- Email: [email protected]
Neural Systems and Cognitive Processes
Psychology in the 1990’s K.M.J. Lagerspetz and P. Niemi (Editors) 0 Elsevier Science Publishers B.V. (North-Holland), 1984
241
NEURAL SYSTEMS AND COGNITIVE PROCESSES Michael I. Posner University of Oregon, and Cognitive Neuropsychology Laboratory, Good Samaritan Hospital, Portland, U.S.A.
The desire t o discover and the fear o f oversimp lifying neural substrates for c o g n i t i v e processes has been a continuing problem f o r psychology since the failure o f phrenology. In the last twenty years, work i n cognition has usually proceeded in isolation f r o m studies o f t h e brain. Du ring this period cognitive researchers have developed detailed componential analyses o f many complex human skills. These analyses break skills such as word finding or scanning images i n t o sets o f elementary mental operations t h a t a r e suitable f o r computer programs. The development o f methods for imaging the human b r a i n and f o r exploring the cellular basis o f cog n i t i o n i n nonhuman animals has provided new impetus f o r e f f o r t s t o explore t h e level o f analysis a t which connections between cognitive processes and neural systems can be best developed. I n several areas o f research this e f f o r t promises t o provide advances which avoid over-simpli f i c a t i o n b u t s t i l l illu minate questions o f interest t o psychology and neuroscience. The solution t o great philosophical debates frequently comes when new methods change attitudes causing the next generation t o ignore w h a t had previously seemed l i k e a n insoluble bar t o progress.
The separation
between m i n d and brain has seemed a bar t o progress i n psychology.
I believe a m a j o r accomplishment o f the n e x t generation o f psychologists w i l l be t o cr eate the conditions that will e f f e c t i v e l y by-pass this separation.
Individual researchers w i l l move between elaborated theories
o f information f l o w and the anatomy and physiology o f neural systems
M.I.Posner
242
in th eir research.
N o r w i l l they have the fear o f the last generation
t h a t psychological theories o f cognition w i l l be reduced t o a m e r e gloss on th e physiology o f neural cells.
Instead neuroscientists w i l l
have come t o appreciate t h a t an understanding o f c o g n i t i v e theory, including the computations t o be performed by a system capable o f cognition, is needed t o guide their research i n t o t h e o f neural systems underlying thought.
Psychiatrists and neurologists interested in under-
standing patients suffering f r o m a wide range o f thought disorders w i l l also seek a theory of normal cognitive function r i c h enough t o a i d t h e m
in re habilitative methods. What w i l l have changed t o produce this new situation?
In part, t h e
change w i l l r e f l e c t an increasing sophistication about the n a t u r e o f t h e brain.
The complexity o f the reentrant processes c o n t r o l l i n g and co-
ordinating d i f f e r e n t neural systems w i l l provide increasing respect f o r t h e complexity o f analysis necessary t o work o u t t h e details o f any one cognitive function.
Thus, the supposition t h a t t h e key t o neural
functions underlying cognition m i g h t directly f a l l out o f t h e study o f simple systems such as the limulus or the grasshopper w i l l continue t o wane.
N e w neuroscience methods w i l l increase t h e opportunity f o r
examining the physiology o f cognitive processes as they a r e p e r f o r m e d by human beings.
The a b i l i t y t o image changes in cerebral blood flow,
u t i l i z a t i o n o f glucose and the interplay o f neural t r a n s m i t t e r systems as cognitive processes proceed w i l l physiology
o f human cognition.
open new ways o f examining the
These methods w i l l lead t o new
topics such as how resources change w i t h the exercise o f thought and how lesions in one area e f f e c t operations of o t h e r systems.
The new
methods w i l l force neuroscientists t o a great e r i n t e r e s t in understanding the dynamic t i m e dependent changes i n the human thought processes as they r e l a t e t o supplies o f dopamine, norepinephrine, serotonin other tra nsmitter systems.
or
243
Neural Systems and Cognitive PTocesses
I n m y opinion, an even greater change, much o f w h i c h has already taken place, is in th e n ature o f our understanding o f cognition.
Phrenology
t r i e d t o lo calize psychological faculties such as imagination, love, intuition, or sympathy.
One hundred years ago, these psychological
faculties were the units o f human cognition.
What c u r r e n t c o g n i t i v e
psychologist would discuss problem solving, or i n t u i t i o n as c o g n i t i v e faculties t o be localized in particular brain tissues?
Almost without
knowing it, cognitive psychologists have developed a d e t a i l e d p i c t u r e
o f the subtle, t i m e dependent processes takin g place i n the nervous systems.
This p i c t u r e is embedded in models o f i n f o r m a t i o n flow.
Moreover, these models have progressed dram a t i c a l l y over the last f i f t e e n years. The i n f o r m a t i o n processing analysis of language began w i t h Broadbent's
(1958) austere flow diagram f o r handling problems i n the p e r c e p t i o n o f speech signals.
