Wilhelm Wundt’s Principles of Physiological Psychology reached English readers in 1904, translated by Edward Bradford Titchener from the fifth German edition. It was the first volume of a projected larger work: an introduction followed by Part I, “The Bodily Substrate of the Mental Life.” Wundt, professor of philosophy at Leipzig and founder of the first laboratory devoted to experimental psychology, wrote the book to stake out a new scientific territory—one where the anatomy and physiology of the nervous system would serve as the material foundation for a genuinely psychological theory. The volume is dense with figures, dissection records, and microscopic detail, but its ambition is larger than description: to show how mental life is conditioned by, without being reducible to, the body.
“The work which I here present to the public is an attempt to mark out a new domain of science.”
Wundt’s central claim, stated plainly in his preface of 1874 and revisited in 1902, is that psychology must be built from two sides at once. The physiological side supplies the substrate—nerve cells, conduction paths, cortical centres—while the psychological side supplies the laws of conscious experience. Neither alone suffices. He insists that the experimental treatment of psychological problems was still in its infancy when he began, and that a general survey of a developing science’s present status is the best means of discovering where ignorance has left blanks. The book is thus both a report and a program: an accounting of what is known about the nervous system, offered in the conviction that an imperfect first attempt will more effectively call for improvement than silence would.
The Reception of Titchener’s Translation
The volume opens with a chorus of press notices assembled to vouch for Edward Bradford Titchener’s translation. The Bookman credits him with a rare service to English students of philosophy; the Pall Mall Gazette calls the work profound and suggestive; the Glasgow Herald concedes Wundt’s laboured, tangled style and the near-impossibility of rendering his long parenthetical sentences into English. The Scotsman and the British Medical Journal both stress the book’s importance for serious students, and Dr. C. W. Saleeby, writing in the Occult Review, goes furthest, calling it the most complete and philosophic account of the human nervous system then obtainable—measuring it against Quain’s Anatomy and finding it superior. The bibliographic facts follow: Wilhelm Wundt, Professor of Philosophy at Leipsic, translated from the fifth German edition of 1902 by Titchener of Cornell, the first volume carrying 105 figures, issued by Swan Sonnenschein in London and Macmillan in New York, first in December 1904 and again in December 1910.
Wundt’s Preface of 1874: Staking Out a New Science
Wundt’s preface, dated Heidelberg, March 1874, presents the book as an attempt to mark out a new domain of science—and he is candid that its anatomical and physiological foundations are in places far from solid, and that the experimental treatment of psychological problems is only beginning. A general survey of a developing science’s present status, he argues, is the best way to expose the blanks left by ignorance; an imperfect first attempt will the more effectively call for improvement. Many problems, he notes, are bound up with apparently remote groups of facts, so a wider view is necessary. The brain anatomy of the first part rests on morphological knowledge gained by repeated dissection of human and animal brains, with debts to Professor Fr. Arnold, former director of the Heidelberg Anatomical Museum. The finer microscopic structure he leaves to specialists, having compared their statements against his own gross-anatomical results; he asks experts to judge whether his account of the central conduction paths in chapter four is correct, conscious that in detail it needs supplementing, though it gains confirmation from the fact that functional derangements following extirpation and transsection of brain parts prove readily explicable in terms of the anatomical plan. Most of the phenomena he describes he has repeatedly observed in his own experiments, and in chapter six he gathers results from his Untersuchungen zur Mechanik der Nerven und Nervencentren on the forces operative in nervous elements.
The Genesis of the Work: Nativism, Empiricism, and Herbart
The second and third parts concern the topics that first drew Wundt to psychology. When he began his Beiträge zur Theorie der Sinneswahrnehmung in 1858, German physiology was dominated almost exclusively by nativistic conceptions; his principal aim was to demonstrate the insufficiency of current hypotheses about the origin of spatial ideas in touch and sight, and to find a physiological basis for a psychological theory. Those views, he notes, have since found general acceptance, though in their usual form they could hardly withstand rigorous criticism. He hopes to have shown the inadequacy of modern physiological empiricism, the relative justification of nativism, and the necessity with which both point toward a deeper psychological theory. The hypothesis of specific sensory energies, a survival from older nativism, has in his judgment become untenable despite its convenient explanation of many facts. The fourth part’s investigations—experiments on how sensory ideas aroused by external impressions appear and run their course in consciousness—occupied him fourteen years, interrupted by other work and the need for apparatus; first results went to the Natural Science Conference at Speyer in 1861, and though notable papers by others have since appeared, no one has turned such results toward a theory of consciousness and attention. He asks the reader encountering his polemics against Herbart to remember that his criticisms prove the importance he attaches to Herbart’s psychological works: after Kant, it is to Herbart that he is chiefly indebted for the development of his own philosophical principles. Toward Darwin he strikes a different note—he opposes the theory of expressive movements in a concluding chapter, yet the work is deeply imbued with those far-reaching conceptions Darwin’s labours made an inalienable possession of natural science.
