Evolution of VIewes on animal intelligence

A tendency to study Human and Animal Intelligence hand in hand has been routed from the very beginning of regular observations and investigations. It was not an easy task to locate the seat of intelligence. The famous Greek physician Hippocrates (b. 460 bc) was the first who preferred to avoid mystical interpretations of mental disease and stick close to the empirical evidence. For example, in a treatise called “On the sacred disease” (meaning epilepsy), he dismissed the usual demonic-possession theory and suggested that it was a hereditary disease of the brain. Hypocrites and with him Plato recognised the significance of the brain. Later, around 280 bc, Erasistratus of Chios dissected the brain and differentiated the various parts.

Galen, a physician to Roman emperors and an early author of works on anatomy and physiology, who acquired great experiences in practising at some time as physician to the gladiators, gave public lectures and anatomical demonstrations in Rome. In 177 he gave his famous lecture " On the Brain". Galen attributed the frontal lobes with being the seat of thought (and the soul). Galen expertly dissected and accurately observed many kinds of animals (mostly dogs, monkeys, and pigs, because human dissection was forbidden) and applied, sometimes mistakenly, what he saw to the human body. In addition to a great deal of fairly decent, concrete advice, Galen theorised that all life is based on pneuma or spirit and believed that the brain generated and transmitted special vital spirit through the hollow nerves to the muscles, allowing movement and sensation (for details see: Young, 1970).

From then on, there was only very slow progress in the development of the concept of intelligence until Rene Descartes, French mathematician, philosopher, and physiologist, proposed his model of nervous system and thus established the first systematic account of the mind/body relationship. The first of Decartes works, ” De homine” was completed in Holland about 1633, on the eve of the condemnation of Galileo. When Descartes learned of Galileo's fate at the hands of the Inquisition, he immediately suppressed his own treatise. As a result, the world's first extended essay on physiological psychology was published only well after its author's death.

Perhaps, one of the first who wrote about animal behaviour in a modern scientific fashion was the British zoologist John Ray. In 1676 he published a scientific text on the study of “instinctive behaviour” in birds. He was astonished by the fact that birds, removed from their nests when young, would still build species-typical nests when adult. He did not try to explain this, but noted the fact that very complex behaviour could develop without learning or practice. Almost 100 years later, French naturalist Charles Georges Leroy published a book on intelligence and adaptations in animals. Leroy criticised those philosophers who spent their time indoors, thinking about the world, rather than observing animals in their natural environments. Only by doing this, he argued, would it be possible to fully appreciate the adaptive capacity and flexibility in the behaviour of animals.

The development of objective methods of analysis of animal behaviour is attributed to psychologists studying animal mind in the nineteenth century, basing on ideas of evolutionism and Charles Darwin’s representation of the common processes that govern natural selection in humans and other species and the psychological continuity between humans and other animals.

The theory of evolution went back to the ideas of Buffon’s and Lamarck’s theory of evolution by means of the inheritance of acquired characteristics and Zoonomia (1794-96) of Erasmus Darwin who elaborated similar ideas. Carl Linnaeus devised a system for organising the diversity of known plants and animals, and George Buffon pursued a massive complication of facts about animals, resulting in 36-volimes encyclopaedia. This stimulated energetic pursuit of discovery, an activity that continues for the present time. Furthermore, new species were not sought in a vacuum. Field workers operated in a framework of taxonomic organisation and encyclopaedic accretion (Arnold, 2003).

Evolutionism in the nineteenth century was primarily concerned with the interpretation of the geological, paleontological, and biological evidence. In mid-1840s two crucial works - Charles Lyell's “Principles of Geology” and Robert Chambers's “Vestiges of the Natural History of Creation” had become the Bible of many explorers and instilled in naturalists an appreciation of how long-term change could be affected through the operation of slow, ongoing processes.

