Conditioning, expectancy, and the placebo effect: comment on Stewart-Williams and Podd (2004)

Classical conditioning is included as a component in the response expectancy model of placebo responding. Though introspectable when attention is drawn to them, expectancies need not be in awareness while guiding behavior. Most placebo effects are linked to expectancies, and classical conditioning is one factor (but not the only factor) by which these expectancies can be produced and altered. Conditioned placebo effects without expectancies exist but are relatively rare in humans. The adaptive advantage of cognition is increased response flexibility. For it to convey that benefit, however, it must be capable of overriding the influence of simpler automatic processes. Thus, the higher up the phylogenetic scale, the smaller the role of nonconscious conditioning processes and the larger the role of cognition.     

Motivation and expectancy influences in placebo responding: The mediating role of attention

Drawing upon research in perception and motivation, the current study proposes a motivation‐attention model of placebo in which more motivated persons pay greater attention to placebo‐related stimuli, directly influencing placebo response. We manipulated both motivation to respond to placebo and expectations of placebo response in a 2 × 2 design. Participants (N = 152) evaluated a series of placebo pheromones (slightly scented water) of potential romantic dates and made desirability ratings. Consistent with hypotheses, more highly motivated participants demonstrated greater placebo responses, as evidenced by higher desirability ratings of the “pheromone” and greater variability among ratings, when compared to less motivated participants. Moreover, the relation between motivation and placebo response was mediated by attention. Contrary to expectations, we found no effect for expectancy. These findings highlight the importance of motivation and the mediating factor of attention in placebo and support goal‐oriented models of placebo.     

The subtractive expectancy placebo procedure: A measure of non-specific factors in behavioural interventions

Placebo procedures currently used in clinical psychology and health psychology are criticized on methodological and ethical grounds. The approach of adding expectation of therapeutic efficacy to an actually inert intervention (Additive Expectancy) is of dubious validity unless the inertness of the ‘treatment’ can be established, which is difficult if not impossible to do with behavioural methods. Withholding treatment from clients is a serious ethical problem. The Subtractive Expectancy Procedure, described in this paper, administers a known active treatment but leads the client to expect no therapeutic effect. This avoids both of the serious difficulties mentioned above, although problems of credibility and deception need to be dealt with in both procedures.     

Revisiting the self-interest versus values debate: The role of temporal perspective

Scholars of public opinion have struggled to explain why people often vote against their economic self-interest in favor of a value-based rationale. Based on Construal Level Theory (Liberman, Trope, & Stephan, 2007), we argue that both values and material self-interest affect social and political attitudes, but in different temporal contexts. Specifically, because material self-interest is more concrete and applicable to everyday concerns, we predict that it should carry more weight with regard to judgments made in the context of the near future. In contrast, values, which are more abstract by nature, should carry greater weight for judgments made in the distant future. In an experimental test of this hypothesis, we presented participants with a fictitious policy that affected their pocketbooks in an otherwise value-laden domain. We found that people's financial self-interest more strongly predicted attitudes toward a proposal to increase tuition in the near condition, whereas antiegalitarian values more strongly predicted attitudes in the far condition. These findings offer new insights into the symbolic politics debate.     

The semantic congruity effect: Some tests of the expectancy hypothesis

Subjects comparing items in memory along some dimension are usually quicker to specify the lesser (than the greater) of two low magnitude items and the greater (than the lesser) of two high magnitude ones. One account explains this congruity effect as due to subjects instructed to specify the higher as expecting high magnitude items to follow and the reverse being true for subjects specifying the lesser. Three experiments tested this expectancy hypothesis. In experiment 1, subjects were set to the actual size range of each pair before the pair was shown but the congruity effect still occurred. In experiments 2 and 3, subjects compared critical pairs from a narrow size range plus more from either the same or much broader ranges. Times to compare the critical pairs were the same regardless of the range of the other pairs that subjects were exposed to. These results are strong evidence against the expectancy hypothesis.     