By 1974, LaBerge and Samuels had elaborated t h i s
simple f l o w diagram i n t o treatment of the subtle complexities of the physical, phonological and semantic codes t h a t individual visual words a c t i vate a utomatically or via attention.
I n the t e n years since t h i s
diagram there has been powerful experimental evidence f o r many o f these proposit ions. LaBerge and Samuels' emphasis on t h e physical t o semantic coding process via phonological routes failed t o elaborate a number of subtle strategies by which a physically presented wor d could be transduced i n t o i t s meaning.
I n 1981, Coltheart, drawing upon t h e convergence o f
work in neuropsychology and cognitive psychology, was able t o provide evidence that delineated three d i f f e r e n t routes by w h i c h people could deal w i t h the individual l e t t e r s o f words.
Some patients c o u l d name
l e t t e r s with out being able t o develop an integ r a t e d visual w o r d ( w o r d form).
Other patients could name nonsense syllables b u t n o t handle
irregular words.
A t h i r d group o f patients could deal w i t h the i r r e g u l a r
words provided they were physically similar bu t could n o t name
M.1. Posner
244
nonsense material.
These routes correspond t o evidence t h a t t h e visual
system can synthesize l e t t e r s i n t o an abstract w o r d f o r m t h a t does n o t care about the case o f the l e t t e r s w i t h i n the visual system.
I t also
has shown t h a t this word f o r m has access t o semantics during the process of reading (Coltheart, 1981).
O f course i t was also c l e a r
from
studies o f the acquisition o f reading where reading i s d i f f i c u l t t h a t readers could sound out words and use the phonological codes as w e l l as the physical codes t o produce a semantic interpretation.
A major disadvantage o f these developing models of cognition in reading was that they failed t o indicate how the computations w e r e made t h a t allowed information t o f l o w f r o m one o f these processing systems t o another.
McClelland and Rumelha r t (1981) have given us
the s t a r t o f a computational model o f how a system sensitive t o visual features and l e t t e r s might have access t o i n f o r m a t i o n a t t h e w o r d level.
The basic process involves excitatory and i n h i b i t o r y connections
between levels and inhibitory connections w i t h i n levels.
McClelland
and Rumelhart were able t o program a computer t o recognize a t least a l i m i t e d number o f four l e t t e r words w r i t t e n in one font. Although much needs t o be done t o capture th e complexities o f the m u lti-ro ute view Coltheart has outlined i n t o a computational f o r m , i t
i s clear that the n e x t generation o f people w o r k i n g in reading w i I l have available computational models t o supplement m o r e f a m i l i a r f l o w diagrams. Models l i k e those o f Rumelhart and McClelland postulate t h e details o f f a c i l i t a t i o n and inhibition w i t h i n different codes produced by t h e occurrence o f an internal mental operation.
I t has been shown t h a t
these facilitations and inhibitions can be trac e d in chronometric experiments o f the ty pe experimental psychologists have been doing for t h e last twenty years (Posner, 1978).
F o r example, when a human subject
thinks about a category the members o f t h a t category become m o r e
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Neural Systems and Cognitive Processes available t o input than when no thought has occurred.
Thus, when one
thinks about the category "body part", processing the t a r g e t w o r d "leg" or "arm" w i l l be f a c i l i t a t e d (Neely, 1977).
This f a c i l i t a t i o n f r o m
the thought is sufficiently t i m e locked so t h a t subtle changes over hundreds o f milliseconds can be measured.
In the case o f active, sus-
tained thought there are also inhibitory consequences.
For some years there was doubt t h a t these pathway a c t i v a t i o n processes o f f a c i l i t a t i o n and inhibition measured in cognitive experiments The
could be connected t o the behavior of populations of neural cells.
advance o f work w i t h event related potentials has c l a r i f i e d this issue considerably.
I t seems increasingly clear t h a t f a c i l i t a t i o n as measured
in chronometric studies can also be seen i n e l e c t r i c a l a c t i v i t y .
For
example, when subjects are asked t o a t t e n d t o a source o f sensory signals not only are they faster i n responding t o signals t h a t come f r o m t h a t source, b u t neurons along t h a t pathway show a negative shift t h a t has been described in some detail b y Naatanen (1982). I t has been shown repeatedly that violations in expectancy which slow
m e n tal operations also produce powerful e l e c t r i c a l changes (Donchin e t al.,
1978).
For example, consider the sentence "I t a k e m y c o f f e e
w i t h sugar and cream".
The last word i s highly p r i m e d and easily pro-
cessed when i t arrives because i t f i t s so w e l l w i t h the context. ever, if the expectancy is violated (e.g.,
How-
w i t h sugar and dog) one finds
a powerful negative s h i f t in the event relate d p o t e n t i a l (Kutas, Lindamood & Hillyard, 1983) that appears t o occur whenever a strong l e x i ca l expectancy is disconfirmed. In yet another domain, Kosslyn (1980) has presented a c o m p u t a t i o n a l
model f o r the process o f visual imagery.
