Prediction outcome probabilities as determinants of choice reaction time

In a two-stimulus two-response choice reaction time (RT) task in which Ss made stimulus predictions, the probability of a correct prediction was manipulated between Ss. The magnitude of the difference in RT to correctly and incorrectly predicted stimuli (i.e., the prediction outcome effect) was an increasing function of the probability of a correct prediction This finding was primarily due to a reliable decrease in RT to correctly predicted stimuli as the probability of a correct prediction increased, since RT to incorrectly predicted stimuli was not affected by prediction outcome probability. These results were interpreted as partially supporting a continuous expectancy notion which involves facilitory and inhibitory mechanisms winch are differentially influenced by the probability of a correct prediction.     

Prediction of choice reaction time from information of individual stimuli

A model is developed to predict the reaction time to stimuli using information content of the individual stimuli. Review of previous research in the area showed inconsistencies due possibly to the mode of stimulus presentation or to the number of stimuli. Two experiments designed to cover the range of variables used in previous experiments were conducted. The results indicate that the model makes accurate predictions over the entire range of variables used. A comparison to earlier studies also indicates a close correspondence. nt|mis|Acknowledgment is due the Office of Naval Research which supported this research through a prime contract, NOnr 2512(00), with General Dynamics Electric Boat Division as a part of the SUBIC. (SUBmarine Integrated Control) program.     

What it takes to defend deceptive placebo use

A complete defense of deceptive placebo use must address this ethical objection: deceptive placebo use violates patient autonomy, because deceiving a patient about the placebo nature of a proposed treatment prevents her from giving informed consent to the treatment. Unfortunately, this objection isn't always recognized and clearly disambiguated from other ethical concerns. I consider how well several bioethicists who write about placebo use have responded to, or evaded, this objection. I conclude that defenders of deceptive placebo use should, following the lead of Onora O'Neill, argue that deceptive placebo use is compatible with informed consent.     

The concept of placebo

This paper attempts to define the concept of placebo as it is used in the clinical context The author claims that X is a placebo if and only if X has such a property d_p, that whenever in a therapeutic situation T a stimulus S appears, then in attending conditions A, it will cause a beneficial reaction R in the patient. Formally, the same structure may be used to define any pharmacologically active drug. The main difference between the drug and a placebo is in the range of possible substitutions for X and the property d. For the active drug there is only one possible substitution for X and property d and it can be scientifically explained why, and how the drug works. In the case of a placebo a set of possible substitutions for X and d is open, and so far it is impossible to offer any scientifically valid explanation of the action mechanism of placebo.     

Conditioned placebo responses

Following earlier animal research, we attempt to condition placebo effects in human subjects. Four groups of 8 voluntary subjects were told that the experimenters would test a powerful new analgesic cream over three sessions by assessing its ability to reduce experimentally induced pain. The analgesic cream was, in fact, a placebo. In the first session all subjects were tested with and without the cream to assess their placebo response. In the second session, to condition two groups (with differing stimulation levels) to experience pain relief in response to the placebo, we repeatedly paired a reduction in nocioceptive stimulation with placebo administration. (Subjects were unaware that stimulation levels were manipulated). To condition the other two groups (with different stimulation levels) to experience an exacerbation of the pain, we paired an increase in nocioceptive stimulation with placebo administration. In the third session, all subjects were again tested for placebo response. Results suggested that placebo responses are conditionable in the laboratory in both a positive and negative direction. The clinical implications of a learning theory of placebo behavior are discussed.     

Prediction outcome and choice reaction time: Inhibition versus facilitation effects

In two-choice RT tasks Ss verbally predicted all stimulus presentations, two-thirds of the presentations, or none of the presentations. Effects of stimulus probability were similar for each type of prediction trial: Correct Prediction Outcome (PO), Incorrect PO, and No-Prediction (NP). When comparisons between Prediction and NP trials were between Ss, reactions on NP trials were significantly faster than reactions POs, but were not slower than reactions to Correct POs. However, when Prediction and NP trials occurred within Ss, reactions on NP trials were not faster than reactions to Incorrect POs, but were significantly slower than reactions to Correct POs. Speculations about Ss' implicit stimulus predictions are offered to interpret differential implications of inhibition and facilitation.     

The placebo concept

Throughout the medical, psychological, and psychiatric literature, the terminology used to characterize placebos is misleading, imprecise, and conducive to conceptual confusion in research on their effects. To remedy this situation, the present paper does the following: (1) It fills the conceptual lacunae left by the defective traditional locutions; (2) It proposes a lucid and precise new vocabulary to supplant the traditional obscure language in which the results of placebo research are couched; and (3) It illustrates the important conceptual refinement accruing from using the new expressions by thoroughly recasting A.K. Shapiro's influential definition of ‘placebo.’     