Evolutionism of Herbert Spencer was significant for the development of conceptions of mind and brain. Spencer's first serious intellectual endeavours were devoted to the study of phrenology, and it was from phrenology that he drew the conception of society as an organism in which interdependent, specialised structures serve diverse functions (see Young, 1970). To Spencer is certainly due the immense credit of having been the first to see in evolution an absolutely universal principle. Spencer's theory of evolution actually preceded Charles Darwin's, when he wrote “The Developmental Hypothesis” in 1852, which is an advocacy against creationism and for a progressive (evolutionary) view. While in " The Development Hypothesis", Spencer simply turns the creationists' arguments against themselves; he also published " A Theory of Population, Deduced from the General Law of Animal Fertility" in 1852. Herein, an early formulation of the mechanism of natural selection can be found. Unlike Darwin, Spencer was never much of an observer, and his independent formulation of a theory of evolution developed from his speculations in social theory and psychology. His theory was not taken into serious consideration largely because of a lack of an effective theoretical system for natural selection. Nevertheless, it was Spencer and not Darwin who first popularised the term " Evolution", and few people outside the field realise that the oft-used phrase " survival of the fittest" was actually coined by Spencer. Although Spencer was wrong about the mechanism of evolution, modern views support his main theme: the adaptations of living things to their surroundings are evoked by problems posed by their environments.

Darwin published his theory of natural selection in “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life”, often abbreviated “The Origin of Species”, in 1859. This book revolutionised biology, and is one of the most revolutionary ever published. Darwin had not read Spencer's Principles of Psychology when he wrote these but added complementary references into later editions. Darwin’s ideas were based on enormous massive of natural observations. He had studied Lamarck's theory of evolution when he was a medical student, but neither this nor his grandfather's (Erasmus Darwin) theory had shaken his belief in the fixity of species by the time he became a professional naturalist in 1830 when he secured a position as ship's naturalist aboard the H. M.S. Beagle. Upon returning to England, he published his observations in “A Naturalist's Voyage on the Beagle” (1839). Darwin, reflecting on his observation, came up with a theory that had a non-Lamarckian basis for the variation that leads to adaptation.

Darwin assumed that organisms naturally vary in almost every attribute that they display, such as morphology, physiology and behaviour. Such variation is heritable; on average offspring tend to resemble their parents more than other individuals in the population. Organisms have a huge capacity for increase in numbers; they produce far more offspring than give rise to breeding individuals, but the number of individuals in a population tends to remain relatively constant over time. Thus there must be competition for scarce resources such as food, mates and places to live. Darwin called this a " struggle for existence." As a result of this competition, some variants will leave more offspring than others. These offspring will inherit the characteristics of their parents and so evolutionary change will take place by natural selection. As a consequence of natural selection organisms will acquire slow changes in traits, behavioural traits included, and become adapted to their environment. The blind force of natural selection drives the evolution of such changes. The key to Darwin's argument is that there are heritable variations among individuals of a single species, and that such differences lead to heritable changes from generation to generation, which ultimately lead to the origin of an entirely new species from existing species.

Upon returning to England, Darwin began to develop his ideas on evolution in several " sketch books" and developed the kernel of his theory, that of natural selection, by the year 1838. He held onto these ideas for nearly 20 years before publishing them, and only moved to publish because of the fear of being scooped. Alfred Russell Wallace, English naturalist, evolutionist, geographer, anthropologist, and social critic, had sent Darwin a manuscript to read and was asking his advice on the content of the manuscript before he presented the ideas on natural selection to the scientific community; ideas very similar to Darwin's own. By that time Wallace travelled in the Amazon and Malay Archipelago for about ten years and his collecting efforts produced the astonishing total of 125, 660 specimens, including more than a thousand species new to science. After publishing three books, Wallace in 1855 wrote and published the essay “On the Law Which Has Regulated the Introduction of New Species” introducing the concept of evolution through natural selection basing on his observations on huge species diversity. In 1858, while on the island of Ternate, Wallace drafted his ideas on " the survival of the fittest". He mailed the letter by mail-boat from the island with the request that if Darwin thought the ideas worthy that he send the letter on to Lyell. Through actions of his friends, the geologist Charles Lyell and the botanist Joseph Dalton Hooker, was it possible for Darwin's long efforts to be acknowledged jointly with those of Wallace. The paper that is made available here is the result of that forced union. Darwin moved to publish in 1858, communicating with Wallace on a joint paper to the Royal Society's meetings in which they described the role of natural selection in evolution (Darwin and Wallace, 1858). Darwin (1859) then published his famous " On the Origin of the Species".

Darwin's “Origin of Species” contained a chapter devoted to an attempt to explain how instincts could evolve by natural selection. He considered this issue one of the most formidable objections to his theory. In another book “ The descent of man and selection in relation to sex ” (1871) Darwin introduced an idea that the difference in mind between humans and “higher” animals, great as it is, certainly is one of a degree and not of a kind. His last published book in 1872, “The Expression of the Emotions in Man and Animals”, was probably the first work on comparative ethology.

