IMPORTANT NOTE: We previously pre-registered an earlier version of this experiment (available online via https://osf.io/3cm6e). However, prior to completion of the data collection we realized that the experimental designed outlined in the previous version did not fully prevent the cluster-learning effect. As such we have decided to modify the setup of experiment 3 to fully exclude this alternative explanation of the results obtained in experiment 2. This preregistration supersedes the old one. ---------------------
During the first experiment we demonstrated a direct effect of similarity: subjects are more likely to select a toy to give to the Fennimal if this toy previously resulted in positive feedback when given to a similar Fennimal. In the second experiment we demonstrated an indirect effect of similarity: subjects are more likely to give a toy to the Fennimal if this toy previously resulted in positive feedback when given to a Fennimal that shares overlap to a Fennimal sharing overlap to the observed Fennimal.
The third experiment is conducted for two reasons. First, we want to rule out an alternative explanation to the results obtained in experiment 2 (demonstrating the indirect effect). This alternative explanation holds that subjects learned to associate which sets of two toys "go together" based on the overlap in Fennimals during the training phase of the experiment. If this explanation held true, then during the test phase of the experiment subjects do not conduct a search of their memory, but instead randomly select one of the two clusters of toys to give to the Fennimal. For one cluster both actions were available (and the subject would randomly pick between them if this cluster is selected). For the other cluster, only one toy is available (the action predicted by the CASES model). Under this strategy the subject would be 50% likely to give the CASES-predicted toy to the Fennimal (which is what was observed during experiment 2). Second, the third experiment is aimed at a self-replication of the effects obtained from the first two experiments.
In experiment 3 we use an identical experimental design as in the first two experiments, with the exception of different training and test sets of Fennimals. In particular, during this experiment we will modify the training and test-set Fennimals such that two Fennimals contain partially overlapping features. The training set will consist of 4 Fennimals. Fennimals 1 and 2 will share a color (but have different types). Fennimals 3 and 4 do not share any overlap in either type or color with any other Fennimal. All Fennimals will have a positive association to a different toy.
The test-set of experiment 3 will consist of 4 trials. Two of these will be “direct trials”, in which the Fennimal will either share a color or a type with Fennimals 3 and 4 respectively. If the new Fennemal shares an overlap with Fennimal 3 (4), then the toy previously associated to Fennimal 4 (3) will be unavailable. All other toys are available. The other two trials will be “indirect trials”. In one of these trials the subject will see a Fennimal that shares a type with either Fennimal 1 or Fennimal 2 (always having a unique and new type). If the type overlaps with Fennimal 1 (2) then the toy associated to Fennimal 1 (2) will not be available. Here the CASES model predicts the subject to select the toy previously associated with Fennimal 2 (1).
This experimental design allows us exclude the possibility of a statistical-clustering strategy. In this design Fennimals 1 and 2 belong to the same cluster, but Fennimals 3 and 4 are in different clusters. As a result a statistical-clustering strategy now results in a 1/3 chance probability for all three available toys (all toys belong to different clusters).