A sudden change in the direction of motion is a particularly salient and relevant feature of visu... more A sudden change in the direction of motion is a particularly salient and relevant feature of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to different features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophysiological data from animals and functional imaging data from humans suggest a number of brain areas responsive to motion, presumably working as a network. Temporal patterns of activity allow the same network to process information in different ways. The present study in humans sought to determine which motion-sensitive areas are involved in processing changes in the direction of motion and to characterize the temporal patterns of processing within this network of brain regions. To accomplish this, we used both magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). The fMRI data w...
Culham, Jody C., Stephan A. Brandt, Patrick Cavanagh, Nancy G. Kanwisher, Anders M. Dale, and Rog... more Culham, Jody C., Stephan A. Brandt, Patrick Cavanagh, Nancy G. Kanwisher, Anders M. Dale, and Roger B. H. Tootell. Cortical fMRI activation produced by attentive tracking of moving targets. J. Neurophysiol. 80: 2657–2670, 1998. Attention can be used to keep track of moving items, particularly when there are multiple targets of interest that cannot all be followed with eye movements. Functional magnetic resonance imaging (fMRI) was used to investigate cortical regions involved in attentive tracking. Cortical flattening techniques facilitated within-subject comparisons of activation produced by attentive tracking, visual motion, discrete attention shifts, and eye movements. In the main task, subjects viewed a display of nine green “bouncing balls” and used attention to mentally track a subset of them while fixating. At the start of each attentive-tracking condition, several target balls (e.g., 3/9) turned red for 2 s and then reverted to green. Subjects then used attention to keep tra...
Ample evidence from monkey electrophysiology suggests that eye movements are controlled by two pa... more Ample evidence from monkey electrophysiology suggests that eye movements are controlled by two parallel cortico-cortical networks, including a frontal eye field (FEF) and a parietal eye field (PEF). Each cortical eye field contains largely separate groups of neurons devoted to either saccadic eye movements, or visual pursuit eye movements (Tian and Lynch 1996). Both eye fields are directly connected to the brain stem oculomotor system. The posterior eye movement network has strong [anatomical and functional] links to the visual “dorsal stream”, and especially to motion perception. Experimental studies in non-human primates suggest that areas MT/MST are intimately involved in pursuit tracking (Newsome et al. 1985; Dursteier et al. 1987). If a given motion is misperceived or not seen at all, the target cannot be pursued faithfully (Baloh et al. 1980). This implies that information about an ongoing eye movement must be incorporated at some level(s) of the visual motion processing hierarchy. Here we ask at a systems level how analoguous regions in human cortex are interrelated. Human neuroimaging studies have clarified the localization of saccade-related activity (for a review see Carter and Zee 1997). However, only few imaging studies have addressed the functional anatomy of smooth pursuit eye movement in extrastri-ate visual cortex (Petit and Clark 1997; Barton et al. 1996). Previous human brain imaging experiments have also examined cortical responses to stimulus motion (e.g. Watson et al. 1993; Dupont et al. 1994; Tootell et al. 1995b; Tootell et al. 1997). Less is known about how the actitvity in specific motion areas is related to different components of an ongoing pursuit eye movement.
Movement in the visual field is an important part of perceptual information. Previous imaging stu... more Movement in the visual field is an important part of perceptual information. Previous imaging studies have identified a number of cortical areas sensitive to visual motion [1,2], including what is considered to be the human homologue of area MT/V5 [3,4]. Our study sought to reproduce and expand upon a previous functional magnetic resonance imaging (fMRI) investigation [4] and to examine the timing of activity in the network of regions participating in the processing of visual motion information with magnetoencephalography (MEG).
Functionalmagneticresonanceimaging(fMRI)hasbeenusedextensivelytoidentifyregionsintheinferiortempo... more Functionalmagneticresonanceimaging(fMRI)hasbeenusedextensivelytoidentifyregionsintheinferiortemporal(IT)cortexthatareselective for categories of visual stimuli. However, comparatively little is known about the neuronal responses relative to these fMRI-defined regions. Here, we compared in nonhuman primates the distribution and response properties of IT neurons recorded within versus outside fMRI regions selective for four different visual categories: faces, body parts, objects, and places. Although individual neurons that preferred each of the four categories were found throughout the sampled regions, they were most concentrated within the corresponding fMRI region, decreasing significantly within 1-4 mm from the edge of these regions. Furthermore, the correspondence between fMRI and neuronal distributions was specific to neurons that increased their firing rates in response to the visual stimuli but not to neurons suppressed by visual stimuli, suggesting that the processes associated with inhibiting neuronal activity did not contribute strongly to the fMRI signal in this experiment.