From the early 1870s experimental ethology (called psychology that time) had started to develop, and it was Douglas Spalding who initiated this, being very ahead of his time in experimental approaches. He was the first to study the phenomenon which we now call imprinting; he began the study of anti- predator reactions; he experimented with both visual and auditory releasers and set out the logic of comparing the behaviour of species born in different developmental stages. Perhaps Spalding would be thought of as a founder of ethology if only he lived longer.

Spalding published series of papers (one of them in Nature, 1872) in which the antecedent conditions of behaviour in young animals were systematically manipulated and variations in response observed. For example, he hatched chicks from eggs by using the heat from a streaming kettle, in order to examine the development of the visual and acoustic senses without the influence of a mother hen. In sum, he described a number of experiments on young chicks and ducklings, carefully blinded for the first few hours after birth. His conclusions were that these young birds not only showed “intuitive” powers of walking, scratching, and pecking, but also possessed intuitive knowledge of various kinds. He asserted that they were afraid of bees and of the cry of a hawk, and that they intuitively knew the meaning of a hen's call-note and danger-signal when heard for the first time. Spalding also kept young house martins in narrow cages thus depriving them from the possibility to flight and then, after maturation, compared with control birds. It turned out that birds did not need practice to develop their vital behavioural patterns.

In his numeral experiments, Spalding tried to demonstrate unwinding of strategy of life as development of an organism. " When, as by a miracle, the lovely butterfly bursts from the chrysalis full-winged and perfect, - he wrote in Macmillan's Magazine in 1873- it has, for the most part, nothing to learn, because its little life flows from its organisation like melody from a music box".

Although systematic and experimental, Spalding’s investigations were based merely on naturalistic observations. One of the first to introduce apparatus and quantification into the study of animal behaviour was John Lubbock. He was introduced to natural history, especially through the efforts of Charles Darwin, a friend of the family who came to live at the family’s country home in Down when Lubbock was only seven years old.

Lubbock published a dozen of books, several of which report his observations of animal behaviour. From these, the book “Ants, Bees, and Wasps. A Record of Observations on the Habits of the Social Hymenoptera”, first published in 1882 and later reprinted many times, is possibly the most remarkable. I would like to note that reading of this book, in its Russian translation, was the event that influenced the author of this book, when a schoolgirl. Indeed, this book moved me from a decision to become a musician, to entomology and ethology. I used to construct my first ant maze completely in the Lubbock’s manner, with the use of small details from my parent’s vacuum cleaner (it stopped working after all).

Lubbock’s Book included the chapter named " General Intelligence, and Power of Finding Their Way." In this chapter Lubbock took a number of critical steps away from the natural history towards the modern animal laboratory. His first innovation was to provide precise, detailed, quantitative descriptions of the conditions on an observation, not much different from those one would find in the methods section of a modern journal article. One of his innovations was to include actual data in the body of his text and to use this data to compute simple summary statistics.

For example, in observing ants learning to take an experimentally contrived route between food and the nest, Lubbock employed experimental techniques of importance for future research. Following his ants with a pencil as they pursued their way, Lubbock made and, in his text reproduced, detailed tracings of the ants' paths. This is certainly one of the first attempts to make an analogue record of behaviour for later coding. To observe the progress made by his ants in learning to follow a new path from food to nest, Lubbock designed a number of simple pieces of apparatus that constrained the ants' movements. These pieces of apparatus were, in effect, the first animal mazes.

Above being a powerful incentive to the development of experimental investigations, Darwin’s ideas of succession in animal and human thinking, gave new arguments for anthropomorphic and anecdotal approach to animal behaviour. Basically, anthropomorphism, that is, attributing animals with the same qualities as humans, goes back to the famous Roman author Pliny the Elder, who considered, for example, the elephant as the nearest to man in intelligence (and surpass humans in chastity and prudence), to present-days examples (Cartwright, 2002). At the turn of 19-th century the conflict between anthropomorphic and objective study of psychology was reaching a boiling point.

For example, G. Romanes regarded animals as possessing the intelligence to solve a problem by reasoning. In his “Animal Intelligence” book (1882) he suggested a criterion of mind in animals as: “Does the organism learn to make new adjustments, or to modify old ones, in accordance with the results of its own individual experience? If it does so, the fact cannot be due merely to reflex action in the sense above described, for it is impossible that heredity can have provided in advance for innovations upon, or alterations of, its machinery during the lifetime of a particular individual “. This was quite reasonable criterion but this claim was based on anecdotal evidences rather than on careful experimentation. After the publication in 1883 of Romanes's book “Mental Evolution in Animals”, the use of the anecdotal method was seriously discredited and retrieval of manifestations of intelligence in animals met strong criticism.

