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Cognition and the Placebo Effect--Dissociating Subjective Perception and Actual Performance.

Schwarz KA, Büchel C - PLoS ONE (2015)

Bottom Line: Such research promises potential benefit for patient treatment by deliberately using expectations as means to stimulate endogenous regulation processes.To this end, we instructed participants about alleged effects of different tone frequencies (high, intermediate, low) on brain activity and cognitive functions.Interestingly, we found no effects of expectation on objective measures, but a strong effect on subjective perception, i.e., although actual performance was not affected by expectancy, participants strongly believed that the placebo tone frequency improved their performance.

View Article: PubMed Central - PubMed

Affiliation: Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

ABSTRACT
The influence of positive or negative expectations on clinical outcomes such as pain relief or motor performance in patients and healthy participants has been extensively investigated for years. Such research promises potential benefit for patient treatment by deliberately using expectations as means to stimulate endogenous regulation processes. Especially regarding recent interest and controversies revolving around cognitive enhancement, the question remains whether mere expectancies might also yield enhancing or impairing effects in the cognitive domain, i.e., can we improve or impair cognitive performance simply by creating a strong expectancy in participants about their performance? Moreover, previous literature suggests that especially subjective perception is highly susceptible to expectancy effects, whereas objective measures can be affected in certain domains, but not in others. Does such a dissociation of objective measures and subjective perception also apply to cognitive placebo and nocebo effects? In this study, we sought to investigate whether placebo and nocebo effects can be evoked in cognitive tasks, and whether these effects influence objective and subjective measures alike. To this end, we instructed participants about alleged effects of different tone frequencies (high, intermediate, low) on brain activity and cognitive functions. We paired each tone with specific success rates in a Flanker task paradigm as a preliminary conditioning procedure, adapted from research on placebo hypoalgesia. In a subsequent test phase, we measured reaction times and success rates in different expectancy conditions (placebo, nocebo, and control) and then asked participants how the different tone frequencies affected their performance. Interestingly, we found no effects of expectation on objective measures, but a strong effect on subjective perception, i.e., although actual performance was not affected by expectancy, participants strongly believed that the placebo tone frequency improved their performance.

No MeSH data available.


Related in: MedlinePlus

A. Success rates (SRs) and reaction times (RTs) as a function of expectancy and Flanker compatibility. Error bars indicate standard errors of paired differences [39], computed separately for each expectancy condition. B. Compatibility effects for each expectancy condition, computed as ΔSR = SRcompatible-SRincompatible and ΔRT = RTincompatible-RTcompatible. Error bars indicate the Loftus-Masson within-subjects standard error for repeated measures ANOVA [40]. Flanker compatibility effects emerged for SRs and RTs, but these effects did not significantly differ between the three expectancy conditions and no main effect of expectancy was significant.
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pone.0130492.g002: A. Success rates (SRs) and reaction times (RTs) as a function of expectancy and Flanker compatibility. Error bars indicate standard errors of paired differences [39], computed separately for each expectancy condition. B. Compatibility effects for each expectancy condition, computed as ΔSR = SRcompatible-SRincompatible and ΔRT = RTincompatible-RTcompatible. Error bars indicate the Loftus-Masson within-subjects standard error for repeated measures ANOVA [40]. Flanker compatibility effects emerged for SRs and RTs, but these effects did not significantly differ between the three expectancy conditions and no main effect of expectancy was significant.

Mentions: To pinpoint the actual effects of the expectancy manipulation and the corresponding conditioning on objective measures, we analyzed SRs and RTs of the test phase (Fig 2). Our data clearly show that the effects established in the conditioning phase did not carry over to the test phase. More precisely, robust Flanker compatibility effects emerged for SRs, F(1,35) = 869.85, p < .001, ηp2 = 0.96, and RTs, F(1,35) = 293.82, p < .001, ηp2 = 0.89, but the effects were virtually identical in size across the three expectancy conditions; SRs: F(2,70) = 0.27, p = .766, ηp2 = 0.01; RTs: F(2,70) = 0.12, p = .883, ηp2<0.01. Also, neither main effect of expectancy was significant; SRs: F(2,70) = 0.41, p = .664, ηp2 = 0.01; RTs: F(2,70) = 1.99, p = .145, ηp2 = 0.05. To follow up on these analyses, we computed Bayes Factors for the most informative comparison—the difference in compatibility effects between the placebo and the nocebo condition. Bayes statistics allow the computation of the probability of a hypothesis conditionally on observed data. Bayes factors represent the posterior odds, the quotient of the probability of the hypothesis given the observed data and the probability of the alternative hypothesis given the observed data. Among other things, they are thus used to identify whether or not a non-significant effect is due to a statistical power problem or due to an actual absence of a real effect—a distinction which cannot be made with traditional significance testing. Generally, odds greater than 3 are considered substantial evidence for one hypothesis over another. The employed analyses indeed yielded substantial evidence in favor of the hypothesis of no effect, BFSR = 5.42, BFRT = 4.93, indicating that the above findings indeed reflect the absence of a real effect rather than insufficient power [24].


