Typicality ratings correlated with the number of features a particular member shared with other members of the category. People unconsciously abstract a prototype or an average representation across encounters with members of a category. More prototypical members are generated first, less prototypical ones later.
People categorize the never seen average of a category better than studied exemplars.
Without knowledge of the rules, S's instructed to study these stimuli for a later memory test. Test Phase S's asked to classify novel items from both categories as belonging to the category they spelled before or the category they pronounced before.