Prior studies suggest the presence of a color-selective area in the inferior occipital-temporal r... more Prior studies suggest the presence of a color-selective area in the inferior occipital-temporal region of human visual cortex. It has been proposed that this human area is homologous to macaque area V4, which is arguably color selective, but this has never been tested directly. To test this model, we compared the location of the human color-selective region to the retinotopic area boundaries in the same subjects, using functional magnetic resonance imaging (fMRI), cortical flattening and retinotopic mapping techniques. The human color-selective region did not match the location of area V4 (neither its dorsal nor ventral subdivisions), as extrapolated from macaque maps. Instead this region coincides with a new retinotopic area that we call 'V8', which includes a distinct representation of the fovea and both upper and lower visual fields. We also tested the response to stimuli that produce color afterimages and found that these stimuli, like real colors, caused preferential activation of V8 but not V4.
Functional Magnetic Resonance Imaging (fMRI) was used to identify a small area in the human poste... more Functional Magnetic Resonance Imaging (fMRI) was used to identify a small area in the human posterior fusiform gyrus that responds selectively to faces (PF). In the same subjects, phase-encoded rotating and expanding checkerboards were used with fMRI to identify the retinotopic visual areas V1, V2, V3, V3A, VP and V4v. PF was found to lie anterior to area V4v, with a small gap present between them. Further recordings in some of the same subjects used moving low-contrast rings to identify the visual motion area MT. PF was found to lie ventral to MT. In addition, preliminary evidence was found using fMRI for a small area that responded to inanimate objects but not to faces in the collateral sulcus medial to PF. The retinotopic visual areas and MT responded equally to faces, control randomized stimuli, and objects. Weakly face-selective responses were also found in ventrolateral occipitotemporal cortex anterior to V4v, as well as in the middle temporal gyrus anterior to MT. We conclude that the fusiform face area in humans lies in non-retinotopic visual association cortex of the ventral form-processing stream, in an area that may be roughly homologous in location to area TF or CITv in monkeys.
A parietal-frontal network in primates is thought to support many behaviors occurring in the spac... more A parietal-frontal network in primates is thought to support many behaviors occurring in the space around the body, including interpersonal interactions and maintenance of a particular "comfort zone" or distance from other people ("personal space"). To better understand this network in humans, we used functional MRI to measure the responses to moving objects (faces, cars, simple spheres) and the functional connectivity of two regions in this network, the dorsal intraparietal sulcus (DIPS) and the ventral premotor cortex (PMv). We found that both areas responded more strongly to faces that were moving toward (vs away from) subjects, but did not show this bias in response to comparable motion in control stimuli (cars or spheres). Moreover, these two regions were functionally interconnected. Tests of activity-behavior associations revealed that the strength of DIPS-PMv connectivity was correlated with the preferred distance that subjects chose to stand from an unfamiliar person (personal space size). In addition, the magnitude of DIPS and PMv responses was correlated with the preferred level of social activity. Together, these findings suggest that this parietal-frontal network plays a role in everyday interactions with others.
In fMRI studies, human lateral occipital (LO) cortex is thought to respond selectively to images ... more In fMRI studies, human lateral occipital (LO) cortex is thought to respond selectively to images of objects, compared with nonobjects. However, it remains unresolved whether all objects evoke equivalent levels of activity in LO, and, if not, which image features produce stronger activation. Here, we used an unbiased parametric texture model to predict preferred versus nonpreferred stimuli in LO. Observation and psychophysical results showed that predicted preferred stimuli (both objects and nonobjects) had smooth (rather than textured) surfaces. These predictions were confirmed using fMRI, for objects and nonobjects. Similar preferences were also found in the fusiform face area (FFA). Consistent with this: (1) FFA and LO responded more strongly to nonfreckled (smooth) faces, compared with otherwise identical freckled (textured) faces; and (2) strong functional connections were found between LO and FFA. Thus, LO and FFA may be part of an information-processing stream distinguished by feature-based category selectivity (smooth Ͼ textured).
