PSYC Call for Book Reviewers: Neuropsychology of Lashley & Hebb

Stevan Harnad harnad at
Sat Sep 18 14:55:16 EST 1999


    Below is the Precis of "The Neuropsychological Theories of Lashley
    and Hebb" by Jack Orbach (427 lines). This book has been selected
    for multiple review in PSYCOLOQUY. If you wish to submit a formal
    book review please write to psyc at indicating what
    expertise you would bring to bear on reviewing the book if you were
    selected to review it.

    (If you have never reviewed for PSYCOLOQUY or Behavioral & Brain
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    Psycoloquy reviews are of the book not the Precis. Length should be
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    My rationale for seeking open peer commentary is primarily that the
    book says some things about both Lashley and Hebb that some peers
    might find controversial and startling if not downright outrageous.
    To get these views out in the open may be of pedagogical value not
    only to to me but to the neuropsychological community at large.
    Obviously, I don't believe that my arguments are wrong or weak. But
    the feedback I get might conceivably persuade me to rethink the

psycoloquy.99.10.029.lashley-hebb.1.orbach              Sat Sep 18 1999
ISSN 1055-0143                (16 paragraphs, 16 references, 427 lines)
PSYCOLOQUY is sponsored by the American Psychological Association (APA)
                Copyright 1999 Jack Orbach

        Precis of:
        Precis of Orbach on Lashley-Hebb
    [University Press of America, 1998 xiv, 395 pp. ISBN: 0-761-81165-6]

        Jack Orbach
        Department of Psychology
        Queens College
        Flushing, NY
        jorbach at

    ABSTRACT: Beginning in the 1920s, K. S. Lashley startled
    psychologists with his theories of the memory trace within the
    cerebral cortex. Using terms such as terms mass action,
    equipotentiality, and sensory/motor equivalence, Lashley presented
    evidence that the engram is widely distributed in the brain, and
    that unactivated synapses, like activated ones, seem to show
    evidence of learning. His research and nativistic theories made him
    world famous by 1929, when he was just 39. He spent his
    professional career searching for a mechanism for the reduplication
    of the engram. While his contemporaries tried to specify the locus
    of the engram in the brain, Lashley found it everywhere. He liked
    to quip that the problem is not to find where the trace is located,
    but where it is not. Lashley's student, D. O. Hebb, published his
    empiricistic theories in 1949, in "The Organization of Behavior,"
    and the monograph created a sensation. Hebb used Lorente de No's
    reverberatory circuit to provide a mechanism to maintain activity
    in the cerebral cortex after the stimulus terminated, the so-called
    central autonomous process. This led him to the cell assembly, a
    complex reverberatory circuit that could be assembled by
    experience. Changes in resistance at the synapse with learning came
    to be called the Hebb synapse. That monograph was highly praised
    for the breadth of its treatment. The present book documents how
    Lashley anticipated Hebb's introduction of the reverberatory
    circuit by some 12 years. Lashley's Vanuxem Lectures of 1952 are
    printed for the first time, together with nine of his previously
    published theoretical papers. Lashley's and Hebb's theories are
    reviewed and reevaluated fifty years after publication of Hebb's
    monograph, and a systematic effort is made to compare and contrast
    the views of teacher and student.

    KEYWORDS: cell assembly, central autonomous process, engram,
    equipotentiality, Hebb, Hebbian learning, Lashley, localization,
    memory trace, nativism, reverberatory circuit, Vanuxem Lectures

1. Part 1 of the book opens with a summary of Lashley's last public
lecture given at the University of Rochester in 1957, one year before
his death and eight years after the publication of Hebb's monograph. In
this lecture, Lashley was still consumed with the notion of irradiating
waves of excitation in the cerebral cortex, a notion he developed in
detail in 1942. In citing theories of stimulus equivalence, Lashley
wrote 'That of Hebb is most in accord with conditioned reflex theory.
He assumes that multiple paths are developed by learning. Such learning
is ruled out by a mass of evidence for innate discriminations and
equivalencies.' In this unpublished address, Lashley cited Hebb's
empiricistic theory for the first and only time. He never cited the
monograph itself in the literature.

