Combining attributes in rapid serial visual presentation tasks

Slippage of the attentional beam when searching in space and in time

"Slippage" of attention in time and space has been studied separately, using visual search (e.g., Snyder, 1972) and rapid serial visual presentation (RSVP) (e.g., McLean, Broadbent, & Broadbent, 1982). The primary purpose of the current study was to see if we could replicate these findings of slippage and if we did, to use individual differences to explore relationships between slippage in the temporal and spatial domains. The participants identified and localized targets in visual search and in RSVP sequences. In Experiment 1, we used visual search and RSVP tasks closely replicating the methods of Snyder and McLean et al. In Experiment 2, we closely equated the two tasks as far as possible while maintaining the crucial space/time difference. Consistent with the previous studies, and reflecting binding errors (or slippage) in both space and time, erroneously reported identities were predominantly from items adjacent to the targets. Correlations between measures of the slippage in space (visual search) and time (RSVP) were near zero, suggesting that different attentional 'beams' bind features in space and time, a possibility that is consistent with other behavioural as well as neuropsychological evidence.

The diachronic account of attentional selectivity

Many models of attention assume that attentional selection takes place at a specific moment in time that demarcates the critical transition from pre-attentive to attentive processing of sensory input. We argue that this intuitively appealing standard account of attentional selectivity is not only inaccurate, but has led to substantial conceptual confusion. As an alternative, we offer a 'diachronic' framework that describes attentional selectivity as a process that unfolds over time. Key to this view is the concept of attentional episodes, brief periods of intense attentional amplification of sensory representations that regulate access to working memory and response-related processes. We describe how attentional episodes are linked to earlier attentional mechanisms and to recurrent processing at the neural level. We review studies that establish the existence of attentional episodes, delineate the factors that determine if and when they are triggered, and discuss the costs associated with processing multiple events within a single episode. Finally, we argue that this framework offers new solutions to old problems in attention research that have never been resolved. It can provide a unified and conceptually coherent account of the network of cognitive and neural processes that produce the goal-directed selectivity in perceptual processing that is commonly referred to as 'attention'.

Aging with a traumatic brain injury: Could behavioral morbidities and endocrine symptoms be influenced by microglial priming?

A myriad of factors influence the developmental and aging process and impact health and life span. Mounting evidence indicates that brain injury, even moderate injury, can lead to lifetime of physical and mental health symptoms. Therefore, the purpose of this mini-review is to discuss how recovery from traumatic brain injury (TBI) depends on age-at-injury and how aging with a TBI affects long-term recovery. TBI initiates pathophysiological processes that dismantle circuits in the brain. In response, reparative and restorative processes reorganize circuits to overcome the injury-induced damage. The extent of circuit dismantling and subsequent reorganization depends as much on the initial injury parameters as other contributing factors, such as genetics and age. Age-at-injury influences the way the brain is able to repair itself, as a result of developmental status, extent of cellular senescence, and injury-induced inflammation. Moreover, endocrine dysfunction can occur with TBI. Depending on the age of the individual at the time of injury, endocrine dysfunction may disrupt growth, puberty, influence social behaviors, and possibly alter the inflammatory response. In turn, activation of microglia, the brain's immune cells, after injury may continue to fuel endocrine dysfunction. With age, the immune system develops and microglia become primed to subsequent challenges. Sustained inflammation and microglial activation can continue for weeks to months post-injury. This prolonged inflammation can influence developmental processes, behavioral performance and age-related decline. Overall, brain injury may influence the aging process and expedite glial and neuronal alterations that impact mental health.

Reconsidering Temporal Selection in the Attentional Blink

Two episodes of attentional selection cannot occur very close in time. This is the traditional account of the attentional blink, whereby observers fail to report the second of two temporally proximal targets. Recent analyses have challenged this simple account, suggesting that attentional selection during the attentional blink is not only (a) suppressed, but also (b) temporally advanced then delayed, and (c) temporally diffused. Here, we reanalyzed six data sets using mixture modeling of report errors, and revealed much simpler dynamics. Exposing a problem inherent in previous analyses, we found evidence of a second attentional episode only when the second target (T2) follows the first (T1) by more than 100 to 250 ms. When a second episode occurs, suppression and delay reduce steadily as lag increases and temporal precision is stable. At shorter lags, both targets are reported from a single episode, which explains why T2 can escape the attentional blink when it immediately follows T1 (Lag-1 sparing).