The Preface of 1902: Twenty-Eight Years of Change
By the fifth edition, Leipsic, February 1902, the landscape had transformed. When the book first appeared nearly twenty-eight years earlier, only one successful attempt—Fechner’s Elemente der Psychophysik—had thrown exact procedure upon philosophical problems ultimately psychological; apart from Fechner, the adventurer of “experimental psychology,” a phrase Wundt appears to have introduced in the 1862 Beiträge, was reduced to borrowing from other disciplines, especially the physiology of sense and the nervous system. Now material pours in from all sides—psychological laboratories and neighbouring disciplines alike.
Mind and Spirit: The Translator’s Supplementary Discussion
An editorial discussion follows on the separation of mental processes. Introspection shows that supposedly independent processes are interconnected and interdependent; to separate them repeats the old faculty-doctrine’s error of translating abstractions into real things. An isolated idea separable from feeling and volition no more exists than an isolated understanding. Distinctions are necessary but rest on abstraction, carrying no real separation of objects; objectively, individual mental processes are inseparable elements of interconnected wholes. English, the discussion notes, distinguishes spirit from mind as a second substance-concept—not necessarily bound to body through the senses, but either externally connected with body or wholly free of it. Spirit carries two meanings: the substrate of inner experiences independent of sense-activity, and a being with no part in corporeal existence. Only the first belongs to psychology, yet it logically passes into the second: if spirit’s connexion with body is merely external and accidental, spirit could occur as pure undivided substance. Early speculation was forced to postulate a single substance as substrate of inner experience, yet saw no escape from separating abstract spiritual activities from sense-perception’s bodily entanglements; alongside the universal dualism of matter and spirit remains the antithesis of spirit and mind. Ancient philosophy never wholly overcame it—Plato, in the Timaeus, regarded mind as a mixture of matter and spirit, while Aristotle transferred to spirit the notion abstracted from mind, substituting a coincident definition for unity of substance. Modern spiritualistic philosophy followed Plato while affirming more decidedly the unity of substance, so real discrimination disappears from scientific vocabulary. Differences were drawn: spirit as general concept containing individual mind, as in Wolff; spirit confused with the higher mental faculties; or mere difference of degree, spirit to man and mind to animals. The concept of spirit loses substantial character. The definition offered: spirit, like mind, is the subject of inner experience, but abstraction is made from relations to a corporeal being; mind is that subject as conditioned by connexion with external existence—leaving open whether spirit is really independent of sensibility.
The Ventricular System and the Architecture of Grey and White Matter
Wundt begins with the brain’s internal cavities, tracing how the single neural tube’s chamber divides first into three and then five pockets as the brain-vesicles separate. The hemispheres split the first pocket into the paired lateral ventricles, the paraceles, which open into the cleft-like third ventricle, the diacele, bounded by the thalami and left roofless by the anterior roof-slit. From there the passage runs into the mesocele, the cavity of the midbrain, which in mammals shrinks to the aqueduct of Sylvius while in birds it throws lateral offshoots into the bigemina. The cerebellum and oblongata each carry their own original cavity; the mesocele forks posteriorly, one branch rising into the cerebellar cavity, the other into the fourth ventricle, a furrow rather than a closed space because the posterior roof-slit leaves it exposed. In mammals the cerebellar cavity vanishes as the vesicle fills with white matter.