A pitfall for the expectancy theory of human eyelid conditioning

Two simple eyeblink conditioning experiments with random intermittent reinforcement schedules were performed. In Experiment 1, subjects had to rate their expectancy for an unconditioned stimulus (US) on a seven-level scale prior to each trial. As anticipated, expectancy for US increased with a successive conditioned stimulus (CS) alone, and decreased with successive CS-US pairings. However, Experiments 1 and 2 showed that the frequency of eyeblink conditioned responses (CRs) evolved in a direction opposite to that of expectancy changes: CRs increased, whereas expectancy for US decreased, and vice versa. The possible effect of sensitization on eyeblink response was ruled out by the lack of a run effect in an unpaired control group in Experiment 2. These results tend to disconfirm the expectancy theory of conditioning. Although they were explicitly predicted by the conventional “strength” theory of conditioning, an alternative interpretation is proposed within a cognitive framework.     

The biochemical bases of the placebo effect

A great variety of medical conditions are subject to the placebo effect. Although there is mounting evidence to suggest that the placebo effect is related to the expectation of clinical benefit, little is still known about the biochemical bases underlying placebo responses. Positron emission tomography studies have recently shown that the placebo effect in Parkinson’s disease, pain, and depression is related to the activation of the limbic circuitry. The observation that placebo administration induces the release of dopamine in the ventral striatum of patients with Parkinson’s disease suggests a link between the placebo effect and reward mechanisms. In addition to Parkinson’s disease, the placebo-reward model may also apply to other disorders. However, the relative contribution of the different neurotransmitters and neuropeptides that are known to be involved in modulating the activity of the limbic system may be disease-specific. Thus, while the placebo-induced clinical benefit observed in Parkinson’s disease would mostly reflect the release of dopamine in the dorsal striatum, the activation of opioid and serotonin pathways could be particularly implicated in mediating placebo responses encountered in pain and depression, respectively. 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.     

The placebo effect in popular culture

This paper gives an overview of the placebo effect in popular culture, especially as it pertains to the work of authors Patrick O’Brian and Sinclair Lewis. The beloved physician as placebo, and the clinician scientist as villain are themes that respectively inform the novels, The Hundred Days and Arrowsmith. Excerpts from the novels, and from film show how the placebo effect, and the randomized clinical trial, have emerged into popular culture, and evolved over time. 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.     

Stereotype threat: the effect of expectancy on performance

The goal of this study was to investigate to role of expectancy as a potential mediator of performance deficits under stereotype threat. In Experiment 1, female students were assigned to one of three experimental conditions in which they were told that women perform worse (Negative information), equally (Control) or better (Positive information) than men in logical–mathematical tests. Later, they were given a difficult math test and asked to estimate their performance prior to taking the test. Consistent with predictions, participants who considered logical–mathematical abilities important and received negative information regarding the ingroup showed lower levels of expectations and a sharp decrease in performance compared to women in the positive and control conditions. Moreover, expectancy was found to partially mediate the effect of stereotype threat on performance. In Experiment 2, we tested the generalizability of these results to non‐stigmatized groups. A group of Black Americans living in Italy were provided with favorable or unfavorable information about either their minority (Blacks) or their majority (Americans) ingroup. Consistent with predictions, participants both in the minority and in the majority condition had lower expectations and under‐performed after negative information about the ingroup. However, the level of expectancy was found to mediate the decrease in performance for participants in the Black but not in the American condition. In the discussion of these results it is suggested that, although comparable performance deficits are found for minority and majority members, the underlying processes may be different. Copyright © 2002 John Wiley & Sons, Ltd.     