Illusory Conjunctions in the Time Domain and the Resulting Time-Course of the Attentional Blink

Illusory conjunctions in the time domain are errors made in binding stimulus features presented In the same spatial position in Rapid Serial Visual Presentation (RSVP) conditions. Botella, Barriopedro, and Suero (2001) devised a model to explain how the distribution of responses originating from stimuli around the target in the series is generated. They proposed two routes consisting of two sequential attempts to make a response. The second attempt (sophisticated guessing) is only employed if the first one (focal attention) fails in producing an integrated perception. This general outline enables specific predictions to be made and tested related to the efficiency of focal attention in generating responses in the first attempt. Participants had to report the single letter in an RSVP stream of letters that was presented in a previously specified color (first target, T1) and then report whether an X (second target, T2) was or was not presented. Performance on T2 showed the typical U-shaped function across the T1-T2 lag that reflects the attentional blink phenomenon. However, as was predicted by Botella, Barriopedro, and Suero's model, the time-course of the interference was shorter for trials with a correct response to T1 than for trials with a T1 error. Furthermore, longer time-courses of interference associated with pre-target and post-target errors to the first target were indistinguishable.

Sources of bias and uncertainty in a visual temporal individuation task

Despite a clear ability to detect temporal modulations of visual stimuli in excess of 50 Hz, temporal individuation and serial order judgment tasks can be performed only when stimuli alternate at much slower rates, and the nature of such sluggishness remains unclear. One example of a task with a slow temporal limit is the individuation of a cued letter in a rapid serial visual presentation (RSVP) stream. The present study investigates the nature of the code used to perform such a slow temporal individuation task and the sources of uncertainty involved. The results demonstrate that temporal, rather than ordinal, position in the RSVP stream is critical in serial order estimation, suggesting the involvement of a noisy temporal code. In addition to variability in temporal coding, observers' choices are also limited by a number of other factors, such as categorical errors and biases related to the position of the cue in the letters' stream. Attentional filtering improves categorization, but crucially, it does not seem to increase the temporal precision of judgment. Generalizing the present results, I suggest that perception of order is limited by an internal temporal sampling instability that is distinct and independent from attention and that, similarly to temporal jitter in a clock, acts as a low-pass filter that hinders the judgment of the order of events that unfold too quickly.

Cortical synchronization and perceptual framing

How does the brain group together different parts of an object into a coherent visual object representation? Different parts of an object may be processed by the brain at different rates and may thus become desynchronized. Perceptual framing is a process that resynchronizes cortical activities corresponding to the same retinal object. A neural network model is presented that is able to rapidly resynchronize desynchronized neural activities. The model provides a link between perceptual and brain data. Model properties quantitatively simulate perceptual framing data, including psychophysical data about temporal order judgments and the reduction of threshold contrast as a function of stimulus length. Such a model has earlier been used to explain data about illusory contour formation, texture segregation, shape-from-shading, 3-D vision, and cortical receptive fields. The model hereby shows how many data may be understood as manifestations of a cortical grouping process that can rapidly resynchronize image parts that belong together in visual object representations. The model exhibits better synchronization in the presence of noise than without noise, a type of stochastic resonance, and synchronizes robustly when cells that represent different stimulus orientations compete. These properties arise when fast long-range cooperation and slow short-range competition interact via nonlinear feedback interactions with cells that obey shunting equations.

Effects of divided attention and operating room noise on perception of pulse oximeter pitch changes: a laboratory study

BACKGROUND

Anesthesiology requires performing visually oriented procedures while monitoring auditory information about a patient's vital signs. A concern in operating room environments is the amount of competing information and the effects that divided attention has on patient monitoring, such as detecting auditory changes in arterial oxygen saturation via pulse oximetry.

METHODS

The authors measured the impact of visual attentional load and auditory background noise on the ability of anesthesia residents to monitor the pulse oximeter auditory display in a laboratory setting. Accuracies and response times were recorded reflecting anesthesiologists' abilities to detect changes in oxygen saturation across three levels of visual attention in quiet and with noise.

