Experimentallyinduced False Memories See Appendix A


EXPERIMENTER EFFECTS. = experimenter bias effects. When a researcher conducts an experiment, she or he hypothesizes that one or several variables will have a particular outcome. The experiment is planned to test the hypotheses under investigation and to eliminate as many alternative or "rival" explanations as possible (cf., investigator paradigm effect - the tendency in researchers, at any one time and place, to be influenced by popular fads or conceptualizations and paradigms in vogue, that determine what particular research questions are asked, what kind of data is collected, and what conclusions are stated; perturbation theory - provides means for disposing of extraneous factors among true psychological factors, controlling for errors such as observer's biases, instrument calibration errors, and participant sampling errors; situ-ational effect - occurs when participants are placed in different settings or situations, such as in a bare room versus a well-furnished office; often, performance in the former type of setting tends to be inferior to that in the latter type of surroundings; in the doctrine of situa-tionalism, it is posited that the environment and one's immediate situational factors primarily determine one's behavior). A major set of rival explanations in this process is called experimenter effect [also known as observer effect or Rosenthal effect - named after the German-born American psychologist Robert Rosenthal (1933- )], which refers to a number of possible effects upon participants in an experiment that may be traced to the biases or behaviors of the experimenter. One such effect is called the experimenter-expectancy effect or expectancy effect, which refers to an experimenter artifact that results when the hypothesis held by the experimenter leads unintentionally to behavior toward the participants that, in turn, increases the likelihood that the hypothesis will be confirmed; this is also called self-fulfilling prophesy. The phenomenon called experimenter bias (where experimenters may unwittingly influence participants' behavior in the direction of the fomer's expectations) is illustrated by the classic case of "Clever Hans" (Pfungst, 1911/1965), which points out that researchers often give cues to participants unintentionally through facial expressions and tones of voice. With this in mind, researchers are attempting constantly to eliminate experimenter-participant interactions that may lead to biased data and conclusions (cf., biosocial effect - an experimenter bias effect in which possible differential influences may be placed on different participants by virtue of the experimenter's differing attitudes and moods; and performance cue effect -knowledge of how a group performed previously may influence an experimenter's/rater's judgments of the group's current or subsequent performance). Another type of experimenter effect focuses on the factor of attention, especially on how attention paid to participants by the experimenter may bias the research results. The classic illustration here is the study by F. Roethlisberger and W. Dickson (cf. Mayo, 1933), who are credited with discovering the Hawthorne effect. This effect (named after the locale of the research - the Hawthorne plant of the Western Electric Company in Cicero, Illinois, near Chicago -where ways to increase worker productivity were studied) refers to the positive influence of attention on participants' performance. In the Hawthorne study (whose results and interpretation today are sometimes controversial), the effects of attention were so powerful that performance improved even when the objective working conditions worsened. Thus, the Hawthorne effect has come today to refer generally to the fact that one's performance in an experiment/study is affected by knowledge that one is participating in an experiment and refers to a change in behavior that results from participants' awareness that someone is interested in them. A phenomenon similar to the Hawthorne effect is called the novelty/disruption effect, which refers to a treatment effect that may result when an experimental treatment condition involves something new or unusual. For instance, inserting a red-colored nonsense syllable in the most difficult position in a serial list of black-on-white nonsense syllables facilitates the learning of that novel stimulus. When the novelty or disruption diminishes, the treatment effect may disappear. Experimenters may also provide the conditions for the pretesting effect, which refers to the influence that administering a pretest may have on the experimental treatment effect: it may sensitize the partici pant in such a way to behave differently than participants who did not receive the pretest. Another category of effects that may occur in psychological experiments is called subject/participant effects, which refer to any response by subjects or participants in a study that does not represent the way they would normally behave if not under study (cf., Hawthorne effect). Two powerful subject/participant effects are the placebo effect (i.e., in a treatment study, any observed improvement in response to a sham treatment that is probably due to the participant's expectations for treatment effectiveness; cf., tomato effect - a person may be affected negatively by something if he/she believes it to be harmful even though it is not; the name here comes from the introduction of tomatoes into Europe and where tomatoes had the bad reputation of causing numerous illnesses); and the demand characteristics of the situation [i.e., cues inadvertently given to individuals in a study concerning how they are expected to behave, including not only characteristics of the setting and procedures but also information, and even rumors, about the researcher and the nature of the research; cf., John Henry effect - named after the hardworking African-American folktale hero of the late 19th century - is a tendency for participants in a control group to adopt a competitive attitude towards the experimental group in certain experiments and, thereby, vitiating the validity of the control group; and the good subject/participant effect, or the Orne effect - named after the Austrian-American psychiatrist/hypnotist Martin Theodore Orne (1927-2000), refers to the situation where if participants in a study know what a researcher is looking for, they will typically behave accordingly in the predicted way]. Researchers conducting psychological experiments should, ideally, include controls for these and other possible experimenter and subject/participant effects to prevent "confounding" (i.e., cases where an extraneous variable systematically varies with variations in the independent variables under study) and to guard against the reduction of a study's validity. Yet other non-experimenter effects that may affect the validity of an experiment include: order effects - the order in which two or more experimental treatments are adminis tered may be significant and needs to be balanced or counterbalanced to control for an artificial progressive change over time; sequence effects - in multiple-treat-ment experimental designs, the different combinations of treatments should be counterbalanced across participants to insure that the sequence in which treatments are given is not the causative factor, but only the treatments themselves; self-selection or selective sampling bias/effect - when a number of people are asked to participate in an experiment, those likely to volunteer are probably not representative of the total group or population; random assignment of participants to treatments/groups may circumvent this bias/effect; and the leniency effect, proposed by the Austrian-born American psychologist Fritz Heider (1896-1988), refers to a judgmental error especially likely to occur in personality assessment situations where well-known or sympathetic individuals are evaluated more favorably than less familiar or less sympathetic persons. See also CLEVER HANS EFFECT/ PHENOMENON; HALO EFFECT; PYGMALION EFFECT. REFERENCES

Pfungst, O. (1911/1965). Clever Hans (the horse of Mr. von Osten): A contribution to experimental animal and human psychology. New York: Holt, Rinehart, and Winston. Mayo, E. (1933). The human problems of an industrial civilization. New York: Macmillan.

Management and the worker. Cambridge, MA: Harvard University Press.

Barber, T. X., & Silver, M. (1968). Fact, fiction, and the experimenter bias effect. Psychological Bulletin Monograph Supplement, 70, 1-29. Parsons, H. (1974). What happened at Hawthorne? Science, 183, 922-932. Barber, T. X. (1976). Pitfalls in human research: Ten pivotal points. New York: Pergamon. Rosenthal, R. (1976). Experimenter effects in behavioral research. New York: Irvington.

Rosenthal, R., & Rubin, D. (1978). Interpersonal expectancy effects: The first 345 studies. The Behavioral and Brain Sciences, 3, 377-386. Ross, M., & Olson, J. M. (1981). An expectancy-attribution model of the effects of placebos. Psychological Review, 88, 408-437. Rice, B. (1982). The Hawthorne defect: Persistence of a flawed theory. Psychology Today, 16, 70-74.


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