2. An early chapter entitled 'Setting the Stage' offers another look at
Lashley's early critique of the native Watsonian connectionism of his
day. Lashley's early efforts to revise and revitalize
neuropsychological theory are reviewed. The problem, Lashley suggested
in the 1920s, was the omission of the brain from the Watsonian S-R
formula. And when a model of cortical function was finally introduced,
using the analogy of the telephone switchboard, it was based on the
idea of linear reflex activity in the spinal cord, as suggested by
Dewey, leaving no room for psychological categories that require
sustained activity in the brain such as thought, memory, emotion,
motivation, selective attention and the like. And then, along came
Pavlov who undercut all contemporary speculations of psychologists with
his physiological theories of conditioned reflexes and brain function.
It was at this point that Lashley burst upon the scene.

3. Hebb must have experienced an epiphany when he was introduced to the
reverberatory circuit of Lorente de N. He realized that this anatomical
curiosity provided him with a mechanism for the autonomous central
process that he developed so masterfully in the 1949 monograph. Hebb's
revelation involving the reverberatory circuit was especially important
for it gave neurological meaning to the earlier proposals of central
motive state of Morgan and central excitatory mechanism of Beach as
well as the putative reduplicated memory trace of Lashley. However,
Lashley had already appropriated the reverberatory circuit for
neuropsychological theory in 1937, some 12 years before Hebb's
monograph was published and some three years before its presentation by
Hilgard and Marquis in their Conditioning and Learning of 1940. This is
documented with excerpts from Lashley's papers published in 1937, 1938,
1941, 1942 and 1949. The latter two papers are republished in their
entirety in this volume.

4. The next chapter deals with the learning theory that synaptic
resistance is reduced by the passage of the nerve impulse. Lashley's
1924 assault on this theory is reviewed in detail. (This 1924 paper is
also reprinted in this volume.) In Lashley's own words, 'Among the many
unsubstantiated beliefs concerning the physiology of the learning
process, none is more widely prevalent than the doctrine that the
passage of the nerve impulse through the synapse somehow reduces
synaptic resistance and leads to the fixation of a new habit . . . but
no direct evidence for synaptic resistance has ever been obtained. The
hypothesis is not based upon neurological data but is merely a
restatement of the observed fact that increased efficiency follows
repeated performance . . . Familiar learning curves are obviously an
expression of these successive integrations and we have no knowledge of
the conditions prevailing in formation of a new simple neural
integration. (On the other hand,) the instantaneous character of
simpler associations in man . . . suggests that . . . a single
performance serves to fix the habit. Even if this were the case for
every simple reintegration within the nervous system, we should still
get the appearance of gradual improvement through practice because of
the formation of many simple associations . . . The fact of gradual
improvement in complex functions cannot therefore be taken as evidence
for a gradual wearing down of synaptic resistance by repeated passage
of the nerve impulse' (Lashley, 1924). The reemergence of this theory
in Hebb's monograph as a neuropsychological postulate is documented and
evaluated. In the fourth edition of Hebb's Textbook (1994), Donderi
refers to the postulate as Hebb's rule. Today, it is frequently
referred to as the Hebb synapse.

5. Next, 'Lashley's Memory Mechanisms', considers:

    i. Lashley's view that the memory trace is reduplicated in the
    cerebral cortex and the implications of that view on the
    interpretation of cerebral localization. In 1952, Lashley wrote 'I
    have never been able by any operation on the brain to destroy a
    specific memory' even when the memory is elicited by electrical
    stimulation of the part of the cerebral cortex that is subsequently

    ii. Lashley's early introduction of the reverberatory circuit in
    neuropsychological theory is documented. It is important to note
    that Lashley never abandoned the principle of synaptic transmission
    in favor of a cortical field theory, as had been alleged by Hebb
    and others. This claim is fully documented.

    iii. Lashley assumed throughout his career that memory is a unitary
    function. He was of course aware of the distinction between long
    and short term memory but he never referred to the modern
    distinction between storage and retrieval. Nor did he ever consider
    associative and working memory as distinct forms of memory when he
    searched for the engram in the cerebral cortex.

    iv. Lashley's position on the continuity-discontinuity debate is
    reviewed as well as his championing the concept of instinct at a
    time when the concept was falling into disfavor in America. In
    1950, Lashley championed the European ethologists' views of fixed
    action patterns though he himself preferred the term instinct. His
    article on instinct in the Encyclopaedia Britannica of 1956 is
    especially noteworthy.