Cognition and the Placebo Effect--Dissociating Subjective Perception and Actual Performance.

Schwarz KA, Büchel C - PLoS ONE (2015)

A. Success rates (SRs) and reaction times (RTs) as a function of expectancy and Flanker compatibility. Error bars indicate standard errors of paired differences [39], computed separately for each expectancy condition. B. Compatibility effects for each expectancy condition, computed as ΔSR = SRcompatible-SRincompatible and ΔRT = RTincompatible-RTcompatible. Error bars indicate the Loftus-Masson within-subjects standard error for repeated measures ANOVA [40]. Flanker compatibility effects emerged for SRs and RTs, but these effects did not significantly differ between the three expectancy conditions and no main effect of expectancy was significant.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493024&req=5

pone.0130492.g002: A. Success rates (SRs) and reaction times (RTs) as a function of expectancy and Flanker compatibility. Error bars indicate standard errors of paired differences [39], computed separately for each expectancy condition. B. Compatibility effects for each expectancy condition, computed as ΔSR = SRcompatible-SRincompatible and ΔRT = RTincompatible-RTcompatible. Error bars indicate the Loftus-Masson within-subjects standard error for repeated measures ANOVA [40]. Flanker compatibility effects emerged for SRs and RTs, but these effects did not significantly differ between the three expectancy conditions and no main effect of expectancy was significant.
Mentions: To pinpoint the actual effects of the expectancy manipulation and the corresponding conditioning on objective measures, we analyzed SRs and RTs of the test phase (Fig 2). Our data clearly show that the effects established in the conditioning phase did not carry over to the test phase. More precisely, robust Flanker compatibility effects emerged for SRs, F(1,35) = 869.85, p < .001, ηp2 = 0.96, and RTs, F(1,35) = 293.82, p < .001, ηp2 = 0.89, but the effects were virtually identical in size across the three expectancy conditions; SRs: F(2,70) = 0.27, p = .766, ηp2 = 0.01; RTs: F(2,70) = 0.12, p = .883, ηp2<0.01. Also, neither main effect of expectancy was significant; SRs: F(2,70) = 0.41, p = .664, ηp2 = 0.01; RTs: F(2,70) = 1.99, p = .145, ηp2 = 0.05. To follow up on these analyses, we computed Bayes Factors for the most informative comparison—the difference in compatibility effects between the placebo and the nocebo condition. Bayes statistics allow the computation of the probability of a hypothesis conditionally on observed data. Bayes factors represent the posterior odds, the quotient of the probability of the hypothesis given the observed data and the probability of the alternative hypothesis given the observed data. Among other things, they are thus used to identify whether or not a non-significant effect is due to a statistical power problem or due to an actual absence of a real effect—a distinction which cannot be made with traditional significance testing. Generally, odds greater than 3 are considered substantial evidence for one hypothesis over another. The employed analyses indeed yielded substantial evidence in favor of the hypothesis of no effect, BFSR = 5.42, BFRT = 4.93, indicating that the above findings indeed reflect the absence of a real effect rather than insufficient power [24].

Bottom Line: Such research promises potential benefit for patient treatment by deliberately using expectations as means to stimulate endogenous regulation processes.To this end, we instructed participants about alleged effects of different tone frequencies (high, intermediate, low) on brain activity and cognitive functions.Interestingly, we found no effects of expectation on objective measures, but a strong effect on subjective perception, i.e., although actual performance was not affected by expectancy, participants strongly believed that the placebo tone frequency improved their performance.

View Article: PubMed Central - PubMed

Affiliation: Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

ABSTRACT
The influence of positive or negative expectations on clinical outcomes such as pain relief or motor performance in patients and healthy participants has been extensively investigated for years. Such research promises potential benefit for patient treatment by deliberately using expectations as means to stimulate endogenous regulation processes. Especially regarding recent interest and controversies revolving around cognitive enhancement, the question remains whether mere expectancies might also yield enhancing or impairing effects in the cognitive domain, i.e., can we improve or impair cognitive performance simply by creating a strong expectancy in participants about their performance? Moreover, previous literature suggests that especially subjective perception is highly susceptible to expectancy effects, whereas objective measures can be affected in certain domains, but not in others. Does such a dissociation of objective measures and subjective perception also apply to cognitive placebo and nocebo effects? In this study, we sought to investigate whether placebo and nocebo effects can be evoked in cognitive tasks, and whether these effects influence objective and subjective measures alike. To this end, we instructed participants about alleged effects of different tone frequencies (high, intermediate, low) on brain activity and cognitive functions. We paired each tone with specific success rates in a Flanker task paradigm as a preliminary conditioning procedure, adapted from research on placebo hypoalgesia. In a subsequent test phase, we measured reaction times and success rates in different expectancy conditions (placebo, nocebo, and control) and then asked participants how the different tone frequencies affected their performance. Interestingly, we found no effects of expectation on objective measures, but a strong effect on subjective perception, i.e., although actual performance was not affected by expectancy, participants strongly believed that the placebo tone frequency improved their performance.

No MeSH data available.


Related in: MedlinePlus