From these spaces Wundt turns to the tissue that forms around them. Cells lining the primitive cavities proliferate; some become connective-tissue formatives mediating the secretion of neuroglia, others become nerve-cells sending out runners. In the spinal cord the fibres radiate outward so that grey matter gathers about the central canal and white matter wraps it round. This arrangement persists in the structures derived from the three stem-vesicles, but where secondary vesicles develop, nerve-cells stay in the cavity walls while fibres trend inward. The result is a distinction between entocinerea, the tubular grey matter of cord and caudex, and ectocinerea, the cortical grey matter of the pallium. In the oblongata, myelinated fibres break the grey matter into masses called nidi, or nuclei, giving a third formation, nidal grey, that lies midway between the other two. Travelling from the central cavity outward, one meets entocinerea, white matter, nidal grey, more white matter, then ectocinerea.
Flexures and the Folding of the Hemisphere
The whole brain bends ventralward, pulling the caudex out of a straight line at angles that are slight in the lowest vertebrates and approach a right angle higher up the series. Wundt distinguishes three flexures—at the junction of cord and oblongata, in the cerebellum, and at the midbrain—and notes that their extent depends chiefly on the growth of the forebrain, so that curvature runs parallel with the development of the hemispheres. In early stages the prosencephalon extends forward beyond the other divisions without covering them. Because the embryo is rigidly attached to the germinative vesicle, forward expansion is blocked, and the growing hemisphere instead arches backward over the diencephalon, then the midbrain, then the cerebellum, following the mesencephalic flexure. The more vigorous the growth, the further the bent portion reaches back toward its starting point, approaching a perfect circle and forming the Sylvian fossa where the hemisphere rests on its stem-vesicle. In highly developed mammalian brains the concavity is nearly obliterated, its walls drawn into a deep narrow fissure.
This backward arching reshapes the lateral ventricles. Originally spherical cavities within the hemispheric vesicles, they extend posteriorly, then inferiorly and anteriorly, giving a central cella with posterior, anterior, and median horns. The outer walls outgrow the inner wall that surrounds the caudex, leaving a narrow vertical slit, the foramen of Monro, through which the paraceles communicate with the third ventricle. Anterior to this opening the hemispheres are held together by a lamella of white matter. As the forebrain arches over the brain, the opening and its limiting lamella arch with it, appearing as a vault above the diencephalon. The posterior part of the opening closes, only the extreme anterior portion remaining as a channel for vascular processes. The lower end of the white lamella becomes the precommissure; the rest follows the hemispheric arch as the primordium of the fornix. Just above, a strong transverse band of white matter, the callosum, unites the hemispheres, and the median wall above it forms another arch concentric with the fornix, the marginal arch, whose anterior division becomes the gyrus fornicatus while its posterior part passes into the hippocampus.
Fissuration: Primates Against Other Mammals
The convolutions ordinarily meander irregularly, but the frontal region breaks the pattern: a little anterior to the Sylvian fissure the longitudinal gyre-tracts give way to roughly transverse ridging, with secondary cross-fissures often disposed radially about the Sylvian fissure. In all mammals except the cetacea and primates, the callosal gyre surfaces in the frontal area, separated from posterior gyres by a transverse or oblique fissure and passing forward into the olfactory gyre. The point of issue may lie near the anterior boundary, as in carnivores where the gyre is exceedingly broad, or further back. As a rule four transverse fissures cross the frontal brain. The cetacea, with olfactory organs wholly atrophied, show no surfacing callosal gyre and no olfactory gyre at all; their brains are extraordinarily broad, with principal fissures running the full length from front to back.
Primates obey a different law. The olfactory gyre, dwindled to a bulb, hides on the brain-base, and the callosal gyre surfaces only in the occipital region, sending a branch that divides into the cuneus and precuneus, an island bounded by fissures and split by the deep transverse occipital fissure. The same transverse arrangement governs the whole occipital portion. Anteriorly, the central fissure of Rolando runs downward between the precentral and postcentral gyres, and the calcarine fissure marks the posterior limit of the occipital brain. Five well-marked transverse fissures appear on the occipital surface. Frontal and temporal areas, by contrast, tend to longitudinal folds—three frontal and three temporal gyres—with the parietal gyres showing a gradual passage between the two directions. The essential difference, Wundt concludes, is that primates have transverse fissures occipitally and longitudinal ones frontally, while most other mammals reverse these relations exactly.
