The Greebles come in two genders and five families.
The Greebles refers to a category of novel objects used as stimuli in psychological studies of object and face recognition, created by Scott Yu at Yale University. They were named by the psychologist Robert Abelson. The greebles were created for Isabel Gauthier's dissertation work at Yale, so as to share constraints with faces: they have a small number of parts in a common configuration. This makes it difficult to distinguish any individual object on the basis of the presence of a feature, and this is thought to encourage the use of all features and the relationships between them. In other words, greebles, just like faces, can be processed configurally. Yu's originals (both the symmetrical and asymmetrical sets) can be obtained from Michael Tarr. Greebles appear in over 25 scientific articles.
Isabel Gauthier (1998). Dissecting face recognition: The role of expertise and level of categorization in object recognition (Ph.D.). Yale University.
Williams, P., Gauthier, I., & Tarr, M. J. (1998). "Feature learning during the acquisition of perceptual expertise" [Commentary on Schyns, Goldstone & Thibault. The development of features in object concepts]. Behavioral and Brain Sciences, 21(1), 40-41.
Rossion, B., Gauthier, I, Goffaux, V., Tarr, M.J., Crommelinck, M. (2002). "Expertise training with novel objects leads to left lateralized face-like electrophysiological responses". Psychological Science. 13(3): 250-257. doi:10.1111/1467-9280.00446.
Lahaie, A., Mottron, L., Arguin, M., Berthiaume, C., Jemel, B., Saumier, D. (2006). "Face perception in high-functioning autistic adults: evidence for superior processing of face parts, not for a configural face-processing deficit". Neuropsychology, 20(1): 30-41.
Richler, J.J., Tanaka, J.W., Brown, D.D. & Gauthier, I. (2008). Why does selective attention to parts fail in face processing? Journal of Experimental Psychology: Learning, Memory, and Cognition. 34(6): 1356-1368. doi:10.1037/a0013080.