself psychology/neuroscience

from

around

sciences

as

a

kind

of

running

of

cognition. between Kim's

there is in fact a kind of division what

group

of mind.

subscribes) approaches philosophy

the sciences upon, commentary wide of attitudes spectrum lying

practice

the

of problems

they

are

Kim's

Jaegwon

that philosophers

fall

AND

camp

(in

problems The

other

of mind/ and

with, there

is a

and Glymour's,

in

dialog While

among philosophers

interested

in addressing.

480

STEVEN HORST

some are interested Chalmers' in "the (1996) Using terminology, of consciousness: hard problems" and metaphysical issues epistemic are about whether like consciousness and phenomena intentionality are states. brain Others interested upon metaphysically supervenient in what Chalmers calls the "easy problems" of course Chal which mers are not easy except by comparison himself admits that are more

continuous

ences,

in the

easily

lead

with of

spirit to a stark

empirical "naturalistic"

and

theoretical

in

work of

science.

the This

sci can

philosophy neu the natural sciences, including a can us tell the about roscience, great deal perhaps everything structure and function of mind and brain, but can tell us nothing of experience. about the phenomenological Some empiri properties conclusion:

cally minded philosophers happy

explanatory explanation are already quite

scientists are

to embrace

and treat questions this conclusion, about phe as uninteresting, or even illu irrelevant, philosophical to to the be inclined attitude: view the may opposite

nomenology sions. Others

We

and philosophically minded

that can be cured by gap itself as an illusion even explanations in the cognitive sciences, perhaps at hand.

might

problematize

these

attitudes

by making

actual that

two questions

explicit:

we look at actual case studies in the explanation of men (1) When a for example tal states having phenomenology seeing colors, or disconfirm the philosophical do these explanations confirm and abiding intuition that there is a principled explanatory gap? after explanation, does this entail the con (2) If such a gap remains can about phenomenol that the sciences clusion nothing explain ogy at all? In this article, dle, as it were. ful

explanations

phenomenology, of explanatory

a way of playing I hope to model it down the mid some The sciences of cognition very power yield of features of cognition, including features of its but they do so in spite of leaving exactly the sort gaps

that have

been

claimed

To motivate

on this

the basis

of philo and to

conclusion, sophical thought-experiments. can help us in real explanations of the mind how case studies model an over see such issues more I will give clearly, introductory-level area: in one sample the study of view of some fairly basic work in of this, I color vision humans. On the basis vision, particularly what is explained kind of and will ask just what explana thereby, In this case, there are actually tion is given. extremely impressive

481

PHILOSOPHY AND THE COGNITIVE SCIENCES and

robust

explanations in early employed

cells

of

data

by properties some of of which

psychophysical out

visual

of the

processing, data simply "falls out". On the other "shape" of the psychophysical to talk about in a comparable hand, we are not position exactly on further is going down the neural that process what pathways I shall illustrate to the area of color this with information. respect

seems to be particularly called V4, which impli cor to but it could be made with other vision, respect are we to tical areas as well. Nor, more able fundamentally, explain or character the presence of visual qualia. There really does seem to be a robust explanatory it was argued on philosoph gap just where the visual

cortex

in color

cated

seems to reinforce ical grounds, and examining the science rather mean neuro not than belie this conclusion. that this does However, science

explains

nothing

about

color

vision,

the qualitative space of color vision. I intend this article to be accessible on

including

the one

hand

readers

even

if we mean

to a wide

who

are familiar

range with

by

that

of

readers, the classic

philosophical articles on the explanatory gap by Levine (1983), Nagel (1974), Jackson (1982) and Chalmers (1996) but are not at all conver sant with

any actual explanations readers who the other hand

on

atory gap but have never taken it seriously in terms far removed from actual scientific assume between through of color

or neuroscience, and heard of the explan cast because it is usually

in psychology may only have

I shall thus explanation. a background an the of idea of gap knowledge explanatory a very elementary mind and brain, but shall present walk of several stages, historically of the understanding arranged,

and ask at each stage what is and is not explained. vision, In the course of these I shall, on several occasions, stress how the a not is The crossed. article of thus form gap explanatory practices of mind/psychology/neuroscience "naturalistic" work philosophy real case

ing from constrain and

scientific

then

context

relates

studies

practice these to issues

of aprioristic

It is useful process

to begin

usually

philosophical

3. PRELIMINARIES:

rather

in explanation on aprioristic,

than

raised

to -

attempting

extrascientific independently,

grounds in the

thought-experiments.

THE FEEDBACK CYCLE OF UNDERSTANDING MIND AND BRAIN with

of understanding

a general mind and

and

schematic

brain.

Three

overview important

of

the

aspects

482

STEVEN HORST

of

this

are:

project

psychophysics, (or more Psychophysics

modeling.

localization, exactly, what

and mathematical Fechner

called

outer

the relationships data about between per gathers stimuli that cause them. In the case of the modeling

psychophysics) cepts and the

supplies a goodly part of the data that

of perception, psychophysics

must Localization is the process of modeling explain. areas of these patterns finding (and perhaps activity, global though are dubiously labeled that are specially in "localized") implicated or come a from Such data processes. particular perceptual cognitive theoretical

of

sources:

of

variety ticular

cognitive scans, lesion studies

brain

and

to be

needs ies

tell us

does

the

study of the brains of patients who have lost par functions due to injuries or strokes, various types of surgical studies anatomical single-cell patients, of animal in the

explained something

about But

study where

of

tells us what

If psychophysics

models.

of perception, to look for

course

localization the machinery

stud that

"because

explaining. something happened We need, addition there" is not yet a very good explanation. the palpable that shows how of the data ally, a model properties curves of the the data) can (e.g., stimulus-to-percept psychophysical be accounted for by neurally-reasonable about specific assumptions over

parts of the brain. This is the job of mathematical modeling of the mind. between

In practice, there is an ongoing and iterated cyclic relationship as well as other more these endeavors, activities peripheral

like attempts form of this

at implementing models is depicted relationship

in artificial in Figure

4. THE STUDY OF COLOR VISION Much

of

the modern

Newton's

discovery,

problematic with the help

agents.

The

rough

1.

- A SELECTIVE HISTORY

in color with vision originated of a refracting white that prism,

light is in fact composed of a mixture of colored lights. It was later discovered

that

the

spectral

colors

are

typified

by

different

wave

lengths of light, and that visible light is in fact just a small portion As psychophysics spectrum. in the nineteenth century,

of

the electromagnetic rics gained momentum to discover

some

perceptions

of color.

We

are more

others. dle

of

familiar

(and

Among

some

not-so-familiar)

and

psychomet researchers began facts about our

them:

to some wavelengths sensitive of light than to we are more to In general, sensitive light in the mid the spectrum than at the ends. (This is actually slightly

483

PHILOSOPHY AND THE COGNITIVE SCIENCES

Model

principles and mechanisms

Behavioral

Brain Data

Data

Mathematical

and

computational analysis

Technological Applications

Figure 1. Flowchart of the theoretical process in cognitive modeling (derived from personal communication with Stephen Grossberg). Process begins with the collection of behavioral

data

(1). From

ples and mechanisms in a new

functional from

top-down

model

this

Once

way.

data

behavioral

and

principles and mechanisms

explanatory

scope

are

theoreticians

this,

able

to derive

new model

princi

(2) in the form of neural networks that explain brain data (3)

with

successive

connection

is established,

bottom-up

from

brain

data

in a continuing modeling theoretical

cycles.

Model

it is possible to further

to work refine

the

cycle that explains its principles

and mecha

nisms get modeled through mathematical and computational analysis (4) which can generate data predictions for both behavioral data (5) and brain data (7). Finally, models can be tested through technological application (7).

complicated by the fact the different kinds of photoreceptors

in the eye the rods and cones have different photoreceptive 2. See Figure curves.) we have greatest The wavelengths to which sensitivity change depending

on whether

Experienced or wavelength.

color

does

our vision not map

is dark-adapted. on to neatly

See Figure 3. color spectral

A

in the yellow portion of the pure wavelength an one can will of But spectrum yellow. produce experience an indistinguishable also produce sensation yellow by carefully red and green is called metameric match mixing light. This

ing. In fact, Thomas Young range pure

can

of

spectral

light

lights

(e.g.,

red, green

(1773-1829) be and

showed that the entire

three generated by combining combinations. blue) in different

484

STEVEN HORST 1.2

c o

1

o jq 0.8 < "O c 0.6 0.4

o c E 3

0.2 0

400 Figure ty of

2. the

The

chemical

(dark-adapted)

500 600 Wavelength (nM)

basis

of

vision.

human

absorbed at the same wavelengths 1978). Visual

curve

The

The

eye.

