Biomedical subjects

Sarah Shomstein

Publications and source records attributed to Sarah Shomstein.

7 recordsLinked to original sources

PubMed2006

Cortical systems mediating visual attention to both objects and spatial locations.

Natural visual scenes consist of many objects occupying a variety of spatial locations. Given that the plethora of information cannot be processed simultaneously, the multiplicity of inputs compete for representation. Using event-related functional MRI, we show that attention, the mechanism by which a subset of the input is selected, is mediated by the posterior parietal cortex (PPC). Of particular interest is that PPC activity is differentially sensitive to the object-based properties of the input, with enhanced activation for those locations bound by an attended object. Of great interest too is the ensuing modulation of activation in early cortical regions, reflected as differences in the temporal profile of the blood oxygenation level-dependent (BOLD) response for within-object versus between-object locations. These findings indicate that object-based selection results from an object-sensitive reorienting signal issued by the PPC. The dynamic circuit between the PPC and earlier sensory regions then enables observers to attend preferentially to objects of interest in complex scenes.

Attention↗

PubMed2006

Parietal cortex mediates voluntary control of spatial and nonspatial auditory attention.

The human posterior parietal cortex (PPC) is widely believed to subserve visually guided spatial behavior, including the control of visual attention, eye movements, and reaching. To explore the generality of this function, we measured human brain activity using functional magnetic resonance imaging during spatial and nonspatial shifts of auditory attention. Both spatial and nonspatial shifts of auditory attention evoked transient activity in the medial superior parietal cortex. These results reveal that the PPC is not exclusively devoted to visuospatial behavior; similar regions within a dorsomedial subcompartment provide a domain-independent reconfiguration signal for the control of spatial and nonspatial attention in both visual and nonvisual modalities.

Adult↗

PubMed2005

Coordination of voluntary and stimulus-driven attentional control in human cortex.

Visual attention may be voluntarily directed to particular locations or features (voluntary control), or it may be captured by salient stimuli, such as the abrupt appearance of a new perceptual object (stimulus-driven control). Most often, however, the deployment of attention is the result of a dynamic interplay between voluntary attentional control settings (e.g., based on prior knowledge about a target's location or color) and the degree to which stimuli in the visual scene match these voluntary control settings. Consequently, nontarget items in the scene that share a defining feature with the target of visual search can capture attention, a phenomenon termed contingent attentional capture. We used functional magnetic resonance imaging to show that attentional capture by target-colored distractors is accompanied by increased cortical activity in corresponding regions of retinotopically organized visual cortex. Concurrent activation in the temporoparietal junction and ventral frontal cortex suggests that these regions coordinate voluntary and stimulus-driven attentional control settings to determine which stimuli effectively compete for attention.

Adult↗

PubMed2004

Control of attention shifts between vision and audition in human cortex.

Selective attention contributes to perceptual efficiency by modulating cortical activity according to task demands. Visual attention is controlled by activity in posterior parietal and superior frontal cortices, but little is known about the neural basis of attentional control within and between other sensory modalities. We examined human brain activity during attention shifts between vision and audition. Attention shifts from vision to audition caused increased activity in auditory cortex and decreased activity in visual cortex and vice versa, reflecting the effects of attention on sensory representations. Posterior parietal and superior prefrontal cortices exhibited transient increases in activity that were time locked to the initiation of voluntary attention shifts between vision and audition. These findings reveal that the attentional control functions of posterior parietal and superior prefrontal cortices are not limited to the visual domain but also include the control of crossmodal shifts of attention.

Adult↗

PubMed2004

Parietal cortex and attention.

The parietal lobe forms about 20% of the human cerebral cortex and is divided into two major regions, the somatosensory cortex and the posterior parietal cortex. Posterior parietal cortex, located at the junction of multiple sensory regions, projects to several cortical and subcortical areas and is engaged in a host of cognitive operations. One such operation is selective attention, the process where by the input is filtered and a subset of the information is selected for preferential processing. Recent neuroimaging and neuropsychological studies have provided a more fine-grained understanding of the relationship between brain and behavior in the domain of selective attention.

Attention↗

PubMed2004

Configural and contextual prioritization in object-based attention.

When attention is directed to a location within an object, other locations within that object also enjoy an attentional advantage. Recently we demonstrated that this object-based advantage is mediated by increased attentional priority assigned to locations within an already attended object and not to early sensory enhancement due to the "spread" of attention within the attended object (Shomstein & Yantis, 2002). At least two factors might contribute to the assignment of attentional priority, one related to the configuration of objects in a scene and the other related to the probability of target appearance in each location imposed by task contingencies. We investigated the relative contribution of these factors by cuing one end of one of a pair of rectangles; a subsequent target appeared most often in the cued location. We manipulated attentional priority setting by varying (1) the probability that a target would appear in each of two uncued locations and (2) the cue to target stimulus onset asynchrony (SOA). On invalidly cued trials, the target appeared in the high-probability location (defined by an absolute spatial location, e.g., upper right) 83% of the time and in the low-probability location (e.g., lower left) 17% of the time. In both conditions, uncued targets appeared in the cued object half the time and in the uncued object half the time. At short SOAs, the same-object and probability effects were approximately additive. However, at longer SOAs, the same-object effects disappeared, and reaction times depended exclusively on location probability. These results suggest that observers adopt an implicit configural scanning strategy (in which unattended locations within an attended object have high priority) or an implicit contextual scanning strategy (in which objectively high-probability locations have high priority) depending on task contingencies and the amount of time that is available to deploy attention.

Attention↗

PubMed2002

Object-based attention: sensory modulation or priority setting?

The detection of an invalidly cued target is faster when it appears within a cued object than when it appears in an uncued object equally distant from the cued location; this is a manifestation of object based attention. Five experiments are reported in which it was investigated whether early sensory enhancement (in which attention "spreads" within an attended object but stops at its borders) or a later attentional prioritization mechanism best accounts for these effects. In Experiments 1-4, subjects identified a centrally located target with a buttonpress while attempting to ignore flanking distractors that were mapped to either a compatible or an incompatible response. The flankers appeared either within the object occupied by the target or in a different object but at the same distance from the target. The well-known effect of distance between the target and the flankers on the magnitude of the compatibility effect was replicated. However, whether the target and the flankers were in the same or different objects had no effect on the magnitude of the compatibility effect. In Experiment 5, when attention could not be narrowly focused in advance, object-based modulation of the flanker effect was observed. These results suggest that object-based selection may reflect an object-specific attentional prioritization strategy, rather than object-based attentional modulation of an early sensory representation.

Attention↗