RESULTS

Results show that visual attentional load substantially affects the ability to detect changes in oxygen saturation concentrations conveyed by auditory cues signaling 99 and 98% saturation. These effects are compounded by auditory noise, up to a 17% decline in performance. These deficits are seen in the ability to accurately detect a change in oxygen saturation and in speed of response.

CONCLUSIONS

Most anesthesia accidents are initiated by small errors that cascade into serious events. Lack of monitor vigilance and inattention are two of the more commonly cited factors. Reducing such errors is thus a priority for improving patient safety. Specifically, efforts to reduce distractors and decrease background noise should be considered during induction and emergence, periods of especially high risk, when anesthesiologists has to attend to many tasks and are thus susceptible to error.

Illusory conjunctions reflect the time course of the attentional blink

Illusory conjunctions in the time domain are binding errors for features from stimuli presented sequentially but in the same spatial position. A similar experimental paradigm is employed for the attentional blink (AB), an impairment of performance for the second of two targets when it is presented 200-500 msec after the first target. The analysis of errors along the time course of the AB allows the testing of models of illusory conjunctions. In an experiment, observers identified one (control condition) or two (experimental condition) letters in a specified color, so that illusory conjunctions in each response could be linked to specific positions in the series. Two items in the target colors (red and white, embedded in distractors of different colors) were employed in four conditions defined according to whether both targets were in the same or different colors. Besides the U-shaped function for hits, the errors were analyzed by calculating several response parameters reflecting characteristics such as the average position of the responses or the attentional suppression during the blink. The several error parameters cluster in two time courses, as would be expected from prevailing models of the AB. Furthermore, the results match the predictions from Botella, Barriopedro, and Suero's (Journal of Experimental Psychology: Human Perception and Performance, 27, 1452-1467, 2001) model for illusory conjunctions.

Toward a framework for the evaluation of feature binding in pigeons

Pigeons were trained in a new procedure to test for visual binding errors between the dimensions of color and shape. In Experiment 1, pigeons learned to discriminate a target compound from 15 non-target compounds (constructed from four colors and shapes) by choosing one of two hoppers in a two-hopper choice task. The similarity of the target to non-target stimuli influenced choice responding. In Experiment 2, pigeons learned to detect a target compound when presented with a non-target compound within the same trial under conditions of simultaneity and sequentiality. Non-target trials were arranged to allow for the testing of binding errors (i.e., false identifications of the target on certain non-target trials). Transient evidence for binding errors in two of the birds occurred at the start of two-item training, but decreased with training. The experiments represent an important step toward developing a framework for the evaluation of visual feature binding in nonhumans.

Attribute pair-based visual recognition and memory

BACKGROUND

In the human visual system, different attributes of an object, such as shape, color, and motion, are processed separately in different areas of the brain. This raises a fundamental question of how are these attributes integrated to produce a unified perception and a specific response. This "binding problem" is computationally difficult because all attributes are assumed to be bound together to form a single object representation. However, there is no firm evidence to confirm that such representations exist for general objects.

METHODOLOGY/PRINCIPAL FINDINGS

Here we propose a paired-attribute model in which cognitive processes are based on multiple representations of paired attributes. In line with the model's prediction, we found that multiattribute stimuli can produce an illusory perception of a multiattribute object arising from erroneous integration of attribute pairs, implying that object recognition is based on parallel perception of paired attributes. Moreover, in a change-detection task, a feature change in a single attribute frequently caused an illusory perception of change in another attribute, suggesting that multiple pairs of attributes are stored in memory.

CONCLUSIONS/SIGNIFICANCE

The paired-attribute model can account for some novel illusions and controversial findings on binocular rivalry and short-term memory. Our results suggest that many cognitive processes are performed at the level of paired attributes rather than integrated objects, which greatly facilitates the binding problem and provides simpler solutions for it.

A solution to the tag-assignment problem for neural networks

Purely parallel neural networks can model object recognition in brief displays – the same conditions under which illusory conjunctions (the incorrect combination of features into perceived objects in a stimulus array) have been demonstrated empirically (Treisman 1986; Treisman & Gelade 1980). Correcting errors of illusory conjunction is the “tag-assignment” problem for a purely parallel processor: the problem of assigning a spatial tag to nonspatial features, feature combinations, and objects. This problem must be solved to model human object recognition over a longer time scale. Our model simulates both the parallel processes that may underlie illusory conjunctions and the serial processes that may solve the tag-assignment problem in normal perception. One component of the model extracts pooled features and another provides attentional tags that correct illusory conjunctions. Our approach addresses two questions: (i) How can objects be identified from simultaneously attended features in a parallel, distributed representation? (ii) How can the spatial selectional requirements of such an attentional process be met by a separation of pathways for spatial and nonspatial processing? Our analysis of these questions yields a neurally plausible simulation of tag assignment based on synchronizing feature processing activity in a spatial focus of attention.

