(Un)Great Expectations: The Role of Placebo Effects in Cognitive Training

Abstract

A growing body of literature demonstrating the malleability of critical higher-order cognitive functions by means of targeted interventions has incited widespread scientific interest, most notably in the form of cognitive training programs. The results are mixed and a point of contention: It has been argued that gains observed in cognitive training are mainly due to placebo effects. To address this, we examined the effect of participant expectations on one type of cognitive training that has been central to the controversy, namely n-back training, by inducing beliefs about expected outcomes. Participants receiving n-back training showed improvements in non-trained n-back performance regardless of expectations, and furthermore, expectations for positive outcomes did not result in any significant gains in an active control group. Thus, there was no detectable expectancy effect in either direction as a function of the cognitive intervention used, suggesting that training-related improvements are unlikely due solely to a placebo effect.

Keywords: Hawthorne effect; brain training; cognitive plasticity; expectancy; working memory.

Figures

Figure 1.

Visualization of Study Procedures.

Figure 2.

Performance in the visual n-back task, tested before and after the intervention as a function of condition. The same task also served as the training vehicle. The overall n-back performance score is the average accuracy (pr; i.e., proportion of hits minus proportion of false alarms) across all three difficulty levels (2-, 3-, and 4-back). Error bars indicate standard errors of the mean.

Figure 3.

Performance in the untrained auditory n-back task. The overall n-back performance score is the average accuracy (pr; i.e., proportion of hits minus proportion of false alarms) across all three difficulty levels (2-, 3-, and 4-back) as a function of condition. Error bars indicate standard errors of the mean.