Models of human visual attention should consider trial-by-trial variability in preparatory neural signals.
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Attention↗
Biomedical subjects
Maurizio Corbetta
Publications and source records attributed to Maurizio Corbetta.
Laboratory of attention and brain recovery at Washington University, St. Louis.
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Animals↗
Attentional selection of moving objects by a serial process.
How does the efficiency of attentional selection depend on the number of attended objects in a display? We measured the channel capacity (CC) of human observers during the attentional tracking of moving targets. The relation between CC and target number was used to estimate target-sampling rate. The sampling rate was halved when the number of targets was doubled, indicating that tracking was accomplished by a mechanism whose processing rate did not vary with target number. Systematically varying the dynamic parameters of the display provided inconclusive evidence for the idea that the time interval between successive samples of the same target increased with target number. These results are consistent with the hypothesis that the selection of multiple moving objects involves a limited capacity processor.
Attention↗
Separate modulations of human V1 associated with spatial attention and task structure.
Functional magnetic resonance imaging (fMRI) was used while normal human volunteers engaged in simple detection and discrimination tasks, revealing separable modulations of early visual cortex associated with spatial attention and task structure. Both modulations occur even when there is no change in sensory stimulation. The modulation due to spatial attention is present throughout the early visual areas V1, V2, V3, and VP, and varies with the attended location. The task structure activations are strongest in V1 and are greater in regions that represent more peripheral parts of the visual field. Control experiments demonstrate that the task structure activations cannot be attributed to visual, auditory, or somatosensory processing, the motor response for the detection/discrimination judgment, or oculomotor responses such as blinks or saccades. These findings demonstrate that early visual areas are modulated by at least two types of endogenous signals, each with distinct cortical distributions.
Adult↗
Spontaneous neuronal activity distinguishes human dorsal and ventral attention systems.
On the basis of task-related imaging studies in normal human subjects, it has been suggested that two attention systems exist in the human brain: a bilateral dorsal attention system involved in top-down orienting of attention and a right-lateralized ventral attention system involved in reorienting attention in response to salient sensory stimuli. An important question is whether this functional organization emerges only in response to external attentional demands or is represented more fundamentally in the internal dynamics of brain activity. To address this question, we examine correlations in spontaneous fluctuations of the functional MRI blood oxygen level-dependent signal in the absence of task, stimuli, or explicit attentional demands. We identify a bilateral dorsal attention system and a right-lateralized ventral attention system solely on the basis of spontaneous activity. Further, we observe regions in the prefrontal cortex correlated with both systems, a potential mechanism for mediating the functional interaction between systems. These findings demonstrate that the neuroanatomical substrates of human attention persist in the absence of external events, reflected in the correlation structure of spontaneous activity.
Attention↗
Losing our brainless minds: how neuroimaging informs cognition.
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Brain Mapping↗
Visuospatial reorienting signals in the human temporo-parietal junction are independent of response selection.
This study contrasts visuospatial reorienting and response selection signals in the right temporo-parietal junction (TPJ) with functional magnetic resonance imaging. The overall goal was to investigate whether spatial orienting signals and motor signals interacted or were independent in TPJ. The right TPJ showed a greater response to targets at in-validly rather than validly cued locations, but no significant modulation from the effector used to respond. We suggest that TPJ may work as a modality-independent 'circuit breaker' for the dorsal fronto-parietal attention system, directing attention to salient events and enabling a variety of responses to those events.
Adult↗
Brain signals for spatial attention predict performance in a motion discrimination task.
The reliability of visual perception is thought to reflect the quality of the sensory information. However, we show that subjects' performance can be predicted, trial-by-trial, by neural activity that precedes the onset of a sensory stimulus. Using functional MRI (fMRI), we studied how neural mechanisms that mediate spatial attention affect the accuracy of a motion discrimination judgment. The amplitude of blood oxygen level-dependent (BOLD) signals after a cue directing spatial attention predicted subjects' accuracy on 60-75% of the trials. Widespread predictive signals, which included dorsal parietal, visual extra-striate, prefrontal and sensory-motor cortex, depended on whether the cue correctly specified the stimulus location. Therefore, these signals indicate the degree of utilization of the cued information and play a role in the control of spatial attention. We conclude that variability in perceptual performance can be partly explained by the variability in endogenous, preparatory processes and that BOLD signals can be used to forecast human behavior.
Attention↗
Neural basis and recovery of spatial attention deficits in spatial neglect.
The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis of both spatial neglect and its recovery is largely unknown. We show that spatial attention deficits in neglect (rightward bias and reorienting) after right frontal damage correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. Furthermore, recovery of these attention deficits correlates with the restoration and rebalancing of activity within these regions. These results support a model of recovery based on the re-weighting of activity within a distributed neuronal architecture, and they show that behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.
Analysis of Variance↗
Cerebellar activity switches hemispheres with cerebral recovery in aphasia.
