#32816 | AsPredicted

'Non-deceptive placebos and the LPP - 2018-2019'
(AsPredicted #32816)


Created:       12/12/2019 11:36 AM (PT)

This is an anonymized version of the pre-registration.  It was created by the author(s) to use during peer-review.
A non-anonymized version (containing author names) should be made available by the authors when the work it supports is made public.

1) Have any data been collected for this study already?
It's complicated. We have already collected some data but explain in Question 8 why readers may consider this a valid pre-registration nevertheless.

2) What's the main question being asked or hypothesis being tested in this study?
We want to answer the following questions:

Primary Question:
Q1) Can non-deceptive placebos, compared to a control group, reduce the amplitude of a neurological marker of emotional distress, the sustained portion of the late positive potential?

Secondary Question:
Q2) Can non-deceptive placebos, compared to a control group, increase the amplitude of a neurological marker of attentional allocation to incoming stimuli?


3) Describe the key dependent variable(s) specifying how they will be measured.
The late positive potential (LPP) consists of an electroencephalogram (EEG) derived event-related brain potential that measures millisecond changes in neural activity that is involved in emotional processing. The LPP has an early time window (400–1000 ms) that indexes attention allocation and a sustained time window (1000–6000 ms) that indexes conscious appraisals and meaning-making mechanisms involved in emotion processing. The primary dependent variable is the sustained portion of the LPP (1000–6000 ms). The secondary dependent variable is the early portion of the LPP (400–1000 ms).

4) How many and which conditions will participants be assigned to?
There are two conditions: a control condition and a non-deceptive placebo condition.

5) Specify exactly which analyses you will conduct to examine the main question/hypothesis.
We will test for moderation of sample, then we will combine both samples to boost statistical power. We will organize the cluster of electrodes in order to reduce the spatial dimensions of the data set following suggestions by Dien & Santuzzi (2005).

Primary Analysis:
We will perform a mixed-factorial ANOVA on the sustained portion of the LPP (1000–6000 ms). Specifically, we will conduct a 2 (Condition: control vs. non-deceptive placebo) X 5 (Time: 1000–2000 ms, 2000–3000 ms, 3000–4000 ms, 4000–5000 ms, 5000–6000 ms) X 2 (Picture Type: neutral vs negative) X 2 (Laterality: left vs right) X 2 (Anterior/Posterior: anterior vs posterior) X 2 (Superior/Inferior: superior vs inferior).

We will focus on any effect of Condition and any interactions with Condition. Any interaction effect with Condition will be probed with follow up contrasts.

Secondary Analysis:
We will perform a second mixed-factorial ANOVA on the early portion of the LPP (400–1000 ms). Specifically, we will conduct a 2 (Condition: control vs. non-deceptive placebo) X 2 (Time: 400–700 ms, 700–1000 ms) X 2 (Picture Type: neutral vs negative) X 2 (Laterality: left vs right) X 2 (Anterior/Posterior: anterior vs posterior) X 2 (Superior/Inferior: superior vs inferior). We will focus on any effect of Condition and any interactions with Condition. Any interaction effect with Condition will be probed with follow up contrasts.

6) Describe exactly how outliers will be defined and handled, and your precise rule(s) for excluding observations.
We will exclude any participants who indicates that English is not their first language. We will exclude any participants with excessive artifacts due to eye and body movements resulting in less than 12 useable trials per picture type.

7) How many observations will be collected or what will determine sample size?
No need to justify decision, but be precise about exactly how the number will be determined.

We will run as many subjects (as close to 100) by the end of the Fall 2019 semester (end of December). We started data collection on July 1, 2019.

8) Anything else you would like to pre-register?
(e.g., secondary analyses, variables collected for exploratory purposes, unusual analyses planned?)

Although we are close to completing data collection, we have not analyzed the data. Existing data have gone through preprocessing in order to determine if a participant will be included in the analysis by meeting the criteria for 12+ trials per picture, which matches our exclusion criteria described earlier.