One of the early lessons about the importance of controlled procedures stem from work that was done with a horse nicknamed Clever Hans. Hans’s owner von Osten devoted 14 years to detailed education of the horse following to syllabus of grammar school. He claimed that the horse could count and was capable of mental arithmetic operations such as subtraction, multiplication and division. Thorough examinations demonstrated that the trainer unwittingly gave the horse barely perceptible cues for a right answer (Pfungst, 1908). When Hans reached the correct number of hoof strikes the trainer’s expression changed slightly. The horse possessed such a great level of keenness of observation, so he could catch sight of pulsation of veins on his owner’s head. Hans responded to these cues and stopped hoof striking. Lacking a possibility to observe the trainer, Hans did not give the correct answer. Although these results were based on conscientious delude, it is worth to note that von Osten first demonstrated the phenomenon which will later called “autoshaping” (see Chapter 6), and that he may be first suggested a variant of intermediate language (see Chapter 30) to develop a direct dialog with animals.

I think it is appropriate mention here that, to my observation, frequency of referring to an anecdote about Clever Hans in scientific and educational texts correlates with the tendency in development of our knowledge about animal intelligence. Of course, fashion changes in science and another set of examples comes to take place of former ones. It would be interesting to note that there is no mentions of Clever Hans in fundamental textbooks on animal behaviour published in 70s and 80s (for example, Hind, 1970; Dewsburry, 1978; Manning, 1979; McFarland, 1985) but the textbooks published during the last decade contain detailed description of this story (Allen and Bekoff, 1997; Shettleworth, 1998; Cook, 2001; Griffin, 2001; Pearce, 2000). I also have noted that frequency of mentioning of the Clever Hans phenomenon in lectures and even in posters at International Ethological conferences have been increased since 1997 till nowadays.

To my mind, this caused not only by fashion based on imitation as well as authors’ wishes to underline their data verification, although these factors also work, but by achievement of the new level of knowledge concerning animal intelligence. As we will see further in this book, recent experimental studies show animals as doing more and cleverer things: they use artificial intermediary languages for direct dialog with experimenters, demonstrate their abilities for rule extracting and representation, counting, using mirror images, creating cognitive maps, shaping cultural traditions and manipulating with other specimens by Machiavellian tricks. This is a natural aspiration of a modern explorer of animal intelligence to underline that although experiments and observations have been resulted in amazingly clever behaviour of animals, they are completely differ from the Clever Hans phenomenon. Perhaps, that is why another citation of that times – Lloyd Morgan’s Law – also sounds more frequently nowadays.

Dominance of anecdotal evidences of animal intelligence led one of pioneers of comparative psychology, Lloyd Morgan to suggest that no animal behaviour should be explained in terms of higher mental processes if it could be explained by simpler processes: “In no case may we interpret an action as the outcome of the exercise of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one which stands lower in the psychological scale” (Morgan, 1900). This became known as Lloyd Morgan’s Canon, or The Law of Parsimony.

Being a successor of Romanes, Morgan drew heavily on Romanes' work and was his literary executor. In 1896 Morgan published a capital tome “Habit and Instinct” which, among others, included chapters as " The Relation of Consciousness to Instinctive Behaviour, " " Intelligence and the Acquisition of Habits, " " Imitation”, " The Emotions in Relation to Instinct". Essential part of the book was based on Morgan’s own experiments and observations. Morgan repeated Spalding's experiments on early development of the behaviour, with a considerable variety of species, and, while confirming many of his observations and conclusions, showed that some of them were erroneous. He decided that newly hatched chicks had no perception of the qualities of objects. They pick up stones as well as grain, bits of red worsted as well as worms, gaudy-coloured inedible caterpillars as well as those which are edible. They do not recognise water till they have felt it, and they do not know that water is drinkable till contact with the beak sets up the nervous and muscular reactions of drinking. By a series of careful experiments Morgan showed that young chicks have no fear of bees as bees, but merely because they are large and unusual. They are equally suspicious of a large fly or beetle, and, though eating small worms greedily, are afraid of a large one. And when the chicks were a few days old, and were no longer afraid of large flies, they showed no fear even of wasps, when presented to them for the first time. Experimenting with fear of predators, Morgan came to the conclusion of similar principle of alarm development in different species: any sight, or sound, or smell, very different from what they have been accustomed to, alarms them, and they learn what is really dangerous either through the actions of their parents or by their own personal experience.