Parallel processing of stimulus features during RSVP: evidence from the second response

When observers are asked to report a feature of a single target displayed in rapid serial visual presentation, they frequently make errors. Most frequently, a feature from the to-be-reported dimension pertaining to a stimulus presented near the target is reported. These migrations are so-called illusory conjunctions in the time domain. From parallel models, it is proposed that during the presentation of the series, the response features of the stimuli are extracted. If a high rate of presentation does not enable proper binding processes, the system could base its response on sophisticated guessing on the basis of the relative levels of activation of the available response features. However, the multiple extractions assumption has not received direct empirical support. We report two experiments in which the observers had to report their first and second response candidates. This double response paradigm makes it possible to test the assumption that more than one response feature is available for making a response. Furthermore, the application of the constant ratio rule (following Botella, Barriopedro, & Suero's, 2001, model) to the first responses allows predictions for the ratios between choices of the items for the second responses. The correlations between the observed and the predicted response proportions were .887 and .956 in the two experiments. This high predictive capacity indicates, first, that the observers have more than one response available, among which to choose, and second, that the choice among responses is determined largely in the same way for both, first and second responses. Nevertheless, the small errors in prediction are further reduced if a proportion of pure guesses is assumed in the second responses. These are probably due to memory losses, misidentifications of the features, and other factors impairing performance in second responses in comparison with first responses.

Effects of task factors on selection by color in the rapid serial visual presentation (RSVP) task

In five experiments, we examined task factors influencing selection by color in a rapid serial visual presentation (RSVP) task. Participants were required to respond to the presence or case of a target letter presented within an RSVP sequence, and they were cued as to the color in which that target was most likely to occur. The first two experiments explored the effect of task difficulty. It was found that a change from the discrimination of upper- versus lowercase targets to the detection of an exact shape had no influence on the color-cuing effect. In contrast, increasing letter set discriminability and decreasing color discriminability reduced the color-cuing effect considerably, although they did not eliminate it. In the third and fourth experiments, the frequency of valid trials was reduced, removing the incentive to use the color information. Again, a small benefit remained, indicating partially automatic and strategic color-processing components. Finally, the fifth experiment showed that an increase in perceptual load had no influence on the color-cuing effect. Together, these five experiments provide further evidence of the robustness of direct selection by color.

Direct selection by color for visual encoding

In two experiments, we used rapid serial visual presentation tasks to examine the usefulness of color for the direct selection of visual information for perceptual encoding. The participants' task was to make a discrimination as to whether a target letter within a rapid sequence appeared in its upper- or lowercase version, and an advance cue indicated the color in which the target letter was most likely to occur. To maximize the usefulness of the cued color, in validly cued trials, we used sequences in which the target was the only item appearing in the cued color. In both experiments, accuracy was highest for validly cued trials. A cost-benefit analysis revealed a facilitory effect of valid cues and an inhibitory effect of invalid ones. These results support the idea that color cuing allows the direct selection of objects for further perceptual processing.

Multiple spotlights of attentional selection in human visual cortex

Spatially directed attention strongly enhances visual perceptual processing. The metaphor of the "spotlight" has long been used to describe spatial attention; however, there has been considerable debate as to whether spatial attention must be unitary or may be split between discrete regions of space. This question was addressed here through functional MR imaging of human subjects as they performed a task that required simultaneous attention to two briefly displayed and masked targets at locations separated by distractor stimuli. These data reveal retinotopically specific enhanced activation in striate and extrastriate visual cortical representations of the two attended stimuli and no enhancement at the intervening representation of distractor stimuli. This finding of two spotlights was obtained within a single cortical hemisphere and across the two hemispheres. This provides direct evidence that spatial attention can select, in parallel, multiple low-level perceptual representations.