Schizophrenia is associated with subtle abnormalities in day-today social behaviors, including a ... more Schizophrenia is associated with subtle abnormalities in day-today social behaviors, including a tendency in some patients to "keep their distance" from others in physical space. The neural basis of this abnormality, and related changes in social functioning, is unknown. Here we examined, in schizophrenic patients and healthy control subjects, the functioning of a parietal-frontal network involved in monitoring the space immediately surrounding the body ("personal space"). Using fMRI, we found that one region of this network, the dorsal intraparietal sulcus (DIPS), was hyper-responsive in schizophrenic patients to face stimuli appearing to move towards the subjects, intruding into personal space. This hyper-responsivity was predicted both by the size of personal space (which was abnormally elevated in the schizophrenia group) and the severity of negative symptoms. In contrast, in a second study, the activity of two lower-level visual areas that send information to DIPS (the fusiform face area and middle temporal area) was normal in schizophrenia. Together, these findings suggest that changes in parietal-frontal networks that support the sensory-guided initiation of behavior, including actions occurring in the space surrounding the body, contribute to social dysfunction and negative symptoms in schizophrenia.
Proceedings of the National Academy of Sciences of the United States of America, Jan 4, 2008
Here, we mapped fMRI responses to incrementally changing shapes along a continuous 3D morph, rang... more Here, we mapped fMRI responses to incrementally changing shapes along a continuous 3D morph, ranging from a head ("face") to a house ("place"). The response to each shape was mapped independently by using single-stimulus imaging, and stimulus shapes were equated for lower-level visual cues. We measured activity in 2-mm samples across human inferior temporal cortex from the fusiform face area (FFA) (apparently selective for faces) to the parahippocampal place area (PPA) (apparently selective for places), testing for (i) incremental changes in the topography of FFA and PPA (predicted by the continuous-mapping model) or (ii) little or no response to the intermediate morphed shapes (predicted by the category model). Neither result occurred; instead, we found approximately linearly graded changes in the response amplitudes to graded-shape changes, without changes in topography-similar to visual responses in different lower-tier cortical areas.
One of the most remarkable properties of the visual system is the ability to identify and categor... more One of the most remarkable properties of the visual system is the ability to identify and categorize a wide variety of objects effortlessly. However, the underlying neural mechanisms remain elusive. Specifically, the question of how individual object information is represented and intrinsically organized is still poorly understood. To address this question, we presented images of isolated real-world objects spanning a wide range of categories to awake monkeys using a rapid event-related functional magnetic resonance imaging (fMRI) design and analyzed the responses of multiple areas involved in object processing. We found that the multivoxel response patterns to individual exemplars in the inferior temporal (IT) cortex, especially area TE, encoded the animate-inanimate categorical division, with a subordinate cluster of faces within the animate category. In contrast, the individual exemplar representations in V4, the amygdala, and prefrontal cortex showed either no categorical structure, or a categorical structure different from that in IT cortex. Moreover, in the IT face-selective regions ("face patches"), especially the anterior face patches, (1) the multivoxel response patterns to individual exemplars showed a categorical distinction between faces and nonface objects (i.e., body parts and inanimate objects), and (2) the regionally averaged activations to individual exemplars showed face-selectivity and within-face exemplar-selectivity. Our findings demonstrate that, at both the single-exemplar and the population level, intrinsic object representation and categorization are organized hierarchically as one moves anteriorly along the ventral pathway, reflecting both modular and distributed processing.
Defining the exact mechanisms by which the brain processes visual objects and scenes remains an u... more Defining the exact mechanisms by which the brain processes visual objects and scenes remains an unresolved challenge. Valuable clues to this process have emerged from the demonstration that clusters of neurons (''modules'') in inferior temporal cortex apparently respond selectively to specific categories of visual stimuli, such as places/scenes. However, the higher-order ''category-selective'' response could also reflect specific lower-level spatial factors. Here we tested this idea in multiple functional MRI experiments, in humans and macaque monkeys, by systematically manipulating the spatial content of geometrical shapes and natural images. These tests revealed that visual spatial discontinuities (as reflected by an increased response to high spatial frequencies) selectively activate a well-known place-selective region of visual cortex (the ''parahippocampal place area'') in humans. In macaques, we demonstrate a homologous cortical area, and show that it also responds selectively to higher spatial frequencies. The parahippocampal place area may use such information for detecting object borders and scene details during spatial perception and navigation.
