Common-fate grouping as feature selection.

The visual system groups elements within the visual field that are physically separated yet similar to each other. Although grouping processes have been intensely studied for a century, the mechanisms of grouping remain elusive. We propose that a primary mechanism for grouping by common fate is attentional selection of a direction of motion. A unique prediction follows from this account: that the visual system must be limited to forming only a single common-fate group at a time, and that attempts to find a particular common-fate group among other groups, or among nongroups, should therefore be highly inefficient. We show that this is true in searches for vertically oriented groups of moving dots among horizontally oriented groups (Experiment 1) and in searches for motion-linked groups among nonlinked objects (Experiment 2). Feature selection may limit the visual system to the construction of only one common-fate group at a time, and thus the experience of simultaneous grouping may be an illusion.

Past rejections lead to future misses: selection-related inhibition produces blink-like misses of future (easily detectable) events.

Our recent experiences can have substantial effects on our future behavior. Here we show influences of prior visual experiences on the future workings of selective attention. Selective attention uses inhibitory processes to suppress distracting information on a given trial. We show that, once in place, this selective inhibition persists across trials and leads to misses of future targets when they belong to the previously distracting category of stimuli. This effect is documented using a single-target RSVP task, in which participants are asked to report the case (or color) of an oddball target. Furthermore, we show that selective inhibition is not present when observers are merely asked to detect the presence or absence of the oddball target. We argue that selective inhibition is a mechanism aimed at facilitating the access to secondary (non-target defining) features of the target stimuli, and that our results provide further evidence that visual stimuli are processed in a hierarchical, non-holistic manner.

Cognition and health literacy in patients with hypertension.

BACKGROUND: Approximately half of the US population has marginal or inadequate health literacy, a measure highly associated with health outcomes. This measure is often linked to age and education, but recent evidence from patients with chronic heart failure suggests that much of age-related variability in health literacy can be explained by cognitive abilities (e.g., working memory, processing speed). OBJECTIVE: We examined the role of cognitive and sensory abilities as mediators of age and education in determining functional health literacy among patients with hypertension. PARTICIPANTS: Four hundred ninety two community-dwelling adults diagnosed with hypertension (aged 21 to 92 years) participated. They were primarily female (73%), African-American (68%), and reported taking on average 7.8 prescribed medications. MEASUREMENTS: Before participation in a medication adherence intervention study, participants completed a battery of health literacy-related tasks. They completed tests that measured health literacy [Short Test of Functional Health Literacy in Adults (STOFHLA)], cognitive abilities (working memory, processing speed), sensory abilities (visual acuity and hearing), and physical health. RESULTS: Regression analyses showed that health literacy was related to age, education, and race (accounting for 24.4% of variance in STOFHLA scores). Cognitive ability accounted for an additional 24% of variance and greatly reduced the influence of age, education, and race (by 75%, 40%, and 48%, respectively). CONCLUSIONS: When controlling for cognitive and sensory variables, the association of age and education with STOFHLA scores was dramatically reduced. Thus, future interventions aimed at improving self-care for patients with low health literacy should aim to reduce demands on patients' cognitive abilities.

Inter-trial inhibition of attention to features is modulated by task relevance.

The Distractor Previewing Effect (DPE) is an inter-trial effect that arises in efficient visual searches where participants are asked to find a feature oddball in the display. Specifically, the DPE is the finding that an observer's ability to focus on an oddball target is impaired if, on the immediately preceding trial, no target was present and all distractors shared a visual feature with the current target (e.g., all objects were red on trial N, and the target was a red oddball on trial N + 1). Though recent evidence suggests that the DPE emerges from an attentional bias against focusing on a recently examined feature common to all stimuli in a target-absent trial, it is unclear whether this inhibition is formed for all features in target-absent trials, or is instead limited to the search-relevant feature. In two experiments we manipulated task instructions while keeping displays identical, alternating which feature (shape or color) was relevant for the search task and which was not. Our results showed that attentional inhibition is applied only to the search-relevant feature. Additionally we found that although search-irrelevant features affect search times, these effects are independent of any relationship to the previous trial.