6. The next chapter, entitled 'Issues of Priority, Opinion and
Criticism', includes:

    i. a reconsideration of Lashley's obsession with theoretical
    criticism in his later years, as alleged by Hebb.

    ii. an interpretation of the meaning of Lashley's refusal of Hebb's
    offer to coauthor the 1949 volume with him.

    iii. the history of the reverberatory circuit in the psychological
    literature, and questions of priority as far as the integration of
    the reverberatory circuit into neuropsychological theory is

    iv. the fact that Lashley failed to acknowledge data and theory
    that were unfavorable to his views, during his search for the
    engram. This is documented.

    v. Lashley's opinion of Hebb's theories was never known because
    Lashley hardly ever spoke of them. But Lashley's 1947 review of
    Hebb's manuscript-in-progress is revealing in this regard.
    Revealing as well is Lashley's letter of congratulations to Hebb
    after publication of his 1949 monograph.

Finally, the personal relationship of Lashley, the teacher, and Hebb,
the student, is delineated.

7. The next chapter, titled 'Hebb's The Organization of Behavior 50
Years After Publication', offers a contemporary view of Hebb's enduring
contributions to neuropsychological theory. Hebb bolstered his theories
with the following facts:

    i. adults seem to be able to sustain brain injury with fewer
    permanent consequences than can infants and children;

    ii. learning in children is much more difficult compared to similar
    learning in adults.

Hebb further argued that:

    iii. distinctions should be made between primitive unity,
    non-sensory figure and identity in perception;

    iv. stimulus equivalence and generalization are learned in early

    v. the ratio of association cortex to sensory cortex should be
    considered in phylogenetic development;

    vi. the evidence of post-tetanic potentiation supports the
    importance of the Hebb synapse in learning (this phenomenon was
    described after the 1949 monograph was published but it found its
    way into Hebb's later writings);

    vii. there is a distinction between intelligence A (innate
    potential) and intelligence B (achievement);

    viii. following Tolman, Hebb introduced a new way of thinking about
    neuropsychological problems in his 1960 presidential address to
    APA. That discourse is today named cognitive psychology;

    ix. later research on the stabilized retinal image supported cell
    assembly theory.

8. The Left and Right Cerebral Hemispheres reviews the case of Alex, a
nine year old boy whose left hemisphere was removed for the relief of
intractable epileptic seizures. Though he never learned to speak before
surgery, Alex began to show remarkable gains in speech and language and
in cognitive skills in general. Alex's postoperative achievements
challenge the widely held view, shared by Hebb, that early childhood is
a particularly critical period for the acquisition of cognitive skills.
It must be concluded that clearly articulated, well-structured, and
appropriate language can be acquired for the first time as late as nine
years of age with the right hemisphere alone. Hebb and Lashley did no
live to see this case. My guess is that Hebb would have had great
difficulty in explaining Alex's achievements, but Lashley would have
chuckled and muttered in so many words, 'You see, not only do you have
reduplication of the memory trace within a hemisphere but also between

9. The next chapter is entitled, 'A Comparison of Lashley and Hebb on
the Concepts of Attention and Stimulus Generalization'. On the concept
of attention, Lashley took off from his observations of attempted
solutions in rats during the learning of the maze. It was Spence's
concession on this matter that persuaded Lashley that he had bested the
neo-behaviorists on the continuity-discontinuity debate. In the 1942
paper (reprinted in this volume), Lashley argued that a pattern of
excitation in the cortex in the form of a reverberatory circuit may
form a relatively stable and permanent foundation, modifying the
effects of later stimulation, as attention determines the selection of
stimuli. These ideas precede Hebb's formulation of the central
autonomous process by some seven years. And then in the Vanuxem
Lectures of 1952, Lashley went way beyond Hebb when he introduced the
ideas of a priming or pre-setting of circuits based upon the spacing of
the end-feet on the post-synaptic cell. Hebb was by far the more
accomplished writer and so, with the publication of his monograph in
1949, he captured the attention of the neuropsychological community
with ideas that did not differ substantially from Lashley's.