Conditioning and the placebo effect: The effects of decaffeinated coffee on simple reaction time in habitual coffee drinkers

An experiment is reported in which reaction time was repeatedly assessed in six subjects (habitual coffee drinkers) up to 90 min after the administration of decaffeinated coffee (i.e. placebo), 250 mg caffeine in coffee and at equivalent times on control days. As predicted reaction time was shorter (but not significantly so) immediately after the administration of the two coffee preparations. This finding was taken to support the hypothesis that through a process akin to classical conditioning, drug effects may become associated with the cues that precede and are concurrent with their administration. The findings are critically assessed and related to previous studies. Finally, it is argued that the conditioning hypothesis can account for a number of clinical findings about the placebo response as observed in therapeutic trials.     

Distraction and placebo: two separate routes to pain control

An explosion of recent research has studied whether placebo treatments influence health-related outcomes and their biological markers, but almost no research has examined the psychological processes required for placebo effects to occur. This study tested whether placebo treatment and cognitive distraction reduce pain through shared or independent processes. We tested the joint effects of performance of an executive working memory task and placebo treatment on thermal pain perception. An interactive effect of these two manipulations would constitute evidence for shared mechanisms, whereas additive effects would imply separate mechanisms. Participants (N = 33) reported reduced pain both when they performed the working memory task and when they received the placebo treatment, but the reductions were additive, a result indicating that the executive demands of the working memory task did not interfere with placebo analgesia. Furthermore, placebo analgesia did not impair task performance. Together, these data suggest that placebo analgesia does not depend on active redirection of attention and that expectancy and distraction can be combined to maximize pain relief.     

The placebo response complex

Placebo effects contribute to beneficial therapeutic responses and are common in anxiety and depressive disorders. It is posited that placebo effects are yielded by autonomous feeling-toned complexes capable of re-establishing background self-states of well-being. The relationship between the placebo response complex and modern neurobiological models of self is explored. The psychological roots of the placebo response complex in implicit memories of organized attachment between child and early caretakers and in Sandler's conception of the benign superego are examined. The relationships between the negative placebo (nocebo) response complex, Freud's negative therapeutic reaction, and Fordham's defence of the self are explored. Finally, it is suggested that approaches fundamental to the analytic encounter, e.g., mirroring, affectual exchanges, attunement, and containment are likely to optimize the salutary effects of both psychological and somatic therapeutic interventions.     

Using empirical data to inform the ethical evaluation of placebo controlled trials

There has been considerable debate about the ethical acceptability of using placebo-controls in clinical research. Although this debate has been rich in rhetoric, considering that much of this research is predicated upon the assumption that data from this research is vital to clinical decision-making, it is ironic that researchers have introduced little data into these discussions. Using some published research concerning the use of placebo-controls in clinical research in hypertension and psychiatric drug trials, I suggest some ways that such data might be incorporated into the ethical analysis concerning placebo use in clinical trials. This approach promises to be important for enhancing conceptual and scientific understanding as well as public policy decision-making. An earlier version of this paper was presented at an international conference, “Placebo: Its Action and Place in Health Research Today,” held in Warsaw, Poland on 12–13 April, 2003.     

Observers' reaction to touchers

20 men and 20 women were shown nine photographs in which two people were interacting. The first photograph shown showed a male and a female engaged in a nontouching interaction. The remaining eight photographs showed a touching interaction. Subjects rated their affective reaction to each of the touching interactions relative to their reaction to the first (nontouch) interaction. In the latter 8 photographs, the person facing the camera was either male or female, the person with back to camera was either male or female, and the touch shown was either a hand touch or a hug. All touching interactions were rated more positively than the standard (nontouch interactions). Male and female subjects tended to show identical reactions to the photographs. More positive reactions were shown to cross-sex hugging than to same-sex hugging and interactions showing hand touch.     

Focus of attention and placebo utility

The effects of focus of attention and expected drug effects on reactions to a placebo were examined in two experiments. In the first experiment self-aware and non-self-aware subjects were given a placebo that was said to be either performance-facilitating or inhibiting and then they worked on a set of arithmetic problems. It was expected that the non-self-aware subjects, but not the self-aware subjects, would display a self-serving bias in their attributions regarding the effects of the placebo. Specifically, it was predicted that non-self-aware subjects would attribute more arousal to the performance-inhibiting drug than the performance-facilitating drug since such attributions would be more psychologically beneficial or “useful” in the sense that they would make actual performance on the task look more impressive. Consistent with these predictions, there was evidence of a self-serving bias in drug reactions only among the non-self-focused subjects. Those who were made self-aware did not respond differentially to the two types of drug information. Instead, they appeared to respond in line with their actual (aroused) internal states by attributing some arousal to both drugs. In the second experiment arousal was reduced by eliminating the task, and this time self-focused subjects again appeared to be more aware of their actual internal states, as they reported less reaction to the placebo, regardless of the effects ascribed to it. Two conclusions are drawn from these results: (a) perceived drug utility does effect placebo responsiveness, and (b) self-focused attention increases awareness of internal states, but not necessarily the causes of those states.