Following Ameel et al. (2005) the data from the sorting task were used to obtain a measure of similarity for each pair of objects since pairwise similarity ratings were not possible given the large number of objects (192). Performing the task on a computer would prevent a good overview of the complete stimulus set. Therefore, we opted to work with a picture set of the objects. Before the start of the sorting task all pictures were spread out over a U-shaped surface, to make sure that participants had a good overview over all objects in the stimulus set. Participants were instructed to first look through the pictures and then place them into piles based on overall qualities of each object, that is, focusing on any feature (or combination of features) of the object that seemed important or natural. Participants were explicitly instructed not to sort two objects into the same pile because of what they contain (such as ketchup and mayonnaise), unless the objects themselves were alike in an overall way. Participants could use as many piles as they wanted and the only restrictions were that participants were not allowed to make less than two piles or to make piles consisting of only one object. Since the stimulus set was considerably large, we adapted the task allowing participants to sort in different levels. They were allowed to organize piles into clusters. To achieve this, participants were informed that they could organize piles into groups consisting of different subgroups and overlap between groups was possible. For example, one was allowed to make piles of “plastic bottle like objects” and “glass bottle like objects” and group them together on a higher level. This was done to obtain more detailed information concerning perceived similarity. The data were recorded by noting down all stimulus numbers in every pile. Pairwise similarity was derived by counting for each of the 18,336 pairs of objects how many participants placed that pair of objects in the same pile. A large number of participants placing the two objects in a pile can be taken to indicate high perceived similarity and a smaller number as indicating lower perceived similarity. Using the split-half technique followed by the Spearman–Brown formula, we first estimated the reliability of the pairwise similarity measure based on the sorting data. Since we aimed at a reliability of at least 0.90, we added participants until this aim was reached as specified in the pre-registered protocol.