Rel y i n g on about one dozen
elementary operations, Kosslyn's model suggests how an image is created f r o m i n f o r m a t i o n stored in long t e r m m e m o r y and i s scanned by a set o f analog processes that move a t t e n t i o n around t h e image
246
MI. Posner
and zoom in on individual parts o f it.
This model is t i e d t o t h e
properties o f a ttention by a number o f experiments on scanning o f visual images (Kosslyn, 1980; Pinker, 1980). I t seems clear that the same internal mechanisms involved in t h e
scanning of visual images are also used when we s h i f t a t t e n t i o n f r o m one part o f the visual f i e l d t o another (Posner, 1980).
Moreover these
studies reveal t i m e locking of the mental operations o f disengagement f r o m the cu rrent focus of attention, movement across the visual field, and engagement o f the target.
It has been possible t o show t h a t
e l e ctrical a c t i v i t y recorded a t the scalp (van Voorhis & Hillyard, 1977) and operations o f individual neural cells (Wurtz, Goldberg & Robinson, 1980) are a f f e c t e d by these t i m e locked shift s o f attention.
Studies
o f patients extend the degree t o which i t has been possible t o connect the operations o f cognitive models w i t h underlying neural systems (Posner, Cohen & Rafal, 1982). Nor do these t w o models of imagery and reading stand in isolation. Research in a r t i f i c i a l intelligence (Duda & S h o r t c l i f f , 1983) suggests t h a t models o f a large number o f expert functions such as the diagnosis o f medical disease, reading psychological articles, composing music, or c i t i n g legal precedents w i l l also be developed.
While these expert
systems are only task analyses and have no necessary psychological implications, the kinds of computational models already developed f o r reading and imagery should allow growing links t o b r a i n function. The f u t u r e appears likely t o bring closer links between chronometric experiments and changes i n underlying brain processes.
The n e x t
generation o f researchers w i l l have increasing confidence t h a t t h e measurement o f cognitive function via chrono m e t r i c studies index imp o r tant brain processes and must be taken seriously.
This w i l l f o l l o w
a simila r s h i f t leading psychophysiologists t o appreciate t h a t measurem e nt o f sensory processes can help .us understand physiological systems t h a t mediate vision and hearing.
Neural Systems and Cognitive Processes
247
What w i l l be the consequences of a change in a t t i t u d e s about t h e relationship o f brain and mind?
Among the early consequences w i l l be
changes in academic institutions themselves. changes i n departments of psychology.
Already we are seeing
Courses in physiological psy-
chology once taught only by people studying non-human animals can now take advantage o f a re-awakening o f inter e s t in the physiology o f human cognitive functions and an understanding t h a t these functions can be studied physiologically.
Psychology departments w i l l house experts
i n the study o f the physiology o f the human b r a i n in very much t h e way that biology departments now dominate i n t h e i r study o f non-human nervous systems. I t seems clear that these changes in academic organization and research w i l l n o t result in the diminished r o l e f o r psychology. For the last several
years, experimental psychology has seemed a b i t schizophrenic
in i t s e f f o r t s on the one hand t o f o l l o w a r t i f i c i a l intelligence i n t o the
complexities o f producing programs t h a t p e r f o r m an i n t e l l e c t u a l funct i o n a t the highest level and on the other hand, a t t e m p t i n g t o f o l l o w neuroscience i n t o how nervous systems p e r f o r m elementary functions l i k e t h e d etection o f individual line slopes or the segmentation o f figure f r o m ground.
B o t h o f these approaches have made progress.
There i s genuine excitement in being able t o develop a c o m p u t e r sirnul a t i o n th at can p e r f o r m an intellectual functio n i n the r e a l w o r l d supplementing human expertness.
On the othe r hand, the b e a u t i f u l
s i m plicity o f neural functioning i n the primar y sensory areas has also been a source o f exciting developments.
Each o f these areas has
developed i t s own approach and technology. threatened by the developments of the other.
N e i t h e r need seem E v e n a deep under-
standing o f neurology w i l l not itself t e l l us how t o design an e x p e r t system.
N o r does our understanding of cogni t i v e f u n c t i o n a t t h e l e v e l
o f f l o w diagrams d i c t a t e any particular struct u r e o f nervous systems. However, many o f the most e x c i t i n g questions of science l i e a t the boundaries between these two areas.
M.I.Power
248
There w i l also be changes in the way i n whi c h research is done. Biologists frequently work on a particular organism a t many levels descri binc i t s behavior, anatomy, recording f r o m individual cells and perhaps even analyzing t h e m chemically.
Psychologists interested in
cognition w i l l also have a t their disposal a va r i e t y o f methods.
At
one level they w i l l be able t o describe a cogn i t i v e task through f o r m s o f protocol analysis (Ericsson & Simon, 1980).
These w i l l lead t o t h e
production o f computer programs which w i l l be capable o f p e r f o r m i n g the tasks by executing a sequence o f specified m e n t a l operations.
