This chapter underscores the increasing importance of understanding the effects of environmental factors in evaluating physiological responses of the behaving person. Most of the relevant environmental factors are internal (e.g., drugs, hormones) whereas a few are external (e.g., illumination). It is important to know about these effects not only for human welfare, but to consider them as possible influences in the conduct of research. Certain commonly used substances--such as coffee, tea, soft drinks, alcohol, nicotine, and prescribed and nonprescribed medications--can affect interpretations of psychophysiological data. Thus, investigators must be aware of these possible effects when carrying out studies in psychophysiology. Researchers can control for unwanted influences by asking participants to abstain from using certain substances for a suitable length of time before taking part in an experiment.
Some of the studies presented here may not be strictly psychophysiological in that they fail to use a behavioral manipulation. However, the influence of environmental factors must be considered because of the effects they exert on both behavioral and physiological responses. Our discussion of environmental effects starts with the EEG and continues in the same order in which the various measures are presented in earlier chapters. The material presented in the EEG section covers, for the most part, research performed subsequent to a review by Shagass ( 1972). In another comprehensive review, Stroebel ( 1972) discussed the behavioral and physiological effects of drugs and included sections on EEG and autonomic response patterns.
The EEG is a valuable tool for objective assessments of psychoactive drugs that have either a psychologically depressing or stimulating effect. The EEG's usefulness is further enhanced when behavioral or performance tests, as well as blood samples to determine the amount of the drug in the bloodstream, are conducted. In addition, the use of drugs in EEG studies may help to understand some of the biochemical factors in the brain that are involved in the production of the EEG.
Table 19.1 is taken from Brown ( 1976) and provides a useful classification of some familiar drugs and their psychological effects. We will consider the effects on EEG of psychoactive drugs in the hallucinogen, opiate, and depressant categories.
The effects of drugs on behavior are by no means always clear-cut and understandable. There are many factors operating, including the placebo effect. The placebo effect refers to