Defining the exact mechanisms by which the brain processes visual objects and scenes remains an u... more Defining the exact mechanisms by which the brain processes visual objects and scenes remains an unresolved challenge. Valuable clues to this process have emerged from the demonstration that clusters of neurons ("modules") in inferior temporal cortex apparently respond selectively to specific categories of visual stimuli, such as places/scenes. However, the higher-order "category-selective" response could also reflect specific lower-level spatial factors. Here we tested this idea in multiple functional MRI experiments, in humans and macaque monkeys, by systematically manipulating the spatial content of geometrical shapes and natural images. These tests revealed that visual spatial discontinuities (as reflected by an increased response to high spatial frequencies) selectively activate a well-known place-selective region of visual cortex (the "parahippocampal place area") in humans. In macaques, we demonstrate a homologous cortical area, and show that it a...
Responses to single and multiple spatial frequency gratings were recorded from eighty-eight cat s... more Responses to single and multiple spatial frequency gratings were recorded from eighty-eight cat striate cortex cells. A cell's response to a grating of its optimum spatial frequency (f) was examined both alone and in the presence of gratings of 1/4, 1/3, 1/2, 2, 3 and 4f, respectively. Some 97% (thirty-seven of thirty-eight) of all simple cells showed significant inhibition of f by one or more of the other frequencies. This inhibition was usually fairly narrowly tuned, with only one or two spatial frequencies producing significant inhibition. Thirty-four simple cells were maximally inhibited by a higher frequency, three by a lower spatial frequency. By far the most common interaction was a considerable inhibition of f by 2f and/or 3f. Of the thirty-seven simple cells showing inhibition to a complex grating, seventeen responded in a manner dependent on the relative phases of the two components. Some showed only inhibition of f; in others, the response to f was either increased or...
A sudden change in the direction of motion is a particularly salient and relevant feature of visu... more A sudden change in the direction of motion is a particularly salient and relevant feature of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to different features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophysiological data from animals and functional imaging data from humans suggest a number of brain areas responsive to motion, presumably working as a network. Temporal patterns of activity allow the same network to process information in different ways. The present study in humans sought to determine which motion-sensitive areas are involved in processing changes in the direction of motion and to characterize the temporal patterns of processing within this network of brain regions. To accomplish this, we used both magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). The fMRI data w...
Culham, Jody C., Stephan A. Brandt, Patrick Cavanagh, Nancy G. Kanwisher, Anders M. Dale, and Rog... more Culham, Jody C., Stephan A. Brandt, Patrick Cavanagh, Nancy G. Kanwisher, Anders M. Dale, and Roger B. H. Tootell. Cortical fMRI activation produced by attentive tracking of moving targets. J. Neurophysiol. 80: 2657–2670, 1998. Attention can be used to keep track of moving items, particularly when there are multiple targets of interest that cannot all be followed with eye movements. Functional magnetic resonance imaging (fMRI) was used to investigate cortical regions involved in attentive tracking. Cortical flattening techniques facilitated within-subject comparisons of activation produced by attentive tracking, visual motion, discrete attention shifts, and eye movements. In the main task, subjects viewed a display of nine green “bouncing balls” and used attention to mentally track a subset of them while fixating. At the start of each attentive-tracking condition, several target balls (e.g., 3/9) turned red for 2 s and then reverted to green. Subjects then used attention to keep tra...
