Multiple object tracking and attentional processing.

Used the multiple object tracking methodology of Z. W. Pylyshyn and R. W. Storm (see record 1989-35304-001) to investigate the relation between "visual indexing" and attentional processing. 17 participants visually tracked a subset of a set of identical, independently randomly moving objects in a display (the targets), and made a speeded identification response when they noticed a target or a nontarget (distractor) object undergo a subtle form transformation. The authors found that target form changes were identified more rapidly than nontarget form changes, and that the speed of responding to target form changes was unaffected by the number of nontargets in the display when the form-changing targets were successfully tracked. They also found that this enhanced processing only applied to the targets themselves and not to nearby nontarget distractors, showing that the allocation of a broadened region of visual attention could not account for these findings. These results confirm that visual indexing bestows a processing priority to a number of objects in the visual field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional MRI reveals spatially specific attentional modulation in human primary visual cortex

Selective visual attention can strongly influence perceptual processing, even for apparently low-level visual stimuli. Although it is largely accepted that attention modulates neural activity in extrastriate visual cortex, the extent to which attention operates in the first cortical stage, striate visual cortex (area V1), remains controversial. Here, functional MRI was used at high field strength (3 T) to study humans during attentionally demanding visual discriminations. Similar, robust attentional modulations were observed in both striate and extrastriate cortical areas. Functional mapping of cortical retinotopy demonstrates that attentional modulations were spatially specific, enhancing responses to attended stimuli and suppressing responses when attention was directed elsewhere. The spatial pattern of modulation reveals a complex attentional window that is consistent with object-based attention but is inconsistent with a simple attentional spotlight. These data suggest that neural processing in V1 is not governed simply by sensory stimulation, but, like extrastriate regions, V1 can be strongly and specifically influenced by attention.     

Callosal involvement in a lateralized stroop task in alcoholic and healthy subjects.

To investigate the role of interhemispheric attentional processes, 25 alcoholic and 28 control subjects were tested with a Stroop match-to-sample task and callosal areas were measured with magnetic resonance imaging. Stroop color-word stimuli were presented to the left or right visual field (VF) and were preceded by a color cue that did or did not match the word's color. For matching colors, both groups showed a right VF advantage; for nonmatching colors, controls showed a left VF advantage, whereas alcoholic subjects showed no VF advantage. For nonmatch trials, VF advantage correlated with callosal splenium area in controls but not alcoholic subjects, supporting the position that information presented to the nonpreferred hemisphere is transmitted via the splenium to the hemisphere specialized for efficient processing. The authors speculate that alcoholism-associated callosal thinning disrupts this processing route. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Saccade target selection and object recognition: evidence for a common attentional mechanism

The spatial interaction of visual attention and saccadic eye movements was investigated in a dual-task paradigm that required a target-directed saccade in combination with a letter discrimination task. Subjects had to saccade to locations within horizontal letter strings left and right of a central fixation cross. The performance in discriminating between the symbols "E" and "E", presented tachistoscopically before the saccade within the surrounding distractors was taken as a measure of visual attention. The data show that visual discrimination is best when discrimination stimulus and saccade target refer to the same object; discrimination at neighboring items is close to chance level. Also, it is not possible, in spite of prior knowledge of discrimination target position, to direct attention to the discrimination target while saccading to a spatially close saccade target. The data strongly argue for an obligatory and selective coupling of saccade programming and visual attention to one common target object. The results favor a model in which a single attentional mechanism selects objects for perceptual processing and recognition, and also provides the information necessary for motor action.     

Visual word recognition: Reattending to the role of spatial attention.

Three experiments examine whether spatial attention and visual word recognition processes operate independently or interactively in a spatially cued lexical-decision task. Participants responded to target strings that had been preceded first by a prime word at fixation and then by an abrupt onset cue either above or below fixation. Targets appeared either in the cued (i.e., valid) or uncued (i.e., invalid) location. The proportion of validly cued trials and the proportion of semantically related prime-target pairs were manipulated independently. It is concluded that spatial attention and visual word recognition processes are best seen as interactive. Spatial attention affects word recognition in 2 distinct ways: (a) it affects the uptake of orthographic information, possibly acting as "glue" to hold letters in their proper places in words, and (b) it (partly) determines whether or not activation from the semantic level feeds down to the lexical level during word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual load influences selective attention across development.

