Greeble (psychology)

While Greebles have been used in a wide variety of research paradigms, the two canonical results are both built on an experimental design in which participants learn to name individual greebles, identify their family, and classify their gender over several experimental sessions. The original behavioral study explores whether expertise with Greebles can produce face-like recognition mechanisms. The authors trained participants to become "Greeble experts" and found that, as with faces, these newly-trained experts exhibited sensitivity to configural transformations—meaning they processed the arrangement of parts more holistically. These results suggest that face-specific effects may stem from general perceptual expertise with homogeneous stimuli rather than from face-exclusive mechanisms. The followup neuroimaging (fMRI) study investigates whether the fusiform face area (FFA) in the brain, traditionally linked to face recognition, is similarly driven by expertise rather than face-specific processing alone. Using fMRI, participants were trained to become experts at recognizing Greebles. With increasing expertise, participants showed heightened activation in the FFA for Greebles, especially in the right middle fusiform gyrus. These results suggest that the FFA is not exclusively specialized for faces but may be recruited for expert-level object recognition more broadly. A similar result was obtained using the same basic design, but ERPs as the dependent measure.

Since those original studies there has been extensive debate on how to interpret these and related results. A somewhat dated discussion of the differing points of view may be found in a paired set of articles written by Tarr & Gauthier, and Kanwisher. Perhaps most pertinent to the debate, similar activation of the FFA may be found for pre-existing experts—car and bird experts—but only for their domain of expertise (i.e., bird experts do not show face-like effects when viewing cars and car experts do not show face-like effects for viewing birds). Moreover, the degree of activation for the FFA was correlated with the behaviorally measured degree of expertise in each individual participant. Similar effect have been found for other visual domains as well, including chess boards for chess experts. For a more modern take on the neural constraints that lead to selective category responses in human visual cortex, see this recent chapter by Mahon.