The
m en tal operations involved can be examined by c h r o n o m e t r i c techniques
in te rms o f th eir t i m e locked facilitations and inhibitions.
I t w i l l be
possible t o investigate the neural basis of these t i m e locked f a c i l i t a tions via event related potentials, cerebral blood flow, m e t a b o l i c changes, and perhaps also on-line biochemical analysis.
Students o f
cognition w i l l be able t o trace disorders o f process by studies o f neurological d e f i c i t s and w i l l be able t o investigate t h e consequences o f various forms
o f rehabilitation, including drug therapy and retraining.
There w i l l doubtless be more emphasis on understanding r e a l l y high levels of performance by a l l these methods.
In t h e process of w r i t i n g
o f programs t o produce expert performance, one may w e l l g e t new ideas on how b e t t e r t o t r a i n exceptional levels o f performance in children and adults. What w i l l be the consequences o f these new developments o f psychological
theory f o r philosophical views about the relationship o f m i n d and
brain?
Although I feel moderately confident about the s c i e n t i f i c pre-
dictions made in this essay, I have relatively l i t t l e idea what e f f e c t they m i g h t have upon the philosophical t h i s d i f f i c u l t issue.
disputes t h a t have attended
No doubt philosophers w i l l continue t o debate
these issues b u t perhaps there is already in th e philosophical l i t e r a t u r e a point of view quite congenial t o the arguments t h a t t h i s paper makes.
In a book on philosophical problems in psychology (Bolton,
1979) C o l i n McGinn, a philosopher a t Universi t y College, London,
Neural Systems and Cognitive Processes
249
concludes his essay on a c t i o n and i t s explanations by saying: "It appears, then, that our earlier c l a i m s together i m p l y a version o f the psycho-physical i d e n t i t y thesis. This was, perhaps, already plain in respect o f actions: they are each severally identical w i t h particular movements o f the body, describable in purely physical terms. B u t it i s something o f a surprise t o f i n d i t entailed t h a t t h e m e n t a l events which cause actions are also physical events o c c u r r i n g in the brain...
This conclusion may prompt t h e hope, or fear, that, a f t e r all, rationalization is reducible to, and t h e r e f o r e in p r i n ciple, replaceable by, purely physical explanation. That does n o t follow, however. F o r the physicalist, thesis just advocated was only t o t h e e f f e c t t h a t each p a r t i c u l a r m e n t a l event which causes an ac t i o n i s i d e n t i c a l w i t h some p a r t i c u l a r physical event which causes a bodily movement, i t d id n o t c l a i m t h a t the m e n t a l properties w h i c h q u a l i f y a mental event as f a l l i n g under a m e n t a l description are id entical w i t h t h e physical properties each such event instantiates. And f o r a reductio n t o be possible m e n t a l and physical properties must be i d e n t i c a l or a t least necessarily one-one correlated." (p. 40-41) According t o this view, our understanding o f physical events o f t h e brain may indeed constrain our understanding o f m e n t a l events but may not e n t i r e l y determine them.
Perhaps in the end, philosophers and psy-
chologists w i l l overcome the inhibitions o f one hundred years and thus,
be able t o reason b o t h f r o m our understanding o f neuroscience and our understanding o f cognition.
M.I.Power
250
REFERENCES
1
Broadbent, D. E.' London, 1958.
2
Coltheart, M. Disorders o f reading and their implications for models o f normal reading. Visible Language, XV, 1981, 245-286.
3
Donchin, E., R i t t e r , W. & McCallum, W. C. Cognitive psychophysiology. The endogenous components o f the ERP. In E. Calloway, P. Tueting & S. H. Koslow (Eds.), Event related potentials in man. N e w York: Academic, 1978.
Perception and communication. Pergamon:
Duda, R. 0. & Shortcliff, E. S. Science, 1983, 220, 261 -268.
Expert systems research.
Ericsson, K. A. & Simon, H. A. Verbal reports as data. Psychological review, 1980, 87, 21 5-251. Kosslyn, S. 1980.
Image and mind.
Harvard Press: Cambridge,
Kutas, M., Lindamood, T. M. & Hillyard, S. A. Word expectancy and event related potentials during sentence processing. In S. Kornblum & J. Requin (Eds.), Preparatory States and Processes. Hillsdale, N. J.: Erlbaum, 1983. LaBerge, D. & Samuels, J. Toward a model o f automatic information processing i n reading. Cognitive psychology, 1974, 6 , 293-323. McClelland, J. L. & Rumelhart, D. E. A n interactive activation model o f context e f f e c t s in l e t t e r perception. P a r t I. A n account o f basic findings. Psychological review, 1981, 88, 375-398.
10
McGinn, C. A c t i o n and i t s explanation. In N. Bolton (Ed.), Philosophical problems in psychology. Msthuen: London, 1979.
