Consider the following scene: an actor watches a man in a gorilla suit hide behind haystack A. The actor leaves the area, and the “gorilla” moves to behind haystack B, after which the actor re-enters. A video of this scene was shown to 22 (real) apes, and eye-tracking software was used to track which haystack they stared at more after the actor re-entered. “False belief” theory says that the viewer will look at haystack A more, matching the actor’s mistaken belief that the gorilla is still there, despite the viewer knowing better. In the study, 17 of the apes spent more time looking at haystack A (“Great Apes Anticipate That Other Individuals Will Act According to False Beliefs,” Science, 7 October 2016).
a. Use a sign test to determine whether the true median looking-time difference (A − B) supports the false belief theory in primates.
b. Since the data is paired (time looking at each of two haystacks for the 22 apes), the paired t procedure of Chapter 10 might also be applicable. What information would that test require, and what assumptions must be met?