Ample evidence from monkey electrophysiology suggests that eye movements are controlled by two pa... more Ample evidence from monkey electrophysiology suggests that eye movements are controlled by two parallel cortico-cortical networks, including a frontal eye field (FEF) and a parietal eye field (PEF). Each cortical eye field contains largely separate groups of neurons devoted to either saccadic eye movements, or visual pursuit eye movements (Tian and Lynch 1996). Both eye fields are directly connected to the brain stem oculomotor system. The posterior eye movement network has strong [anatomical and functional] links to the visual “dorsal stream”, and especially to motion perception. Experimental studies in non-human primates suggest that areas MT/MST are intimately involved in pursuit tracking (Newsome et al. 1985; Dursteier et al. 1987). If a given motion is misperceived or not seen at all, the target cannot be pursued faithfully (Baloh et al. 1980). This implies that information about an ongoing eye movement must be incorporated at some level(s) of the visual motion processing hierarchy. Here we ask at a systems level how analoguous regions in human cortex are interrelated. Human neuroimaging studies have clarified the localization of saccade-related activity (for a review see Carter and Zee 1997). However, only few imaging studies have addressed the functional anatomy of smooth pursuit eye movement in extrastri-ate visual cortex (Petit and Clark 1997; Barton et al. 1996). Previous human brain imaging experiments have also examined cortical responses to stimulus motion (e.g. Watson et al. 1993; Dupont et al. 1994; Tootell et al. 1995b; Tootell et al. 1997). Less is known about how the actitvity in specific motion areas is related to different components of an ongoing pursuit eye movement.
Movement in the visual field is an important part of perceptual information. Previous imaging stu... more Movement in the visual field is an important part of perceptual information. Previous imaging studies have identified a number of cortical areas sensitive to visual motion [1,2], including what is considered to be the human homologue of area MT/V5 [3,4]. Our study sought to reproduce and expand upon a previous functional magnetic resonance imaging (fMRI) investigation [4] and to examine the timing of activity in the network of regions participating in the processing of visual motion information with magnetoencephalography (MEG).
Functionalmagneticresonanceimaging(fMRI)hasbeenusedextensivelytoidentifyregionsintheinferiortempo... more Functionalmagneticresonanceimaging(fMRI)hasbeenusedextensivelytoidentifyregionsintheinferiortemporal(IT)cortexthatareselective for categories of visual stimuli. However, comparatively little is known about the neuronal responses relative to these fMRI-defined regions. Here, we compared in nonhuman primates the distribution and response properties of IT neurons recorded within versus outside fMRI regions selective for four different visual categories: faces, body parts, objects, and places. Although individual neurons that preferred each of the four categories were found throughout the sampled regions, they were most concentrated within the corresponding fMRI region, decreasing significantly within 1-4 mm from the edge of these regions. Furthermore, the correspondence between fMRI and neuronal distributions was specific to neurons that increased their firing rates in response to the visual stimuli but not to neurons suppressed by visual stimuli, suggesting that the processes associated with inhibiting neuronal activity did not contribute strongly to the fMRI signal in this experiment.
Prior studies suggest the presence of a color-selective area in the inferior occipital-temporal r... more Prior studies suggest the presence of a color-selective area in the inferior occipital-temporal region of human visual cortex. It has been proposed that this human area is homologous to macaque area V4, which is arguably color selective, but this has never been tested directly. To test this model, we compared the location of the human color-selective region to the retinotopic area boundaries in the same subjects, using functional magnetic resonance imaging (fMRI), cortical flattening and retinotopic mapping techniques. The human color-selective region did not match the location of area V4 (neither its dorsal nor ventral subdivisions), as extrapolated from macaque maps. Instead this region coincides with a new retinotopic area that we call 'V8', which includes a distinct representation of the fovea and both upper and lower visual fields. We also tested the response to stimuli that produce color afterimages and found that these stimuli, like real colors, caused preferential activation of V8 but not V4.
Functional Magnetic Resonance Imaging (fMRI) was used to identify a small area in the human poste... more Functional Magnetic Resonance Imaging (fMRI) was used to identify a small area in the human posterior fusiform gyrus that responds selectively to faces (PF). In the same subjects, phase-encoded rotating and expanding checkerboards were used with fMRI to identify the retinotopic visual areas V1, V2, V3, V3A, VP and V4v. PF was found to lie anterior to area V4v, with a small gap present between them. Further recordings in some of the same subjects used moving low-contrast rings to identify the visual motion area MT. PF was found to lie ventral to MT. In addition, preliminary evidence was found using fMRI for a small area that responded to inanimate objects but not to faces in the collateral sulcus medial to PF. The retinotopic visual areas and MT responded equally to faces, control randomized stimuli, and objects. Weakly face-selective responses were also found in ventrolateral occipitotemporal cortex anterior to V4v, as well as in the middle temporal gyrus anterior to MT. We conclude that the fusiform face area in humans lies in non-retinotopic visual association cortex of the ventral form-processing stream, in an area that may be roughly homologous in location to area TF or CITv in monkeys.
