Shifting attention within memory representations involves early visual areas

Prior studies have shown that spatial attention modulates early visual cortex retinotopically, resulting in enhanced processing of external perceptual representations. However, it is not clear whether the same visual areas are modulated when attention is focused on, and shifted within a working memory representation. In the current fMRI study participants were asked to memorize an array containing four stimuli. After a delay, participants were presented with a verbal cue instructing them to actively maintain the location of one of the stimuli in working memory. Additionally, on a number of trials a second verbal cue instructed participants to switch attention to the location of another stimulus within the memorized representation. Results of the study showed that changes in the BOLD pattern closely followed the locus of attention within the working memory representation. A decrease in BOLD-activity (V1-V3) was observed at ROIs coding a memory location when participants switched away from this location, whereas an increase was observed when participants switched towards this location. Continuous increased activity was obtained at the memorized location when participants did not switch. This study shows that shifting attention within memory representations activates the earliest parts of visual cortex (including V1) in a retinotopic fashion. We conclude that even in the absence of visual stimulation, early visual areas support shifting of attention within memorized representations, similar to when attention is shifted in the outside world. The relationship between visual working memory and visual mental imagery is discussed in light of the current findings.     

Orientation of attention in the visual space]

The display was composed of four boxes, horizontally aligned above the fixation point. In Experiment I, each box was cued by a digit shown at fixation. In Experiment II there were only two numeric cues, signalling the inner or the outer boxes, depending on the experimental condition. The subject was instructed to orient attention to the cued box, and to respond to the imperative stimulus as fast as possible, wherever it appeared. By using four time interval (SOAs), we tried to determine the route covered by attention movements. In Experiment I, with the shortest SOA (100 msec), it was shown that attention does not reach the cued box through a direct path. Rather it moves first on the inner boxes, thereafter focusing on the cued location. The same results were obtained in Experiment II, where the cue directed attention to the inner boxes. When the external boxes were cued, however, this trend was not observed.     

Mislocalization of visual stimuli: independent effects of static and dynamic attention

Shifts of visual attention cause systematic distortions of the perceived locations of visual objects around the focus of attention. In the attention repulsion effect, the perceived location of a visual target is shifted away from an attention-attracting cue when the cue is presented before the target. Recently it has been found that, if the visual cue is presented after the target, the perceived location of the target shifts toward the location of the following cue. One unanswered question is whether a single mechanism underlies both attentional repulsion and attraction effects. We presented participants with two disks at diagonal locations as visual cues and two vertical lines as targets. Participants were asked to perform a forced-choice task to judge targets' positions. The present study examined whether the magnitude of the repulsion effect and the attraction effect would differ (Experiment 1), whether the two effects would interact (Experiment 2), and whether the location or the dynamic shift of attentional focus would determine the distortions effects (Experiment 3). The results showed that the effect size of the attraction effect was slightly larger than the repulsion effect and the preceding and following cues have independent influences on the perceived positions. The repulsion effect was caused by the location of attnetion and the attraction effect was due to the dynamic shift of attentional focus, suggesting that the underlying mechanisms for the retrospective attraction effect might be different from those for the repulsion effect.     

The effects of cross-modal manipulations of attention on the detection of vibrotactile stimuli in humans

Although it is well known that attention to a visual or auditory stimulus can enhance its perception, less is known concerning the effects of attention on the perception of natural tactile stimuli. The present study was conducted to examine the magnitude of the effect of cross-modal manipulations of attention in human subjects on the detection of weak, low-frequency vibrotactile stimuli delivered to the glabrous skin of the finger pad of the right index finger via an Optacon. Three suprathreshold vibrotactile arrays (40 Hz), varying in the number of activated pegs and hence the area of skin stimulated, were used. Subjects were trained to detect the occurrence of vibrotactile or visual stimuli and to respond by pressing a foot pedal as quickly as possible thereafter. Two instructional lights were used to cue the subjects as to which stimulus modality they should attend, in three experimental conditions. In the first cue condition, the forthcoming stimulus modality was indicated by the illumination of its associated light. In the second cue condition, both instructional lights were illuminated, and the subjects were asked to divide their attention equally between the two modalities. In the third cue condition, the stimulus modality was falsely indicated by the illumination of the cue not associated with the stimulus to be presented. Reaction times (RTs) were calculated for each trial. For each modality, tactile and visual, the RTs varied significantly with the cue condition, with the mean RT changing in a graded manner across the experimental conditions (being shortest for the correctly cued condition, intermediate for the neutrally cued condition, and longest for the incorrectly cued condition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects on discrimination performance of selective attention to tactile features