Frontal and striatal brain lesions increase susceptibility to masking in perceptual decisions

Recent data suggest that perceptual decisions on masked stimuli involve neural activity in frontal cortex. We examined the effect of damage to frontal and striatal brain regions in man on the susceptibility to backward masking in rapid stimulus streams. Patients with unilateral frontal excisions and patients with early Huntington's disease were compared to controls in the identification of a brief white letter embedded in short streams of black letters at two presentation rates: (a) 9 letters/s; (b) 12.5 letters/s and also in a control condition in which the first post-target masking letter was absent. Patients could identify the target when the post-target mask was absent, but reducing the delay between stimuli significantly increased the error rates in patients. Intrusion errors often involved reporting post-target or pre-target distractors instead of the target. These results suggest that fronto-striatal lesions increase the period during which perceptual decisions are susceptible to perturbation. This deficit is compatible with a functional role of frontal systems in the cognitive control of brief perceptual decisions.

A model of the formation of illusory conjunctions in the time domain

The authors present a model to account for the miscombination of features when stimuli are presented using the rapid serial visual presentation (RSVP) technique (illusory conjunctions in the time domain). It explains the distributions of responses through a mixture of trial outcomes. In some trials, attention is successfully focused on the target, whereas in others, the responses are based on partial information. Two experiments are presented that manipulated the mean processing time of the target-defining dimension and of the to-be-reported dimension, respectively. As predicted, the average origin of the responses is delayed when lengthening the target-defining dimension, whereas it is earlier when lengthening the to-be-reported dimension; in the first case the number of correct responses is dramatically reduced, whereas in the second it does not change. The results, a review of other research, and simulations carried out with a formal version of the model are all in close accordance with the predictions.

Evidence for distinct attentional bottlenecks in attention switching and attentional blink tasks

E. Weichselgartner and G. A. Sperling (1987), using rapid serial visual presentation (RSVP), estimated that attention could be moved to a new spatial location within 300-400 ms. H. J. Müller and P. M. Rabbit (1989) used a spatial cuing task and found a similar time course for voluntarily redeploying attention. A separate phenomenon known as the attentional blink (AB) also follows a similar time course, yet occurs when participants attend to a single spatial location. The present study found that attention can be shifted more quickly than previously estimated and that part of the deficit observed during searches of spatially distinct RSVP streams is due to an AB. The results support some early and late selection accounts for the temporal dynamics of visual attention and suggest different bottlenecks during visual selection. The implications for visual search and visual processing are discussed.

A self-organizing neural system for learning to recognize textured scenes

A self-organizing ARTEX model is developed to categorize and classify textured image regions. ARTEX specializes the FACADE model of how the visual cortex sees, and the ART model of how temporal and prefrontal cortices interact with the hippocampal system to learn visual recognition categories and their names. FACADE processing generates a vector of boundary and surface properties, notably texture and brightness properties, by utilizing multi-scale filtering, competition, and diffusive filling-in. Its context-sensitive local measures of textured scenes can be used to recognize scenic properties that gradually change across space, as well as abrupt texture boundaries. ART incrementally learns recognition categories that classify FACADE output vectors, class names of these categories, and their probabilities. Top-down expectations within ART encode learned prototypes that pay attention to expected visual features. When novel visual information creates a poor match with the best existing category prototype, a memory search selects a new category with which classify the novel data. ARTEX is compared with psychophysical data, and is bench marked on classification of natural textures and synthetic aperture radar images. It outperforms state-of-the-art systems that use rule-based, backpropagation, and K-nearest neighbor classifiers.