Research suggests that visual selective attention develops across childhood. However, there is relatively little understanding of the neurological changes that accompany this development, particularly in the context of adult theories of selective attention, such as N. Lavie's (1995) perceptual load theory of attention. This study examined visual selective attention across development from 7 years of age to adulthood. Specifically, the author examined if changes in processing as a function of selective attention are similarly influenced by perceptual load across development. Participants were asked to complete a task at either low or high perceptual load while processing of an unattended probe stimulus was examined using event related potentials. Similar to adults, children and teens showed reduced processing of the unattended stimulus as perceptual load increased at the P1 visual component. However, although there were no qualitative differences in changes in processing, there were quantitative differences, with shorter P1 latencies in teens and adults compared with children, suggesting increases in the speed of processing across development. In addition, younger children did not need as high a perceptual load to achieve the same difference in performance between low and high perceptual load as adults. Thus, this study demonstrates that although there are developmental changes in visual selective attention, the mechanisms by which visual selective attention is achieved in children may share similarities with adults. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

What''s new in surgery of flexor tendons?]

BACKGROUND: Visual acuity and vision related quality of life outcomes in cataract surgery were evaluated in a population based survey in two geographic zones in Nepal. METHODS: Case finding was based on random sampling using a stratified cluster design with door to door enumeration of people aged > or = 45 years followed by eye examinations at village sites. All aphakics/pseudophakics, those with visual acuity less than 6/60 in either eye, and a sample of those with normal visual acuity were administered visual functioning (VF) and quality of life (QOL) questionnaires. RESULTS: 15% of the 159 cataract operated cases had presenting visual acuity > or = 6/18 in both eyes, 38% with best corrected visual acuity. 21% were still blind with presenting visual acuity < 6/60 in both eyes, 7% with best correction. On a 0-100 scale, mean VF and QOL scores were 87.2 and 93.9 respectively in normally sighted unoperated individuals, dropping to 15.6 and 29.5 for those severely blind (< 3/60). Among the cataract operated, mean VF and QOL scores were 47.5 and 55.4, respectively. VF and QOL scores correlated with vision status at statistically significant levels (p < 0.0001). CONCLUSION: Cataract surgery outcomes, whether measured by traditional visual acuity or by patient reported VF/QOL, are at levels many would consider unacceptably low. It is apparent that in the quest to reduce cataract blindness much more attention must be given to improving surgery outcomes.     

On the orienting value of attitudes: Attitude accessibility as a determinant of an object's attraction of visual attention.

Tested the hypothesis that objects toward which individuals hold attitudes that are highly accessible from memory (i.e., attitude-evoking objects) are more likely to attract attention when presented in a visual display than objects involving less accessible attitudes. In Exps 1 and 2, Ss were more likely to notice and report such attitude-evoking objects. Exp 3 yielded evidence of incidental attention; Ss noticed attitude-evoking objects even when the task made it beneficial to ignore the objects. Exp 4 demonstrated that inclusion of attitude-evoking objects as distractor items interfered with Ss' performance of a visual search task. Apparently, attitude-evoking stimuli attract attention automatically. Thus, accessible attitudes provide the functional benefit of orienting an individual's visual attention toward objects with potential hedonic consequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How Does Attention Select and Track Spatially Extended Objects? New Effects of Attentional Concentration and Amplification.

Real-world situations involve attending to spatially extended objects, often under conditions of motion and high processing load. The present experiments investigated such processing by requiring observers to attentionally track a number of long, moving lines. Concurrently, observers responded to sporadic probes as a measure of the distribution of attention across the lines. The results revealed that attention is concentrated at the centers of lines during tracking, despite their uniformity, and that this center advantage grew as the lines became longer: Not only did observers get worse near the endpoints, but they became better at the lines' centers, as if attention became more concentrated as the objects became more extended. These results begin to show how attention is flexibly allocated in online visual processing to extended dynamic objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Review of Attentional processing: The brain's art of mindfulness.

