Tuesday, January 24, 2006

Fusiform -- not alone

One of the important basic discussions in congitive neuroscience is that of the fusiform face area (FFA). The FFA has been suggested as a part of the fusiform gyrus that is solely dedicated to face perception. The rationale is that faces have been evolutionary special and selected for, and that the FFA is an evolved module specifically dealing with faces.

As the story goes, researchers such as Isabel Gauthier and her colleagues have demonstrated that the FFA is also active when study participants are asked to discriminate between different types of birds and cars and even when participants become expert at distinguishing computer generated nonsense shapes known as greebles. These activations were not as profound as those seen when subjects perceived faces, but they still demonstrate a less clear-cut role of the FFA. At the Human Brain Mapping 2005 in Toronto , Canada, we saw Gauthier and Nancy Kanwisher battle it out, and it is clear that this is by no means a settled issue. The selectivity and encapsulation of neuro-cognitive modules is one of the hot topics in modern cognitive neuroscience, though even in its infancy it was a much debated issue. Just take John Hughlings Jackson's (1882/1932) famous and excellent quote:

"I am neither a universalizer nor a localizer...In consequence I have been attacked as a universalizer and also as a localizer. But I do not remember that the view I really hold as to localization has ever been referred to. If it is, it will very likely be supposed to be a fusion of, or a compromise of recent doctrines"

In a recent study reported in Neuropsychologia by Steeves et al., the FFA does not seem to be sufficient to produce face recognition. Well, that does not come as such a surprise maybe, since we do know that face perception is the result of processes starting in the retina. But the whole idea is that the FFA is something special for face processing. But Steeves et al.s study show that the FFA is part of a larger network, and that face processing consists of many different steps and subprocesses. Their patient study of D.F., combined with fMRI studies demonstrate that
  1. For gross detection of face-nonface decitions, the FFA does not seem necessary although it can be activated. For this, the occipital face area (OFA) seems to do the work.
  2. For face identification -- i.e. recognising a familiar face -- the FFA is involved, but still involves a network of different modules (including the OFA)
In short, Oma und Opa get your OFA going, too. Here is the article's abstract, but you can get the article here (PDF):

The fusiform face area is not sufficient for face recognition: Evidence from a patient with dense prosopagnosia and no occipital face area

Steeves et al.

We tested functional activation for faces in patient D.F., who following acquired brain damage has a profound deficit in object recognition based on form (visual form agnosia) and also prosopagnosia that is undocumented to date. Functional imaging demonstrated that like our control observers, D.F. shows significantly more activation when passively viewing face compared to scene images in an area that is consistent with the fusiform face area (FFA) (p < 0.01). Control observers also show occipital face area (OFA) activation; however, whereas D.F.'s lesions appear to overlap the OFA bilaterally.

We asked, given that D.F. shows FFA activation for faces, to what extent is she able to recognize faces? D.F. demonstrated a severe impairment in higher level face processing—she could not recognize face identity, gender or emotional expression. In contrast, she performed relatively normally on many face categorization tasks. D.F. can differentiate faces from non-faces given sufficient texture information and processing time, and she can do this is independent of color and illumination information. D.F. can use configural information for categorizing faces when they are presented in an upright but not a sideways orientation and given that she also cannot discriminate half-faces she may rely on a spatially symmetric feature arrangement.

Faces appear to be a unique category, which she can classify even when she has no advance knowledge that she will be shown face images. Together, these imaging and behavioral data support the importance of the integrity of a complex network of regions for face identification, including more than just the FFA—in particular the OFA, a region believed to be associated with low-level processing.

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