Biomedical subjects

Shaun P Vecera

Publications and source records attributed to Shaun P Vecera.

13 recordsLinked to original sources

PubMed2006

Eye gaze does not produce reflexive shifts of attention: evidence from frontal-lobe damage.

Humans are able to predict the behavior of others using visual information. Several studies have argued that social cues, such as eye gaze direction, can influence the allocation of visual attention in a reflexive manner. We have previously shown that a patient with frontal-lobe damage, patient EVR, can use peripheral cues to direct attention but cannot use either word cues or gaze cues to allocate attention. These findings suggest that 'social attention' may involve frontal-lobe processes that control voluntary, not automatic, shifts of visuospatial attention. In the current paper, we further examine 'social attention' in EVR and demonstrate that his failure to orient attention voluntarily cannot be attributed to either cue predictability or a 'sluggish' attentional system. EVR exhibits a general impairment in orienting attention endogenously, and this impairment includes orienting from gaze cues. Gaze cues direct attention in a voluntary, not a reflexive, manner.

Aged↗

PubMed2006

Figure-ground assignment in pigeons: evidence for a figural benefit.

Four pigeons discriminated whether a target spot appeared on a colored figural shape or on a differently colored background by first pecking the target and then reporting its location: on the figure or the background. We recorded three dependent variables: target detection time, choice response time, and choice accuracy. The birds were faster to detect the target, to report its location, and to learn the correct response on figure trials than on background trials. Later tests suggested that the pigeons might have attended to the figural region as a whole rather than using local properties in performing the figure-background discrimination. The location of the figural region did not affect figure-ground assignment. Finally, when 4 other pigeons had to detect and peck the target without making a choice report, no figural advantage emerged in target detection time, suggesting that the birds' attention may not have been automatically summoned to the figural region.

Animals↗

PubMed2006

Grounding the figure: surface attachment influences figure-ground organization.

We investigated whether the lower region effect on figure-ground organization (Vecera, Vogel, and Woodman, 2002) would generalize to contextual depth planes in vertical orientations, as is predicted by a theoretical analysis based on the ecological statistics of edges arising from objects that are attached to surfaces of support. Observers viewed left/right ambiguous figure-ground displays that occluded middle sections of four types of contextual inducers: two types of attached, receding, vertical planes (walls) that used linear perspective and/or texture gradients to induce perceived depth and two types of similar trapezoidal control figures that used either uniform color or random texture to reduce or eliminate perceived depth. The results showed a reliable bias toward seeing as "figure" the side of the figure-ground display that was attached to the receding depth plane, but no such bias for the corresponding side in either of the control conditions. The results are interpreted as being consistent with the attachment hypothesis that the lower region cue to figure-ground organization results from ecological biases in edge interpretation that arise when objects are attached to supporting surfaces in the terrestrial gravitational field.

Color Perception↗

PubMed2005

Object discrimination in pigeons: effects of local and global cues.

We trained two pigeons to report whether a pair of differently colored 2-D objects had two target dots on either one or both of the objects. Follow-up tests disclosed that the colored regions surrounding the task-relevant targets were necessary, but not sufficient to support the birds' discrimination. Moreover, when local and global color cues provided contradictory information, pigeons failed to discriminate the stimuli, suggesting that the birds attended to both local and global information. Finally, one bird learned the object discrimination in the absence of differential color cues suggesting that, with suitable training, pigeon can attend to entire objects.

Animals↗

PubMed2005

Object discrimination by pigeons: effects of object color and shape.

Can nonhuman animals attend to visual stimuli as whole, coherent objects? We investigated this question by adapting for use with pigeons a task in which human participants must report whether two visual attributes belong to the same object (one-object trial) or to different objects (two-object trial). We trained pigeons to discriminate a pair of differently colored shapes that had two targets either on a single object or on two different objects. Each target equally often appeared on the one-object and two-object stimuli; therefore, a specific target location could not serve as a discriminative cue. The pigeons learned to report whether the two target dots were located on a single object or on two different objects; follow-up tests demonstrated that this ability was not entirely based on memorization of the dot patterns and locations. Additional tests disclosed predominate stimulus control by the color, but not by the shape of the two objects. These findings suggest that human psychophysical methods are readily applicable to the study of object discrimination by nonhuman animals.