700

represents

jc's represent

gray

by the pigment

the the

rhodopsin

photosensitivi amount of light

(based on Gregory

Sensitivity

Photopic{Daylight) Scotopic (Dark-adapted)

500 600 Wavelength (nM) Figure 3.

Photoreceptivity

700

curves for daylight and dark-adapted

vision.

are

three canonical colors that must be not, however, used for this effect any three wavelengths suitably separated in the spectrum will do the trick. See Figure 4.

There

The

rules

for mixing

pigments. we Not everything three-color process. can

example, tain context

lights

are different

from

see as a "color"

can

No

pure

mixture browns.

produce and contrast

effects,

of These such

those

for mixing

be produced spectral

only appeal an as when

by

lights, amidst area

this for cer

has

a

485

PHILOSOPHY AND THE COGNITIVE SCIENCES 100 r

100 r

100

50

50

0 400

500

(nm)

Wavelength 4. Figure distributions

distributions

Light will

and a

produce

Wavelength matameric

500

Each -

matches.

green

of

these

one

that

ceived as having any mixture of yellow or blue. From Hurvich reproduced from Clark (1993, p. 43).

are

unable And ence

several

kinds

of

Sensitivity than humans

seems

wavelength is not per

(1981, p. 78),

are people and yellow. does not experi

blue

in other

respects. species. Other

across

to differ

a partic

Some

colorblindness.

to distinguish red and green, others a very small percentage of the population color at all, while being normally sighted to color

(nm)

by an area with

and is surrounded particular pigment ular contrasting pigment. There

700

600

Wavelength

(nm)

a unique

of

sensation

0 400

700

600

500

400

700

600

greatly some other primates, the mammals perhaps seem to be are largely colorblind, while many fish and birds to color, and to portions in some cases of the very sensitive our own spectrum beyond perception. electromagnetic Edwin

and

color of an area that the perceived (1959) noted area as an affected whether the is construed by

Land

is sometimes object. Some

of

these The

models.

were

observations "color

systematized early was modeled of humans

space"

on

into in the

of Munsell.

is not

but

laws,

(See Figure 5.) This kind of formal model can like the curves of the Weber be viewed, explanatory, as a systematization of data the final stage of psychophysics. solid"

explicit "color

On the basis of such information, visual theorists like Helmholtz to formulate of how we theoretical models (of physics fame) began see an to In be able color. color vision respect, might important turns out to be very different from how the auditory system enables us hear for

to hear the this

transducers

tones. When result

is that that

as

two distinct

a chord, in the inner respond

and

not

ear,

there

to particular

are played together, we a pure reason tone. The are a very great number of tones. But there are distinct

tones as

STEVEN HORST

486

5.

Figure human

The

color

Munsell

rior. From Hurvich

not

hundreds

color

A

space.

portion

a

solid, of

(1981, p. 274). Reproduced

of different

of

representation geometric cut away solid has been

the

kinds

of color

to

trichromatic

reveal

the

inte

from (Clark 1993, p. 122).

receptors

in the eye,

corre

sponding to the different hues that we can distinguish. And combi

of pure chromatic say, frequencies - are as not visual "chords", green perceived a chord; In hearing such as yellow. entirely, of red and green seeing a mixture light, we

nations

color, yellow. Helmholtz any

experienced pure chromatic that has three This

we

hear

are

aware

two

tones,

of only

in one

(1867) suggested that Young's evidence that

can be produced of three by the combination a to mechanism color-detection frequencies pointed color

elements

that are model

three-color

does

a great

to different

frequencies. as a theoret originally presented in the nervous of system, though into the visual deal to guide research

was

process a localization without

ical model, course the model

a pure red and a pure color but as a different

responsive

487

PHILOSOPHY AND THE COGNITIVE SCIENCES

400 440 480 520 560 600 640 680 Wavelength 6.

Figure tal

curves

Response

axis

each

represents type of cone.

of

the the

wavelength,

three

cone

vertical

systems

axis

the

in humans. of

fraction

The

light

horizon

absorbed

by

to look for if the theoretical It tells us what model is to be system. that can underwrite the functionality confirmed: namely, something needed for the three-color theory. The nervous

turned theory proposed by Helmholtz a structure neural substrate i.e., straightforward that matches its functionality. system Investigation

human

retina

have

three-color a

reveals

cells, each of which wavelengths. three different

that most

humans

is differentially we

spikes

to

in the of

the of cone

sensitive to light of different

curves of the the response 6, above, The vertical of axis represents the fraction receptors. cone each of while the horizontal axis type repre by

In Figure

light absorbed sents wavelength. cone cell, taken alone, Each discriminate between different send

three kinds

possess

out

down

the visual

see

is "colorblind" colors.

cascade.

What But

the

it is not

that cone

is, it cannot cell does is

sensitive

to just

one wavelength of light: a little bit of yellow light, to which a par strongly, will cause it to spike at a certain amount of red light, to which it responds rate, but so will less strongly. So, if you are a cell at the other end of the optic nerve to that cone cell's output, tell whether it is you cannot "listening" ticular

cone

cell

responds a larger

"saying" that there is a little bit of yellow light or a lot of red light.

488 And

STEVEN HORST the problem is not but the entire frequencies,

of course,

different

to a choice

limited range

between

two

to which

of

the

spectrum

of

the

of the properties that we have more

that cell

responds. mathematical However,

different

of cone

types

investigation reveals that

cells

the fact

infor chromatic type of cone cell allows us to extract more than we could with chro type. In particular, just a single in the differences and ratios between is encoded information

than one mation matic

curves the response curves will between

of

cone

the different

often

determine

cells.

the ratios

Specifically, chromatic

a unique

frequency,

regardless of the intensity of the light. (See Table I.) The chromatic in the ratios

carried

information cones

is not

can mimic ple. But as these

are

there

perfect: a pure signal, from a standpoint

between

the sensitivities even

for example, of psychological

of different

of frequencies

still combinations

that

in normally

sighted peo this is good, explanation also found in the psycho

are of the stimulus ambiguities want to have the same model data, and you your theoretical physical to model. you find in the system you are attempting idiosyncracies Individual

cone

an explanation for how such provide nervous the this takes system by place at in the visual cascade. But the facts that such encod not

do

cells

is extracted

information a

later point over the cone distributed information ing preserves of the psychophysical it matches the peculiarities the model matches there are metameric just where tion

to be

helps

both ambiguous), research. guide further

confirms

TABLE Sample

data

of

the

Wavelength (nm)

percentages,

absorption

um) and L(ong wavelength) Quanta incident

this part

the model

of

and

differences

ratios

Absorbed by M

Absorbed by L 27

by L

Difference

165

1000 520

(16.5%) 62

103 2.66:1

3814 560

(16.5%) 732

(6.2%) 629

the Medi

1.16:1 103

intensity.

