The “first-round” of studies viewing meditation as a self-regulation strategy helped establish interest in the field. Generally these “first-round” studies consisted of anecdotal case reports, intensive design studies containing “non-specific variables,” and/or combining techniques for treatment and/or comparing meditation to control groups, but not to other, similar techniques. With regard to demand characteristics, the most experienced meditators noted that they had “strong positive feelings about the experience of meditation”. This positive feeling about meditation, coupled with the instructions in the transcendental meditation (TM) initiation that drug use adversely affects TM performance, may have contributed to an exaggeration on the retrospective questionnaire about the decrease in drug use and the magnitude of prior drug-use patterns. W. D. Curtis and H. W. Wessberg tested differences between a meditation group, a deep muscle relaxation group, and non-experienced individuals and found no difference either between groups or between trials on galvanic skin response, heart rate, or respiration.