Khena M. Swallow

Reading Stories Activates Neural Representations of Visual and Motor Experiences

To understand and remember stories, readers integrate their knowledge of the world with information in the text. Here we present functional neuroimaging evidence that neural systems track changes in the situation described by a story. Different brain regions track different aspects of a story, such as a characters physical location or current goals. Some of these regions mirror those involved when people perform, imagine, or observe similar real-world activities. These results support the view that readers understand a story by simulating the events in the story world and updating their simulation when features of that world change.

The Attentional Boost Effect: Transient increases in attention to one task enhance performance in a second task

Recent work on event perception suggests that perceptual processing increases when events change. An important question is how such changes influence the way other information is processed, particularly during dual-task performance. In this study, participants monitored a long series of distractor items for an occasional target as they simultaneously encoded unrelated background scenes. The appearance of an occasional target could have two opposite effects on the secondary task: It could draw attention away from the second task, or, as a change in the ongoing event, it could improve secondary task performance. Results were consistent with the second possibility. Memory for scenes presented simultaneously with the targets was better than memory for scenes that preceded or followed the targets. This effect was observed when the primary detection task involved visual feature oddball detection, auditory oddball detection, and visual color-shape conjunction detection. It was eliminated when the detection task was omitted, and when it required an arbitrary response mapping. The appearance of occasional, task-relevant events appears to trigger a temporal orienting response that facilitates processing of concurrently attended information (Attentional Boost Effect).

Activation of human motion processing areas during event perception

Observers are able to segment continuous everyday activity into meaningful parts. This ability may be related to processing low-level visual cues, such as changes in motion. To address this issue, the present study combined measurement of evoked responses to event boundaries with functional identification of the extrastriate motion complex (MT+) and the frontal eye field (FEF), two regions related to motion perception and eye movements. The results provided strong evidence that MT+ is activated by event boundaries: Individuals’ MT+ regions showed strong responses to event boundaries, and MT+ was collocated with a lateral posterior region that responded at event boundaries. The evidence regarding the FEF was less conclusive: The FEF showed reliable but relatively reduced responses to event boundaries, but the FEF was medial and superior to a frontal area that responded at event boundaries. These results suggest that motion cues, and possibly eye movements, may play key roles in event structure perception.

Rapid acquisition but slow extinction of an attentional bias in space.

Substantial research has focused on the allocation of spatial attention based on goals or perceptual salience. In everyday life, however, people also direct attention using their previous experience. Here we investigate the pace at which people incidentally learn to prioritize specific locations. Participants searched for a T among Ls in a visual search task. Unbeknownst to them, the target was more often located in one region of the screen than in other regions. An attentional bias toward the rich region developed over dozens of trials. However, the bias did not rapidly readjust to new contexts. It persisted for at least a week and for hundreds of trials after the targets position became evenly distributed. The persistence of the bias did not reflect a long window over which visual statistics were calculated. Long-term persistence differentiates incidentally learned attentional biases from the more flexible goal-driven attention.

Reliability of functional localization using fMRI

Neuroimaging researchers increasingly take advantage of the known functional properties of brain regions to localize them and probe changes in their activity under different conditions. The utility of this approach depends in part on the reliability of the methods used to define these regions of interest. Two operations may affect the reliability of functionally identified regions: spatially normalizing data to a stereotactic atlas and statistically combining data across participants to form a composite region (as opposed to identifying individual regions for each participant). The effect of these two operations on reliability was evaluated for two functionally identifiable regions: the MT complex and the frontal eye fields. Spatial normalization had almost no effect on within-subject reliability, while grouping across participants negatively affected retest measures of the activation and location of regions defined on separate occasions. We conclude that, for typical sample sizes and numbers of observations per subject, functional localization is most reliable when performed for each individual using data in atlas space.

Guidance of spatial attention by incidental learning and endogenous cuing.