Ratio

1.16:1

(16.5%)_ _(19.2%) From Clark (1993, p. 34) Note that the ratio of M/L of

of

cone systems

192

regardless

and

I

(19.2%) 165

1000 560

wavelength

system, and that data (e.g., that shows informa

preserves

information about

PHILOSOPHY AND THE COGNITIVE SCIENCES This nations color

489

turns out to yield fairly strong system simple neural amount of the psychophysical data of a surprising curves of the individual vision. the sensitivity First, can

receptors different

be

to derive

used

the

psychophysical of different functions

data

expla about color of

the

of luminance-to-brightness portions In Figure 2 earlier, for example, we see a curve plotted the spectrum. over the spectrum. of human vision for the photoreceptivity Across curve

are

the photoresponse of representing a extracted from photoreceptor rhodopsin frog's eye. fall along the human data points These curve, and photosenstivity in one kind of cone cell explains of rhodopsin the presence the pho tometric that of cell. of response type that

also

data

points

the chemical

behavior

Cell

also

a single state can be internal why of different stimuli (e.g., light in the in blue in yellow bands): namely,

explains a number

between ambiguous or a combination green band because cone sible

that

the information

is transmitted

from

the stimulus two

between

is ambiguous receptors literally states environmental that would

produce is driven by

the

to the

pos (or more) same effects in

the eye. The firing of a cone cell the number of light And in that it is determined absorbs. the turn, this, quanta by prod uct of (a) the number at a given wavelengh of quanta it, striking of quanta absorbed will absorb receptor

and

(b) the percentage length. Since a given

at some

wave for that particular a greater portion of light more light of a less sensi

than at others, adding frequencies as less light tive frequency the same overall absorption will produce can also add wavelengths of a more You sensitive frequency. alge as to II in It obtain shown in Table below. matches, is, braically a that thus would necessary fact, metaphysically system configured result

in ambiguities

exactly

such

where

ambiguities

have

discovered

by psychophysicists. data about the cone cells explain the phe physiological at least if we interpret of colorblindness, "colorblindness" an absence to mean to chromatic of sensitivity information. Nor cone three different individuals have cells. types of mally sighted Finally, nomenon

But

a small

the cone

portion system of

the chromatic range

of

upon

which

guish lows.

The

reds

of these

features

stimuli

of

has the population carries dichromats their are

and there is a greater environment, to unable distinguish. Depending to distin they will either be unable

from

that they are missing, greens or be unable

very

rare

cells

individuals

two. As a result, only less information about

who

to distinguish blues from yel have only one kind of cone

490

STEVEN HORST

are "monochromatic" in them altogether, cell, or are lacking they at all, but only differences do not distinguish colors in brightness. can be generated All of these phenomena from the neural model, through largely mathematical techniques. a localiza to say that we have Are we, licensed found then, cone in the tion of color cell system of the eye? Tempt qualia answer to this the has be no. First, there seem, may ing though are a wide of about data color variety psychophysical perception of the cone system, that are not explained and indeed by properties which

need

to be

idealized

it does the properties of tioned the problem are

also

several

kinds

for the cone

to explain system have already men such as brown. There

from

away

we

For

explain. example, the non-spectral colors, of idealizations that have

been

in the

made

for example, that the results apply only to stim explanation: 4 in central of the visual the field, phenom presented degrees ena that arise when are one another, set alongside colors contrasting dark and light-adaptation, and the effect of priming the eye with one color before can it to another. Some of these effects exposing above

uli

be predicted from the particulars of the cone cells: e.g., sus communicate chemical and neurotransmitters, through one can of tained activity receptor cones) (say, the long-frequency to a new its level of transmitter lower ions, so that its response

themselves cells

stimulus hence not

be

be

will be proportionally seem off). the hue will

decreased But

simply by appeal of features by other

the visual

TABLE and

absorption

Quanta (count)

incident

matches

Metameric

of

(and can effects) system. These may but they have system,

(like to the cone

explained

explained

to the others

relative

others

contrast

II

light

by M

cone

L

and

cells.

Predictions

of a Match Wave-length (nm) 560 515

1576 2100

Percent absorbed M _by 19.7 13.1

1166

3.0

Percent absorbed by L_by 16.5 5.7

Quanta absorbed by M 310 275

+

+

615

Quanta absorbed L 260 120 +

35

140

12.0

Total_310_310 The

combinations

stimulus

in the

L and the M

of wavelengths first row, producing

systems. From

in

the the

second same

and

number

(Clark 1993, p. 39).

third of

rows

absorptions

will

match

the

in both

the

PHILOSOPHY AND THE COGNITIVE SCIENCES not

been

in what

explained

our

explanations fact we should

idealize note

the fact Second, does discrimination

we

have from

away

said features

491

so far, and the fact that in vivo is a that matter

well. that

the cone

not

entail

are responsible they are the part

for chromatic

cells

that

of

the nervous

for associated with color experiences. Many specially people, can dream in color, even though and visualize this is not example, nerve if severed or the is caused by retinal stimulation. Indeed, optic and visualization need not be imme the eyes are lost, such dreams system

to the retina will cease to cause while stimulation affected, diately color qualia. removed eyes presumably (And conversely, surgically no on even are still able to color their while cells own, experience for a special location associated with all color to in look deeper have the brain. Finally, this experiences, we have presented thus far does not explain the kind of explanation If we

fire.)

are to look we will

at all: what is to presume it does qualia as one of the to then and the psychophysical facts about data, explain such as the "shape" of the color solid. There the quality-space is, to be sure, a more of color discrimination capac complete explanation ities. But why these should be accompanied either by their partic

qualia relata

as such

of

or indeed by any qualia at all, has counterparts, qualitative A Martian with scientist, gone unaddressed. unacquainted qualia, human the visual could derive system, investigating psychophysical assurance like metameric matches from with complete phenomena ular

its knowledge of the functional anatomy in this stage of visual processing nothing it the conclusion that humans experience

5. COMPLICATING While of

the properties

THE MODEL:

of the cone

the psychophysical data, was One explain. problem

of

the visual

would visual

remotely

system.

But

suggest

to

qualia.

COLOR OPPONENCY

system explain a surprising there is also a great deal that

amount

they do very early on by Hering (1878): on the basis of the Young-Helmholtz As one might three predict - a we can a we in color theory, red which expe "pure red" perceive or blue - and likewise a "pure blue" rience no admixture of yellow and a "pure green". And, with this theory, we per again consistent as a mixture ceive many hues as "mixed" for of aqua, example, blue and green. However, out, we also experience Hering points yel - one we do not perceive in which low as a pure color red and not

noted

492

STEVEN HORST

green components, low seems to be a hue

experience "bluish yellow".

wrong, the basis

suggested there is competition yellow. He proposed

be

sensation

The

theory.

of yel to impossible

it seems

In fact, as a "reddish

of this was

that

and

the

be described

was

theory

three-receptor story. He in which can

that would

interpretation

Hering's

blue

as predicted by simple or unmixed.

not

that

but

that

for hue that

the Young-Helmholtz not it was the whole lies in a process green and between

sensations red and

between

or a

green"

all

of

our

sensations

of

color

for

accounted

of these "primary" hues, by combinations axes a the processes: opponent arranged along generated by a as axis and axis. known red-green yellow-blue Hering's theory, the "opponent process acceptance, theory," has gained widespread a neural and has itself found correlate system. early in the visual two

visual

Early

in the processing to the transmission

stages prior of the optic nerve. Information horizontal cells, cells, bipolar nerve. down the passes optic

eye of

turns

out

in the cone and

retinal

(See Figure

a number

to have

of

to the brain

information

by way is influenced by cells before it

system

ganglion 7.) In the ganglion

cells

(with the help of the horizontal and bipolar cells) we find the kind of

opponent connections

process between

postulated

in Hering's theoretical model. The and cones are in what is called

cells

ganglion an architecture in that is also found architecture, nervous of the other many system. parts we are dealing In a center-surround with the rela architecture, two layers of cells, LI and L2. In Figure tions between is a 8, X a X in L2. cell of number great (has inputs from) samples sample a center-surround

an area of its surface. The connections covering In center the of X's there are field, types. receptive area of LI are activated, connections: when cells in this

are

in LI,

cells of

two

atory "excite" other

X,

which

connections,

is to say they raise its likelihood in the periphery of X's receptive

of

excit

spiking. behave

they The

field,

in

just the opposite way: when cells in the periphery of the field are fir ing, they inhibit X, or make it less likely that it will fire. The ques tion of whether X will in fact fire is then governed by a weighted summation example,

of

and excitatory the center of the field

inhibitory is excitatory

In

inputs. (or ON)

this and

particular the periph

ery is inhibitory (or OFF). This kind of center-surround structure is called

OFF-surround." "ON-center, can tecture take other forms as well:

and

an

excitatory

periphery

But

the center-surround

it can have

(OFF-center,

an

archi center

inhibitory

ON-surround),

or

if the

493

PHILOSOPHY AND THE COGNITIVE SCIENCES

cell

Ganglion

cell

Bipolar Amacrine

cell

Horizontal

cell

mm

Cone Rod

Plgmented

HZ*

cell

Back of the eye 7.