3-D vision and figure-ground separation by visual cortex

A neural network theory of three-dimensional (3-D) vision, called FACADE theory, is described. The theory proposes a solution of the classical figure-ground problem for biological vision. It does so by suggesting how boundary representations and surface representations are formed within a boundary contour system (BCS) and a feature contour system (FCS). The BCS and FCS interact reciprocally to form 3-D boundary and surface representations that are mutually consistent. Their interactions generate 3-D percepts wherein occluding and occluded object parts are separated, completed, and grouped. The theory clarifies how preattentive processes of 3-D perception and figure-ground separation interact reciprocally with attentive processes of spatial localization, object recognition, and visual search. A new theory of stereopsis is proposed that predicts how cells sensitive to multiple spatial frequencies, disparities, and orientations are combined by context-sensitive filtering, competition, and cooperation to form coherent BCS boundary segmentations. Several factors contribute to figure-ground pop-out, including: boundary contrast between spatially contiguous boundaries, whether due to scenic differences in luminance, color, spatial frequency, or disparity; partially ordered interactions from larger spatial scales and disparities to smaller scales and disparities; and surface filling-in restricted to regions surrounded by a connected boundary. Phenomena such as 3-D pop-out from a 2-D picture, Da Vinci stereopsis, 3-D neon color spreading, completion of partially occluded objects, and figure-ground reversals are analyzed. The BCS and FCS subsystems model aspects of how the two parvocellular cortical processing streams that join the lateral geniculate nucleus to prestriate cortical area V4 interact to generate a multiplexed representation of Form-And-Color-And-DEpth, or FACADE, within area V4. Area V4 is suggested to support figure-ground separation and to interact with cortical mechanisms of spatial attention, attentive object learning, and visual search. Adaptive resonance theory (ART) mechanisms model aspects of how prestriate visual cortex interacts reciprocally with a visual object recognition system in inferotemporal (IT) cortex for purposes of attentive object learning and categorization. Object attention mechanisms of the What cortical processing stream through IT cortex are distinguished from spatial attention mechanisms of the Where cortical processing stream through parietal cortex. Parvocellular BCS and FCS signals interact with the model What stream. Parvocellular FCS and magnocellular motion BCS signals interact with the model Where stream.(ABSTRACT TRUNCATED AT 400 WORDS)

Filtering versus parallel processing in RSVP tasks

An experiment of McLean, D. E. Broadbent, and M. H. P. Broadbent (1983) using rapid serial visual presentation (RSVP) was replicated. A series of letters in one of 5 colors was presented, and the subject was asked to identify the letter that appeared in a designated color. There were several innovations in our procedure, the most important of which was the use of a response menu. After each trial, the subject was presented with 7 candidate letters from which to choose his/her response. In three experimental conditions, the target, the letter following the target, and all letters other than the target were, respectively, eliminated from the menu. In other conditions, the stimulus list was manipulated by repeating items in the series, repeating the color of successive items, or even eliminating the target color. By means of these manipulations, we were able to determine more precisely the information that subjects had obtained from the presentation of the stimulus series. Although we replicated the results of McLean et al. (1983), the more extensive information that our procedure produced was incompatible with the serial filter model that McLean et al. had used to describe their data. Overall, our results were more compatible with a parallel-processing account. Furthermore, intrusion errors are apparently not only a perceptual phenomenon but a memory problem as well.

Movement and proximity constrain miscombinations of colour and form

A relatively frequent error when reporting brief visual displays is to combine presented features incorrectly. It has been proposed that Gestalt grouping constrains such errors so that miscombined features tend to come from the same perceptual group. In three experiments it was examined whether this principle applies to grouping by motion, and to grouping by proximity. Miscombinations of colour and form were more likely to consist of a colour and form that had moved in the same direction than features which had moved in opposite directions. Miscombinations were also more likely for adjacent items. The implications of these results for the mechanisms of feature integration are discussed.

The processing of non-target words: semantic or not?

It is known that people reacting to visual words may be affected by the meaning of accompanying non-target words. On the approach to perception developed by Treisman (e.g. 1986), this is surprising, because meaning might be thought to require analysis of conjunctions of physical features and so should remain uncomputed for non-target words. Treisman's approach does, however, assert that analysis of the target may unleash further processes that would prime the system for detection of related words. If this were so, then presentation of the target earlier than the distractors would increase the effect of the latter; whereas if analysis of non-targets were independent of priming, they might be expected to have a smaller effect when delayed. Further, if the sets of words involved are small and familiar, then individual features of primed non-targets, rather than conjunctions of features, might trigger interference. They might especially do so when spatial separation of target and non-target is small. Five experiments using a paradigm developed by Shaffer and LaBerge confirm that the meaning of non-target words affects response to targets; but (1) this is more true for early than for late arrival of the target; (2) it is affected by target/non-target separation in space; (3) it is true for familiar sets of repeated words but not, in these data, for words used once only in the experiment. It is therefore concluded that the results are more consistent with a Treisman type of explanation than with a theory of universal and automatic full analysis.