11
Naatanen, R. Processing negativity: an evoked potential r e f l e c t i o n o f selective attention. Psychological bulletin, 1982, 92, 605-640.
12
Neely, 3. Semantic priming and r e t r i e v a l from lexical memory: Roles in inhibitionless spreading activation and l i m i t e d capacity attention. Journal of experimental psychology: General, 1977, 106, 226-?.'J1..
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Pinker, 5.
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Posner, M. I. Chronometric explorations of mind: The third Paul M. F i t t s lectures. Hillsdale, N. J.: L a w r e n c e Erlbaum Associates, 1978.
15
Posner, M. I. Orienting of Attention. The VIIth Sir F r e d e r i c B a r t l e t t l e c t u r e , Quarterly journal of experi-
Mental imagery and t h e third dimension.
Journal of experimental psychology: General, 1980, 109, 354-371.
mental psychology, 1980, 32, 3-25.
16
Posner, M. I., Cohen, Y . & R a f a l , R. D. Neural s y s t e m s control o f s p a t i a l orienting. Philosophical transactions of
the Royal Society London, 1982, 8298, 187-198.
17
R u m e l h a r t , D. E. & McClelland, J. L. An i n t e r a c t i v e a c t i v a t i o n model of c o n t e x t e f f e c t s in l e t t e r perception: P a r t 2. The c o n t e x t u a l e n h a n c e m e n t effect and s o m e tests and extensions of t h e model. Psychological review, 1982, 89, 60-77.
18
van Voorhis, 5. & Hillyard, S. A. Visual evoked potentials a n d s e l e c t i v e a t t e n t i o n t o points in space. Perception and psychophysics, 1977, 22, 54-62.
19
Wurtz, R. H., Goldberg, M. E. & Robinson, D. L. Behavioral modulation of visual responses in t h e monkey: Stimulus selection f o r a t t e n t i o n and movement. Proaress in psychobiology & physiological psychology, 1980, 9,
43-83.
2
241
NEURAL SYSTEMS AND COGNITIVE PROCESSES Michael I. Posner University of Oregon, and Cognitive Neuropsychology Laboratory, Good Samaritan Hospital, Portland, U.S.A.
The desire t o discover and the fear o f oversimp lifying neural substrates for c o g n i t i v e processes has been a continuing problem f o r psychology since the failure o f phrenology. In the last twenty years, work i n cognition has usually proceeded in isolation f r o m studies o f t h e brain. Du ring this period cognitive researchers have developed detailed componential analyses o f many complex human skills. These analyses break skills such as word finding or scanning images i n t o sets o f elementary mental operations t h a t a r e suitable f o r computer programs. The development o f methods for imaging the human b r a i n and f o r exploring the cellular basis o f cog n i t i o n i n nonhuman animals has provided new impetus f o r e f f o r t s t o explore t h e level o f analysis a t which connections between cognitive processes and neural systems can be best developed. I n several areas o f research this e f f o r t promises t o provide advances which avoid over-simpli f i c a t i o n b u t s t i l l illu minate questions o f interest t o psychology and neuroscience. The solution t o great philosophical debates frequently comes when new methods change attitudes causing the next generation t o ignore w h a t had previously seemed l i k e a n insoluble bar t o progress.
The separation
between m i n d and brain has seemed a bar t o progress i n psychology.
I believe a m a j o r accomplishment o f the n e x t generation o f psychologists w i l l be t o cr eate the conditions that will e f f e c t i v e l y by-pass this separation.
Individual researchers w i l l move between elaborated theories
o f information f l o w and the anatomy and physiology o f neural systems
M.I.Posner
242
in th eir research.
N o r w i l l they have the fear o f the last generation
t h a t psychological theories o f cognition w i l l be reduced t o a m e r e gloss on th e physiology o f neural cells.
Instead neuroscientists w i l l
have come t o appreciate t h a t an understanding o f c o g n i t i v e theory, including the computations t o be performed by a system capable o f cognition, is needed t o guide their research i n t o t h e o f neural systems underlying thought.
Psychiatrists and neurologists interested in under-
standing patients suffering f r o m a wide range o f thought disorders w i l l also seek a theory of normal cognitive function r i c h enough t o a i d t h e m
in re habilitative methods. What w i l l have changed t o produce this new situation?
In part, t h e
change w i l l r e f l e c t an increasing sophistication about the n a t u r e o f t h e brain.
The complexity o f the reentrant processes c o n t r o l l i n g and co-
ordinating d i f f e r e n t neural systems w i l l provide increasing respect f o r t h e complexity o f analysis necessary t o work o u t t h e details o f any one cognitive function.
Thus, the supposition t h a t t h e key t o neural
functions underlying cognition m i g h t directly f a l l out o f t h e study o f simple systems such as the limulus or the grasshopper w i l l continue t o wane.
N e w neuroscience methods w i l l increase t h e opportunity f o r
examining the physiology o f cognitive processes as they a r e p e r f o r m e d by human beings.