The right postero-lateral cerebellum participates with the left frontal lobe in the selection and production of words. Using fMRI, we examined whether cerebellar activity switches hemispheres in parallel with recruitment of putative compensatory right homologous frontal regions in post-stroke aphasia. Re-examining the data of Blasi et al. [Blasi, V., Young, A. C., Tansy, A. P., Petersen, S. E., Snyder, A. Z., & Corbetta, M. (2002). Word retrieval learning modulates right frontal cortex in patients with left frontal damage. Neuron, 36(1), 159-170], we asked: (1) if activity in the right cerebellum was disrupted by a left frontal lesion, (2) if activity switched to the left cerebellum, and (3) if activity in the left cerebellum was modulated by learning, as was right frontal cortex. Fourteen age-matched controls and eight mildly aphasic stroke patients participated. Aphasic participants all had lesions due to unilateral left hemisphere stroke at or near Broca's area. Subjects silently performed a word stem completion task with either novel or repeated items. Activity in right cerebellum of aphasic individuals was minimal and was not modulated by learning, as for controls. However, we observed robust learning-related attenuation of the BOLD signal in the left postero-lateral cerebellum consistent with learning-related effects in right frontal cortex. These findings support the hypothesis that right frontal and left cerebellar circuits are likely to be functionally relevant to recovered/residual verbal function.
Adult↗
The human brain is intrinsically organized into dynamic, anticorrelated functional networks.
During performance of attention-demanding cognitive tasks, certain regions of the brain routinely increase activity, whereas others routinely decrease activity. In this study, we investigate the extent to which this task-related dichotomy is represented intrinsically in the resting human brain through examination of spontaneous fluctuations in the functional MRI blood oxygen level-dependent signal. We identify two diametrically opposed, widely distributed brain networks on the basis of both spontaneous correlations within each network and anticorrelations between networks. One network consists of regions routinely exhibiting task-related activations and the other of regions routinely exhibiting task-related deactivations. This intrinsic organization, featuring the presence of anticorrelated networks in the absence of overt task performance, provides a critical context in which to understand brain function. We suggest that both task-driven neuronal responses and behavior are reflections of this dynamic, ongoing, functional organization of the brain.
Attention↗
Distribution of activity across the monkey cerebral cortical surface, thalamus and midbrain during rapid, visually guided saccades.
To examine the distribution of visual and oculomotor activity across the macaque brain, we performed functional magnetic resonance imaging (fMRI) on awake, behaving monkeys trained to perform visually guided saccades. Two subjects alternated between periods of making saccades and central fixations while blood oxygen level dependent (BOLD) images were collected [3 T, (1.5 mm)3 spatial resolution]. BOLD activations from each of four cerebral hemispheres were projected onto the subjects' cortical surfaces and aligned to a surface-based atlas for comparison across hemispheres and subjects. This surface-based analysis revealed patterns of visuo-oculomotor activity across much of the cerebral cortex, including activations in the posterior parietal cortex, superior temporal cortex and frontal lobe. For each cortical domain, we show the anatomical position and extent of visuo-oculomotor activity, including evidence that the dorsolateral frontal activation, which includes the frontal eye field (on the anterior bank of the arcuate sulcus), extends anteriorly into posterior principal sulcus (area 46) and posteriorly into part of dorsal premotor cortex (area 6). Our results also suggest that subcortical BOLD activity in the pulvinar thalamus may be lateralized during voluntary eye movements. These findings provide new neuroanatomical information as to the complex neural substrates that underlie even simple goal-directed behaviors.
Animals↗
An event-related functional magnetic resonance imaging study of voluntary and stimulus-driven orienting of attention.
Attention can be voluntarily directed to a location or automatically summoned to a location by a salient stimulus. We compared the effects of voluntary and stimulus-driven shifts of spatial attention on the blood oxygenation level-dependent signal in humans, using a method that separated preparatory activity related to the initial shift of attention from the subsequent activity caused by target presentation. Voluntary shifts produced greater preparatory activity than stimulus-driven shifts in the frontal eye field (FEF) and intraparietal sulcus, core regions of the dorsal frontoparietal attention network, demonstrating their special role in the voluntary control of attention. Stimulus-driven attentional shifts to salient color singletons recruited occipitotemporal regions, sensitive to color information and part of the dorsal network, including the FEF, suggesting a partly overlapping circuit for endogenous and exogenous orienting. The right temporoparietal junction (TPJ), a core region of the ventral frontoparietal attention network, was strongly modulated by stimulus-driven attentional shifts to behaviorally relevant stimuli, such as targets at unattended locations. However, the TPJ did not respond to salient, task-irrelevant color singletons, indicating that behavioral relevance is critical for TPJ modulation during stimulus-driven orienting. Finally, both ventral and dorsal regions were modulated during reorienting but significantly only by reorienting after voluntary shifts, suggesting the importance of a mismatch between expectation and sensory input.
