Author(s) This pre-registration is currently anonymous to enable blind peer-review. It has 3 authors.
Pre-registered on 2018/04/24 - 02:30 AM (PT)
1) Have any data been collected for this study already? No, no data have been collected for this study yet.
2) What's the main question being asked or hypothesis being tested in this study? This study is a follow-up on research by Brass and colleagues (2001, 2009) in which an interference effect has consistently been found when participants are asked to respond to numerical cues by lifting one of two fingers while concurrently observing a video of a hand lifting an incompatible finger. It is also a follow-up on our previous study in which we hypothesized that this effect can be eliminated or even reversed if participants perceive the incompatible finger movement as a contribution to a joint action with a joint effect. This hypothesis wasn’t confirmed (we believe this was due at least in part to participants' misunderstanding of the instructions). In the simultaneous condition of Brass et al (2009), participants were required to imitate the observed movement when a green cross appeared or counter-imitate when a red cross appeared. We hypothesize that the interference effect can be eliminated or even reversed if participants perceive the incompatible finger movement as a contribution to a shared goal. To test this, we will use the same task as Brass et al (2009), only the crosses will be replaced by numbers („1“ for imitate, „2“ for counter-imitate) and we will add Phase 2 in which the joint action effect arises (two lightbulbs will be turned on) if the participant and the observed hand perform complementary (motorically incompatible) movements. We predict that we will replicate the previous findings (that is, reaction times will be significantly faster in congruent compared with incongruent trials) in phase 1 (with no joint outcome). We also predict that performance on incompatible trials will be better (RTs will be shorter) in phase 2 than in phase 1, and that this improvement will be larger than any improvement we may observe in the compatible conditions (ruling out an explanation in terms of a learning effect).
3) Describe the key dependent variable(s) specifying how they will be measured. Reaction times in two conditions (incompatible, compatible) in two phases (non-joint, joint)
4) How many and which conditions will participants be assigned to? Every participant will perform the same task with 2 phases: in phase 1, when the participants see the number ‚1‘ they are required to imitate the observed movement on the upcoming trial, whilst when the number ‚2‘ is displayed, they are required to counter-imitate the movement. The instruction for phase 2 remains the same, but there is a joint goal: when the participant and the observed hand perform complementary movements, both lightbulbs (turned off in the Phase 1) will turn on.
5) Specify exactly which analyses you will conduct to examine the main question/hypothesis. Analysis of Variance with Compatibility (compatible or incompatible observed movement) and Phase (Phase 1 – „non-joint“ and Phase 2 – „joint“) as factors
6) Describe exactly how outliers will be defined and handled, and your precise rule(s) for excluding observations. We will eliminate responses more than 2.5 SD from the mean (calculated for each participant for the whole experiment), and of eliminating participants whose mean response is more than 3 SD greater or less than the mean.
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 have used G* to arrive at 30 as the ideal sample size for power of .80 and alpha= .05. We predict a small to medium effect size.
8) Anything else you would like to pre-register? (e.g., secondary analyses, variables collected for exploratory purposes, unusual analyses planned?)