Conduction Paths of the Lower Brain
A cross-section of the oblongata displays the pyramid, olive, lemniscal tract, and the nidi of the hypoglossus, trigeminus, acusticus, and glossopharyngeus. Wundt conjectures that these nidi are centres of excitation and transmission for heartbeat, respiration, articulation, and mimetic movement, though the mechanics of innervation remain incompletely known. The olives appear chiefly to give off branch-conductions, relating intimately to conduction toward the cerebellum; the trapezium or superior olive is a nodal point for acoustic conduction. Cerebellar conduction resembles a shunt in an electrical circuit: restes fibres deflect round the dentatum and radiate to the cortex, cortical transverse fibres form the medipeduncles, and the dentata give rise to the prepeduncle funicles. Wundt infers that all postpeduncle fibres terminate in the cortex.
Decussation and the Functional Architecture of the Visual Centres
Wundt turns to the theory of decussation, arguing that the visual centre holds no pictorial projection resembling the retinal image. What it contains instead are mechanisms of release—devices transforming sensory into motor impulses—arranged with symmetry about the median plane, so that a point opened in the right hemisphere answers to a functionally co-ordinated point in the left. This arrangement is a product of development. In the earliest stage, as in the visual organs of invertebrates, the two eyes stand in no functional relation at all, and each optic ganglion is organised symmetrically to the median plane. Once development advances to panoramic vision, that symmetry becomes insufficient: it cannot sustain the regular sequence of eye movements. Tracing an object followed across the field, Wundt shows how innervation must pass from the externus to the internus and then across to the second eye; without decussation the sequence would break and the impulse would shoot across to the left visual centre. The arrangement governing movement also fixes the localisation of the resting eyes, so that one stretch of the field is seen as the direct continuation of another—not because images are projected in that order, but because this is the order of congruity between sensory and motor functions in spatial perception. Total decussation, he concludes, applies from the outset to both sensory and motor areas, mediating their co-operation.
From this Wundt generalises to the entire sensorimotor system, whose organisation is determined by the necessary co-ordination of particular sensory and motor points. Only this hypothesis, he holds, explains why the shift from total to partial decussation accompanies the passage from panoramic to stereoscopic vision. When the eyes sit far enough forward for their fields to overlap, the synergy of eye movements becomes medianly symmetrical rather than laterally symmetrical: parallel movement belongs to panoramic vision, convergent movement to stereoscopic. The movements become simultaneous instead of successive, and the muscles paired are internus with internus, externus with externus. The farther inward a retinal point lies, the farther out in the third dimension lies its object; stimulation of the nasal halves drives the interni into symmetrical convergence, stimulation near the near limit brings the externi into synergic action. Given mechanisms distributed symmetrically about the median plane, the inversion of the image produced by the dioptric apparatus actually serves the needs of stereoscopic vision. It is a condition of adaptation that the optic paths stay uncrossed across the whole common field; but each eye also keeps its own particular field, governed by panoramic vision, where the organs are laterally symmetrical and the necessary crossing follows the older pattern. Partial decussation thus gives an accurate picture of binocular co-operation and of the eyes’ independent functions, and the chiasma probably carries the same functional significance for terminations in the mesencephalic region.
Decussations recur at every level from the spinal cord upward, though nowhere is the functional meaning as obvious as in the optic crossing. Wundt refuses to derive them all from the transposition of optic fibres: the same synergy obtains for other organs of sense and movement and may arise independently at many points. Lower vertebrates, with total optic decussation, show much less complete crossing of the motor paths of skeletal muscles than man; the cord retains the character of a central area where paths stay largely on the same side, while the medulla oblongata shows many partial decussations, owing to the bilaterally symmetrical motor functions—respiration, mastication, swallowing, mimetic movement—centred there. Similar crossings appear in the olfactory and acoustic areas, probably tied to motor synergies. Finally he considers the preponderant one-sided development of certain centres, above all the speech centre, seated in the great majority of cases in the left frontal and temporal areas. Since the left side holds the centres for the right half of the body, the arrangement may connect with right-handedness, and may be referred partly to the human preference for one side in movement, partly to the asymmetrical position of organs such as the heart.
