The correct answer to this open question is the following.
The results of the study were the following.
The students that read the essay and were told to freely choose their opinion, rated the attitude of the author according to the position it had when writing the essay. This means, they supported Castro's essay or were against it.
Regarding the students that were told that the author chose its position, they rated the attitude of the author as being according to the essay written, supporting, or against Castro. What these students did was to infer the author's attitude just from their own essays.
The experiment was conducted by Jones and Harris in 1967.