10. However, on the matter of stimulus generalization their positions
were radically different. Lashley's position is nativistic stimulus
generalization, if it exists at all, is built into the organism. His
conception derived from his critique of the neo-Pavlovian view of a
gradient in stimulus similarity underlying stimulus generalization. His
discontinuity position on learning led him to write in 1946 'Stimulus
generalization is generalization only in the sense of failure to note
distinguishing charateristics of the stimulus or to associate them with
the conditioned reaction. A definite attribute of the stimulus is
abstracted and forms the basis of reaction; other attributes are either
not sensed or are disregarded. So long as the effective attribute is
present, the reaction is elicited as an all-or-none function of that
attribute. Other characteristics of the stimulus may be radically
changed without affecting the reaction' (Lashley and Wade, 1946). The
neo-Pavlovian gradient of similarity on a stimulus continuum is an
artifact of inattention. Such a stimulus generalization is
generalization by default.

11. Hebb's concept of stimulus generalization was developed in
connection with his delineation of the formation of the cell assembly
underlying the perception of a triangle. Hebb's contribution was to
perceptual theory. He proposed the startling idea that a simple figure
like an outline triangle is not perceived as a whole, innately, as
alleged by the gestaltists. He went on to show how the elements of line
and angle become integrated into a unified perception of a triangle. To
persuade the skeptical reader, Hebb introduced the idea of perceptual
identity, something that has to be learned. He then proposed a
mechanism involving neural fractionation and recruitment. Fractionation
eliminates the variable cells that are excited extramacularly. Macular
excitation, which is due to ocular fixation, remains constant despite
the variable angular size of the stimulus object.

12. In short, stimulus generalization emerges secondarily from the slow
development of each complex concept. And yet, there is some doubt
regarding the universality of stimulus generalization according to
Hebb. His theory cannot always predict stimulus generalization from the
learning of a simple discrimination. Take for example the learning to
discriminate a vertical from a horizontal line. In this case, the
stimuli belong to the category of primitive unity for which, unlike the
triangle, no learning is required, according to Hebb, to build a
unified percept. Nevertheless, our best guess is that, empirically,
after the initial learning to discriminate the two lines, the organism
would show stimulus generalization to a vertical rectangle vs. a
horizontal rectangle and even to a vertical row of circles vs. a
horizontal row of circles. Since there is no initial learning to build
a unified perception of the vertical and horizontal lines, it is
difficult to see how Hebb would derive the empirical data of stimulus
generalization in this case.

13. A late chapter of commentary is entitled, 'Lashley's Enduring
Legacy to Neuropsychological Theory'. A contemporary perspective is
offered in reviewing the concepts of vicarious functioning,
equipotentiality, reduplicated memory trace, the reverberatory
circuit. Lashley's lesson that synapses inactive during learning can
show the effects of learning is emphasized. Lashley's lesson was never
acknowledged by Hebb or any of his students. Lashley derided the use of
wiring diagrams in neuropsychological theory especially those derived
from computer technology. Neurons are live metabolizing cells, he
argued, not inert paths like copper wires. They interact at synapses,
which are not solder joints like soldered copper wires. The synaptic
contacts are variable. Furthermore, synaptic contacts may be excitatory
and/or inhibitory. Soldered wires are always excitatory and fixed. Both
are pathways to be sure but the differences between neurons and copper
wires far outnumber their similarities. Thus brain organization cannot
be modelled by circuit diagrams representing inert pathways.

14. An epilogue presents a number of personal vignettes of both Lashley
and Hebb. Lashley's career was reviewed earlier in some detail in
Orbach (1982). The most disturbing part of this story has to do with
Lashley's racism, as alleged by Weidman (1996). I would not have raised
this matter in a scholarly volume concerned with Lashley's
contributions to neuropsychological theory were it not for Weidman's
allegation that Lashley's racist attitudes influenced his theoretical
views. But, did these odious attitudes of Lashley affect his science? I
can attest to Lashley's anti-African-American attitudes, but I can find
no evidence that Lashley's racism colored his theories. A lifelong
student of genetics, Lashley had an abiding interest in the concept of
instinct and in the genetics of behavior in general. These facts must
have eluded Weidman. Both Hebb and Lashley were honored many times
during their lifetimes. It is especially noteworthy that Hebb was
appointed Chancellor of McGill University, and that he was nominated,
in 1965, for the Nobel Prize.