The Midbrain as a Centre of Psychical Function
The dominance of strict localisation, held by Munk and others, prompts Wundt to ask what the midbrain and diencephalon actually do. He argues they are more than centres of complicated reflexes: they are centres for simpler psychically conditioned functions. Removing the prosencephalon leaves fishes psychically unchanged; amphibia, reptiles and birds suffer an initial interruption, then recover fairly completely, their remaining functions showing only slight adaptation—interpretable as complicated reflexes. In mammals the same picture is more pronounced: greater lapse, longer recovery, clearer permanent defect, though injury is compensated within wide limits. Functions permanently lost in higher mammals—recognition, expressions of pleasure and attachment—do not exist in lower animals at all. Two explanations offer themselves: either inhibitory effects of the operation must gradually wear off, or the uninjured remnant takes over a share of prosencephalic function. Wundt doubts operative interference is decisive, since the contrast between proximate effects and subsequent state is too striking and uniform, and it would not explain the graduation across species—a frog needs considerable time before compensation, fishes recover at once. He invokes the law of functional substitution, noting that vicarious function is inherent in the nature of the quadrigemina and thalami as intermediate stations where sensory and many motor paths are interrupted by interpolated neurone chains.
His genetic conclusion: at the lowest brain stages the mesencephalic region—especially the former colliculi, since the diencephalon is comparatively insignificant—is the principal central organ, with the medulla and cord subordinate on one side and the prosencephalon adjoining as an appendicular structure, originally an outgrowth of the olfactory development. Ascending the series, the conduction paths gathered in the bigemina acquire superior centres in the prosencephalon; the midbrain and diencephalon become intermediate stations where peripheral excitations touch off complicated reflexes and cerebral excitations evoke reactions depending on extended colligation of impressions. Removal of the higher regulatory mechanisms may let the lower centres gradually recover an autonomy they fully possessed at a lower level. This region always matters as a centre connecting the principal organs of sense and movement, confirmed by symptoms after direct removal or impairment. The most striking sensory symptom is blindness in mammals, correlated with the pregemina including the pregeniculum. Motor disturbances, if the lesion stays within the quadrigemina, are confined to the eye muscles; injury to the diencephalon produces pronounced general derangement—with unilateral injury, circus movements, the animal turning in a circle instead of going straight, also seen after injury to the crura, the cerebellar hemispheres, or unilateral extirpation of the semicircular canals. In the frog such movements are invariably toward the uninjured side; in mammals the rule is toward the injured side if the anterior thalamus is divided, toward the uninjured side if the section lies posterior. Abnormalities of muscular tonicity accompany them, the resting animal bending upon itself in the direction of the circus movement; movements may appear as rolling about the longitudinal axis or “clock hand” movements, supposedly occasioned by asymmetrical innervation, though which condition is at work cannot presently be determined.
The book’s organizing conviction is that mental processes are never isolated atoms but elements of interconnected wholes. Wundt returns to this point repeatedly, and it shapes his treatment of the nervous system at every level. Just as introspection shows that an idea separable from feeling and volition no more exists than an isolated “understanding,” so the nervous system presents no truly independent parts: every nerve cell, every conduction path, every cortical centre is defined by its relations to others. The old faculty psychology, which translated abstractions into real things, committed the same error in the mental realm that a purely localizing anatomy would commit in the bodily one. Wundt’s alternative is a functional anatomy—one that asks not merely where a structure lies but what it does within a system of co-operating parts.
This principle governs his treatment of the neurone theory, which he presents as the morphological foundation of modern neurology. The discoveries of Deiters, Golgi, Ramón y Cajal, and Nissl had established that nerve cells are individual units with processes—dendrites and neurites—that connect by contact rather than by continuous fibrils. Wundt adopts the theory while noting the dissenters who claimed to observe unbroken fibrils running through entire systems. His own reading of the evidence is cautious: the tussock-like corpuscles described by Nissl, which diminish under fatigue or poison and disappear in inflammatory conditions, suggest that the nerve cell exercises a trophic influence over the fibres proceeding from it, making it their nutritive as well as functional centre. The degeneration of fibres cut off from their cell-body confirms this. Yet Wundt refuses to build psychological theories on such slender physiological grounds; he dismisses the speculations about sleep and dissociation that some authors had erected on observations of amoeboid dendrite movements as “purely imaginary psychological constructions.”