Figure

Layers

cells before These

bipolar

center also

information

pass

amacrine,

of

cells

in

the

retina.

passes

Light

through

several

of

layers

it is detected by rod and cone cells, located at the back of the eye. and

on

to further

ganglion

and periphery be

implemented Center-surround

of

layers

processors,

such

as

the

horizontal,

cells.

are different as an ON/ON architectures

of cells, the architecture or an OFF/OFF function.

kinds

can

are

useful. are, extremely They other things, the basis for detecting the contrasts of light and among 9 illustrates dark that signal edges and boundaries. Figure organi information that compare from the different kinds of cone zations cells,

here

M(edium)

designated and L(ong).

by the wavelengths The center-surround

they respond cells are of

to: S(hort), three types,

(only two of which are shown in Figure 9). The first type involves opponency cells have some

also

between

the M

and L cones. either

centers, excitatory centers. have inhibitory

and inhibitory excitatory nent" cells. The second

The

in the M Such

greater or L

cells

have

number systems, peaks

of

such

though for both

and are called responses oppo "red-green of cell the S and the combi compares type

494

STEVEN HORST

Inhibitory Connections

8.

Figure

Basic

Excitatory

Connections

diagram.

A

center-surround

cell

X

in

layer

L2

has

connections

to cells in a region of layer LI. X is excited by activity of cells in the center of the region in LI (bold lines), and inhibited by the activity of those that surround it (lighter lines).

Figure varieties

nation

9.

Spatial of

of

opponent." chromatic and

hence

structure

color-opponent

the M

and

frequency cells.

of

incidences

of

the

six most

common

ganglion

and L functions.

This process is called "yellow-blue not appear to make of cell does type ganglion but follows the photopic distinctions, function, luminosity seems to code brightness and darkness. (See Figure 10.) A

third

basis for types of cells we have a neurological a called for number of psy opponency by Hering. Again, can or be predicted data demonstrated from the model, chophysical such as the fact that there is a phenomenologically pure yellow but a The luminance not, say, pure orange. phenomenologically spectral In these

the color

first

two

495

PHILOSOPHY AND THE COGNITIVE SCIENCES

blue 10.

Figure of

cone

matic

curve test

competitively red yellow,

(blue,

approximates on a white

spots

to activate and

for

localization

that "shape" model theoretical

formal shape. And candidates that had in the visual

point often

far. We

particular was the model

known.

luminosity.

The

data

a

produce sensitivity theoretical before

the

a provided to explain.

at a plausible located properties we are study of higher cognition, studies reveal can position: things like trauma of a capacity such as speech com localization

requisite cascade. (In

the color

explained But are we now by Hering. vision in the retinal ganglion entirely temmatic with the cone cooperation same

empirical phenomena the contrast effects

chro

the

have

for the very

four

the underlying mechanism needed showed a structure of producing that capable later investigations into cell physiology revealed

tulated

and

producing

suggested data psychophysical

in the opposite for the gross didates or face recognition before we prehension how such functions be achieved.) might to specify But we must be very careful thus

cells, for

background. Helmholtz and Hermann

formal The

cells. Inputs from the three types ganglion and one

green)

both Historically, models that could explain neural

luminosity

also architectures the antagonist the data for human chromatic

of

sensitivities that

in the ganglion

opponency

interact

channels

contrast for

Color

cells

red

green

yellow

have

a formal

what

we

have

model

of

explained

opponency pos phenomena to localize in a position color in their sys cells, or perhaps

is still no, system? The answer as before: First, there are still purely are not explained at this level. Notably,

reasons that

that

produce

the nonspectral

hues,

and

inter

496

STEVEN HORST cues

with

actions

of depth

and

Land

boundaries

object

are not

noted

by Edwin thus far

our

localization Second, seems the wrong to localize place dreams and visualization, during

yet explained. (1959) to the retina, and this is confined color qualia, since these can occur

can persist of stimulation after loss of one or both eyes, while live retinal cells will not cause qualia discrimina (or, for that matter, are too dam if the optic nerve or the geniculate tive abilities) body

which

is still in the And finally, our explanation aged to carry information. states about business of explaining qualitative things (e.g., why there are more than kinds of cone cells, and why there is "pure" colors a hue

as a greenish is experienced red) without explaining own in its character right. The first two issues qualitative - can data if we follow for additional be pushed farther accounting down the perceptual cascade. The visual information further third not

that

their

will

but we will

remain

tion

intractable, it until we have

of

pushed

save

the more

as far as we

careful

examina

can.

6. FROM EYE TO BRAIN the more

Among vision that

was are

field, objects.

not

but

20th century surprising Land's claim that there

Edwin

dependent

also

upon

This

discoveries are

the properties upon simply are of color whether patches is that there feedback suggests

color

about

color

vision

effects

of

visual

the

as interpreted from whatever

strongly to some point in the brain play a role in object groupings system(s) stream in color perception. And since that eventuates in the causal to look to the retina, we apparently need there is no such feedback our localization of further into the brain before we are done with

color The optic

sensation. cells ganglion nerve. (Indeed,

in the retina some

are

are connected

to the brain

to view

inclined

by the as a part

the retina

of the brain that happens to extend into the eye, but the difference is not

important

for our

The

purposes.)

passes

signal

through

the

optical chiasm, where signals from the left side of the visual field in both

eyes

are routed

to the right

side of

the brain,

and

from

signals

the right side of both visual fields to the left side of the brain. These input to) a small project (provide and from there eral geniculate nucleus (LGN), located at the back of the brain. There are also connections

from

parts

of

the cortex

to the LGN,

and

called body to the visual feedback

indeed

it seems

the

lat

cortex,

projections to be the

PHILOSOPHY AND THE COGNITIVE SCIENCES rule that when there is a projection general brain A to another part B, there are usually B to A as well. The brain

497

one

part of the channels from

from feedback

the striate cortex) is an area of (also called It is takes of our visual processing place. areas is itself divided and each of these V1-V5,

cortex

visual in which

much

divided

into areas, enter VI into layers. Projections from the LGN in the internally seems to middle Past that information divide visual layers. point, one for color, one for shape, and streams: itself into three different one for movement, location and spatial relations. The visual cortex to other parts projects more functions. yet complex also

visual

Studies

and Mishkin

Ungerleider cortex

seem

that

by Mishkin

to be

in

involved

associates

and

(e.g.

1982) suggest that information from the two

into

splits

the cortex

of

further

streams.

A

stream

dorsal

(one

projecting to the top of the brain) goes into the parietal lobe and seems

to be

to objects. have who to identify their spatial

for perception responsible This is sometimes called to

had

damage but objects,

to the underside responsible sometimes called

of

the brain) for various

the "what

in both

orientation

stream."

"where

are

the brain

Patients often

able

or

report on that projects lobe, and seems

to grasp them properly, stream ventral second, (one

of

to be

parts

and

location

unable A

relations.

these

of the

goes to the temporal sorts of recognition of objects. This is of the temporal stream." One sub-area seems to have the highly humans, spe

and monkeys function of recognizing faces of conspecifics. It was a por tion of this "what" area that was damaged in Oliver Sacks's (1985) famous "man who mistook his wife for a hat", who was as a con to identify unable in this extreme faces case, the patient sequence was to tell one face from another, indeed not only unable but even lobe, cialized

to recognize the localization has

unable visual

information

In the case

of

the chiasm, In contrast change.

optic

a face preceded flow are color type to

as a face.