Adult↗
A functional MRI study of preparatory signals for spatial location and objects.
We investigated preparatory signals for spatial location and objects in normal observers using functional magnetic resonance imaging (fMRI). Activity for attention-directing cues was separated from activity for subsequent test arrays containing the target stimulus. Subjects were more accurate in discriminating a target face among distracters when they knew in advance its location (spatial directional cue), as compared to when the target could randomly appear at one of two locations (spatial neutral cue), indicating that the spatial cue was used. Spatially specific activations occurred in a region at the intersection of the ventral intraparietal sulcus and transverse occipital sulcus (vIPS-TOS), which showed significantly stronger activation for rightward- than leftward-directing cues, while other fronto-parietal areas were activated by the cue but did not show spatial specificity. In visual cortex, activity was weak or absent in retinotopic occipital regions following attention-directing cues and this activity was not spatially specific. In a separate task, subject discriminated a target outdoor scene among distracters after the presentation of spatial neutral cues. There was no significant difference in dorsal frontoparietal activity during the face versus scene discrimination task. Also, there was only weak evidence for selective preparatory activity in ventral object-selective regions, although the activation of these regions to the subsequent test array did depend upon which discrimination (face or place) was performed. We conclude first that under certain circumstances, spatial cues that produce strong behavioral effects may modulate parietal-occipital regions in a spatially specific manner without producing similar modulations in retinotopic occipital regions. Second, attentional modulations of object-selective regions in temporal-occipital cortex can occur even though preparatory object-selective modulations of those regions are absent or weak.
Analysis of Variance↗
Extrastriate body area in human occipital cortex responds to the performance of motor actions.
A region in human lateral occipital cortex (the 'extrastriate body area' or EBA) has been implicated in the perception of body parts. Here we report functional magnetic resonance imaging (fMRI) evidence that the EBA is strongly modulated by limb (arm, foot) movements to a visual target stimulus, even in the absence of visual feedback from the movement. Therefore, the EBA responds not only during the perception of other people's body parts, but also during goal-directed movements of the observer's body parts. In addition, both limb movements and saccades to a detected stimulus produced stronger signals than stimulus detection without motor movements ('covert detection') in the calcarine sulcus and lingual gyrus. These motor-related modulations cannot be explained by simple visual or attentional factors related to the target stimulus, and suggest a potentially widespread influence of actions on visual cortex.
Adult↗
The study of neural connectivity using diffusion tensor tracking.
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Animals↗
Quantitative analysis of attention and detection signals during visual search.
Prior work has distinguished regions in the intraparietal sulcus (IPs) and frontal eye field (FEF) involved in the voluntary control of attention, from more ventral regions in the temporoparietal junction (TPJ) involved in target detection. The present results show that when subjects search for and detect a visual target stimulus among nontargets, these regions show sensory-, search-, and detection-related signals that both confirm and refine these functional distinctions. The different signals were isolated by an additive model that accounted for a large fraction of BOLD (blood oxygenation level-dependent) signal modulation over the brain. Both IPs and FEF were activated during search through nontargets, consistent with a role in maintaining attention-related signals during search. However, unlike FEF, IPs also showed stimulus-related activations, and may combine signals related to sensory and task-dependent components of salience. Although IPs-FEF showed search-related activations, the TPJ was deactivated during search. TPJ activations were confined to detection-related signals. These results provide a much stronger dissociation between the TPJ and IPs-FEF than previous work, while indicating functional differences between frontal and parietal regions that are often coactivated in studies of attention. Finally, continuous flow models of information processing predict that during search, signals from missed targets should be fed from sensory to associative regions rather than being gated by the decision criterion. Correspondingly, missed targets significantly activated parietal (e.g., right TPJ) and frontal (e.g., anterior insula, anterior cingulate) regions, although with a smaller magnitude than detected targets. Surprisingly, many cortical regions showed equivalent signals from detected targets and the completion of target-absent trials, reflecting a widespread signal unrelated to motor execution.
Attention↗
Functional organization of human intraparietal and frontal cortex for attending, looking, and pointing.
We studied the functional organization of human posterior parietal and frontal cortex using functional magnetic resonance imaging (fMRI) to map preparatory signals for attending, looking, and pointing to a peripheral visual location. The human frontal eye field and two separate regions in the intraparietal sulcus were similarly recruited in all conditions, suggesting an attentional role that generalizes across response effectors. However, the preparation of a pointing movement selectively activated a different group of regions, suggesting a stronger role in motor planning. These regions were lateralized to the left hemisphere, activated by preparation of movements of either hand, and included the inferior and superior parietal lobule, precuneus, and posterior superior temporal sulcus, plus the dorsal premotor and anterior cingulate cortex anteriorly. Surface-based registration of macaque cortical areas onto the map of fMRI responses suggests a relatively good spatial correspondence between human and macaque parietal areas. In contrast, large interspecies differences were noted in the topography of frontal areas.
Animals↗