A parietal-frontal network in primates is thought to support many behaviors occurring in the spac... more A parietal-frontal network in primates is thought to support many behaviors occurring in the space around the body, including interpersonal interactions and maintenance of a particular "comfort zone" or distance from other people ("personal space"). To better understand this network in humans, we used functional MRI to measure the responses to moving objects (faces, cars, simple spheres) and the functional connectivity of two regions in this network, the dorsal intraparietal sulcus (DIPS) and the ventral premotor cortex (PMv). We found that both areas responded more strongly to faces that were moving toward (vs away from) subjects, but did not show this bias in response to comparable motion in control stimuli (cars or spheres). Moreover, these two regions were functionally interconnected. Tests of activity-behavior associations revealed that the strength of DIPS-PMv connectivity was correlated with the preferred distance that subjects chose to stand from an unfamiliar person (personal space size). In addition, the magnitude of DIPS and PMv responses was correlated with the preferred level of social activity. Together, these findings suggest that this parietal-frontal network plays a role in everyday interactions with others.
In fMRI studies, human lateral occipital (LO) cortex is thought to respond selectively to images ... more In fMRI studies, human lateral occipital (LO) cortex is thought to respond selectively to images of objects, compared with nonobjects. However, it remains unresolved whether all objects evoke equivalent levels of activity in LO, and, if not, which image features produce stronger activation. Here, we used an unbiased parametric texture model to predict preferred versus nonpreferred stimuli in LO. Observation and psychophysical results showed that predicted preferred stimuli (both objects and nonobjects) had smooth (rather than textured) surfaces. These predictions were confirmed using fMRI, for objects and nonobjects. Similar preferences were also found in the fusiform face area (FFA). Consistent with this: (1) FFA and LO responded more strongly to nonfreckled (smooth) faces, compared with otherwise identical freckled (textured) faces; and (2) strong functional connections were found between LO and FFA. Thus, LO and FFA may be part of an information-processing stream distinguished by feature-based category selectivity (smooth Ͼ textured).
Schizophrenia is associated with subtle abnormalities in day-today social behaviors, including a ... more Schizophrenia is associated with subtle abnormalities in day-today social behaviors, including a tendency in some patients to "keep their distance" from others in physical space. The neural basis of this abnormality, and related changes in social functioning, is unknown. Here we examined, in schizophrenic patients and healthy control subjects, the functioning of a parietal-frontal network involved in monitoring the space immediately surrounding the body ("personal space"). Using fMRI, we found that one region of this network, the dorsal intraparietal sulcus (DIPS), was hyper-responsive in schizophrenic patients to face stimuli appearing to move towards the subjects, intruding into personal space. This hyper-responsivity was predicted both by the size of personal space (which was abnormally elevated in the schizophrenia group) and the severity of negative symptoms. In contrast, in a second study, the activity of two lower-level visual areas that send information to DIPS (the fusiform face area and middle temporal area) was normal in schizophrenia. Together, these findings suggest that changes in parietal-frontal networks that support the sensory-guided initiation of behavior, including actions occurring in the space surrounding the body, contribute to social dysfunction and negative symptoms in schizophrenia.
Proceedings of the National Academy of Sciences of the United States of America, Jan 4, 2008
Here, we mapped fMRI responses to incrementally changing shapes along a continuous 3D morph, rang... more Here, we mapped fMRI responses to incrementally changing shapes along a continuous 3D morph, ranging from a head ("face") to a house ("place"). The response to each shape was mapped independently by using single-stimulus imaging, and stimulus shapes were equated for lower-level visual cues. We measured activity in 2-mm samples across human inferior temporal cortex from the fusiform face area (FFA) (apparently selective for faces) to the parahippocampal place area (PPA) (apparently selective for places), testing for (i) incremental changes in the topography of FFA and PPA (predicted by the continuous-mapping model) or (ii) little or no response to the intermediate morphed shapes (predicted by the category model). Neither result occurred; instead, we found approximately linearly graded changes in the response amplitudes to graded-shape changes, without changes in topography-similar to visual responses in different lower-tier cortical areas.
