An experimental test of stimulus estimation theory: danger and safety with snake phobic stimuli

The stimulus estimation model (Taylor & Rachman, 1994) asserts that fear overprediction stems from: (a) overprediction of the danger elements of a phobic stimulus, and (b) underprediction of existing safety resources. Using a 2x2 factorial design, with danger (high vs low) and safety (high vs low) as between-subjects variables, an experimental test of the model was conducted with 25 snake-fearful participants per condition. The four experimental conditions were matched on initial levels of snake fearfulness, as assessed by the Snake Questionnaire (SNAQ). For the 51 participants who demonstrated overprediction of fear, high danger led to reliably more fear overprediction than low danger; and low safety led to reliably more fear overprediction than high safety. The interaction between danger and safety was not statistically significant. The results offer the first convincing experimental support for the stimulus estimation model of fear overprediction.     

An experimental comparison of stimulus and response translated power functions for brightness

A threshold parameter has been introduced into the power law in two different ways, one involving, translation on the stimulus axis (the Ф-Law) and the second involving translation on the response axis (the Ψ-Law). In this study the two laws were compared using the data from 6 Ss making magnitude estimation judgments of brightness. Although the prevalent view appears to favor the Ф -Lau, the data of this study clearly dictate a choice of the Ψ-Law over the $-Law for brightness.     

The Obama effect: An experimental test

Past research on stereotype threat and role model effects, as well as a recent quasi-experiment (Marx, Ho, & Freidman, this issue) suggested the possibility of an “Obama effect” on African American’s standardized test performance, whereby the salience of Barack Obama’s stereotype defying success could positively impact performance. We tested this reasoning in a randomized experiment with a broad sample of college students from across the country. Specifically, we tested the hypothesis that students prompted to think about Barack Obama prior to taking a difficult standardized verbal test would improve their performance relative to white students, and to African American students in control conditions that were not prompted to think about Obama. Our results did not support this hypothesis. Test scores were unaffected by prompts to think about Obama and no relationship was found between test performance and positive thoughts about Obama, a disconfirmation of both the findings and conclusions of the Marx, Ho, and Freidman study.     

An experimental test of three choice shift hypotheses*

The present experiment pitted three choice shift hypotheses against each other in an attempt to eliminate one or more of the hypotheses and find support for those remaining. Ss responded three times to the 12 CDQ items, once as a pretest and twice following presentation of homogeneous sets of three arguments which advocated either a risky or a cautious position. The risk-as-value, relevant arguments, and conformity/attitude change hypotheses generated three separate predictions for the Ss' responses. Results mirrored the prediction of the relevant arguments hypothesis: New information, whether contained in cautious or risky arguments, caused a shift toward the type of argument presented. The risk-as-value and the conformity/attitude change hypotheses could not explain the present data.     

Responsibility and obsessive-compulsive disorder: an experimental test

To test the causal status of responsibility in obsessive-compulsive disorder (OCD), an experiment was executed in which responsibility was experimentally manipulated. OCD patients, non-OCD anxiety controls, and non-patients executed a classification task in either a high or a low responsibility (LoRes) condition. Subjective ratings related to danger and responsibility indicated that the manipulation was successful. Subjective OCD-like experiences and checking behaviors were higher in OCD patients in the high responsibility (HiRes) condition than in all other groups. Although the checking subscale of the Padua Inventory correlated with subjective ratings in the OCD patients in the HiRes condition, it was not associated with checking behaviors. The results confirm the hypothesis that responsibility plays a causal role in OCD.     

Eysenck's incubation of fear hypothesis: an experimental test

The present experiment was designed to test Eysenck's hypothesis that repeated exposure to an unreinforced CS of brief duration following acquisition of a classical aversive CR may lead to a progressive increase in the strength of that CR, provided that the UCS is intense and the CR has drive-like properties. Using a between-groups design, normal human subjects were given identical classical acquisition trials, followed by extinction trials where CS duration was either 2, 8 or 16 sec. The UCS was of fixed high intensity. Dependent measures were tonic and phasic heart rate and skin conductance. No evidence of incubation was found as a function of CS duration. Nor was there any indication that CS duration differentially affected resistance to extinction. A small number of subjects showed evidence of incubation with heart rate measures during extinction. However, there was no indication that this enhancement was governed by the parameters suggested by Eysenck. UCR amplitude, which showed a positive correspondence with CS-bound activity throughout the trials, did not reliably predict incubation. Problems concerning both the definition and the demonstration of incubation are discussed.     

Iontophoretically applied potassium ions as an experimental pain stimulus for investigating pain mechanisms

The present study investigated the psychophysical characteristics of potassium iontophoresis and its suitability as an experimental pain stimulus. Experiment 1 investigated the optimal duration of the pain stimulus for reliable reporting across repeated trials and whether the relationship between stimulus and subject response was linear, logarithmic, or a power function. In Experiment 2, the optimal interstimulus interval (ISI) was determined for reliable pain reporting, and stimulus history effects, both in terms of session effects and the effects of immediately preceding stimuli, were evaluated. In Experiment 3, potassium iontophoresis was compared with a sodium iontophoresis control. Linear functions described the stimulus-pain relationship best. No significant differences in the goodness-of-fit coefficients of determination, correlations, or coefficients of variation were found for the stimulus durations of 1, 2, and 4 sec. Significant stimulus history effects were found across a session, with adaptation and enhancement of responding for low- and moderate-intensity stimuli, respectively. The effects of the immediately preceding stimuli were suppression or enhancement of pain response, depending on the ISI, the preceding stimulus intensity, and the present stimulus intensity. Potassium iontophoresis was a significantly more effective pain stimulus than was sodium iontophoresis. It was concluded that potassium iontophoresis is a convenient and reliable experimental pain stimulus, which can be presented rapidly and repeatedly with minimal loss in consistency of subject pain report. Potassium iontophoresis provides a tool for investigating the neural modulation of pain in the relative absence of inflammation processes and tissue damage.