Neural processing for individual categories of objects
Encyclopedia
Discrete categories of objects such as faces, body parts, tools, animals and buildings have been associated with preferential activation in specialised areas of the cerebral cortex
, leading to the suggestion that they may be produced separately in discrete neural regions.
Several such regions have been identified within the occipito-temporal cortex. The fusiform face area
(FFA) was first described by Sergent et al.(1992) who conducted a PET (positron emission tomography
) study on subjects viewing gratings, faces, and objects. Facial identification exclusively produced increased bilateral activation in the fusiform gyrus
, highlighting the dissociation between faces and other object processing. Similar results have also ben reported for activation of the parahipppocampal place area
(PPA) in response to stimuli depicting places and spatial layouts; and in the extrastriate body area (EBA) in response to human body parts.
Studies of patients with brain damage
have revealed pure agnosic disorders
that selectively impair recognition of specific object categories. Such agnosic disorders have been reported for faces (prosopagnosia
), living vs. nonliving stimuli, fruits, vegetables, tools, and musical instruments among others, suggesting that such categories may be processed independently within the brain.
Object-specific areas have been identified consistently across subjects and studies, however their responses are not always exclusive. Martin et al. (1996) found using fMRI that although object-specific responses were found in the left premotor cortex
and left medial occipital lobe
s respectively, identification of both tools and animals produced increased bilateral activation of the ventral temporal lobe
s. Thus it appears that tools and animals, at least, are not wholly processed by discrete brain areas (despite selective impairment)and alternative theories propose that rather that being object-specific, cortical regions may show preferential activation as a result of greater expertise in one category, greater homogeneity between category members, task-related biases, and attentional preference amongst others.
It may be that the use of distinct brain regions for processing different object categories results from different processing requirements necessary for each class. Indeed, Malach et al. (2002) detail findings that buildings and faces require processing at different resolutions in order to be recognised - face recognition requires the analysis of fine detail, while buildings can be recognised using larger scale feature integration. As a result, faces are associated with central visual field processing while buildings are processed more peripherally. Malach et al. (2002) report that points on the retina
sharing foveal centricity are mapped onto parallel cortical bands and it therefore follows that object classes that are processed differently by retinal cells should be represented distinctly within the brain. Consistently, faces and buildings were found to be processed independently of each other and in discrete cortical regions suggesting that processing is facilitated by assigning object categories to distinct cortical regions according to the level and type of processing that they require.
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, leading to the suggestion that they may be produced separately in discrete neural regions.
Several such regions have been identified within the occipito-temporal cortex. The fusiform face area
Fusiform face area
The fusiform face area is a part of the human visual system which might be specialized for facial recognition, although there is some evidence that it also processes categorical information about other objects, particularly familiar ones.-Localization:...
(FFA) was first described by Sergent et al.(1992) who conducted a PET (positron emission tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
) study on subjects viewing gratings, faces, and objects. Facial identification exclusively produced increased bilateral activation in the fusiform gyrus
Fusiform gyrus
The fusiform gyrus is part of the temporal lobe in Brodmann Area 37. It is also known as the occipitotemporal gyrus. Other sources have the fusiform gyrus above the occipitotemporal gyrus and underneath the parahippocampal gyrus....
, highlighting the dissociation between faces and other object processing. Similar results have also ben reported for activation of the parahipppocampal place area
Parahippocampal gyrus
The parahippocampal gyrus is a grey matter cortical region of the brain that surrounds the hippocampus. This region plays an important role in memory encoding and retrieval....
(PPA) in response to stimuli depicting places and spatial layouts; and in the extrastriate body area (EBA) in response to human body parts.
Studies of patients with brain damage
Brain damage
"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...
have revealed pure agnosic disorders
Agnosia
Agnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss...
that selectively impair recognition of specific object categories. Such agnosic disorders have been reported for faces (prosopagnosia
Prosopagnosia
Prosopagnosia is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact...
), living vs. nonliving stimuli, fruits, vegetables, tools, and musical instruments among others, suggesting that such categories may be processed independently within the brain.
Object-specific areas have been identified consistently across subjects and studies, however their responses are not always exclusive. Martin et al. (1996) found using fMRI that although object-specific responses were found in the left premotor cortex
Premotor cortex
The premotor cortex is an area of motor cortex lying within the frontal lobe of the brain. It extends 3 mm anterior to the primary motor cortex, near the Sylvian fissure, before narrowing to approximately 1 mm near the medial longitudinal fissure, which serves as the posterior border for...
and left medial occipital lobe
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
s respectively, identification of both tools and animals produced increased bilateral activation of the ventral temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
s. Thus it appears that tools and animals, at least, are not wholly processed by discrete brain areas (despite selective impairment)and alternative theories propose that rather that being object-specific, cortical regions may show preferential activation as a result of greater expertise in one category, greater homogeneity between category members, task-related biases, and attentional preference amongst others.
It may be that the use of distinct brain regions for processing different object categories results from different processing requirements necessary for each class. Indeed, Malach et al. (2002) detail findings that buildings and faces require processing at different resolutions in order to be recognised - face recognition requires the analysis of fine detail, while buildings can be recognised using larger scale feature integration. As a result, faces are associated with central visual field processing while buildings are processed more peripherally. Malach et al. (2002) report that points on the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
sharing foveal centricity are mapped onto parallel cortical bands and it therefore follows that object classes that are processed differently by retinal cells should be represented distinctly within the brain. Consistently, faces and buildings were found to be processed independently of each other and in discrete cortical regions suggesting that processing is facilitated by assigning object categories to distinct cortical regions according to the level and type of processing that they require.
See also
- Domain specificityDomain specificityDomain specificity is a theoretical position in cognitive science that argues that many aspects of cognition are supported by specialized, presumably evolutionarily specified, learning devices...
- Face perceptionFace perceptionFace perception is the process by which the brain and mind understand and interpret the face, particularly the human face.The human face's proportions and expressions are important to identify origin, emotional tendencies, health qualities, and some social information. From birth, faces are...
- Modularity of mindModularity of mindModularity of mind is the notion that a mind may, at least in part, be composed of separate innate structures which have established evolutionarily developed functional purposes...
- Structural information theoryStructural information theoryStructural information theory is a theory about human perception and in particular about perceptual organization: the way the human visual system organizes a raw visual stimulus into objects and object parts. SIT was initiated, in the 1960s, by Emanuel Leeuwenberg and has been developed further by...
- Principles of groupingPrinciples of groupingThe Principles of grouping are a set of principles in psychology, first proposed by Gestalt psychologists to account for the observation that humans naturally perceive objects as organized patterns and objects...
- Cognitive neuroscience of visual object recognitionCognitive neuroscience of visual object recognitionObject recognition is the ability to perceive an object’s physical properties and apply semantic attributes to the object, which includes the understanding of its use, previous experience with the object and how it relates to others.- Basic Stages of Object Recognition :One model of object...