The a b i l i t y t o image changes in cerebral blood flow,
u t i l i z a t i o n o f glucose and the interplay o f neural t r a n s m i t t e r systems as cognitive processes proceed w i l l physiology
o f human cognition.
open new ways o f examining the
These methods w i l l lead t o new
topics such as how resources change w i t h the exercise o f thought and how lesions in one area e f f e c t operations of o t h e r systems.
The new
methods w i l l force neuroscientists t o a great e r i n t e r e s t in understanding the dynamic t i m e dependent changes i n the human thought processes as they r e l a t e t o supplies o f dopamine, norepinephrine, serotonin other tra nsmitter systems.
or
243
Neural Systems and Cognitive PTocesses
I n m y opinion, an even greater change, much o f w h i c h has already taken place, is in th e n ature o f our understanding o f cognition.
Phrenology
t r i e d t o lo calize psychological faculties such as imagination, love, intuition, or sympathy.
One hundred years ago, these psychological
faculties were the units o f human cognition.
What c u r r e n t c o g n i t i v e
psychologist would discuss problem solving, or i n t u i t i o n as c o g n i t i v e faculties t o be localized in particular brain tissues?
Almost without
knowing it, cognitive psychologists have developed a d e t a i l e d p i c t u r e
o f the subtle, t i m e dependent processes takin g place i n the nervous systems.
This p i c t u r e is embedded in models o f i n f o r m a t i o n flow.
Moreover, these models have progressed dram a t i c a l l y over the last f i f t e e n years. The i n f o r m a t i o n processing analysis of language began w i t h Broadbent's
(1958) austere flow diagram f o r handling problems i n the p e r c e p t i o n o f speech signals.
By 1974, LaBerge and Samuels had elaborated t h i s
simple f l o w diagram i n t o treatment of the subtle complexities of the physical, phonological and semantic codes t h a t individual visual words a c t i vate a utomatically or via attention.
I n the t e n years since t h i s
diagram there has been powerful experimental evidence f o r many o f these proposit ions. LaBerge and Samuels' emphasis on t h e physical t o semantic coding process via phonological routes failed t o elaborate a number of subtle strategies by which a physically presented wor d could be transduced i n t o i t s meaning.
I n 1981, Coltheart, drawing upon t h e convergence o f
work in neuropsychology and cognitive psychology, was able t o provide evidence that delineated three d i f f e r e n t routes by w h i c h people could deal w i t h the individual l e t t e r s o f words.
Some patients c o u l d name
l e t t e r s with out being able t o develop an integ r a t e d visual w o r d ( w o r d form).
Other patients could name nonsense syllables b u t n o t handle
irregular words.
A t h i r d group o f patients could deal w i t h the i r r e g u l a r
words provided they were physically similar bu t could n o t name
M.1. Posner
244
nonsense material.
These routes correspond t o evidence t h a t t h e visual
system can synthesize l e t t e r s i n t o an abstract w o r d f o r m t h a t does n o t care about the case o f the l e t t e r s w i t h i n the visual system.
I t also
has shown t h a t this word f o r m has access t o semantics during the process of reading (Coltheart, 1981).
O f course i t was also c l e a r
from
studies o f the acquisition o f reading where reading i s d i f f i c u l t t h a t readers could sound out words and use the phonological codes as w e l l as the physical codes t o produce a semantic interpretation.
A major disadvantage o f these developing models of cognition in reading was that they failed t o indicate how the computations w e r e made t h a t allowed information t o f l o w f r o m one o f these processing systems t o another.
McClelland and Rumelha r t (1981) have given us
the s t a r t o f a computational model o f how a system sensitive t o visual features and l e t t e r s might have access t o i n f o r m a t i o n a t t h e w o r d level.
The basic process involves excitatory and i n h i b i t o r y connections
between levels and inhibitory connections w i t h i n levels.
McClelland
and Rumelhart were able t o program a computer t o recognize a t least a l i m i t e d number o f four l e t t e r words w r i t t e n in one font. Although much needs t o be done t o capture th e complexities o f the m u lti-ro ute view Coltheart has outlined i n t o a computational f o r m , i t
i s clear that the n e x t generation o f people w o r k i n g in reading w i I l have available computational models t o supplement m o r e f a m i l i a r f l o w diagrams. Models l i k e those o f Rumelhart and McClelland postulate t h e details o f f a c i l i t a t i o n and inhibition w i t h i n different codes produced by t h e occurrence o f an internal mental operation.
I t has been shown t h a t
these facilitations and inhibitions can be trac e d in chronometric experiments o f the ty pe experimental psychologists have been doing for t h e last twenty years (Posner, 1978).
F o r example, when a human subject
thinks about a category the members o f t h a t category become m o r e
245
Neural Systems and Cognitive Processes available t o input than when no thought has occurred.
Thus, when one
thinks about the category "body part", processing the t a r g e t w o r d "leg" or "arm" w i l l be f a c i l i t a t e d (Neely, 1977).