Fruitful visual search: inhibition of return in a virtual foraging task.

Inhibition of return (IOR) has long been viewed as a foraging facilitator in visual search. We investigated the contribution of IOR in a task that approximates natural foraging more closely than typical visual search tasks. Participants in a fully immersive virtual reality environment manually searched an array of leaves for a hidden piece of fruit, using a wand to select and examine each leaf location. Search was slower than in typical IOR paradigms, taking seconds instead of a few hundred milliseconds. Participants also made a speeded response when they detected a flashing leaf that either was or was not in a previously searched location. Responses were slower when the flashing leaf was in a previously searched location than when it was in an unvisited location. These results generalize IOR to an approximation of a naturalistic visual search setting and support the hypothesis that IOR can facilitate foraging. The experiment also constitutes the first use of a fully immersive virtual reality display in the study of IOR.

Spatial updating relies on an egocentric representation of space: effects of the number of objects.

Models of spatial updating attempt to explain how representations of spatial relationships between the actor and objects in the environment change as the actor moves. In allocentric models, object locations are encoded in an external reference frame, and only the actor's position and orientation in that reference frame need to be updated. Thus, spatial updating should be independent of the number of objects in the environment (set size). In egocentric updating models, object locations are encoded relative to the actor, so the location of each object relative to the actor must be updated as the actor moves. Thus, spatial updating efficiency should depend on set size. We examined which model better accounts for human spatial updating by having people reconstruct the locations of varying numbers of virtual objects either from the original study position or from a changed viewing position. In consistency with the egocentric updating model, object localization following a viewpoint change was affected by the number of objects in the environment.

Rotation rate and duration effects on the somatogyral illusion.

INTRODUCTION: Aviation spatial disorientation mishaps remain a concern, especially due to their fatality rate. Some of the most insidious disorientations are due to vestibular stimuli in the absence of visual cues. A category of such disorientations are known as somatogyral illusions. METHODS: To determine the effects of spin rate and duration on the perception of the somatogyral illusion, we examined the subjective response of pilots and non-pilots to rotation around the yaw axis in a flight simulator in a manner that would mimic two vestibular illusions found in flight: the washout of the semi-circular canals following sustained turns, and the illusory counter-rotation following return to straight and level flight. There were 29 subjects (14 pilots) who were seated blindfolded in a flight simulator which accelerated to constant plateau rotation rates of 20, 70, and 120 degrees x s(-1) and then decelerated to stationary; plateaus were 10, 20, or 40 s. Subjects reported 1) the time when the perception of rotation ceased (i.e., the subjective time until washout was reached); 2) the relative magnitude of the counter-rotation experienced; and 3) the time until the perception of counter-rotation ceased. Subjects also manipulated a slider to provide a continuous subjective measure of their experience of rotation. RESULTS: The two time measures increased with increases in both the duration and magnitude of the spin. The increase in perceived washout time with spin rate was non-linear (geometric). There was an interaction between spin duration and spin rate on the experience of illusory counter-rotation magnitude such that at low rates, spin duration had no effect, but its effect increased at faster rates. The time constant of adaptation of the semicircular canals was estimated to be 8.3 s. DISCUSSION: The effects were validated against a model of semicircular canal and cupola adaptation, which predicted the data with high accuracy. Pilots and non-pilots did not differ in their illusory experience.

Average orientation is more accessible through object boundaries than surface features.