(Here we have a case where the theoretical The features of model.)

in Figure 11. we when vision, however, pass and quality of our explanations the

of generative explanations came from looking at two at present know that only

illustrated

strikingly a number cell

beyond begin

rich, exact, quantitative of psychophysical data in the back

groups certain regions

of

of

the brain

the to and that

eye, we are selec

the

to chromatic data, but do not know tively sensitive just what they do or how they do it. We know, area for example, that the cortical V4 seems to be involved in higher of color information, processing

STEVEN HORST

498

Parts of parietal lobe implicated inspatial orientation towards objects Dorsal

Stream

it

Visual

Cortex

Parts of temporal lobe implicated in various kinds of object recognition, e.g., face recognition Figure

11.

passes

from

into

ventral

and

that

Schematic the

retina

"where"

there

the of diagram the LGN through and dorsal "what"

seems areas

parvocellular there into

the

to be a color the LGN

of

thin

stripes

flow to

of the

visual visual

information. cortex,

from

Information it splits

which

streams.

that passes the pathway through into the blob cells in VI and from

of V2,

which

then

to V4.

project

(See

Figure 12.) in these areas is still a matter of speculation. happens there are, indeed, difficult in pro methodological problems here. Whereas further the explanations of psychophysical ceeding data that could be read off the responses of cones and retinal gan What

And

glion

cells

(or

at worst

could

be

from

determined the

from

feed-forward

examinations behavior

of

of

single cells single

cells and

their projections), higher cortical activity seems to be typified by more

highly both

tions, level and of

cells

the visual

global in the

in the form in different

behavior, form of

complicated between

feedback cells

at

rela

a

competition single resonance between phenomena populations areas of and particular systems (say, the LGN of

els,

cortex; Grossberg the cortical of encoding

gle

cells or

involving

1987). Moreover, does information

in many not

at all, but in activity distributed patterns in the connection between them. strengths

useful

mod

in sin take place over groups of

Land's Indeed, that there is important the interaction between suggest so color system and systems for shape and object that recognition, to adequately it may be impossible model color vision just by under

cells, discoveries

PHILOSOPHY AND THE COGNITIVE SCIENCES

499

Primary Visual Cortex

Figure 12. Schematic diagram of the flow of visual information through layers of LGN and visual cortex. Figure 23 and accompanying text from Spillman and Werner (1990, p. 195).

"color

the standing of cortical ity

so-called

that unlikely in the cortex

the explanation will be so closely

structures

in the

retina.

Because

formal

models

and

our

when

we

and

of

Because of the complex pathways". relations it is feedback them, among of psychological phenomena residing linked

as it was physiology our the distance between

to cell

these

problems, in the cortex is far greater neurophysiology to test the than it is in the retina. As a result, it is far more difficult because neural plausibility of the some of rival models. Likewise, nature of the coding of neural networks, what opaque, distributed it to guess or verify what task a cortical module functional is difficult is performing Here we

do not

even

know

the units

of

the "code".

an

have issue for the philosophy arguably important In early vision the within retinal cells), (processing the psychophysical data are localized relevant units for explaining as one might in isolation, in specific much cells that can studied

of neuroscience.

study a particular cuit. And indeed, erties of individual

a simple electronic cir and electrical it is the structural, chemical prop of the explaining. But once cells that do much

mechanical

structure

or

500

STEVEN HORST

we

the retina, it is less clear just what the relevant units get past some cases in It is possible that cells really do per individual form functions that can be inferred the data. But from it seems cases are in the that units relevant of many likely patterns activity

are.

across

fields

several

like V4), areas

or

This

creates

distributed areas

cal ing

V2). different than Hence

do

on

a life of

layers

of at least

feedback sorts.

like Grossberg

(ART) (cf. articles in Grossberg

corti relat

patterns

between two

or

the LGN

of modeling circuit-like behavior

techniques

modeling

of

sorts

complicated understanding

onance Theory

(e.g.,

in complicated relations

complications

for

network

cells

feedback

(e.g.,

and more

we

of even

LGN,

V4

and

First,

we

need here

techniques in cone

cells.

'sAdaptive

Res

1987) have taken

own

in exploring cortical it is Second, dynamics. to sample not currently all of the cells in a region of the possible a perceptual or cognitive brain as a subject performs task. Imag or not the of does level necessary provide ing technology temporal their

cannot be performed Single-cell spatial resolution. sampling in a human lions of cells at once and would be too invasive

on mil

subject in any case. And EEGs, which do provide information good global of temporal with a high degree do not provide the spa resolution, to distinguish tial resolution distributed necessary patterns spatially a particular are of activity within These of our limitations region. or may not be insuper current which may technology experimental on at least some possible scenarios such as that it able. Moreover, areas are in of that the cortical is patterns units, significant activity these limitations rather than single-cell activations might keep us the physical that correspond able to discern from being properties to the significant

units.

As

a result,

for at least must

of cortical

often

some

types

of prob at a fairly

lems, modeling dynamics proceed from the details of the implementing level, in abstraction sys global vs. hard to the software-level tem. Nor is this really comparable in a digital know There we might distinction ware-level computer. that

a number

is represented even if we do

crete location, or 32 bits, or whether sistors, or integrated With

the brain, we in discrete

localized

do

not

are

some

of bits in some dis pattern if it is represented know by 8, 16 vacuum in tubes, tran implemented

or in a Pentium 3 or G4 chip. boards, units are know whether the significant

over a popula or are patterns distributed or two con two of data the encoding perceptual (E.g., same in the very of cells, and be implemented population

tion of cells. cepts may

these circuit

by not

areas

501

PHILOSOPHY AND THE COGNITIVE SCIENCES factorable

some

through

separate

kind

of vector

rather

algebra

than

in

stored

cells.)

A MORE

7. PROJECTING

MODEL

COMPLETED

can take the lib and theoreticians lab scientists, philosophers we were to tran if of what look like erty things might projecting our current experimental look limitations. We might therefore scend

Unlike

at the overall take. V4,

Suppose has all of

shape that a completed we were to find that the

right properties for example, Suppose, of V4 was isomorphic

experience.

state-space areas different physics

of

of

the visual

field,

account to be that we

vision

were

to find

that

the

to a and

had

color

of color

might such as area, particular the localization of color

some

for solids space of color that all effects in the psycho to V4-state. from stimulus

parallel mappings to V4 were to prove to that selective moreover, Suppose, damage cause cortical colorblindness without total loss of discrimi (perhaps

native

abilities

tion

to V4 with of

performed a neural

traumas

by "upstream" probe caused

and

systems),

that

stimula

color sensations, predictable to upstream Then we would modules. have a we then have in V4. Would of color experience

regardless localization plausible an explanation of color

as well? experience we mean an If, by 'explanation', explanation the answer color experience, is surely no. Figure sort

of

explanation

that we we

physical

would

are able

have.

On

to construct

of everything about 13 schematizes the the basis

of psycho of visual color

models

experiments, such as the color solid. On the space (and discrimination space) we are able to examine basis of neurological the prop experiments, erties of various the retina, the LGN, system: parts of the visual In our projected this culminates scenario, parts of the visual cortex. in revealing that color vision "all comes in some specific together" for purposes of our musings, V4 where we part of the cortex have a state-space to the state-space that (a) is isomorphic arrived at by our psychophysics, and (b) covaries with it: e.g., you experi ence a particular shade of red in a particular and when, position

a portion of V4 is in state V4,-. This convergence of for only when, to provide mal is enough the basis for call shape and covariation the localization of color and an occurrence of ing V4 experience, a the of of localization that of red shade V4/ particular experience in that portion

of

the visual

field,

if all we mean

by

"localization"

502

STEVEN HORST

is "part

of

implicated erful kind

that could

ventions of cortical even

activation But

patterns. there is an

and what

matic

conditions, they discriminate differential response, functional behavior

cone

in a lawlike way, to neural phenomenology

variables

cells

different and

we would of

have

chromatic

once we have There, ganglion to different chro differentially respond to ask, be nonsensical how but "Yes,

and

it would

do

out

disparate of visual

difference between what important case in the had of discrimination

we

by the retinal

how

forms treating scientific important and

in, say, diagnosing also provide the

It would

the

information seen

be useful

blindness.

two previously of relating it is not a reduction though

virtue

here

of brain activity) the brain that is specially (or pattern in the experience".2 And this is a very empirically pow as it licenses all sorts of predictions of relation, and inter

cells.