Animals↗

PubMed2005

Attentional control parameters following parietal-lobe damage: evidence from normal subjects.

Attentional control involves the factors, or cognitive parameters, that determine which environmental inputs receive attention and which do not. Cognitive studies of attentional control have highlighted two general classes of control parameters, bottom-up (data driven or exogenous) parameters and top-down (goal driven or endogenous) parameters. Which of these control parameters is affected following parietal-lobe damage? In parietal-damaged patients, it is possible that a disorder in one control parameter (e.g. goal driven) would appear as a disorder in another parameter (e.g. data driven). To investigate the control parameters that might be affected in parietal patients, we simulated neglect in normal participants by disrupting data-driven information processing. When half of a computer monitor was degraded by translucent tracing paper while normal participants performed a cued spatial attention task (Experiment 1), the normal participants showed a pattern of results similar to patients with unilateral parietal-lobe damage--the so-called "disengage deficit." This pattern of results replicated when neutral attentional cues were included in the experiment (Experiment 2). However, the disengage deficit was not simulated in normal participants with predictive central symbolic cues (Experiment 3) or predictive peripheral cues (Experiment 4). Because perceptual degradation influences data-driven attentional control parameters, we suggest that these control parameters may be disrupted following parietal-lobe damage.

Adolescent↗

PubMed2005

Visual cognition influences early vision: the role of visual short-term memory in amodal completion.

A partly occluded visual object is perceptually filled in behind the occluding surface, a process known as amodal completion or visual interpolation. Previous research focused on the image-based properties that lead to amodal completion. In the present experiments, we examined the role of a higher-level visual process-visual short-term memory (VSTM)-in amodal completion. We measured the degree of amodal completion by asking participants to perform an object-based attention task on occluded objects while maintaining either zero or four items in visual working memory. When no items were stored in VSTM, participants completed the occluded objects; when four items were stored in VSTM, amodal completion was halted (Experiment 1). These results were not caused by the influence of VSTM on object-based attention per se (Experiment 2) or by the specific location of to-be-remembered items (Experiment 3). Items held in VSTM interfere with amodal completion, which suggests that amodal completion may not be an informationally encapsulated process, but rather can be affected by high-level visual processes.

Attention↗

PubMed2004

What are you looking at? Impaired 'social attention' following frontal-lobe damage.

Humans are able to predict the behavior of others. Several studies have investigated this capability by determining if social cues, such as eye gaze direction, can influence the allocation of visual attention. When a viewer sees a face looking to the left, the viewer's attention is allocated in the gazed-at direction. These 'social attention' studies have asked if this allocation of attention is automatic or under voluntary control. In this paper, we show that a patient with frontal-lobe damage is impaired at allocating attention to peripheral locations voluntarily, although attention can be allocated there automatically. The patient, EVR, can use peripheral cues to selectively process one location over another but cannot use symbolic cues (words) to allocate attention. EVR is also impaired in using eye gaze cues to allocate attention, suggesting that 'social attention' may involve frontal-lobe processes that control voluntary, not automatic, shifts of visuospatial attention.

Adult↗

PubMed2004

Exogenous spatial attention influences figure-ground assignment.

In a hierarchical stage account of vision, figure-ground assignment is thought to be completed before the operation of focal spatial attention. Results of previous studies have supported this account by showing that unpredictive, exogenous spatial precues do not influence figure-ground assignment, although voluntary attention can influence figure-ground assignment. However, in these studies, attention was not summoned directly to a region in a figure-ground display. In three experiments, we addressed the relationship between figure-ground assignment and visuospatial attention. In Experiment 1, we replicated the finding that exogenous precues do not influence figure-ground assignment when they direct attention outside of a figure-ground stimulus. In Experiment 2, we demonstrated that exogenous attention can influence figure-ground assignment if it is directed to one of the regions in a figure-ground stimulus. In Experiment 3, we demonstrated that exogenous attention can influence figure-ground assignment in displays that contain a Gestalt figure-ground cue; this result suggests that figure-ground processes are not entirely completed prior to the operation of focal spatial attention. Exogenous spatial attention acts as a cue for figure-ground assignment and can affect the outcome of figure-ground processes.