This f a c i l i t a t i o n f r o m
the thought is sufficiently t i m e locked so t h a t subtle changes over hundreds o f milliseconds can be measured.
In the case o f active, sus-
tained thought there are also inhibitory consequences.
For some years there was doubt t h a t these pathway a c t i v a t i o n processes o f f a c i l i t a t i o n and inhibition measured in cognitive experiments The
could be connected t o the behavior of populations of neural cells.
advance o f work w i t h event related potentials has c l a r i f i e d this issue considerably.
I t seems increasingly clear t h a t f a c i l i t a t i o n as measured
in chronometric studies can also be seen i n e l e c t r i c a l a c t i v i t y .
For
example, when subjects are asked t o a t t e n d t o a source o f sensory signals not only are they faster i n responding t o signals t h a t come f r o m t h a t source, b u t neurons along t h a t pathway show a negative shift t h a t has been described in some detail b y Naatanen (1982). I t has been shown repeatedly that violations in expectancy which slow
m e n tal operations also produce powerful e l e c t r i c a l changes (Donchin e t al.,
1978).
For example, consider the sentence "I t a k e m y c o f f e e
w i t h sugar and cream".
The last word i s highly p r i m e d and easily pro-
cessed when i t arrives because i t f i t s so w e l l w i t h the context. ever, if the expectancy is violated (e.g.,
How-
w i t h sugar and dog) one finds
a powerful negative s h i f t in the event relate d p o t e n t i a l (Kutas, Lindamood & Hillyard, 1983) that appears t o occur whenever a strong l e x i ca l expectancy is disconfirmed. In yet another domain, Kosslyn (1980) has presented a c o m p u t a t i o n a l
model f o r the process o f visual imagery.
Rel y i n g on about one dozen
elementary operations, Kosslyn's model suggests how an image is created f r o m i n f o r m a t i o n stored in long t e r m m e m o r y and i s scanned by a set o f analog processes that move a t t e n t i o n around t h e image
246
MI. Posner
and zoom in on individual parts o f it.
This model is t i e d t o t h e
properties o f a ttention by a number o f experiments on scanning o f visual images (Kosslyn, 1980; Pinker, 1980). I t seems clear that the same internal mechanisms involved in t h e
scanning of visual images are also used when we s h i f t a t t e n t i o n f r o m one part o f the visual f i e l d t o another (Posner, 1980).
Moreover these
studies reveal t i m e locking of the mental operations o f disengagement f r o m the cu rrent focus of attention, movement across the visual field, and engagement o f the target.
It has been possible t o show t h a t
e l e ctrical a c t i v i t y recorded a t the scalp (van Voorhis & Hillyard, 1977) and operations o f individual neural cells (Wurtz, Goldberg & Robinson, 1980) are a f f e c t e d by these t i m e locked shift s o f attention.
Studies
o f patients extend the degree t o which i t has been possible t o connect the operations o f cognitive models w i t h underlying neural systems (Posner, Cohen & Rafal, 1982). Nor do these t w o models of imagery and reading stand in isolation. Research in a r t i f i c i a l intelligence (Duda & S h o r t c l i f f , 1983) suggests t h a t models o f a large number o f expert functions such as the diagnosis o f medical disease, reading psychological articles, composing music, or c i t i n g legal precedents w i l l also be developed.
While these expert
systems are only task analyses and have no necessary psychological implications, the kinds of computational models already developed f o r reading and imagery should allow growing links t o b r a i n function. The f u t u r e appears likely t o bring closer links between chronometric experiments and changes i n underlying brain processes.
The n e x t
generation o f researchers w i l l have increasing confidence t h a t t h e measurement o f cognitive function via chrono m e t r i c studies index imp o r tant brain processes and must be taken seriously.
This w i l l f o l l o w
a simila r s h i f t leading psychophysiologists t o appreciate t h a t measurem e nt o f sensory processes can help .us understand physiological systems t h a t mediate vision and hearing.
Neural Systems and Cognitive Processes
247
What w i l l be the consequences of a change in a t t i t u d e s about t h e relationship o f brain and mind?
Among the early consequences w i l l be
changes in academic institutions themselves. changes i n departments of psychology.
Already we are seeing
Courses in physiological psy-
chology once taught only by people studying non-human animals can now take advantage o f a re-awakening o f inter e s t in the physiology o f human cognitive functions and an understanding t h a t these functions can be studied physiologically.
Psychology departments w i l l house experts
i n the study o f the physiology o f the human b r a i n in very much t h e way that biology departments now dominate i n t h e i r study o f non-human nervous systems. I t seems clear that these changes in academic organization and research w i l l n o t result in the diminished r o l e f o r psychology. For the last several
years, experimental psychology has seemed a b i t schizophrenic
in i t s e f f o r t s on the one hand t o f o l l o w a r t i f i c i a l intelligence i n t o the
complexities o f producing programs t h a t p e r f o r m an i n t e l l e c t u a l funct i o n a t the highest level and on the other hand, a t t e m p t i n g t o f o l l o w neuroscience i n t o how nervous systems p e r f o r m elementary functions l i k e t h e d etection o f individual line slopes or the segmentation o f figure f r o m ground.