Our visual system is highly sensitive to regularities in the environment. Locations that were important in ones previous experience are often prioritized during search, even though observers may not be aware of the learning. In this study we characterized the guidance of spatial attention by incidental learning of a targets spatial probability, and examined the interaction between endogenous cuing and probability cuing. Participants searched for a target (T) among distractors (Ls). The target was more often located in one region of the screen than in others. We found that search reaction time (RT) was faster when the target appeared in the high-frequency region rather than the low-frequency regions. This difference increased when there were more items on the display, suggesting that probability cuing guides spatial attention. Additional data indicated that on their own, probability cuing and endogenous cuing (e.g., a central arrow that predicted a targets location) were similarly effective at guiding attention. However, when both cues were presented at once, probability cuing was largely eliminated. Thus, although both incidental learning and endogenous cuing can effectively guide attention, endogenous cuing takes precedence over incidental learning.

Changes in events alter how people remember recent information

Observers spontaneously segment larger activities into smaller events. For example, “washing a car” might be segmented into “scrubbing,” “rinsing,” and “drying” the car. This process, called event segmentation, separates “what is happening now” from “what just happened.” In this study, we show that event segmentation predicts activity in the hippocampus when people access recent information. Participants watched narrative film and occasionally attempted to retrieve from memory objects that recently appeared in the film. The delay between object presentation and test was always 5 sec. Critically, for some of the objects, the event changed during the delay whereas for others the event continued. Using fMRI, we examined whether retrieval-related brain activity differed when the event changed during the delay. Brain regions involved in remembering past experiences over long periods, including the hippocampus, were more active during retrieval when the event changed during the delay. Thus, the way an object encountered just 5 sec ago is retrieved from memory appears to depend in part on what happened in those 5 sec. These data strongly suggest that the segmentation of ongoing activity into events is a control process that regulates when memory for events is updated.

Attentional Load and Attentional Boost: A Review of Data and Theory

Both perceptual and cognitive processes are limited in capacity. As a result, attention is selective, prioritizing items and tasks that are important for adaptive behavior. However, a number of recent behavioral and neuroimaging studies suggest that, at least under some circumstances, increasing attention to one task can enhance performance in a second task (e.g., the attentional boost effect). Here we review these findings and suggest a new theoretical framework, the dual-task interaction model, that integrates these findings with current views of attentional selection. To reconcile the attentional boost effect with the effects of attentional load, we suggest that temporal selection results in a temporally specific enhancement across modalities, tasks, and spatial locations. Moreover, the effects of temporal selection may be best observed when the attentional system is optimally tuned to the temporal dynamics of incoming stimuli. Several avenues of research motivated by the dual-task interaction model are then discussed.

Sequences learned without awareness can orient attention during the perception of human activity

Human activity contains sequential dependencies that observers may use to structure a task environment (e.g., the ordering of steps when tying shoes or getting into a car). Two experiments investigated how people take advantage of sequential structure to understand activity and respond to behaviorally relevant events. Participants monitored animations of simplified human movement to identify target hand gestures. In the first experiment, participants were able to use predictive sequential dependencies to more quickly identify targets. In addition, performance was best at the point in time that followed the sequence. However, the second experiment revealed that how sequential structure affects detection depends on whether the sequence predicts the timing of target events. In all cases, sequence learning was observed without participants’ awareness of the sequential dependencies. These results suggest that human activity sequences can be learned without awareness and can be used to adaptively guide behavior.

Visual search and location probability learning from variable perspectives

Do moving observers code attended locations relative to the external world or relative to themselves? To address this question we asked participants to conduct visual search on a tabletop. The search target was more likely to occur in some locations than others. Participants walked to different sides of the table from trial to trial, changing their perspective. The high-probability locations were stable on the tabletop but variable relative to the viewer. When participants were informed of the high-probability locations, search was faster when the target was in those locations, demonstrating probability cuing. However, in the absence of explicit instructions and awareness, participants failed to acquire an attentional bias toward the high-probability locations even when the search items were displayed over an invariant natural scene. Additional experiments showed that locomotion did not interfere with incidental learning, but the lack of a consistent perspective prevented participants from acquiring probability cuing incidentally. We conclude that spatial biases toward target-rich locations are directed by two mechanisms: incidental learning and goal-driven attention. Incidental learning codes attended locations in a viewer-centered reference frame and is not updated with viewer movement. Goal-driven attention can be deployed to prioritize an environment-rich region.