Wilhelm Wundt

Wilhelm Wundt

Experimental psychology emerged as a modern academic discipline in the 19th century when Wilhelm Wundt introduced a mathematical and experimental approach to the field. Wundt founded the first psychology laboratory in Leipzig, Germany.^[2] Other experimental psychologists, including Hermann Ebbinghaus and Edward Titchener, included introspection in their experimental methods.

Charles Bell

Charles Bell

Charles Bell was a British physiologist whose main contribution to the medical and scientific community was his research on the nervous system. He wrote a pamphlet summarizing his research on rabbits. His research concluded that sensory nerves enter at the posterior (dorsal) roots of the spinal cord, and motor nerves emerge from the anterior (ventral) roots of the spinal cord. Eleven years later, a French physiologist, Francois Magendie, published the same findings without being aware of Bell's research. As a result of Bell not publishing his research, this discovery was called the Bell–Magendie law to honor both individuals. Bell's discovery disproved the belief that nerves transmitted either vibrations or spirits.

Ernst Heinrich Weber

Ernst Heinrich Weber, a German physician, is credited as one of experimental psychology's founders. Weber's main interests were the sense of touch and kinesthesis. His most memorable contribution to the field of experimental psychology is the suggestion that judgments of sensory differences are relative and not absolute. This relativity is expressed in "Weber's Law," which suggests that the just-noticeable difference or jnd is a constant proportion of the ongoing stimulus level. Weber's Law is stated as an equation:

${\displaystyle {\frac {\Delta I}{I}}=k,}$

where ${\displaystyle I\!}$ is the original intensity of stimulation, ${\displaystyle \Delta I\!}$ is the addition to it required for the difference to be perceived (the jnd), and k is a constant. Thus, for k to remain constant, ${\displaystyle \Delta I\!}$ must rise as I increases. Weber's law is considered to be the first quantitative law in the history of psychology.^[3]

Gustav Fechner

Fechner published in 1860 what is considered to be the first work of experimental psychology, "Elemente der Psychophysik."^[4] Some historians date the beginning of experimental psychology to the publication of "Elemente." Ernst Heinrich Weber was not a psychologist, but it was Fechner who realized the importance of Weber's research to psychology. Weber's law and Fechner's law was published in Fechner's work, "Elemente der Psychophysik," and Fechner, a student of Weber named his first law in honor of his mentor.^[5] Fechner was profoundly interested in establishing a scientific study of the mind-body relationship, which became known as psychophysics. Much of Fechner's research focused on the measurement of psychophysical thresholds and just-noticeable differences. He invented the psychophysical method of limits, the method of constant stimuli, and the method of adjustment, which are still in use.

Oswald Külpe

Oswald Külpe is the main founder of the Würzburg School in Germany. He was a pupil of Wilhelm Wundt for about twelve years. Unlike Wundt, Külpe believed experiments were possible to test higher mental processes. In 1883 he wrote Grundriss der Psychologie, which had strictly scientific facts and no mention of thought.^[6] The lack of thought in his book is odd because the Würzburg School put a lot of emphasis on mental set and imageless thought.

Würzburg School

The work of the Würzburg School was a milestone in the development of experimental psychology. The School was founded by a group of psychologists led by Oswald Külpe, and it provided an alternative to the structuralism of Edward Titchener and Wilhelm Wundt. Those in the School focused mainly on mental operations such as mental set (Einstellung) and imageless thought. Mental set affects perception and problem solving without the awareness of the individual; it can be triggered by instructions or by experience. Similarly, according to Külpe, imageless thought consists of pure mental acts that do not involve mental images. William Bryan, an American student, working in Külpe's laboratory, provided an example of mental set. Bryan presented subjects with cards that had nonsense syllables written on them in various colors. The subjects were told to attend to the syllables, and in consequence, they did not remember the colors of the nonsense syllables. Such results made people question the validity of introspection as a research tool, leading to a decline in voluntarism and structuralism. The work of the Würzburg School later influenced many Gestalt psychologists, including Max Wertheimer.

George Trumbull Ladd

George Trumbull Ladd introduced experimental psychology into the United States and founded Yale University's psychological laboratory in 1879. In 1887, Ladd published Elements of Physiological Psychology, the first American textbook that extensively discussed experimental psychology.^[7] Between Ladd's founding of the Yale Laboratory and his textbook, the center of experimental psychology in the US shifted to Johns Hopkins University, where George Hall and Charles Sanders Peirce were extending and qualifying Wundt's work.

