Expectancy Effects Threaten the Inferential Validity of Synchrony-Prosociality Research

Many studies argue that synchronized movement increases prosocial attitudes and behavior. We reviewed meta-analytic evidence that reported effects of synchrony may be driven by experimenter expectancy, leading to experimenter bias; and participant expectancy, otherwise known as placebo effects. We found that a majority of published studies do not adequately control for experimenter bias and that multiple independent replication attempts with added controls have failed to find the original effects. In a preregistered experiment, we measured participant expectancy directly, asking whether participants have a priori expectations about synchrony and prosociality that match the findings in published literature. Expectations about the effects of synchrony on prosocial attitudes directly mirrored previous experimental findings (including both positive and null effects)—despite the participants not actually engaging in synchrony. On the basis of this evidence, we propose an alternative account of the reported bottom-up effects of synchrony on prosociality: the effects of synchrony on prosociality may be explicable as the result of top-down expectations invoked by placebo and experimenter effects.

sensitivity power analyses using G*Power (Faul, Erdfelder, Buchner, & Lang, 2009) revealed that our sample size had >99% power to detect effects of a similar magnitude to those reported by Wiltermuth & Heath (e.g., d = 0.96) and a minimum effect size of interest of d = 0.29 using two-tailed two-sample independent t-tests with a Bonferroni-adjusted alpha of 0.00625 (for 8 comparisons).

Procedure
Using instructions modeled directly on Wiltermuth and Heath's task (S. Wiltermuth, personal communication), participants were asked to imagine that three people had taken a 7minute walk around a college campus together with an experimenter. Participants in the experimental condition were asked to imagine that people were instructed to "walk in step with one another, or in synchrony", while participants in the control read a nearly identical set of instructions that excluded the phrase that instructed people to walk in synchrony (see Supplement Text S3 for full-text for both conditions). This was the key difference between conditions, i.e., that participants in the experimental condition imagined people were instructed to complete the task in synchrony, while participants in the control condition read a nearly identical set of instructions that excluded any reference to synchrony, in a fashion identical to Wiltermuth & Heath (2009; see below for full-text of both vignettes). Participants took only a short time to read the vignettes (completion of the entire study took an average of 3 minutes and 9 seconds with a standard deviation of 1 minute and 37 seconds), consistent with the idea that they did not engage in elaborate first-person mental imagery (see Introduction).
After imagining the hypothetical scenario, participants were then asked to complete a survey where they imagined on how people would feel and act toward the other participants after engaging in the scenario they read about. This survey was modeled on the one used in Wiltermuth and Heath's original study. We included the measures of synchrony, coordination, and frustration because they were present on the survey instrument as provided by the authors (S. Wiltermuth, personal communication), though they were not reported in the original paper (Wiltermuth & Heath, 2009

Vignette and Survey Full-Text
In this study, you will be asked to imagine a situation where other people participate in a live, inperson experiment. We are interested in your expectations and predictions about this situation. As you imagine it, think about what it would be like and how the people participating in the experiment might feel.

Synchrony Condition:
Imagine three college students show up to a psychology experiment here at [institution]. They are greeted by a researcher.
The researcher tells them that as part of the study, they will be taking a walk around campusand during this walk, they will walk in step with one another, or in synchrony. They are instructed not to talk with one another while on the walk.
The three participants and the researcher then go on a seven-minute walk around campus. They walk in step with each other the whole time.

Control Condition:
Imagine three college students show up to a psychology experiment here at [institution]. They are greeted by a researcher.
The researcher tells them that as part of the study, they will be taking a walk around campus. They are instructed not to talk with one another while on the walk.
The three participants and the researcher then go on a seven-minute walk around campus.
Afterward, the participants are asked how they feel about this experience, and about the other people in the group. Imagine how they might answer as you respond to the questions below.
Presented on a subsequent page: As you respond to the questions below, we will ask you to judge how the three participants in the scenario might feel about one another after this experience.
Remember: In the scenario you read, three college students showed up for a psychology study, and were asked to [walk around campus with one another] / [walk around campus in step with one another, in synchrony].
Please imagine how these people might feel after this experience, as you answer the questions below.

1.
How coordinated would each participant's actions be with the other participants on the walk? • Take a walk around campus. Get to know each other while on the walk.
• Take a walk around campus. Do not talk with one another.
• Take a walk around campus, and walk in synchrony. Get to know each other while on the walk. • Take a walk around campus, and walk in synchrony. Do not talk with one another.
What is your gender? • What is your age in years? _________  Participants were asked to rate on a scale from 1 to 7 how connected, coordinated, frustrated, and so on (x-axis) they imagined people would feel, if they had just walked around campus in synchrony (red bars) or in a normal manner, with no mention of synchrony (blue bars) with their group. Error bars represent 95% confidence intervals. **p < .00625, *p < .05, from two-sample independent t-tests.