The same sobriety marks his account of nervous excitation. Wundt describes nervous substance as existing in a state of simultaneous positive and negative molecular work: positive work manifests as heat or muscular contraction, negative work as inhibition or the storing of potential energy. A stimulus increases both, and the equilibrium between them is largely restored during the progress of contraction. This tendency to maintain equilibrium, founded in the chemical constitution of nervous substance, distinguishes it from all other tissues. The argument is technical, but its implication is philosophical: stimulation consists not in a permanent disturbance of equilibrium but in a different distribution of work over time. The nerve is not a passive conductor but an active system that regulates its own expenditure.
The Brain as a Developing Organ
Wundt’s morphological chapters trace the brain from its embryonic vesicles to the complex fissures of the mammalian cortex, and the guiding thread is development. The neural tube divides into three vesicles, then five; the cavities become ventricles; the gray matter arranges itself in layers—entocinerea lining the cavities, ectocinerea on the surface, nidal cinerea in between. The flexures of the brain follow the growth of the hemispheres, which arch backward over the diencephalon and mesencephalon as the embryo’s attachment to the germinative vesicle prevents forward expansion. The more vigorous the hemisphere growth, the more the bent portion extends back toward its departure point, approaching a perfect circle. This is not mere description: Wundt uses the developmental sequence to explain why the conduction paths run as they do, and why the cortical centres are arranged as they are.
The comparative anatomy of fissures carries the argument further. In most mammals, the callosal gyre comes to the surface in the frontal region, and the principal fissures run transversely; in primates, the relations are exactly reversed—transverse fissures in the occipital region, longitudinal fissures in the frontal. Wundt explains this difference by growth: the same laws of expansion produce different arrangements depending on the relative development of the parts. The human brain is not a special creation but an extreme case of tendencies present throughout the vertebrate series.
Localization and Its Limits
The chapters on cortical localization bring the argument to its most contested ground. Wundt reviews the animal experiments of Munk, Ferrier, Goltz, and Luciani alongside the clinical evidence from human pathology, and he is skeptical of easy conclusions. Munk’s division of cortical functions he calls “hazardous in the extreme,” noting that rabbits and dogs react appropriately to light and sound after removal of the entire cortex, and that removal of a cortical area never equals destruction of a peripheral organ. The symptoms of cortical lesion correspond rather to what Goltz termed “cerebral weakness”—a general impairment of function rather than the loss of a specific sensory modality.
What can be established, Wundt argues, is a broad correspondence between the centromotor areas of man and monkey, and a localization of the visual centre in the occipital lobe that agrees with the visual-field defects observed after partial destruction of the visual cortex. The auditory area lies in the posterior section of the supertemporal gyre, near the motor areas of speech—which is why hearing impairment is invariably accompanied by profound speech modification. The olfactory and gustatory centres are harder to demonstrate, and Wundt admits that all statements on the relation of centrosensory to centromotor areas remain hypothetical, resting on foregone psychological or physiological assumptions.
The theory of decussation receives a similarly careful treatment. Wundt argues that the partial crossing of the optic fibres at the chiasma is not a mere anatomical accident but a functional necessity: it mediates the co-operation of the two eyes in binocular vision, allowing the interni and externi to act in synergy as the eyes converge on an object. The arrangement of the mechanisms of release is symmetrical about the median plane, and this symmetry, not any pictorial projection of the retinal image, explains how spatial perception is possible. The same principle of synergy extends to other decussations, though Wundt cautions that we have no right to conclude that all are simple consequences of the optic crossing.
The Legacy of a Founding Text
Principles of Physiological Psychology stands at the threshold of psychology’s emergence as an independent discipline. Wundt’s insistence that mental life must be studied through both its bodily substrate and its own laws—that physiology alone cannot exhaust psychology, and that psychology cannot ignore physiology—set the terms for decades of debate. His laboratory at Leipzig became the model for experimental psychology worldwide, and Titchener’s translation carried his program to English-speaking students who would build on, and argue with, his conclusions. The book’s caution is as instructive as its ambition: Wundt repeatedly marks the limits of what the evidence will support, refusing to let speculation outrun observation. That discipline, no less than his systematic vision, helped make psychology a science.
