8.2: Human Object Recognition System

We first need to explore specialized regions in the brain where are activated or not when recognizing objects or faces (Johnson, 1980) in order to adapt human object recognition theory into computational pattern models. This section will review how we perform object recognition in the brain.

The homology of human and macaque’s visual systems

Object recognition task seems easy to perform for human and primates. When representing visual stimuli, the common features of the brain activations in the lateral occipital complex (LOC) (Orban, Van Essen, & Vanduffel, 2004) and in the inferotemporal cortex (IT) (Kriegeskorte et al., 2008) have been observed in the studies on a comparison of macaques to humans. Compared to macaques’ brain, we have little figured out how neurons in the human brain are associated with each other or how neuronal chemical reactions are responded when performing object recognition (Clarke et al., 1999). However, Orban et al. (2004) found that there were similar brain activities of both the humans and the macaques in retinotopic visual regions, including early visual cortex (V1, V2, V3) and several mid-level visual areas (V4, MT, and V3A). Thus, each area transmits a population-based visual information to other brain areas (Felleman, & Van Essen, 1991). Beyond retinotopic cortex, several visual fields work on object recognition differently: the regions of MT/MST act as identifying object motion (Watson et al., 1993; Tootell & Taylor, 1995); the fields of TEO, V4, and V8 function as color detector (Engel, Zhang, & Wandell, 1997; Hadjikhani, Liu, Dale, Cavanagh, & Tootell, 1998; Bartels & Zeki, 2000); the area of KO is activated by the kinetic motion recognition (Van Oostende, Sunaert, Van Hecke, Marchal, & Orban, 1997).

The lateral occipital complex (the LOC) known as non-retinotopic areas is a crucial region in performing the recognition task as well (Grill-Spector et al., 1998; Tootell, Mendola, Hanjikhani, Liu &, Dale, 1998). The LOC includes several brain fields like the lateral bank of the fusiform gyrus (Grill-Spector et al., 1998; Tootell, Mendola, Hanjikhani, Liu &, Dale, 1998). The LOC is sensitive to identify pieces of objects as well as objects as a whole (Grill-Spector et al., 1998). In addition to the functions of the LOC, such capability to recognize visual items is also observed in the inferotemporal cortex (IT) (Gross, Rocha, & Bender, 1972; Ito, Tamura, Fujita, & Tanaka, 1995). Specifically, IT neuronal activities are shown in at least more than six areas (Taso et al., 2003; Tsao et al., 2008a; Ku et al., 2011), suggesting that the IT might establish face recognition processing as well as non-human visual stimuli (Tsao et al., 2008b). Overall, studies on the homology of humans and macaques in visual mechanisms emphasizes the crucial role of the LOC and the IT in object recognition.

Object-selective visual areas in the human brain

The advent of brain image techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) makes it possible to explore the neurobiological basis of object recognition in humans. A large body of literature has been revealed that working on object recognition is localized in specific areas, which are called the ventral visual processing stream including the occipital and temporal lobes (Miyashita, 1993; Orban, 2008; Rolls, 2000). For example, several studies using PET have provided evidence that the ventral and temporal areas were strongly activated when subjects were visually presented to individuals’ faces and objects (Haxby, Grady, Ungerleider, & Horwitz, 1991; Kosslyn et al., 1994; Nobre, Allison, & McCarthy, 1994; Woldorff, et al., 1997). In addition, those fields are even stimulated when subjects are asked to see shapes of objects passively (Corbetta, Miezin, Dobmeyer, Shulman, & Petersen, 1991; Haxby et al., 1994). Furthermore, the study using fMRI found that the extent of activation in the LOC depends on the qualities of visual stimuli and whether they provide apparent shape or not (Malach et al., 1995).

A variety of recognition deficits have been revealed when patients have damages in the fusiform and occipito-temporal junction (Farah, Hammond, Mehta, & Ratcliff, 1989; Damasio, Tranel, & Damasio, 1990; Goodale, Milner, Jakobson, & Carey, 1991; Feinberg, Schindler, Ochoa, Kwan, & Farah, 1994; Farah, Klein, & Levinson, 1995; Moscovitch, Winocur, & Behrmann, 1999). The studies used by Event-related potentials (ERPs) found that compared to when presenting jumbled control images, stronger activities in the LOC were shown for a vast array of artifacts (e.g., furniture, buildings, and tools) (McCarthy, Puce, Belger, & Allison, 1999; Allison, Puce, Spencer, & McCarthy, 1999). These studies also reported that when presenting individuals’ faces, the brain activities are specialized in the areas of the middle and anterior fusiform gyrus (McCarthy, Puce, Belger, & Allison, 1999; Allison, Puce, Spencer, & McCarthy, 1999). In conclusion, the development of brain image techniques has led to understand the significant role of the ventral visual stream where the brain regions are associated with recognition in object items.

Facial visual areas in the human brain

Evidence from a large body of studies suggests that the brain regions working on face recognition are different from the areas involved in object recognition, though partially overlapped with each other (Behrmann et al., 1992; Caldara et al., 2003; Desimone, 1991; Tanaka, & Farah, 1993; Turk, & Pentland, 1991; Perrett et al., 1992). For example, it is hard for patients with prosopagnosia to recognize human faces since they have damages in specific brain areas, particularly of bilateral (Damasio et al., 1982; Gauthier et al., 1999) or unilateral right occipito-temporal lesions (De Renzi, 1986; Landis et al., 1986). On the other hand, it has been reported that while preserving face recognition, patients suffering from agnosia cannot identify object stimuli (Moscovitch et al., 1997). These findings suggest that the brain works independently for object and face recognition.

In the same vein, neuroimaging studies using fMRI report the significant role of the occipito-temporal regions in face recognition (Kanwisher et al., 1991; McCarthy et al., 1997). Specifically, the human fusiform gyrus, the fusiform face area (FFA) is exclusively dedicated to face processing (Kanwisher, McDermott, & Chun, 1997; Grill-Spector, Knouf, & Kanwisher, 2004). Neuronal evidence revealed that neuronal activities in the FFA were strongly responded when presented face images rather than when presented non-face stimuli (Tsao et al., 2006). Taken together, FFA is a crucial area which acts as face recognition, thus suggesting there are the distinct brain areas between object and face recognition.