Reviews the book, Attentional processing: The brain's art of mindfulness by David LaBerge (see record 1995-97550-000). David LaBerge has crafted a book on visual attention that will be accessible and interesting to a broad audience, from students doing their first project in cognitive psychology, to accomplished researchers in the field. The goal of the book is to present a coherent cognitive-neuroscience model of attention - a framework within which one can understand the rich database of findings pertaining to visual attention. In some respects, the book is also an overview and synthesis of LaBerge's own work on spatial attention. The first half of the book covers behavioural investigations; the second half covers cognitive-neuroscience investigations. When most books in psychology are tomes with each chapter written by a different author, it was rewarding to review a scientific book that one could conveniently carry in one's hand, written from cover to cover by one author. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overt orienting in the rat: Parametric studies of cued detection of visual targets.

Covert shifts of visual attention in space have been quantified by measuring the effects of visual cues on the detection of visual targets in humans and monkeys maintaining visual fixation. These observations of "covert orienting" have provided important information regarding the neurobiology of visual attention in primates. This article describes a cued spatial target detection task for physically unrestrained rats. Valid cues (spatially contiguous with the target) enhanced target detection, and invalid cues (spatially discontiguous with the target) degraded target detection. Both visual and auditory cues were effective. These validity effects could not be explained by stimulus additivity or response preparation mechanisms, whereas a cue-independent "alerting effect" appeared to reflect response preparation. The effects compare favorably with primate work and suggest that this method may enable assessment of visual attention shifts in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pip and pop: Nonspatial auditory signals improve spatial visual search.

Searching for an object within a cluttered, continuously changing environment can be a very time-consuming process. The authors show that a simple auditory pip drastically decreases search times for a synchronized visual object that is normally very difficult to find. This effect occurs even though the pip contains no information on the location or identity of the visual object. The experiments also show that the effect is not due to general alerting (because it does not occur with visual cues), nor is it due to top-down cuing of the visual change (because it still occurs when the pip is synchronized with distractors on the majority of trials). Instead, we propose that the temporal information of the auditory signal is integrated with the visual signal, generating a relatively salient emergent feature that automatically draws attention. Phenomenally, the synchronous pip makes the visual object pop out from its complex environment, providing a direct demonstration of spatially nonspecific sounds affecting competition in spatial visual processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative availability of surface and object properties during early haptic processing.

How the relative order in which 4 property classes of haptically perceived surfaces becomes available for processing after initial contact was studied. The classes included material, abrupt-surface discontinuity, relative orientation, and continuous 3-D surface contour properties. Relative accessibility was evaluated by using the slopes of haptic search functions obtained with a modified version of A. Treisman's (A. Treisman & S. Gormican, 1988) visual pop-out paradigm; the y? intercepts were used to confirm and fine-tune order of accessibility. Target and distractors differed markedly in terms of their value on a single dimension. The results of 15 experiments show that coarse intensive discriminations are haptically processed early on. In marked contrast, most spatially encoded dimensions become accessible relatively later, sometimes considerably so. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophysiological evidence for the "missing link" in crossmodal attention.

Notes that orienting attention involuntarily to the location of a sensory event influences responses to subsequent stimuli that appear in different modalities with one possible exception; orienting attention involuntarily to a sudden light sometimes fails to affect responses to subsequent sounds (e.g., C. Spence and J. Driver, 1997). Here the authors investigated the effects of involuntary attention to a brief flash on the processing of subsequent sounds in a design that eliminates stimulus–response compatibility effects and criterion shifts as confounding factors. 13 18–31 yr olds participated in the study. In addition, the neural processes mediating crossmodal attention were studied by recording event-related brain potentials. The data show that orienting attention to the location of a spatially nonpredictive visual cue modulates behavioral and neural responses to subsequent auditory targets when the stimulus onset asynchrony is short (between 100 and 300 ms). These findings are consistent with the hypothesis that involuntary shifts of attention are controlled by supramodal brain mechanisms rather than by modality-specific ones. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple mechanisms of visual-spatial attention: recent evidence from human electrophysiology

Natural visual scenes contain vast quantities of information--far more than the visual system can process in a short period of time-and spatial attention is therefore used to focus the visual system's processing resources onto a subset of the incoming visual information. Most psychological theories of attention posit a single mechanism for this focusing of attention, but recent electrophysiological studies have provided evidence that the visual system employs several separable neural mechanisms of spatial attention. This paper describes the evidence for multiple attentional mechanisms and suggests links between these neurophysiologically defined mechanisms and specific functional processes that have been proposed in psychological theories of attention.     