Discrimination wavelengths?" just is we have the right sort of circuit, its once we have necessarily. By contrast,

once

follows

of the visual and system, to the color space is isomorphic sense to ask, our psychophysics, it makes arrived at through perfect area are firing in red cells V4 when do look but my "Yes, things why out of differential red" does not just emerge that way?" "Looking

mapped shown

the discriminative

some

that

the way response It is an additional

abilities

area

or functional

that discrimination

description

explanandum.3 are two additional

here. explananda is the very presence 1996, Jacobson 1997.) One do not simply emerge out of lower-level explanations there

Indeed, Chalmers These

downstream

abilities

discriminative out

struction

of neural

do:

color

states. A

qualia second

cannot

be viewed

does.

(Compare of qualia. the way as a con

is the association

of partic states: brain why does the this particular reddish hue

characters with particular ular qualitative of V4? co-occur with my seeing presence hue? We may I call a bluish rather than, say, what put this prob will colorblind who is thus: the lem more person red-green pointedly a state mine different than and color have both a different space

the V4 in our projected can, scenario, identify or we to to But red either that she is in when green. exposed on the of the this basis cannot, alone, predict qualitative particular For exam she has on those occasions. character of the experiences space states

for V4. We

ple, might

they be likemy experiences of red?Might

they be likemy

is simply There of green? Or perhaps they are neither? experiences an answer us to lets that in the generate neurophysiology nothing a of it this. (We can, perhaps, knowledge given pre-existing predict

503

PHILOSOPHY AND THE COGNITIVE SCIENCES Raw Phenomenology

Physical Stimulus Invariants Psychophysical Laws

Color Space

Isomorphismand Empirically Adequate Co-Occurrence Property Space forV*

Visual System

Physiological Data Figure

13.

Diagram

of

projected

On

diagram).

the

basis

completed

of

these

data,

it

of

explanation

the relationships between

physics yields data about

color

vision.

stimuli and percepts to

is possible

construct

Psycho

(top of

geometric

or

color space like the Munsell color solid. topological models of phenomenological Such models provide criteria for testing the adequacy of any hypothesized local ization same

of form

color we

must have the the properties of the localizing system can data. We the properties of psychophysical study a variety as single-cell EEG of means, such sampling,

experience: in the find

like V4 through regions as well as in vitro studies and imaging techniques, when the known is found of localization properties

isomorphic

to those produced by the psychophysics

of the

animal location

A plausible are in question

cells.

(middle of diagram).

504

STEVEN HORST

a correlation but

that

between

leaves

It would states

and

color phenomenological the connection unexplained.)

thus

that appear is likely to

qualia in the sciences

the explanatory us remain with

types

and V4

states,

gap

between

brain

foreseeable

through of cognition. Neither the properties of cells, nor the abstract seem to have of cortical the properties dynamics resources kind of even to within them candi right explanatory yield of either the presence date explanations of the qualitative dimension or the particular of experience of character individ qualitative advances

ual seem

states. Friends of the explanatory gap would this part right: their claim is reinforced rather a of closer examination the But should science. what by from this? Should we conclude, for example, that we as opposed to visual about visual nothing experience,

phenomenological to have gotten

than

refuted

we

conclude

can

explain discrimination?

I think

to draw, the wrong conclusion color that is spe First, given grounds. experience we can in fact neural phenomena, upon particular cially dependent a deal the about that in this of great explain shape experience between different color qualia. the case, the inter-relations Second, or to the of character presence inability explain specific qualitative

on

at

this would

to a complete of explanation absence must be an all-or-nothing affair, and

experience only amounts assume that explanation not

be

two

least

if we this

is

the case.

8. THE SHAPE OF QUALITY-SPACE the

Even the early findings of visual following: psycho us some are with that present physics problems puzzling. intuitively it be that there is a phenomenologically-pure should Why yellow but Consider

a phenomenologically-pure chromatic patterns (different

not

should very different orange? Why of frequencies combinations of light) does human selfsame color sensations? Why

to produce the take form the color-space

be able some

it does

and not

different

from

people's color-spaces as questions about qualitative space, and tive abilities. And there is nothing about

some

other

others?

are form? Why can be cast

These

not

just about discrimina as such that visual qualia in these ways rather than

entails that we should them experience in empirical consists alternative ways. Psychophysics discoveries, a priori necessities, were and many of these discoveries indeed surprising.

not quite

PHILOSOPHY AND THE COGNITIVE SCIENCES And

to answer

are ways

there

The such questions. two distinct components:

such

an explanation

requires

(El)

The

properties

qualitative the activation

of particular we are assuming cussion, to states of V4, normally and activity), (E2) The

explained.

ship

color

qualia

activated

are

related specially retinal and LGN

through

a full description of V4 state-space

(one projects) result in a model

to the phenomenological

isomorphic

color

space.

color

that

of

form

are specially to in question related states of dis neural (for purposes

and

system explains metamers, of the visual system would

has this specific phenomenology the of color-space peculiarities activity,

to V4

basic

to these states have the right mechanisms leading to explain to be the formal shape of the problems For example, of the cone and ganglion the nature

neural

properties

Given

505

relation strong can thereby be

explained. Indeed, they simply fall out of the model. This is by no means

a trivial

sort of explanation. an abiding to in how is, of course, philosophical puzzle an of nature understand element such What is the (El) explanation. as Descartes of this "special Is it one of causation, relationship"? There

would

have it? Or

is it better captured by notions

token of

identity, supervenience, reduction that we do not out? Or

work

terms:

cal of

reduce

them have

moment, at least,

property yet have better cast

is it perhaps as an artifact of our

two different

models to a single a conclusive

like type or

or even some form dualism, to the conceptual machinery in epistemic than metaphysi

to simply associate elements having the same processes without being able to common denominator? We do not, at the

of

answer

to such questions; and at present, an answer, the science has supplied

it does not appear that the questions thus be trans-empirical. may It seems to me, however, such philosophical that having ment to the science is not any kind of barrier itself. A and

association move

in

elements

science.

from

Sometimes more

on

different such

to guide persisting inquiry rather or a sound metaphysical principle.

models

is not

identifications

the order

stronger, But the assumption that seems more successful cases)

something identities. in the

of

of

reductions

later

puzzle pragmatic an unusual turn

into

or ontological do so (at least

they will always like a methodological than either an empirical

principle discovery

506

are

STEVEN HORST let us

However, in the

of

remain

sciences

on

neutral

just

how

many

our

in which

cases

there

an

element explanations require at just how such expla (El), and look for a moment from explanations differ that lack such an element, such

the form

nations as

the explanation of certain discriminative abilities the retinal latter sort of explanation has cells. The

of by features a sort of epi to it: given a description stemic of the mechanisms in transparency "fall the retinal cells, certain discriminative out" properties simply or constructed of from the properties that is, they can be deduced the

cells.

is an

This

of

example

the

type

of

explanation and 20th century

that was

Positiv upon by 17th century Rationalists case of explanation: deduction and construc the paradigm or logic. I have (Horst such tion in mathematics 1996) characterized we can as conceptually treat the explaining adequate: explanations a as axioms of deductive and the definitions and system system seized

ists as

or

demonstrate tem

to be

conceptual resources, laws from

construct

explained content. as

such

classical

the

without (We might the statistical interactions

math-functional

of

properties of any new

corresponding the addition sometimes

the

sys

(non-formal) additional formal

need

to derive the gas machinery or an independent of gas molecules, of a circuit that is not itself construc needed

description of the circuit. However, these are the physical properties as and innocuous, they add presumably ontologically epistemically on we are at least the that new, assumption nothing fundamentally resources to to for formal entitled free.) help ourselves tible

from

Naturalistic and Positivist

of

philosophy

science

has

assumption the philosophical

adequate.

Yet

adequate

explanations or math-envy.

(CAEs) CAEs

the Rationalist

criticized

that all explanations

must

be conceptually with conceptually

preoccupation of misguided is not solely an artifact are of particular inter philosophical neces CAEs guarantee metaphysical

apriorism reason: est for a very good we can as A from phenomenon If derive phenomenon well. B, sity -> meta B A is hence B -> A and is true in every possible world, and A is metaphysically upon B. necessary supervenient physically an onto of A to B) guarantees An reduction (a CAE explanatory logical

reduction

(that A

is nothing

over

and

above

B)

as well. We

might put this in the form of the following principle:

Positive is a CAE

Explanation-to-Metaphysics of in terms of A

Connection B,

then

B -> A

EMC): (Positive Principle is metaphysically necessary.