In fact, this statement was not strongly adequate, and this problem is still discussible. But this was the first time when the problem of development of complex behavioural patterns had been systematically attacked on the basis of experimental method. Since that time, this has been re-examined by many researchers. The first coherent theory of instinctive behaviour within the frame of ethology was developed in early 40-s of the 20-s century (see details in Chapter 2).

Morgan tried to divide innate and learned behaviour and thus to construct the idea of intelligence. Among other examples of learned behaviour, he described competitions for sheepdogs in the north of England, where dogs have to cope with rather complex tasks, such as driving sheep over a definite course, just obeying their masters’ six or eight whistle signals, often accompanied by gestures. The dogs behaved like Clever Hans demonstrating a remarkable ability to respond to their masters’ cues but in this situation a process is carefully watched. So, Morgan said, the intelligent animal is what he is trained to be - one whose natural powers are under the complete control of his master, with whom the whole plan of action lies.

This idea was corrected by Morgan’s own fox terrier Tony. Tony was not trained to lift the latch of the garden gate and thus to let himself out. The way in which the dog learnt the trick was on his own wise. Tony naturally wanted to go out into the road and after several experiences he raised the latch with the back of his head, and thus released the gate, which swung open. Once firmly established, the behaviour remained constant throughout the remainder of the dog’s life, some five or six years. And the famous psychologist could not succeed, not withstanding much expenditure of biscuits, in teaching Tony to lift the latch more elegantly with his muzzle instead of the back of his head.

Morgan’s dog became an inspirer of infinite numbers of animals doomed for searching for specific ways to open doors. It was Morgan’s influential American lecture on habit and instinct in Harvard of 1896 that moved Edward Lee Thorndike for elaborating his experimental approach based on the study of animals escaping from puzzle boxes. Thorndike was experimenting with chicks, and when he moved to Columbia in 1897, he took along his two best educated chicks. At Columbia he expanded his sample, and in 1898 when he published his doctoral thesis, “Animal Intelligence: An Experimental Study of the Associative Processes in Animals”, he reported data on chicks, cats, and dogs. So 1898 could be considered the year of birth of the puzzle-box-method.

The introduction of the puzzle-box method into comparative psychology was the point at which objective experimental methods were introduced into psychology, and prepared the way for its absorption into behaviourism. This was to exert a profound influence on the study of animal intelligence. Like Morgan, Thorndike reacted to anthropomorphic representations of animal reasoning and began his experiments in order to discredit the anecdotal approach for describing the behaviour. Many observers of animals, he argued, have looked for animal intelligence, and never for animal stupidity.

Figuratively speaking, the objective study of intelligent behaviour from the earliest stages has been based on several “corner boxes”. First of all, there were Thorndike’s puzzle-box and, later, Skinner’s reinforcement-box (a so-called Skinner’s chamber). Both were aimed to develop experimental methods for controlling and manipulating the presentation of stimuli, but in different ways. Being placed into the puzzle-box, an animal has to extricate itself, while in the Skinner’s box it only desired to stay there as long as possible in order to get more and more awards. Differing by a presentation of reinforcement, these ways for studying animals’ capabilities of solving problems resemble in principle: the animal is unaware of how the apparatus works. A combination of these two variants much later resulted in another kind of a box, a so-called “artificial fruit”. You are not placed into the box, instead, you are presented by a sort of a puzzle box containing food, so, it is a challenge for you to extract a reward - but not yourself - from the box. The principle is the same: it is not necessary for a subject to understand machinery, just to find a way of opening the box by trials and errors and then to repeat the found way again and again. The artificial fruit has been constructed mainly for studying animals’ abilities for imitation (see Chapter 25), and it is worth to note that the first attempts in this direction were based on Thorndike’s early experiments with chicks. First variants of mazes that applied for studying animal intelligence were also constructed within boxes. American psychologist W.S. Small described his research which involved an apparatus for the study of intelligence and learning in rats that he had modelled after the Hampton Court Maze. While the specific design was taken from a diagram provided in the Encyclopedia Britannica, the suggestion for use of the Hampton Court maze was that of Edmund Sanford. Published in two parts in American Journal of Psychology (1900/1901), " An Experimental Study of the Mental Processes of the Rat" this paper moved many explorers to use mazes for studying intelligence in animals. Besides operating with- and within locked boxes, animals had a possibility to demonstrate their intelligence by placing one box on another. This came from an alternative Gestalt approach in which thought was seen as an organisational process by which a problem was reorganised or solved (see Chapter 17). Gestalt was not part of psychology's mainstream in the first half of the twentieth century in which behaviourism dominated. In the second half of the century cognitive psychology would come together as a relatively coherent movement.