15. During his freshman year, at the age of 16, Lashley studied general
zoology and comparative anatomy with Albert M. Reese at the University
of West Virginia. Reese appointed him departmental assistant, at a
salary of $0.25 per hour. One of the new assistant's first tasks was to
sort out various materials in the basement. The result of this
assignment can best be expressed in Lashley's own words: 'Among them I
found a beautiful Golgi series of the frog brain. I took these to Reese
and proposed that I draw all of the connections between the cells. Then
we would know how the frog worked (sic!). It was a shock to learn that
the Golgi method does not stain all cells, but I think almost ever
since I have been trying to trace those connections' (Beach in Orbach,
1982). Only later did Lashley realize that functional variables such as
spatial and temporal summation, excitatory and inhibitory states, and
micro-movements of elements influencing synaptic contact need not be
represented microscopically. The lesson is that neurons are not inert
and static, like soldered wires. They are live metabolizing cells with
synaptic contacts that vary. If Lashley were alive today, there is no
doubt that he would continue to scold modern neuroscientists who still
have not become aware of the importance of this fact.

16. Part 2 of the book consists of nine of Lashley's major theoretical
papers reprinted in their entirety. These are listed in the References
below. Part 2 also includes Lashley's four Vanuxem Lectures given at
Princeton University in 1952, and published here for the first time. In
these lectures, Lashley referred to the anatomical observations of
Lorente de N and emphasized the neural net as the active neural unit in
the cerebral cortex. He introduced the idea of a neural priming or
presetting, concepts all highly reminiscent of Hebb's theorizing on the
central autonomous process and the cell assembly. The term neural
lattice was coined by Lashley in 1949. This term was discarded by Hebb
in his 1949 monograph in favor of cell assembly.


Hebb, D. O. (1949) The Organization of Behavior: a Neuropsychological
Theory. New York: Wiley.

Hebb, D. O. and Donderi, D.C. (1994) Textbook of Psychology, fourth
edition, revised. Dubuque, Iowa: Kendall/Hunt Publishing Company.

Hilgard, E. R. and Marquis, D. G. (1940) Conditioning and Learning,
NY:  Appleton-Century.

Lashley, K. S. (1924) 'Studies of cerebral function in learning. VI.
The theory that synaptic resistance is reduced by the passage of the
nerve impulse.' Psychol. Rev., 31, 369-375.

Lashley, K. S. (1931) 'Mass action in cerebral function.' Science 73,

Lashley, K. S. 'The problem of cerebral organization in vision.' Biol.
Symp, 1942, 7, 301-322.

Lashley, K. S. (1949) 'Persistent problems in the evolution of mind.'
Quart. Rev. Biol., 24, 28-42.

Lashley, K. S. (1950) 'In search of the engram.' In Symp. Soc. Exp.
Biol. No. 4, Cambridge, Eng.,: Cambridge Univ. Press.

Lashley, K. S. (1951) 'The problem of serial order in behavior.' In
Jeffress, L. A. (Ed.) Cerebral mechanisms in behavior, New York,

Lashley, K. S. (1952) Vanuxem Lectures delivered at Princeton
University in Feb. 1952. Untitled.

Lashley, K. S. (1954) 'Dynamic processes in perception.' In Adrian, E.
D. Bremer, F. and Jasper, H. H. (Eds.) Brain Mechanisms and
Consciousness. Illinois, Charles C. Thomas, 422-443.

Lashley, K. S. (1968) 'Cerebral organization and behavior.' In The
Brain and Human Behavior, Proc. Ass. Res. Nerv. Ment. Dis., 36, 1-18.

Lashley, K. S. and Wade, M. (1946) 'The Pavlovian theory of
generalization.' Psychol. Rev., 53, 72-87.

Lashley, K. S., Chow, K.-L, and Semmes, J., (1951) 'An examination of
the electrical field theory of cerebral integration.' Psychol. Rev.,
58, 123-136.

Orbach, J. (1982) Neuropsychology After Lashley: Fifty Years Since the
Publication of Brain Mechanisms and Intelligence. Hillsdale, NJ.:
Lawrence Erlbaum Associates.

Weidman, N. (1996) 'Psychobiology, progressivism, and the
anti-progressive tradition.' J. Hist. Biol, 29, 267-308.

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