Charles Sanders Peirce

Charles Sanders Peirce

Joseph Jastrow

With his student Joseph Jastrow, Charles S. Peirce randomly assigned volunteers to a blinded, repeated-measures design to evaluate their ability to discriminate weights.^{[8][9][10][11]} Peirce's experiment inspired other researchers in psychology and education, which developed a research tradition of randomized experiments in laboratories and specialized textbooks in the 1800s.^{[8][9][10][11]} The Peirce-Jastrow experiments were conducted as part of Peirce's pragmatic program to understand human perception; other studies considered perception of light, etc. While Peirce was making advances in experimental psychology and psychophysics, he was also developing a theory of statistical inference, which was published in "Illustrations of the Logic of Science" (1877–78) and "A Theory of Probable Inference" (1883); both publications that emphasized the importance of randomization-based inference in statistics. To Peirce and to experimental psychology belongs the honor of having invented randomized experiments decades before the innovations of Jerzy Neyman and Ronald Fisher in agriculture.^{[8][9][10][11]}

Peirce's pragmaticist philosophy also included an extensive theory of mental representations and cognition, which he studied under the name of semiotics.^[12] Peirce's student Joseph Jastrow continued to conduct randomized experiments throughout his distinguished career in experimental psychology, much of which would later be recognized as cognitive psychology. There has been a resurgence of interest in Peirce's work in cognitive psychology.^[13][14][15] Another student of Peirce, John Dewey, conducted experiments on human cognition, particularly in schools, as part of his "experimental logic" and "public philosophy."

20th century

In the middle of the 20th century, behaviorism became a dominant paradigm within psychology, especially in the United States. This led to some neglect of mental phenomena within experimental psychology. In Europe, this was less the case, as European psychology was influenced by psychologists such as Sir Frederic Bartlett, Kenneth Craik, W.E. Hick, and Donald Broadbent, who focused on topics such as thinking, memory, and attention. This laid the foundations for the subsequent development of cognitive psychology.

In the latter half of the 20th century, the phrase "experimental psychology" had shifted in meaning due to the expansion of psychology as a discipline and the growth in its sub-disciplines. Experimental psychologists use a range of methods and do not confine themselves to a strictly experimental approach, partly because developments in the philosophy of science have affected the exclusive prestige of experimentation. In contrast, experimental methods are now widely used in fields such as developmental and social psychology, which were not previously part of experimental psychology. The phrase continues in use in the titles of a number of well-established, high prestige learned societies and scientific journals, as well as some university courses of study in psychology.

Empiricism

Perhaps the most basic assumption of science is that factual statements about the world must ultimately be based on observations of the world. This notion of empiricism requires that hypotheses and theories be tested against observations of the natural world rather than on a priori reasoning, intuition, or revelation.^[17]

Testability

Closely related to empiricism is the idea that, to be useful, a scientific law or theory must be testable with available research methods. If a theory cannot be tested in any conceivable way then many scientists consider the theory to be meaningless. Testability implies falsifiability, which is the idea that some set of observations could prove the theory to be incorrect.^[18] Testability has been emphasized in psychology because influential or well-known theories like those of Freud have been difficult to test.

Determinism

Experimental psychologists, like most scientists, accept the notion of determinism. This is the assumption that any state of an object or event is determined by prior states. In other words, behavioral or mental phenomena are typically stated in terms of cause and effect. If a phenomenon is sufficiently general and widely confirmed, it may be called a "law"; psychological theories serve to organize and integrate laws.

Parsimony

Another guiding idea of science is parsimony, the search for simplicity. For example, most scientists agree that if two theories handle a set of empirical observations equally well, we should prefer the simpler or more parsimonious of the two. A notable early argument for parsimony was stated by the medieval English philosopher William of Occam, and for this reason, the principle of parsimony is often referred to as Occam's razor.^[19]

Operational definition

Some well-known behaviorists such as Edward C. Tolman and Clark Hull popularized the idea of operationism, or operational definition. Operational definition implies that a concept be defined in terms of concrete, observable procedures. Experimental psychologists attempt to define currently unobservable phenomena, such as mental events, by connecting them to observations by chains of reasoning.^[20]

Reliability

Reliability measures the consistency or repeatability of an observation. For example, one way to assess reliability is the "test-retest" method, done by measuring a group of participants at one time and then testing them a second time to see if the results are consistent. Because the first test itself may alter the results of a second test, other methods are often used. For example, in the "split-half" measure, a group of participants is divided at random into two comparable sub-groups, and reliability is measured by comparing the test results from these groups, It is important to note that a reliable measure need not yield a valid conclusion.^[21]

Validity

Validity measures the relative accuracy or correctness of conclusions drawn from a study. To determine the validity of a measurement quantitatively, it must be compared with a criterion.^[17] For example, to determine the validity of a test of academic ability, that test might be given to a group of students and the results correlated with the grade-point averages of the individuals in that group. As this example suggests, there is often controversy in the selection of appropriate criteria for a given measure. In addition, a conclusion can only be valid to the extent that the observations upon which it is based are reliable.