One of the first presentations of comparative and objective investigations of human and animal mental representation belonged to Leonard T. Hobhouse. In his book “Mind in Evolution” (1901), Hobhouse articulated a theory of intelligence defined in terms of levels of adaptive behaviour, introduced a series of animal problem solving tasks that initiated the experimental study of complex animal behaviour, and reported evidence of sudden improvement in the learning curve that appeared to reflect animals' ability to employ perceptual relations in problem solution. Hobhouse referred to this as “practical judgement, ” and later students in animal behaviour have termed it “insight”. Hobhouse considered the development of adaptive ability of animals from the simplest tendencies to maintain “organic equilibrium, through the relatively stereotyped, inherited, stimulus-specific reflexes and more variable but also inherited patterns of instinctive behaviour, to the individually acquired adaptations of intelligence”. According to his definition, intelligent behaviour was that “devised by the individual on the basis of its own experience for compassing the ultimate and proximate ends to which it is impelled “. The presence of intelligence was indicated by the modification of action in accordance with the results of experience, showing that in some degree the animal can correlate its own past experiences with its subsequent action. At the lower levels of intelligence, Hobhouse placed behaviour that is habitual-acquired correlations that functioned as general modes of reaction to circumstance. At the higher levels of intelligence, however, behaviour, was, in his view, purposive. Purposive action dealt with the complex and varying circumstances of individual cases; and, unlike habit, which was a general mode of reaction, higher intelligence was selective, choosing appropriate means from among a host of possible actions best suited to achieve the desired aims.

After canvassing the broad trend of mental development, Hobhouse then turned to the general question of whether the higher levels of intelligence were attained by animals other than man. To address this question, he introduced an ingenious set of problems and described a long series of experiments employing these tasks with dogs, cats, monkeys, an elephant, and an otter. The problems involved manipulations with a simple mechanism (e.g., pulling a string, pushing a door, pushing a lever, sliding a lid, lifting a catch) or even more complicated behaviour (e.g., box stacking or rake use with monkeys) to obtain food. In the animals' response to these problems, Hobhouse found evidence of sudden improvement in the learning curve, improvement that he interpreted as the evidence that animals are, indeed, capable of some degree of higher intelligence.

Extending his analysis first to conceptual and then to systematic thought in humans, Hobhouse presented a four stage theory of the development of intelligent adaptation from Unconscious Readjustment (Stage 1) through Concrete Experience and the Practical Judgment (Stage 2), to Conceptual Thinking and Will (Stage 3), and finally Rational System (Stage 4) that anticipated certain of Jean Piaget's mach more later. Piaget also accepted ideas of Watson and J. M. Baldwin, with his classic study of infant behavioural development, " The Origin of Right-Handedness". Thus a tendency of studying Human and Animal Intelligence hand in hand had been developed.

Among other great persons who rocked the cradle of experimental psychology were Wilhelm Wundt and William James. They established the first two laboratories in the world (in Leipzig and in Harvard, simultaneously in 1875) dedicated to experimental psychology and pioneered the concept of stating mental events in relation to objectively knowable and measurable stimuli and reactions. James used Spencer's Principles of Psychology as the text for his first course in physiological psychology at Harvard (1876-77), although he was very critical of Spencer's detailed formulations. Thorndike was one of graduate students supervised by James and learned experimental psychology by his two-volume Course “The Principles of Psychology”, 1890. At that time, students from all over the world journeyed to Leipzig to learn experimental technique and to return to their home institutions imbued with the spirit of scientific psychology.

Wundt considered mind as an activity, not a substance. The basic mental activity was designated by Wundt as “apperception”. He concerned the process of excitations from stimulation of the sense organs, through sensory neurones to the lower and higher brain centres, and from these centres to the muscles. Parallel with this process run the events of mental life, known through introspection. Introspection became, for Wundt, the primary tool of experimental psychology. The method that Wundt developed was a sort of experimental introspection: the researcher was to carefully observe some simple events - one that could be measured as to quality, intensity, or duration - and record his responses to variations of those events.

In the next chapters we will consider early development of two main approaches to study intelligence which had been expanded in parallel from the beginning.