Attention↗

PubMed2004

The reference frame of figure-ground assignment.

Figure-ground assignment involves determining which visual regions are foreground figures and which are backgrounds. Although figure-ground processes provide important inputs to high-level vision, little is known about the reference frame in which the figure's features and parts are defined. Computational approaches have suggested a retinally based, viewer-centered reference frame for figure-ground assignment, but figural assignment could also be computed on the basis of environmental regularities in an environmental reference frame. The present research used a newly discovered cue, lower region, to examine the reference frame of figure-ground assignment. Possible reference frames were misaligned by changing the orientation of viewers by having them tilt their heads (Experiments 1 and 2) or turn them upside down (Experiment 3). The results of these experiments indicated that figure-ground perception followed the orientation of the viewer, suggesting a viewer-centered reference frame for figure-ground assignment.

Environment↗

PubMed2003

Spatial attention: normal processes and their breakdown.

Although "attention" is a general term in everyday folk and psychologic use, using research from cognitive psychology allows a focus on the processes associated with attention. A process-oriented definition of attention [2] makes "attention" a concept that can be studied rigorously. Attention is necessary for eliminating unwanted sensory inputs or irrelevant behavioral tasks and is useful when some cognitive system or process receives too many inputs. Attention acts to restrict the number of inputs and allow processing to continue in an effective manner. Although there are many forms of attentional selection, spatial attention is the most studied and perhaps the best understood form of selection. Spatial attention is the variety of attention most widely studied in neuropsychologic populations. As was evident from the authors' review, different neuropsychologic syndromes can be characterized as involving different difficulties with the component processes of spatial attention. Different neural structures work in concert to produce normal spatial selection, and damage to any of these neural structures, including the parietal and frontal lobes, pulvinar, and superior colliculus, produce an attentional impairment. Attentional impairments often have been studied in cases of focal brain damage resulting from stroke, traumatic brain injury, tumor, and surgical resection. Focal or multifocal lesions caused by neurodegenerative impairments, such as PSP and AD, however, also have marked effects on neural processes of attention. Patients with AD exhibit a range of impairments in spatial attention, and these impairments have been studied relatively little. Despite the understanding of attention provided by various patient populations, gaps remain in knowledge of the mechanisms involved in attending to space. For example, most studies of neurologic patients have used a simple spatial cuing paradigm with highly predictive cues. Although this task yields robust results and can be adapted for use with many different patient groups, the spatial cuing effects produced by such tasks have multiple interpretations (e.g., allocation of resources versus reduction of decision noise). This review highlights the general point that different neural sites seem to be responsible for different forms of attentional control, such as object-based attention, attentional task switching, and the executive control of attention [8.33]. Understanding the integration of these neural sites and their relationship to cognitive processes and, ultimately, behavior, will increase understanding of normal and disordered attentional selection.

Alzheimer Disease↗

PubMed2003

Perceptual organization influences visual working memory.

Previous studies have demonstrated that top-down factors can bias the storage of information in visual working memory. However, relatively little is known about the role that bottom-up stimulus characteristics play in visual working memory storage. In the present study, subjects performed a change detection task in which the to-be-remembered objects were organized in accordance with Gestalt grouping principles. When an attention-capturing cue was presented at the location of one object, other objects that were perceptually grouped with the cued object were more likely to be stored in working memory than were objects that were not grouped with the cued object. Thus, objects that are grouped together tend to be stored together, indicating that bottom-up perceptual organization influences the storage of information in visual working memory.

Adult↗

PubMed2002

Lower region: a new cue for figure-ground assignment.

Figure-ground assignment is an important visual process; humans recognize, attend to, and act on figures, not backgrounds. There are many visual cues for figure-ground assignment. A new cue to figure-ground assignment, called lower region, is presented: Regions in the lower portion of a stimulus array appear more figurelike than regions in the upper portion of the display. This phenomenon was explored, and it was demonstrated that the lower-region preference is not influenced by contrast, eye movements, or voluntary spatial attention. It was found that the lower region is defined relative to the stimulus display, linking the lower-region preference to pictorial depth perception cues. The results are discussed in terms of the environmental regularities that this new figure-ground cue may reflect.

Cognition↗