This study examined selective attention to tactile dimensions by combining a selective cueing paradigm with a test of integrality. In Experiment 1, subjects selectively attended to changes in the frequency or duration of pairs of vibrotactile stimuli and identified the higher frequency or longer duration stimulus. In Experiment 2, using surface gratings in an identical experimental procedure, subjects identified the rougher or longer duration stimulus. In both experiments, greater performance accuracy was found on trials where the cue correctly (valid) predicted the changing dimension, vs incorrectly (invalid) cued or no-cue (neutral) trials. More errors on the invalidly vs neutrally cued trials show the cost of focal attention. Increases in performance on validly vs neutrally cued trials show a benefit of filtering irrelevant stimuli in the cued conditions. Results effectively demonstrate focal attention to tactile features. Tests of integrality, in terms of the effects of correlated change in both dimensions, showed no redundancy gain for either vibrotactile or grating tasks, suggesting that frequency and roughness are separable from stimulus duration. Interference of negative correlated change for frequency but not roughness discriminations may be explained by differences in task difficulty.     

Effects on discrimination performance of selective attention to tactile features

This study examined selective attention to tactile dimensions by combining a selective cueing paradigm with a test of integrality. In Experiment 1, subjects selectively attended to changes in the frequency or duration of pairs of vibrotactile stimuli and identified the higher frequency or longer duration stimulus. In Experiment 2, using surface gratings in an identical experimental procedure, subjects identified the rougher or longer duration stimulus. In both experiments, greater performance accuracy was found on trials where the cue correctly (valid) predicted the changing dimension, vs incorrectly (invalid) cued or no-cue (neutral) trials. More errors on the invalidly vs neutrally cued trials show the cost of focal attention. Increases in performance on validly vs neutrally cued trials show a benefit of filtering irrelevant stimuli in the cued conditions. Results effectively demonstrate focal attention to tactile features. Tests of integrality, in terms of the effects of correlated change in both dimensions, showed no redundancy gain for either vibrotactile or grating tasks, suggesting that frequency and roughness are separable from stimulus duration. Interference of negative correlated change for frequency but not roughness discriminations may be explained by differences in task difficulty.     

Task attention facilitates learning of task-irrelevant stimuli

Attention plays a fundamental role in visual learning and memory. One highly established principle of visual attention is that the harder a central task is, the more attentional resources are used to perform the task and the smaller amount of attention is allocated to peripheral processing because of limited attention capacity. Here we show that this principle holds true in a dual-task setting but not in a paradigm of task-irrelevant perceptual learning. In Experiment 1, eight participants were asked to identify either bright or dim number targets at the screen center and to remember concurrently presented scene backgrounds. Their recognition performances for scenes paired with dim/hard targets were worse than those for scenes paired with bright/easy targets. In Experiment 2, eight participants were asked to identify either bright or dim letter targets at the screen center while a task-irrelevant coherent motion was concurrently presented in the background. After five days of training on letter identification, participants improved their motion sensitivity to the direction paired with hard/dim targets improved but not to the direction paired with easy/bright targets. Taken together, these results suggest that task-irrelevant stimuli are not subject to the attentional control mechanisms that task-relevant stimuli abide.     

Nonretinotopic exogenous attention

Attention is crucial for visual perception because it allows the visual system to effectively use its limited resources by selecting behaviorally and cognitively relevant stimuli from the large amount of information impinging on the eyes. Reflexive, stimulus-driven attention is essential for successful interactions with the environment because it can, for example, speed up responses to life-threatening events. It is commonly believed that exogenous attention operates in the retinotopic coordinates of the early visual system. Here, using a novel experimental paradigm [1], we show that a nonretinotopic cue improves both accuracy and reaction times in a visual search task. Furthermore, the influence of the cue is limited both in space and time, a characteristic typical of exogenous cueing. These and other recent findings show that many more aspects of vision are processed nonretinotopically than previously thought.     

Event-Related Potentials Dissociate Effects of Salience and Space in Biased Competition for Visual Representation

Background

Selective visual attention is the process by which the visual system enhances behaviorally relevant stimuli and filters out others. Visual attention is thought to operate through a cortical mechanism known as biased competition. Representations of stimuli within cortical visual areas compete such that they mutually suppress each others'' neural response. Competition increases with stimulus proximity and can be biased in favor of one stimulus (over another) as a function of stimulus significance, salience, or expectancy. Though there is considerable evidence of biased competition within the human visual system, the dynamics of the process remain unknown.

