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.

No, no data have been collected for this study yet.

Previous research has found that infants look longer at events that violate their expectations than those that do not. In this study, we ask if the observation of someone else’s surprise modulates infants’ looking time to expected vs. unexpected events. Infants will observe a sampling event (adapted from Xu & Garcia, 2008) and see the experimenter expressing surprise (or unsurprised happiness) at the outcome before it is revealed to the infants. After the outcome is revealed, we will measure infants’ looking time. Our main hypothesis is that the surprised expression will change the relative looking time to probable (expected) vs. improbable (unexpected) outcomes. More specifically, they will no longer show the typical pattern of looking time (i.e., looking longer at the improbable outcome than the probable outcome); instead, they will either look equally long at the two types of outcomes, or even look longer at the probable outcome than the improbable outcome.

Infants’ looking time to an event outcome

There are four conditions, crossing two factors: outcome probability (Probable vs. Improbable) and the experimenter’s emotional response to the outcome (Surprise vs. Happiness), and each participant will see all 4 trials. However, instead of fully counterbalancing all four trials, infants will see the Surprise-Probable and Surprise-Improbable trials first (order counterbalanced); pilot data suggest that the effect of surprise declines over trials and may be present only on the first trial, and therefore we choose to focus on identifying the main contrast of interest in this study by using just the first trial. We nevertheless show the other two conditions (Happy-Probable and Happy-Improbable, order counterbalanced) at the end because there is little cost for us to get more data from each participant, and those extra data might help us identify an interaction between emotion and event probability (pilot data suggest that the effect of unsurprised happiness declines to a lesser degree). Also these extra data can be combined with other datasets for further exploratory analyses.

Our main analysis will focus on the first test trial. We will use two-sample t-test to compare infants’ looking time between the Surprise-Probable and Surprise-Improbable conditions. If the data violate assumptions of Student’s t-test (e.g., homoscedasticity, normal distribution) we will use appropriate alternative tests such as Welch t-test or Mann-Whitney U test.

We will exclude data points (i.e., looking time in a given trial) if the following happens: infant fussiness, parental or sibling interference, experimenter error, or infant looking time over 3 standard deviations of the mean. Data from an infant will be excluded (and replaced) if the first test trial is excluded, or more than two of the four test trials are excluded.

No need to justify decision, but be precise about

We plan to collect N= 64 infants between 12 and 17 months. Half of them will start with the Surprise-Probable condition; the other half will start with the Surprise-Improbable condition.

(e.g., secondary analyses, variables collected for exploratory purposes, unusual analyses planned?)

Exploratory analyses:

- We will run the analyses with data from the first two test trials (two datapoints per infant) using paired t-test, because the effect may be present even in the second trial and within-subject comparison offers more power.

- We will also look at the last two test trials (where the agent expresses unsurprised happiness), testing if infants look longer at the improbable than probable outcomes using paired t test.

- We will use data from all four trials, looking at the interaction between event outcome and emotion.