Several types of validity have been distinguished, as follows:

Nominal measurement

In a nominal scale, numbers are used simply as labels – a letter or name would do as well. Examples are the numbers on the shirts of football or baseball players. The labels are more useful if the same label can be given to more than one thing, meaning that the things are equal in some way, and can be classified together.

Ordinal measurement

An ordinal scale arises from the ordering or ranking objects, so that A is greater than B, B is greater than C, and so on. Many psychological experiments yield numbers of this sort; for example, a participant might be able to rank odors such that A is more pleasant than B, and B is more pleasant than C, but these rankings ("1, 2, 3 ...") would not tell by how much each odor differed from another. Some statistics can be computed from ordinal measures – for example, median, percentile, and order correlation – but others, such as standard deviation, cannot properly be used.

Interval measurement

An interval scale is constructed by determining the equality of differences between the things measured. That is, numbers form an interval scale when the differences between the numbers correspond to differences between the properties measured. For instance, one can say that the difference between 5 and 10 degrees on a Fahrenheit thermometer equals the difference between 25 and 30, but it is meaningless to say that something with a temperature of 20 degrees Fahrenheit is "twice as hot" as something with a temperature of 10 degrees. (Such ratios are meaningful on an absolute temperature scale such as the Kelvin scale. See next section.) "Standard scores" on an achievement test are said to be measurements on an interval scale, but this is difficult to prove.^[27]

Ratio measurement

A ratio scale is constructed by determining the equality of ratios. For example, if, on a balance instrument, object A balances two identical objects B, then one can say that A is twice as heavy as B and can give them appropriate numbers, for example "A weighs 2 grams" and "B weighs 1 gram". A key idea is that such ratios remain the same regardless of the scale units used; for example, the ratio of A to B remains the same whether grams or ounces are used. Length, resistance, and Kelvin temperature are other things that can be measured on ratio scales. Some psychological properties such as the loudness of a sound can be measured on a ratio scale.^[27]

One-way designs

The simplest experimental design is a one-way design, in which there is only one independent variable. The simplest kind of one-way design involves just two-groups, each of which receives one value of the independent variable. A two-group design typically consists of an experimental group (a group that receives treatment) and a control group (a group that does not receive treatment).^[28]

The one-way design may be expanded to a one-way, multiple groups design. Here a single independent variable takes on three or more levels.^[29] This type of design is particularly useful because it can help to outline a functional relationship between the independent and dependent variables.

Factorial designs

One-way designs are limited in that they allow researchers to look at only one independent variable at a time, whereas many phenomena of interest are dependent on multiple variables. Because of this, R.A Fisher popularized the use of factorial designs. Factorial designs contain two or more independent variables that are completely "crossed," which means that every level each independent variable appears in combination with every level of all other independent variables. Factorial designs carry labels that specify the number of independent variables and the number of levels of each independent variable there are in the design. For example, a 2x3 factorial design has two independent variables (because there are two numbers in the description), the first variable having two levels and the second having three.

Main effects and interactions

The effects of independent variables in factorial studies, taken singly, are referred to as main effects. This refers to the overall effect of an independent variable, averaging across all levels of the other independent variables. A main effect is the only effect detectable in a one-way design.^[30] Often more important than main effects are "interactions", which occur when the effect of one independent variable on a dependent variable depends on the level of a second independent variable. For example, the ability to catch a ball (dependent variable) might depend on the interaction of visual acuity (independent variable #1) and the size of the ball being caught (independent variable #2). A person with good eyesight might catch a small ball most easily, and person with very poor eyesight might do better with a large ball, so the two variables can be said to interact.

Within- and between-subjects designs

Two basic approaches to research design are within-subjects design and between-subjects design. In within-subjects or repeated measures designs, each participant serves in more than one or perhaps all of the conditions of a study. In between-subjects designs each participant serves in only one condition of an experiment.^[31] Within-subjects designs have significant advantages over between-subjects designs, especially when it comes to complex factorial designs that have many conditions. In particular, within-subjects designs eliminate person confounds, that is, they get rid of effects caused by differences among subjects that are irrelevant to the phenomenon under study. However, the within-subject design has the serious disadvantage of possible sequence effects. Because each participant serves in more than one condition, the passage of time or the performance of an earlier task may affect the performance of a later task. For example, a participant might learn something from the first task that affects the second. ^[32]

Animal cognition

Animal cognition refers to the mental capacities of non-human animals, and research in this field often focuses on matters similar to those of interest to cognitive psychologists using human participants. Cognitive studies using animals can often control conditions more closely and use methods not open to research with humans. In addition, processes such as conditioning my appear in simpler form in animals, certain animals display unique capacities (such as echo location in bats) that clarify important cognitive functions, and animal studies often have important implications for the survival and evolution of species.