Attention To Spatial Location Research Articles

The Spatiotemporal Link of Temporal Expectations: Contextual Temporal Expectation Is Independent of Spatial Attention.

Temporal expectation is the ability to construct predictions regarding the timing of events, based on previously experienced temporal regularities of different types. For example, cue-based expectations are constructed when a cue validly indicates when a target is expected to occur. However, in the absence of such cues, expectations can be constructed based on contextual temporal information, including the onset distribution of the event and recent prior experiences, both providing implicit probabilistic information regarding the timing of the event. It was previously suggested that cue-based temporal expectation is exerted via synchronization of spatially specific neural activity at a predictable time of a target, within receptive fields corresponding to the expected location of the target. Here, we tested whether the same theoretical model holds for contextual temporal effects. Participants (n = 40, 25 females) performed a speeded spatial-cuing detection task with two-thirds valid spatial cues. The hazard-rate function of the target was modulated by varying the foreperiod-the interval between the spatial cue and the target-among trials and was manipulated between groups by changing the interval distribution. Reaction times were analyzed using both frequentist and Bayesian generalized linear mixed models, accounting for hazard and sequential effects. Results showed that the effects of contextual temporal structures on reaction times were independent of spatial attention. This suggests that the spatiotemporal mechanisms, thought to account for cue-based expectation, cannot explain other sources of temporal expectations. We conclude that expectations based on contextual structures have different characteristics than cue-based temporal expectation, suggesting reliance on distinct neural mechanisms.SIGNIFICANCE STATEMENT Temporal expectation is the ability to predict an event onset based on temporal regularities. A neurophysiological model suggested that temporal expectation relies on the synchronization of spatially specific neurons whose receptive fields represent the attended location. This model predicts that temporal expectation would be evident solely within the locus of spatial attention. Existing evidence supported this model for expectation based on associations between a temporal cue and a target, but here we show that it cannot account for temporal expectation that is based on contextual information, that is, the distribution of intervals and recent priors. These findings reveal the existence of different predictive mechanisms for cued and contextual temporal predictions, with the former depending on spatial attention and the latter nonspatially specific.

Weighted integration of visual position information

The ability to localize visual objects is a fundamental component of human behavior and requires the integration of position information from object components. The retinal eccentricity of a stimulus and the locus of spatial attention can affect object localization, but it is unclear whether these factors alter the global localization of the object, the localization of object components, or both. We used psychophysical methods in humans to quantify behavioral responses in a centroid estimation task. Subjects located the centroid of briefly presented random dot patterns (RDPs). A peripheral cue was used to bias attention toward one side of the display. We found that although subjects were able to localize centroid positions reliably, they typically had a bias toward the fovea and a shift toward the locus of attention. We compared quantitative models that explain these effects either as biased global localization of the RDPs or as anisotropic integration of weighted dot component positions. A model that allowed retinal eccentricity and spatial attention to alter the weights assigned to individual dot positions best explained subjects' performance. These results show that global position perception depends on both the retinal eccentricity of stimulus components and their positions relative to the current locus of attention.

Feature-Specific Attentional Priority Signals in Human Cortex

Human can flexibly attend to a variety of stimulus dimensions, including spatial location and various features such as color and direction of motion. Although the locus of spatial attention has been hypothesized to be represented by priority maps encoded in several dorsal frontal and parietal areas, it is unknown how the brain represents attended features. Here we examined the distribution and organization of neural signals related to deployment of feature-based attention. Subjects viewed a compound stimulus containing two superimposed motion directions (or colors) and were instructed to perform an attention-demanding task on one of the directions (or colors). We found elevated and sustained functional magnetic resonance imaging response for the attention task compared with a neutral condition, without reliable differences in overall response amplitude between attending to different features. However, using multivoxel pattern analysis, we were able to decode the attended feature in both early visual areas (primary visual cortex to human motion complex hMT+) and frontal and parietal areas (e.g., intraparietal sulcus areas IPS1-IPS4 and frontal eye fields) that are commonly associated with spatial attention. Furthermore, analysis of the classifier weight maps showed that attending to motion and color evoked different patterns of activity, suggesting that different neuronal subpopulations in these regions are recruited for attending to different feature dimensions. Thus, our finding suggests that, rather than a purely spatial representation of priority, frontal and parietal cortical areas also contain multiplexed signals related to the priority of different nonspatial features.

The instructed context of a motor task modulates covert response preparation and shifts of spatial attention

We investigated how covert response preparation is modulated by the instructed cognitive context of a motor task. Participants prepared left-hand or right-hand movements toward or away from the body midline, as indicated by a response cue (S1) presented prior to a go/no-go stimulus (S2). Different participants were instructed that response cues specified the response hand or movement direction, respectively. This emphasis on effector versus movement direction selection modulated lateralized ERP components triggered during the S1-S2 interval. Attention shifts during movement preparation were assessed by measuring ERPs to irrelevant visual probes. Enhanced N1 components were found for probes near the effector when effector selection was emphasized, but for probes near the movement target location when movement direction selection was emphasized. Results demonstrate strong top-down contextual biases on motor control and on the locus of spatial attention during response preparation.

The locus of spatial attention during the temporal integration of visual memories and visual percepts.

Temporal integration is a process by which two serially presented visual stimuli are mentally integrated to form a composite representation. In the present research, we explored how spatial selective attention is used during the delay separating stimuli, in order to determine the contents of spatial working memory in this task. A two-task situation was created. On the primary task, two dot arrays were serially presented within a grid, leaving one space empty, which subjects identified. On the secondary task, instead of the second array, a discrimination probe was presented. Integration accuracy increased through delays of 1,500 msec, revealing an estimate of the time required to form an optimal memory trace for integration. Once the memory trace was formed (but not before), response time to the probe was faster if it was presented in a location previously occupied by a dot from Array 1. This indicates that during the delay separating the arrays, the subjects assigned spatial attention to the locations occupied by the first array and actively maintained the leading array in working memory. Implications for theories of visual processing and memory are discussed.

The role of spatial attention in visual word processing.

Subjects made lexical decisions on a target letter string presented above or below fixation. In Experiments 1 and 2, target location was cued 100 ms in advance of target onset. Responses were faster on validly than on invalidly cued trials. In Experiment 3, the target was sometimes accompanied by irrelevant stimuli on the other side of fixation; in such cases, responses were slowed (a spatial filtering effect). Both cuing and filtering effects on response time were additive with effects of word frequency and lexical status (words vs. nonwords). These findings are difficult to reconcile with claims that spatial attention is less involved in processing familiar words than in unfamiliar words and nonwords. The results can be reconciled with a late-selection locus of spatial attention only with difficulty, but are easily explained by early-selection models.

Spatial attention in vision. Evidence for early selection.

Human observers can selectively allocate processing resources to different areas of the visual field within a single fixation. This spatial attention system may affect either the quality of information extraction or the decisions and responses based on this information. This paper reviews evidence from behavioral, single-unit, and event-related potential paradigms; the evidence suggests a relatively “early” locus of spatial attention.