Response bias in the yoked control procedure

Rodent models of depression: learned helplessness using a triadic design in rats

Certain types of human depression are precipitated by stressful life events, and vulnerable individuals experiencing these stressors may develop clinical depression. Understanding the neurobiology of stress vulnerability (depression) as well as stress resiliency (coping) is critical for guiding the development of novel pharmacotherapeutic agents for stress-related disorders such as depression in humans. The use of a triadic design (escapable shock, yoked-inescapable shock and restrained control) allows the investigator to examine the various sequella of stress exposure, while manipulating and quantifying the impact of psychological dynamics of stress such as active behavioral coping (i.e., stress control). Both escape and yoked subjects are exposed to the identical amount, intensity, pattern and duration of stress. The critical distinction between these two groups is that the escape group has the opportunity to terminate the shock stress by turning a wheel at the front of a chamber, while wheel-turning for the yoked subject is of no consequence. Any difference observed between the escape and yoked subjects is a result of the effects of coping, rather than stress exposure per se. The restrained group is included to control for the effects of handling. Any differences between this group and the escape and yoked subjects reflects the impact of stress per se.

Judgments of causal efficacy under constant and changing interevent contingencies

How do people judge constant and varying interevent contingencies? In two experiments, 150 college students rated the efficacy of a potential cause (an experimental fertilizer) of an effect (a plant's blooming). The prevailing probabilistic interevent relation could remain constant for the entirety of the problem or it could change without warning at the midway point: by contingency reversal, by shifting from noncontingency to contingency, or by shifting from contingency to noncontingency. Participants' trial-by-trial ratings sensitively tracked the prevailing positive, negative, and noncontingent interevent relations, even those that entailed an unsignaled change in contingency. Changes in specific cells of the 2 x 2 contingency table differentially affected participants' response to the altered interevent relations. All of this evidence was well described by an associative account of contingency and causal judgments.

Analysis of the importance of controllable versus uncontrollable stress on subsequent behavioral and physiological functioning

Original observations of the effects of stress exposure on behavioral, physiological and pathological indices were documented in the mid 1960s [J.B. Overmier, Interference with avoidance behavior: failure to avoid traumatic shock, J. Exp. Psychol. 78 (1968) 340-343 [12]; J.B. Overmier, M.E.P. Seligman, Effects of inescapable shock upon subsequent escape and avoidance learning, J. Comp. Physiol. Psychol. 63 (1967) 28-33 [13]; M.E.P. Seligman, S.F. Maier, Failure to escape traumatic shock, J. Exp. Psychol. 74 (1967) 1-9 [15]; J.M. Weiss, Effects of coping responses on stress, J. Comp. Physiol. Psychol. 65 (1968) 251-260 [18]]. Studies employing the triadic design (e.g. escapable stress, yoked-inescapable stress and no stress) indicated that the deficits following stress exposure were not caused by stress per se, rather the uncontrollability of the stress was the critical determinant. In this paradigm, the first group (escape) receives exposure to an environmental event that it can "control" by performing a behavioral response. Stress control or coping behavior includes the ability to alter the onset, duration, intensity or pattern of an aversive experience [S.F. Maier, M.E.P. Seligman, Learned helplessness: theory and evidence, J. Exp. Psychol.: Gen. 105 (1976) 3-46 [10]]. The second group is "yoked" to its escape partner and receives the identical physical stressor as its escape counterpart, but there is no behavioral response that the yoked subject can make to alter the outcome. The third group (naive) receives no stress exposure and is either restrained in the experimental apparatus or remains in the home cage until subsequent testing. Researchers using this triadic design should be aware of the concerns of certain investigators [R.M. Church, Systematic effect of random error in the yoked control design, Psychol. Bull. 62 (1964) 122-131 [3]; E.A. Wasserman, Response bias in the yoked control procedure, Behav. Brain Sci. 11 (1988) 477-478 [17]] who have raised important issues about the validity of the yoked control design because of the possibility of systematic biases. For example, individual differences in stress reactivity may result in random error in the yoked control group. This point will be addressed further in Section 5. This procedure allows the investigator to analyze the contributions of the importance of psychological dynamics of stress on a variety of dependent measures including: behavioral, pharmacological, neurochemical and immunological indices.