The operant conditioning of response variability: Free-operant versus discrete-response procedures

The operant conditioning of response variability under free-operant and discrete-response procedures was investigated. Two pigeons received food only if their pattern of four pecks on two response keys differed from the patterns emitted on the two immediately preceding trials. Under the free-operant procedure, the keys remained illuminated and operative throughout each trial. There was little variability in the response patterns that resulted, and the pigeons received fewer than one third of the available reinforcers. Under the discrete-response procedure, a brief timeout period followed each response. Variability increased under this procedure, and the pigeons obtained three fourths of the available reinforcers. Previous successes and failures to produce response variability may have been due to the use or failure to use, respectively, a discrete-response procedure. Respondent effects inherent in the free-operant procedure may encourage the development of response stereotypy and, in turn, prevent the development of response variability.     

The effect of continuous, intermittent, and "placebo" reinforcement on the effectiveness of the conditioning treatment for enuresis nocturna

It has been suggested that intermittent reinforcement may be of value in reducing the rate of relapse in bedwetting conditioning therapy. An experiment was conducted with 30 enuretic boys to examine acquisition and extinction parameters of continuous (100%), intermittent (70% variable ratio), and “placebo” (0%) reinforcement schedules. Reinforced trials were administered as in the typical Mowrer conditioning procedure. Non-reinforced trials were achieved by means of a time delay with the subsequent alarm being activated in the parent's room rather than in the child's room. These procedures required the development of a new conditioning device which could be programmed to automatically administer the desired schedule of reinforcement. The results of the field investigation revealed that continuous reinforcement (CR) and intermittent reinforcement (IR) groups attained acquisition in approximately the same number of trials and with essentially the same success rate. Relapse rate was significantly greater in the CR group than in the IR group. The placebo group showed no improvement over the 6 weeks of treatment. The results of this study may be interpreted as supporting the tenet that relapse can be viewed and treated as an extinction of the acquired response.     

T1 difficulty and the attentional blink: expectancy versus backward masking

According to bottleneck models of the attentional blink (AB), first-target (T1) processing difficulty should be related to AB magnitude. Tests of this prediction that have varied T1 difficulty in the context of a standard AB paradigm, however, have yielded mixed results. The present work examines two factors that may mediate the relationship between T1 difficulty and the AB: observer expectancy and backward masking of T1. In two experiments, omission of the backward mask consistently yielded the predicted relationship between T1 difficulty and the AB. In contrast, observer expectancy influenced target identification accuracy but did not mediate the relationship between T1 difficulty and the AB.     

Mind-set matters: exercise and the placebo effect

In a study testing whether the relationship between exercise and health is moderated by one's mind-set, 84 female room attendants working in seven different hotels were measured on physiological health variables affected by exercise. Those in the informed condition were told that the work they do (cleaning hotel rooms) is good exercise and satisfies the Surgeon General's recommendations for an active lifestyle. Examples of how their work was exercise were provided. Subjects in the control group were not given this information. Although actual behavior did not change, 4 weeks after the intervention, the informed group perceived themselves to be getting significantly more exercise than before. As a result, compared with the control group, they showed a decrease in weight, blood pressure, body fat, waist-to-hip ratio, and body mass index. These results support the hypothesis that exercise affects health in part or in whole via the placebo effect.     

The hot-hand fallacy in cognitive control: Repetition expectancy modulates the congruency sequence effect

In this study, the role of expectancies in cognitive control was tested. On the basis of the original interpretation of the congruency sequence effect (Gratton, Coles, & Donchin, Journal of Experimental Psychology: General 121:480–506, 1992), we sought evidence for a repetition bias steering attentional control. In a series of four Stroop experiments, we investigated how participants’ explicit predictions about the upcoming (in)congruency proactively influenced subsequent Stroop performance. Similar to the fallacious “hot-hand” belief in gambling, repeating stimulus events were overpredicted, as participants consistently expected more repetitions of the congruency level than the actual presented number of congruency-level repetitions (50 %). Moreover, behavioral adjustments (i.e., a congruency sequence effect) were only found when participants anticipated a congruency-level repetition, whereas no modulation of the Stroop effect was found following alternation predictions. We propose that proactive control processes in general, and repetition expectancy in particular, should be given more attention in current theorizing and modeling of cognitive control, which is characterized by an emphasis on reactive, conflict-induced control adjustments.