Abstract
Whereas there is considerable evidence for the preferential employment of nonaccidental properties when distinguishing among instances of many domains of objects, some have insisted that with highly similar classes, appeal is made to metric and “configural” properties, as is evident when individuating highly similar faces. How do humans distinguish between exemplars of a highly similar subordinate class of natural entities, such as members of a subspecies of birds? Subjects without experience in bird classification were shown sets of 4–5 birds of the same family (all on the same page in the bird guide). They were to describe each bird sufficiently so that a “friend on the phone” who has those birds moving around in a cage would know which bird they are referring to. Almost all the descriptors were nonaccidental in that they could be employed to individuate a particular bird independent of pose (as long as that surface was in view) without appealing to metrics. The descriptors described either the shape of parts (e.g. “curved beak”) or surface features (“e.g. black spot on belly”). To a large extent, these descriptors matched those that in the bird guide book. A subsequent test confirmed that the descriptions were indeed sufficient for naïve subjects to individuate the members of the subspecies. Even with subordinate classification of natural categories, naïve subjects seek and use nonaccidental (rather than metric) properties–the same properties used by professionals.
NSF BCS 04-20794, 05-31177, & 06-17699 to I.B.