If there

507

PHILOSOPHY AND THE COGNITIVE SCIENCES For

in establishing

larly itive EMC

of mind,

particu Pos metaphysics, it can be least when

at is a very powerful principle, error of many in my view, reductive naturalists, on a the assumption that CAEs (often priori grounds)

The

applied. making

to be had, and that or even ontological

always

ological It is much has

in the metaphysics a materialist

interested

philosophers those interested

absence

implies

suspicion. whether contentious

more

any metaphysical

(2000) have

Connection

Explanation-to-Metaphysics

supposed

that a principled

and

A

is not

upon

supervenient

metaphysically

and

(Negative

Principle

cannot be explained by B by way of a CAE, B ? A essary

for method

the ^availability of CAEs to from Descartes

a failure of CAEs entails of necessity unavailability as well. They a second principle: nience thus employ Negative

are

Dualists

consequences.

and Jackson

Chalmers

their

cause

is in

superve

If A

EMC):

nec

is not metaphysically B.

a principle, is only persuasive if one assumes that however, - or at least metaphysical in its entirety the world necessities to creatures should be epistemically like us. But once transparent Such

one

it becomes this assumption, clear that there is also alternative articulated like Colin view, by "mysterians" that there are features of the world that are either (1991): to us, or at least not susceptible to com incomprehensible

articulates

a reasonable McGinn entirely

in terms

of something in that argued particular themselves understanding

plete

explanation have mysterians in human

minds

and

else. McGinn there might - a failure

other

be problems of

"cognitive the general failure of the reductionist pro - even in philosophy of science in the biological and phys gramme ical sciences that there might be abiding and principled suggests as well. a, b) (Note gaps elsewhere explanatory (Horst, forthcoming that if this is true, Negative EMC should but lead, not to dualism, more to a much radical in which chemical ontological pluralism, closure".

But

I think

and

facts biological of basic physics.)

that

are not metaphysically

upon

supervenient

facts

This is a juncture at which philosophers of mind and the sciences of cognition might naturalistic tionist,

Darden have

and Maull

begun short ways,

do well

to pay

philosophers

heed of

to the works

science

such

as

of post-reduc Simon (1977),

(1977) and Bechtel and Richardson

the

important

of

reduction,

of cataloguing project that elements in two

(1993), who

important scientific

sorts

of

domains

can be linked. Of particular importance are what Simon (1977) calls

508

STEVEN HORST

we have in which systems, "non-decomposable" one nations of system A in terms of the relations

only partial of its known

expla mate

rial parts B. In cognitive science and cognitivist of mind, philosophy a larger it is common to of the relation between practice speak a characterized such as a system (particularly system functionally or "real and its parts as one of "instantiation" digital computer) a One ization". is to be said say, system program computer or "realized" a "instantiated" of arrangement compo by particular nents states of circuits in the hardware). The (say, the activation are given a variety 'instantiation' and 'realization', however, of meanings and scientists who them, and by philosophers employ a more to stipulate hence it is useful usage. exacting Robert Cummins the notion of an "instantiation (1983) proposes

words

in the following analysis" a P in erty system S has

(6i) Anything

instantiation way. An the following form:

Q

components has ...Cn, O]

having

analysis

[C\

(6ii) S has analysis

[Q...C,,,

...Cn

of a prop

analysis

in manner

organized

-

O

i.e,

having

P;

property

O];

(6iii) S has property P. (Cummins, text)

1983, p. 17, numbering preserved from original

One should be able to derive a proposition of the form (6i) from a description of the properties that when we can do this we in S." is, from system The

(6a)

of can

the components of the system, and "understand how P is instantiated

underscoring (p. 18, italics in original, a specification of the properties of in the form of Q

properties

...Cn

are

,

added) That emphasis the components of the

respectively;

we should be able to derive (6i): (6i) Anything analysis

Horst

[C\

without

...Cn

property

in manner

organized

-

O

i.e.,

having

P;

system any

account". account

realization

in a

C\

(1996) contrasts this with a weaker form of explanation called

a "realization A

components has ...Cn, O]

having

S

through

implication

sufficient condition

a specification of how provides set of the satisfactions of some that

the

satisfaction

of Q

for the presence of P. (Horst

... C?

a property

P

conditions provides

1996, p. 242.)

C\ a

is ...Cn

realized but

metaphysically

PHILOSOPHY AND THE COGNITIVE SCIENCES

509

act. A generous act must of a generous the example some or overt action other be realized say, giving money through a characterization to the needy. However, of the act itself say, a a to not to is sufficient check charitable organization writing Horst

gives

it might, for example, been done that the act is generous: guarantee an as or as a to tax write-off attempt impress one's friends. purely some palpable or behavior is always expressed through Generosity the performance of some such action is necessary for act to have been performed. But it is not a sufficient some economist solved the problem of condition. suppose Similarly, an that world of economic model machine way by hunger required and other, a generous

A total explanation event of provid of the historical computation. an an to of how such would solution ing require appeal explanation was the computation but computer, by the economist's performed not explain why the overall this computational alone would process a solution

event was to additional a part,

of

that

be said might the computation

to world as well.

facts

as that would

hunger,

computation of the problem story. The solving a computational to be realized through alone

is not

a sufficient

condition

of hunger. ipe for the abolition In these paradigm it is clear both cases, are not CAEs in question and that specifiable (such as the tial application

that

but process; a rec for finding the

additional

explanations conditions

or poten giver or the application a are to real-world of the model specific problem) in question to actually for the type of event take place. account of a realization the notion itself can be regarded

required However, at

simply

to appeal part, but only of world hunger need

is a vital

The

Negative fall short

the

intentions

the

on the while neutral explanation, remaining are incomplete that part-whole explanations of CAEs). instantiation (or, more analyses generally,

EMC: of

of

level

of

there

even though it falls short of the power, explanatory a are a number There of CAE. of dis power explanatory probably most is of useful for realization but it accounts, types tinguishable as a to treat realization accounts broad purposes present category,

They

still have

as neutral with to the proper metaphysical respect interpreta tion of a given instance of their application. What is important accounts about realization is that properties can accrue as well. to of the realizing the realized system system on December If Jones wrote the check 31, then Jones's generous and

act was formed

on December performed the Jones using algorithm,

was per If the computation of a remedy the production for

31.

510

STEVEN HORST

hunger was if human Likewise,

world

cesses

and V4

to color as

its

vision

color

processes, as well,

phenomenological solid as well. not

if some are

will

color-space

is a non-trivial

form

of

reached

be

by introspection of phenomenological explanation color space, of phenomenological is a phenomenologically

there

orange. Likewise, of dichromats

pure logically ical color-space

of

aspects

color

vision

(such thereby qualia) explained. If color and these processes result through such processes, like that described the Munsell color then solid, by

in a state-space

This

even

color

involving is realized

vision

as well. by way of the Jones algorithm is accomplished vision retinal pro through accrue relevant features of those processes

abolished

not

take a form

described is one

It

explanation. or a priori

by

the color

that

And

reasoning. the abstract namely, local facts such and more

could it is an

facts:

but pure yellow it explains why is different from

not

as

shape that

a phenomeno

the phenomenolog that of trichromats

can tell us about in ways wholly from what neurocience predictable can the fact that the neuroscience of seeing, the process despite not explain why there is this special realization between relationship and the brain. qualia What this broad notion is to keep

of realization

allows

us

to do

in cognitive contained.

well gap relatively explanatory in color color gap experience: experience explanatory some brain states there is a special and empir is realized through not what that between them but we know relation ically robust

science

the

is one

There

it. We do not, therefore, need is nor can we explain relation special or contrast a separate account color process of, say, the opponent once we have one for discriminative in abilities effects for qualia the nervous topology of

space

and

system. The of discriminative brain

activity

color

structure

of

the

the visual

which abilities, our fanciful (in in us is realized

system explains eventuate in some

speculations, these through

state

in states

of

states.

very experience for each of us at a given time ?there is such a state accurately, are realized. our color qualia It may be differ space through which The ent across times in a given and across individuals individual.)

V4),

(More

topography tem as well.

