Abstract
Some of the brain areas in the ventral temporal lobe, such as the fusiform face area (FFA), are critical for face perception, but what determines this specialization is a matter of debate. The face specificity hypothesis claims that faces are processed domain specifically. However, the alternative expertise hypothesis states that the FFA is specialized in processing objects of expertise. To disentangle these views, some experiments used an artificial class of novel objects called Greebles. These experiments combined a learning and fMRI paradigm. However, there are some problems with these studies: the limited number of brain regions examined (only face-selective regions), the high similarity between faces and Greebles, and other methodological issues. Given the high impact of this paradigm, we investigated these issues further. In our experiment eight participants were trained for ten 1-hour sessions at identifying a set of novel objects, Greebles. We scanned participants before and after training and examined responses in the FFA as well as in the lateral occipital complex (LOC). To isolate expert processing, we compared responses to upright and inverted images for faces and for Greebles. In contrast to previous reports, we found an inversion effect for Greebles before training. This result suggests that people interpret the ‘novel’ Greebles as faces, even before training. This prediction was confirmed in a post-experimental debriefing. In addition, we did not find an increase of the inversion effect for Greebles in the FFA after training. This indicates that the activity in the FFA does not depend on the degree of expertise acquired with the objects. In the LOC we find some indications for an increase of activation for Greebles after training. These findings are in favor of the face specificity hypothesis, with the understanding that the notion ‘face’ refers to “every stimulus that is interpreted as containing a face”.
This work was supported by the Research Council of K.U.Leuven (CREA/07/004), the Fund for Scientific Research – Flanders (1.5.022.08), the Human Frontier Science Program (CDA 0040/2008) and by the Methusalem program by the Flemish Government (METH/08/02).