Have you gotten a COVID vaccination yet? If not, grab a chopstick and read this article before you go. Here's a link to a journalist's summary of a study on the effect of making a face (such as a smile or a grimace) on the pain of an injection.
The background for the research is the "facial feedback hypothesis:" If you've read Chapter 14 already, you'll recognize this line of work.
The idea that manipulating our facial expressions can affect our emotions has a long and storied history. There are many advocates of [this] hypothesis, and many critics, too. Indeed, one of the classic findings in the field — that people find cartoons funnier if they hold a pen between their teeth, inducing a smile — recently failed to replicate. This mixed research background was well known to Sarah D. Pressman and Amanda M. Acevedo at the University of California, Irvine, who led the new work, published in Emotion.
Here is some detail about the study:
The team randomised 231 student participants to hold either a neutral expression, a regular smile (which involves the cheek muscles), a Duchenne smile (which also recruits muscles by the eyes, resulting in creasing around the eyes) or a grimace (which recruits both these sets of muscles, plus those which allow us to wrinkle our brows.
In the study they manipulated the facial expressions unobtrusively, by asking participants to hold a chopstick in different ways:
To induce these expressions, the participants (who thought they were taking part in an investigation of multi-tasking) were given chopsticks to hold in one of four positions between their teeth, and asked to imitate an example photo. Each participant then held their assigned facial position while they received an injection of saline solution into the upper arm, designed to mimic a flu jab. Their heart rates and skin conductance were measured throughout [before, during, and after the jab], as objective markers of their stress levels, and they also reported on levels of pain (anticipated and then actual) and other emotions, such as being jittery or relaxed.
This study was an experiment. Before we get to the results, let's identify some of its features.
a) What was the independent variable (IV) here? How many levels in this IV, and what were they?
b) Was the IV manipulated as independent groups or within groups?
c) The journalist writes, "The team randomised 231 student participants to hold either....". Is the word "randomized" here referring to random assignment or random sampling?
d) There are several dependent variables (DVs) reported here. Name three of them.
e) Which type of experiment was this? posttest only? pretest-posttest? repeated measures? or concurrent measures?
Now for the results. The researchers collected multiple DVs and the patterns were not the same across all DVs. I will summarize the results for only one DV, self-rated pain:
The Duchenne smiling and grimacing groups gave lower pain ratings than the neutral group while waiting for the injection, during the injection, and immediately after it. The regular smiling group fell somewhere in between.
f) Sketch a graph of this result (placing the DV on the y-axis, as usual).
g) Now a big challenge: Apply Chapter 11's twelve internal validity threats to this example. How does the study's design help rule these threats out? I've done a few of these for you. You'll find Table 11.1 helpful here!
| Design confound | |
| Selection effect | |
| Order effect | |
| Maturation | This was a pretest-posttest design that took place in a single session. The single session helps rule out maturation. We can also rule out maturation because all four groups had the same opportunity to "mature." |
| History | |
| Regression to the mean | |
| Attrition | |
| Testing | All groups were tested multiple times, which means this potential threat was held constant in all groups, ruling it out as an internal validity threat. |
| Instrumentation | |
| Observer bias | |
|
Demand characteristic |
The independent-groups design and cover story about multitasking can probably help disguise the true nature of the experiment. |
| Placebo effect |