B o t h o f these approaches have made progress.
There i s genuine excitement in being able t o develop a c o m p u t e r sirnul a t i o n th at can p e r f o r m an intellectual functio n i n the r e a l w o r l d supplementing human expertness.
On the othe r hand, the b e a u t i f u l
s i m plicity o f neural functioning i n the primar y sensory areas has also been a source o f exciting developments.
Each o f these areas has
developed i t s own approach and technology. threatened by the developments of the other.
N e i t h e r need seem E v e n a deep under-
standing o f neurology w i l l not itself t e l l us how t o design an e x p e r t system.
N o r does our understanding of cogni t i v e f u n c t i o n a t t h e l e v e l
o f f l o w diagrams d i c t a t e any particular struct u r e o f nervous systems. However, many o f the most e x c i t i n g questions of science l i e a t the boundaries between these two areas.
M.I.Power
248
There w i l also be changes in the way i n whi c h research is done. Biologists frequently work on a particular organism a t many levels descri binc i t s behavior, anatomy, recording f r o m individual cells and perhaps even analyzing t h e m chemically.
Psychologists interested in
cognition w i l l also have a t their disposal a va r i e t y o f methods.
At
one level they w i l l be able t o describe a cogn i t i v e task through f o r m s o f protocol analysis (Ericsson & Simon, 1980).
These w i l l lead t o t h e
production o f computer programs which w i l l be capable o f p e r f o r m i n g the tasks by executing a sequence o f specified m e n t a l operations.
The
m en tal operations involved can be examined by c h r o n o m e t r i c techniques
in te rms o f th eir t i m e locked facilitations and inhibitions.
I t w i l l be
possible t o investigate the neural basis of these t i m e locked f a c i l i t a tions via event related potentials, cerebral blood flow, m e t a b o l i c changes, and perhaps also on-line biochemical analysis.
Students o f
cognition w i l l be able t o trace disorders o f process by studies o f neurological d e f i c i t s and w i l l be able t o investigate t h e consequences o f various forms
o f rehabilitation, including drug therapy and retraining.
There w i l l doubtless be more emphasis on understanding r e a l l y high levels of performance by a l l these methods.
In t h e process of w r i t i n g
o f programs t o produce expert performance, one may w e l l g e t new ideas on how b e t t e r t o t r a i n exceptional levels o f performance in children and adults. What w i l l be the consequences o f these new developments o f psychological
theory f o r philosophical views about the relationship o f m i n d and
brain?
Although I feel moderately confident about the s c i e n t i f i c pre-
dictions made in this essay, I have relatively l i t t l e idea what e f f e c t they m i g h t have upon the philosophical t h i s d i f f i c u l t issue.
disputes t h a t have attended
No doubt philosophers w i l l continue t o debate
these issues b u t perhaps there is already in th e philosophical l i t e r a t u r e a point of view quite congenial t o the arguments t h a t t h i s paper makes.
In a book on philosophical problems in psychology (Bolton,
1979) C o l i n McGinn, a philosopher a t Universi t y College, London,
Neural Systems and Cognitive Processes
249
concludes his essay on a c t i o n and i t s explanations by saying: "It appears, then, that our earlier c l a i m s together i m p l y a version o f the psycho-physical i d e n t i t y thesis. This was, perhaps, already plain in respect o f actions: they are each severally identical w i t h particular movements o f the body, describable in purely physical terms. B u t it i s something o f a surprise t o f i n d i t entailed t h a t t h e m e n t a l events which cause actions are also physical events o c c u r r i n g in the brain...
This conclusion may prompt t h e hope, or fear, that, a f t e r all, rationalization is reducible to, and t h e r e f o r e in p r i n ciple, replaceable by, purely physical explanation. That does n o t follow, however. F o r the physicalist, thesis just advocated was only t o t h e e f f e c t t h a t each p a r t i c u l a r m e n t a l event which causes an ac t i o n i s i d e n t i c a l w i t h some p a r t i c u l a r physical event which causes a bodily movement, i t d id n o t c l a i m t h a t the m e n t a l properties w h i c h q u a l i f y a mental event as f a l l i n g under a m e n t a l description are id entical w i t h t h e physical properties each such event instantiates. And f o r a reductio n t o be possible m e n t a l and physical properties must be i d e n t i c a l or a t least necessarily one-one correlated." (p. 40-41) According t o this view, our understanding o f physical events o f t h e brain may indeed constrain our understanding o f m e n t a l events but may not e n t i r e l y determine them.
Perhaps in the end, philosophers and psy-
chologists w i l l overcome the inhibitions o f one hundred years and thus,
be able t o reason b o t h f r o m our understanding o f neuroscience and our understanding o f cognition.
M.I.Power
250
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2