We might whether

they in combination

thus

explained

the realizing then accrues system Horst 1996, p. 357.) (Compare

of

thus distinguish are

explained other with

to the realized

three types of problems

by neuroscientific

sys

in terms of

alone or explanation, the features and whether

assumptions, are phenomenological. (See Table

III.) This

last cat

PHILOSOPHY AND THE COGNITIVE SCIENCES TABLE Phenomenon

Explained

Functional

and

dis-

Neural

criminative abilities Presence

of

Particular

511

III

by

Phenomenological? and

anatomy

cortical

No

dynamics

qualia

qualitative

Not

explained

Not

explained

Yes

Yes

characters

Topology

of visual

Neural

space

qualitative

anatomy

dynamics realization

Yes

plus cortical of

assumption plus of phenomenologi

cal seeing through visual system

egory of explanation that neuroscientific logical facts even of qualia. character

has

and shows largely unremarked-upon, can some to be explanation applied phenomeno or precise it cannot the presence though explain gone

9. CONCLUSION in the sciences of case studies of cogni investigation our is philosophically It allows of psy productive. philosophy to us armchair chology proceed beyond speculation by confronting

A

"hands-on"

tion

with ter

the different in different

mechanism-like and

eling lems first

situations

(For

differences

example, of retinal of

explanations localization

in which does

of explanatory

explanations

distributed

cases

types cases.

so.)

It also

enables

leads us

systems

we

actually between

and

encoun the

local

the more

global or between the dynamics, the way and those in which mod to see more clearly whether prob such as the explanatory gap, are

cortical

by philosophers, posed in the face of empirical dissolved and theory. investigation (I argue that they have not been thus dissolved, to be dis and seem unlikely solved in the future.) But perhaps most it helps us to interestingly, see how

and philosophical rather empirical problems really intersect them in isolation. than treating For example, there does seem to be an abiding or epistemic inter gap, whose metaphysical explanatory is still in doubt. But this does not mean that nothing about pretation qualitative

is explained

phenomenology

by

the sciences

of cognition.

NOTES 1

In much of the material

Grossberg

and

the

Center

presented here about vision, for

Adaptive

Systems

at

I am indebted to Stephen

Boston

University,

where

I

STEVEN HORST

512 a

spent cerns

1993.

much

and Joseph Rouse, which of

philosophy

science.

on sabbatical

to

color-perception color

of

in

science Paul

note

that

either

of

this

phenomenology

this would

3

On

of

are,

and cal

not

does

a

employs spaces

such

equate

or

in

colors

with

He

admits

that

to

this might

to posit

have

would

at

of

this

their

exhausts

my of but

brain,

are

solipsism" constrained

a

such

color global a model of

structure

to color. As Clark

(1993) points

to that of Clark

(1993). While

to distinguish objective phenomena, in which the data for phenomenologi the of what by the phenomenology

the resulting relational description which another

generate

each

dimensions.

is contrary

capacities

one

six

least

with

space. I agree that qualia are best that

the

own.

for

he believes

respect

wholly a model

an NEH

of

auspices

of either

"methodological as color space

subject distinguishes, say,

qualia

course,

is not

solid

I was

while

for the Study of

in one region of the visual field. The model

I believe my analysis

this point,

Clark

Fraassen

or V4

a model

require

written

the

under

University

presentation the color

were

paper

portion of the visual field capable of responding out,

I

section,

introductory van Bas

and the Center

phenomenologically

possibilities

the

Humphreys,

retinal

In the con

awoke me from the illusions of reductionist

Statford

in my

of

properties

(1993) Sensory Qualities.

with

versions

at

errors

activity,

perception

the mathematical

Clark's

collectively

Previous

Information

Fellowship. Any 2 It is important

visual

on

work

in 1997-8 at Princeton University

and

Language

The

indebted to Austen

of philosophy the history influenced by conversations

about

was

in

sabbatical

cells is highly

a

provides

account

complete of the case

a

locates,

of

qualia. color

problems

in

identified

in the way he describes, but deny

symmetrical

nature.

REFERENCES Rudder: 1995, Explaining Attitudes, Lynne Cambridge and Robert C. Richardson: William 1993, Discovering as Strategies in Scientific and Localization Research, position

Baker,

Press.

University

Bechtel,

Deconm

Complexity: Princeton

University

Press Chalmers,

David:

Chalmers,

D.

tion', Clark,

1996,

J. and

Philosophical Austen: 1993, Robert:

Cummins,

The

Conscious F:

Jackson,

Oxford

Press.

University

'Conceptual

analysis

and

reductive

explana

Review. Oxford: Clarendon Press. Sensory Qualities, The Nature of Psyhcological Explanation,

MIT

1983,

Darden, Lindley and Nancy Maull: 44,

Mind,

2001.

Press.

1977. Tnterfield Theories', Philosophy of Science

43-64.

Glymour, Clark: Jaegwon Kim,

Notice: 1999, A mind Is a Terrible Thing to Waste-Critical "Mind in a Physical World"', Philosophy of Science 66 (3):

455-471.

Gregory, R. L: 1978, Eye And Brain: The Psychology Hill/World University Library, New York. Grossberg, Helmholtz,

Stephen: Hermann

1987, von:

1878, Zur

Lehre

of Seeing,

The

Brain, North-Holland, Adaptive der Physiologischen 1867, Handbuch

Amsterdam. Optik,

Leipzig. Hering,

E:

vom Lichtsinn,

Gerald

u.

S?hne,

3rd ed., McGraw

Wien.

1st ed., Voss,

PHILOSOPHY AND THE COGNITIVE SCIENCES Steven:

Horst,

1996,

and

Computation

Symbols,

A

Intentionality:

513

Critique

the

of

of California Press, Berkeley and Los

Computational Theory of Mind, University Angeles. Steven:

Horst,

Philosophy Reduction.

Forthcoming-b, L. M.: 1981, Color

Hurvich,

F:

Jackson,

Broad

1982, John.:

Jacobson,

Kim,

of

Steven:

Horst,

Levine,

1959,

J.: 1983,

64,

Black

Colin:

Inc.,

Associates,

thesis, Wesleyan

Press,

Cambridge,

in Colour

'Experiments

MA.

Sunderland,

32, 27-136. Quarterly and the Foundations

and

qualia:

of Color,

Form,

The

of

the

CT.

Middletown,

University,

Problem

Massachusetts.

Scientific American

Vision', Explanatory

Gap',

Pacific

5, 84

Philosophi

354-361.

Livingstone, Segregation and Perception, Science McGinn,

of Mind

Philosophy

in Physical World: An Essay on theMind-Body

MIT

'Materialism

cal Quarterly,

Sinauer

Vision,

Undergraduate

Causation,

Can

Beyond

jaegwon: 1998, Mind

Land, Edwin: (1959).

What

Science?'

qualia,' Philosophical 'Epiphenomenal of Consciousness 1997, "The Mysteries

Approach."

and Mental

Reduction:

'Beyond

Forthcoming-b, Post-Reductionist

from

Learn

1991,

240,

The

Motion

and Depth:

Anatomy,

Philosophy

Toward

a Resolution,

740-750.

Problem

of Consciousness:

Essays

well.

Nagel, Thomas: 1974, 'What is it like to be a bat?', Philosophical Review 4, 435-450. Sacks, Oliver: 1985, 'TheMan who Mistook his Wife for a Hat and Other Clinical Tales', Simon, Spillman,

Summit

Books,

Herbert:

New

York. D. of Discovery, S. Werner (eds.):

1977, Models

Lorthar

and

John

Academic

Dordrecht.

Reidel, 1990,

Visual

San Diego, Press, 'Two Cortical 1982,

The Neuro

Perception:

CA.

Foundations, physiological L. G and Mishkin, Ungerleider sis of Visual Behavior, Ingle,

D.J.

Young, Thomas:

'On the Theory of Light and Colours', Reprinted

R.C.

Teevan

Department Wesleyan

Binney

of Philosophy

University

Middletown, USA E-mail:

1801/1961,

and R.C

CT 06457

[email protected]

M.:

(eds.),

Colour

Vision,

Van

Visual

Nostrand

Systems',

(1961).

in Analy

in