What is Expert Object Recognition?
The expert object recognition pathway was first identified in fMRI studies of
human face recognition [6, 14, 29]. In these studies, patients were shown images of
faces while in a scanner. The resulting fMRI images revealed activation not only in
the primary visual cortex, but also in the fusiform gyrus. Subsequent PET studies
(which imaged a larger portion of the brain) confirmed the activation in the fusiform
gyrus, while also noting activation in the right inferior frontal gyrus, an area
previously associated through lesion studies with visual memory [20] (see also [23]).
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More recent evidence suggests that this pathway is used for more than recognizing
faces. Tong, et al. report that the fusiform gyrus is activated by animal faces and
cartoon faces [33]. Chao, et al. report that the fusiform gyrus is activated by images
of full-bodied animals with obscured faces [5]. Ishai et al. find that the fusiform
gyrus responds to chairs [11]. Tarr and Gauthier considered the past experience of
their subjects, and found fusiform gyrus activation in dog show judges when they
view dogs, and in bird experts when they view birds [31]. Most important of all, Tarr
and Gauthier show that the expert recognition pathway is trainable. They created a
class of cartoon characters called greebles, which are grouped by gender and family.
When novice subjects view greebles, fMRIs show no activity in the fusiform gyrus.
The subjects are then trained to be experts who can identify a greeble’s identity,
gender or family in equal time. When the experts view greebles, their fusiform gyrus
is active [31]. Gauthier and Logothetis provide evidence that training produces
similar results in monkeys [8]. We conclude that expert object recognition is a
general mechanism that can be trained to recognize any class of familiar objects.
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Why use a Biomimetic Model for Object Recognition?
Brain imaging studies suggest that expert object recognition is a distinct visual skill,
implemented by a dedicated anatomic pathway. Like all visual pathways, the expert
recognition pathway begins with the early visual system (retina, LGN/SC, striate cortex).
It is defined, however, by subsequent diffuse activation in the lateral occipital cortex (LOC),
and sharp foci of activation in the fusiform gyrus and right inferior frontal gyrus. This
pathway recognizes familiar objects from familar viewpoints under familiar illumination.
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