The temporal dynamics of reading: a PET study

The temporal dynamics of evoked brain responses are normally characterized using electrophysiological techniques but the positron emission tomography study presented here revealed a temporal aspect of reading by correlating the duration a word remained in the visual field with evoked haemodynamic response. Three distinct types of effects were observed: in visual processing areas, there were linear increases in activity with duration suggesting that visual processing endures throughout the time the stimulus remains in the visual field. In right hemisphere areas, there were monotonic decreases in activity with increased duration which we relate to decreased attention for longer stimulus durations. In left hemisphere word processing areas there were inverted U-shaped dependencies between activity and word duration indicating that, after 400-600 ms, activity in word processing areas is progressively reduced if the word remains in the visual field. We conclude that these inverted U effects in left hemisphere language areas reflect the temporal dynamics of visual word processing and we highlight the implication of these effects for the design of activation studies involving reading.     

Effects of stimulus integrality on visual attention in older and younger adults: a quantitative model-based analysis

Twenty-one older and 21 younger adults were administered a series of visual attention tasks. A series of quantitative models was applied to each observer's data to determine whether he or she performed optimally or suboptimally or showed a deficit-in-attentional processing. The results suggested that (a) older and younger observers were affected equally by the integrality-separability manipulation, (b) there are no age-related differences in selective attention performance for either integral or separable-dimension stimuli, (c) there are no age-related differences in dimensional integration performance with separable-dimension stimuli, and (d) older observers were more likely to be suboptimal when asked to integrate information from integral-dimension stimuli. Implications for current theories of attentional processing in normal aging are discussed.     

Adult age differences in the inhibition of return of visual attention.

Responses to targets are slower when they appear at a location to which attention has previously been directed than when they appear at other locations. This inhibition of return (IOR) effect is subserved by posterior brain attentional systems. In 4 experiments the IOR effect in elderly adults was found to be at least as large as in young adults for both discrimination tasks and for detection tasks. The time course and the spread of inhibition within the visual field were also equivalent in the 2 age groups. Additive factors logic was then used to test the hypothesis that the Stroop and IOR effects are due to a common mechanism, a failure to suppress attention. This hypothesis was not confirmed. The results of the 6 experiments are consistent with the hypothesis that there are changes in posterior brain systems responsible for selective attention to a location, contrary to prior claims. They cannot be explained by a general slowing of processing in old age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multimodal Events and Moving Locations: Eye Movements of Adults and 6-Month-Olds Reveal Dynamic Spatial Indexing.

The ability to keep track of locations in a dynamic, multimodal environment is crucial for successful interactions with other people and objects. The authors investigated the existence and flexibility of spatial indexing in adults and 6-month-old infants by adapting an eye-tracking paradigm from D. C. Richardson and M. J. Spivey (2000). Multimodal events were presented in specific locations, and eye movements were measured when the auditory portion of the stimulus was presented without its visual counterpart. Experiment 1 showed that adults spatially index auditory information even when the original associated locations move. Experiments 2 and 3 showed that infants are capable of both binding multimodal events to locations and tracking those locations when they move. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Mechanisms of directed attention in the human extrastriate cortex as revealed by functional MRI

A typical scene contains many different objects, but the capacity of the visual system to process multiple stimuli at a given time is limited. Thus, attentional mechanisms are required to select relevant objects from among the many objects competing for visual processing. Evidence from functional magnetic resonance imaging (MRI) in humans showed that when multiple stimuli are present simultaneously in the visual field, their cortical representations within the object recognition pathway interact in a competitive, suppressive fashion. Directing attention to one of the stimuli counteracts the suppressive influence of nearby stimuli. This mechanism may serve to filter out irrelevant information in cluttered visual scenes.