One of the most remarkable properties of the visual system is the ability to identify and categor... more One of the most remarkable properties of the visual system is the ability to identify and categorize a wide variety of objects effortlessly. However, the underlying neural mechanisms remain elusive. Specifically, the question of how individual object information is represented and intrinsically organized is still poorly understood. To address this question, we presented images of isolated real-world objects spanning a wide range of categories to awake monkeys using a rapid event-related functional magnetic resonance imaging (fMRI) design and analyzed the responses of multiple areas involved in object processing. We found that the multivoxel response patterns to individual exemplars in the inferior temporal (IT) cortex, especially area TE, encoded the animate-inanimate categorical division, with a subordinate cluster of faces within the animate category. In contrast, the individual exemplar representations in V4, the amygdala, and prefrontal cortex showed either no categorical structure, or a categorical structure different from that in IT cortex. Moreover, in the IT face-selective regions ("face patches"), especially the anterior face patches, (1) the multivoxel response patterns to individual exemplars showed a categorical distinction between faces and nonface objects (i.e., body parts and inanimate objects), and (2) the regionally averaged activations to individual exemplars showed face-selectivity and within-face exemplar-selectivity. Our findings demonstrate that, at both the single-exemplar and the population level, intrinsic object representation and categorization are organized hierarchically as one moves anteriorly along the ventral pathway, reflecting both modular and distributed processing.
Defining the exact mechanisms by which the brain processes visual objects and scenes remains an u... more Defining the exact mechanisms by which the brain processes visual objects and scenes remains an unresolved challenge. Valuable clues to this process have emerged from the demonstration that clusters of neurons (''modules'') in inferior temporal cortex apparently respond selectively to specific categories of visual stimuli, such as places/scenes. However, the higher-order ''category-selective'' response could also reflect specific lower-level spatial factors. Here we tested this idea in multiple functional MRI experiments, in humans and macaque monkeys, by systematically manipulating the spatial content of geometrical shapes and natural images. These tests revealed that visual spatial discontinuities (as reflected by an increased response to high spatial frequencies) selectively activate a well-known place-selective region of visual cortex (the ''parahippocampal place area'') in humans. In macaques, we demonstrate a homologous cortical area, and show that it also responds selectively to higher spatial frequencies. The parahippocampal place area may use such information for detecting object borders and scene details during spatial perception and navigation.
Defining the exact mechanisms by which the brain processes visual objects and scenes remains an u... more Defining the exact mechanisms by which the brain processes visual objects and scenes remains an unresolved challenge. Valuable clues to this process have emerged from the demonstration that clusters of neurons ("modules") in inferior temporal cortex apparently respond selectively to specific categories of visual stimuli, such as places/scenes. However, the higher-order "category-selective" response could also reflect specific lower-level spatial factors. Here we tested this idea in multiple functional MRI experiments, in humans and macaque monkeys, by systematically manipulating the spatial content of geometrical shapes and natural images. These tests revealed that visual spatial discontinuities (as reflected by an increased response to high spatial frequencies) selectively activate a well-known place-selective region of visual cortex (the "parahippocampal place area") in humans. In macaques, we demonstrate a homologous cortical area, and show that it a...
Responses to single and multiple spatial frequency gratings were recorded from eighty-eight cat s... more Responses to single and multiple spatial frequency gratings were recorded from eighty-eight cat striate cortex cells. A cell's response to a grating of its optimum spatial frequency (f) was examined both alone and in the presence of gratings of 1/4, 1/3, 1/2, 2, 3 and 4f, respectively. Some 97% (thirty-seven of thirty-eight) of all simple cells showed significant inhibition of f by one or more of the other frequencies. This inhibition was usually fairly narrowly tuned, with only one or two spatial frequencies producing significant inhibition. Thirty-four simple cells were maximally inhibited by a higher frequency, three by a lower spatial frequency. By far the most common interaction was a considerable inhibition of f by 2f and/or 3f. Of the thirty-seven simple cells showing inhibition to a complex grating, seventeen responded in a manner dependent on the relative phases of the two components. Some showed only inhibition of f; in others, the response to f was either increased or...
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Papers by R. Tootell