The neural basis of object perception
Introduction
Humans can recognize an object within a fraction of a second. The neural mechanisms underlying this remarkable ability are not well understood. A promising strategy for attempting to understand human visual recognition is to characterize the neural system that accomplishes it — that is, the ventral visual pathway. This system extends from the occipital lobe into ventral and lateral regions of the temporal lobe.
Here, I describe recent findings from neuroimaging studies of humans that have examined cortical regions involved in visual perception of faces and objects. The findings from these studies have begun to elucidate the general organization and functional properties of these regions. I focus on two main issues in this review. First, what is the functional organization of the human ventral visual pathway? Second, what is the role of these regions in visual object recognition? I will show that ventral occipito-temporal (VOT) and lateral occipito-temporal object-selective regions are involved in representing the shape of an object and are correlated with perceiving objects in many different recognition tasks.
Section snippets
Object-selective regions in the human brain
Object-selective regions respond strongly when subjects view pictures of objects but not when they view pictures of textures, noise or highly scrambled objects. These regions comprise a large constellation of areas in both the ventral and dorsal visual pathways that lie anterior and lateral to early retinotopic cortex. The parcellation of these areas is difficult because they are largely non-retinotopic [1] and different types of objects activate slightly different regions (Figure 1).
Whereas
Representation of objects in higher order areas
In the first section, I described the cortical regions that are activated when people look at objects. In this section, I discuss how objects are represented in the cortex. Any useful object recognition system should have ‘perceptual constancy’ — that is, it should be relatively insensitive to the precise physical cues that define an object.
Converging evidence suggests that object-selective regions in the ventral and dorsal stream show perceptual constancy under many manipulations:
The role of object-selective regions in object recognition
Although occipito-temporal object-selective regions are activated strongly when subjects view pictures of objects and have a large degree of perceptual constancy, this does not by itself prove that they are the loci in the brain that ‘perform’ object recognition. Activation during object viewing could be induced by other processes, such as visual attention, arousal, figure-ground segmentation and surface extraction among others. However, several recent studies show that activation in ventral
Conclusions
Neuroimaging studies have shown that several object-selective regions in the occipito-temporal cortex are involved in representing and perceiving objects and faces. These regions represent object shape rather than contours or other low-level features. In addition, higher activation in these regions occurs when subjects successfully recognize an object than when an object is present but not recognized. Future studies are required to elucidate the nature of object representations in the ventral
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
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of special interest
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of outstanding interest
Acknowledgements
I would like to thank Sookung Kim for reconstructing and flattening subjects’ brains, and for help in analyzing the localizer experiments.
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