Changes in subject performance during the semester: An empirical investigation

Abstract

Two experiments were conducted to probe for performance differences between early-semester subjects and late-semester subjects in an introductory psychology subject pool. In Experiment 1A, hypotheses regarding changes in performance included differential effort, changes in subjects' attention to the task, and changes in subjects' sensitivity. A signal detection paradigm was used, and 278 subjects were sampled over the course of the semester. No evidence of changes in subject performance was found, in spite of sufficient power to detect relevant patterns of change. The results of a replication (N = 135) were consistent with those ofExperiment 1A. Experiment 2 (N = 118) employed a text comprehension task to examine possible differences in subject performance with a more cognitive task. Again, there was no evidence to support the idea that latesemester subjects were performing differently from early-semester subjects.In the field of psychology, details of experimental design are thoroughly scrutinized. Particularly when the experimental task is complex, great care must be taken to ensure that the subject is attempting to follow the directions ofthe experimenter. A foundational assumption for any experiment not explicitly investigating subject differences is that the population of subjects sampled is homogeneous. Systematic changes in subject behavior across the semester could influence the pattern of results or reduce the power of an experimental manipulation. Additionally, if systematically different groups are sampled, the generalizability of the conclusions may be seriously reduced.Interestingly, the belief is common among researchers utilizing an undergraduate subject pool that students do vary in important respects across the semester. Subjects participating in the early weeks of the semester are usually believed to follow directions more closely or attend more fully during the experiment.Several studies have been conducted yielding significant differences between early-semester subjects and latesemester subjects on such demographic attributes as academic orientation and locus of control (Evans & Donnerstein, 1974), preoccupation with death (Blatt & Quinlan, 1967), and respect for the scientific enterprise (Holmes, 1967). However, absent theoretical connections between such indices and performance for a given task, these reThe authors would like to thank Arthur Glenberg, Yei-Yu Yeh, Mike Hogan, Steve Morgan, and Bob Kachelski for their helpful comments on an earlier version ofthe manuscript. We thank John Theios and Arthur Glenberg for the use of their lab space and equiprnent in conducting the experiment. The order of the first and second and the third and fourth authors was determined by a coin f1ip. Peter Kruley was partialiy supported by AASERT Grant F4962D-92-J-Q31O from the Air Force Office of Sponsored Research during preparation of this report. Requests for reprints may be sent to William Langston, Department of Psychology, 1202 W. Johnson, Madison, WI 53706. sults provide little support for the inf...

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