In a glance, the visual system can provide a summary of some kinds of information about objects in a scene. We explore how summary information about orientation is extracted and find that some representations of orientation are privileged over others. Participants judged the average orientation of either a set of 6 bars or 6 circular gratings. For bars, orientation information was carried by object boundary features, while for gratings, orientation was carried by internal surface features. The results showed more accurate averaging performance for bars than for gratings, even when controlling for potential differences in encoding precision for solitary objects. We suggest that, during orientation averaging, the visual system prioritizes object boundaries over surface features. This privilege for boundary features may lead to a better representation of the spatial layout of a scene.

The effects of ageing and visual noise on conceptual integration during sentence reading.

The effortfulness hypothesis implies that difficulty in decoding the surface form, as in the case of age-related sensory limitations or background noise, consumes the attentional resources that are then unavailable for semantic integration in language comprehension. Because ageing is associated with sensory declines, degrading of the surface form by a noisy background can pose an extra challenge for older adults. In two experiments, this hypothesis was tested in a self-paced moving window paradigm in which younger and older readers' online allocation of attentional resources to surface decoding and semantic integration was measured as they read sentences embedded in varying levels of visual noise. When visual noise was moderate (Experiment 1), resource allocation among young adults was unaffected but older adults allocated more resources to decode the surface form at the cost of resources that would otherwise be available for semantic processing; when visual noise was relatively intense (Experiment 2), both younger and older participants allocated more attention to the surface form and less attention to semantic processing. The decrease in attentional allocation to semantic integration resulted in reduced recall of core ideas in both experiments, suggesting that a less organized semantic representation was constructed in noise. The greater vulnerability of older adults at relatively low levels of noise is consistent with the effortfulness hypothesis.

Complex attentional control settings.

The visual system prioritizes information through a variety of mechanisms, including "attentional control settings" that specify features (e.g., colour) that are relevant to current goals. Recent work shows that these control settings may be more complex than previously thought, such that participants can monitor for independent features at different locations (Adamo, Pun, Pratt, & Ferber, 2008). However, this result leaves unclear whether these control settings affect early attentional selection or later target processing. We dissociated between these possibilities in two ways. In Experiment 1, participants were asked to determine whether a target object, which was preceded by an uninformative cue, matched one of two target templates (e.g., a blue vertical object or a green horizontal object). Participants monitored for independent features in the same location, but in different objects, which should reduce the effectiveness of the control setting if it is due to early attentional selection, but not if it is due to later target processing. In Experiment 2, we removed the ability of the cue to prime the target identity, which makes the opposite prediction. Together, the results suggest that complex attentional control settings primarily affect later target identity processing, and not early attentional selection.

The remains of the trial: goal-determined inter-trial suppression of selective attention.

When an observer is searching through the environment for a target, what are the consequences of not finding a target in a given environment? We examine this issue in detail and propose that the visual system systematically tags environmental information during a search, in an effort to improve performance in future search events. Information that led to search successes is positively tagged, so as to favor future deployments of attention toward that type of information, whereas information that led to search failures is negatively tagged, so as to discourage future deployments of attention toward such failed information. To study this, we use an oddball-search task, where participants search for one item that differs from all others along one feature or belongs to a different visual category, from the other stimuli in the display. We find that when participants perform oddball-search tasks, the absence of a target delays identification of future targets containing the feature or category that was shared by all distractors in the target-absent trial. We interpret this effect as reflecting an implicit assessment of performance: target-absent trials can be viewed as processing "failures" insofar as they do not provide the visual system with the information needed to complete the task. Here, we study the goal-oriented nature of this bias in three ways. First, we show that the direction of the bias is determined by the experimental task. Second, we show that the effect is independent of the mode of presentation of stimuli: it happens with both serial and simultaneous stimuli presentation. Third, we show that, when using categorically defined oddballs as the search stimuli (find the face among houses or vice versa), the bias generalizes to unseen members of the "failed" category. Together, these findings support the idea that this inter-trial attentional biases arise from high-level, task-constrained, implicit assessments of performance, involving categorical associations between classes of stimuli and behavioral outcomes (success/failure), which are independent of attentional modality (temporal vs. spatial attention).