Methodology/Principal Findings

Here, we used scalp-recorded electroencephalography (EEG) to examine neural correlates of biased competition in the human visual system. In two experiments, subjects performed a task requiring them to either simultaneously identify two targets (Experiment 1) or discriminate one target while ignoring a decoy (Experiment 2). Competition was manipulated by altering the spatial separation between target(s) and/or decoy. Both experimental tasks should induce competition between stimuli. However, only the task of Experiment 2 should invoke a strong bias in favor of the target (over the decoy). The amplitude of two lateralized components of the event-related potential, the N2pc and Ptc, mirrored these predictions. N2pc amplitude increased with increasing stimulus separation in Experiments 1 and 2. However, Ptc amplitude varied only in Experiment 2, becoming more positive with decreased spatial separation.

Conclusions/Significance

These results suggest that N2pc and Ptc components may index distinct processes of biased competition—N2pc reflecting visual competitive interactions and Ptc reflecting a bias in processing necessary to individuate task-relevant stimuli.     

What Happens in Between? Human Oscillatory Brain Activity Related to Crossmodal Spatial Cueing

Previous studies investigated the effects of crossmodal spatial attention by comparing the responses to validly versus invalidly cued target stimuli. Dynamics of cortical rhythms in the time interval between cue and target might contribute to cue effects on performance. Here, we studied the influence of spatial attention on ongoing oscillatory brain activity in the interval between cue and target onset. In a first experiment, subjects underwent periods of tactile stimulation (cue) followed by visual stimulation (target) in a spatial cueing task as well as tactile stimulation as a control. In a second experiment, cue validity was modified to be 50%, 75%, or else 25%, to separate effects of exogenous shifts of attention caused by tactile stimuli from that of endogenous shifts. Tactile stimuli produced: 1) a stronger lateralization of the sensorimotor beta-rhythm rebound (15-22 Hz) after tactile stimuli serving as cues versus not serving as cues; 2) a suppression of the occipital alpha-rhythm (7-13 Hz) appearing only in the cueing task (this suppression was stronger contralateral to the endogenously attended side and was predictive of behavioral success); 3) an increase of prefrontal gamma-activity (25-35 Hz) specifically in the cueing task. We measured cue-related modulations of cortical rhythms which may accompany crossmodal spatial attention, expectation or decision, and therefore contribute to cue validity effects. The clearly lateralized alpha suppression after tactile cues in our data indicates its dependence on endogenous rather than exogenous shifts of visuo-spatial attention following a cue independent of its modality.     

Strategy of auditory discrimination of scale in Java sparrows: they use both "imagery" and specific cues

We examined whether Java sparrows use imagery of auditory stimuli (imagery is a subject's mental representation of a stimulus by which the subject's behaviour may be governed under stimulus control even in the absence of the physical stimulus). Three types of ascending tone sequences were used. In the intact scale, sequence tones were played in ascending order. In the intact-masked scale, part of the sequence was masked by noise but the remaining scale was identical with the intact scale, whereas in the violated scale, the sequence could be heard as if tones were played slowly (Experiment 1) or quickly (Experiment 2). Subjects were divided into two groups: one group was trained to respond to the intact and intact-masked scales and to suppress response to the violation scale (imagery-positive group). The contingency was reversed for the other (violation-positive) group. In Experiment 1, all the birds acquired discrimination, but successful transfer to novel stimuli was observed only in the imagery-positive group, suggesting that the imagery of the tone sequence was used as a discriminative cue. Experiment 2 confirmed that the stimulus duration was a discriminative cue for both groups, suggesting that the birds also acquired discrimination using only specific cues.     

Mismatch negativity of ERP in cross-modal attention

Event-related potentials were measured in 12 healthy youth subjects aged 19-22 using the paradigm "cross-modal and delayed response" which is able to improve unattended purity and to avoid the effect of task target on the deviant components of ERP. The experiment included two conditions: (i) Attend visual modality, ignore auditory modality; (ii) attend auditory modality, ignore visual modality. The stimuli under the two conditions were the same. The difference wave was obtained by subtracting ERPs of the standard stimuli from that of the deviant stim-uli. The present results showed that mismatch negativity (MMN), N2b and P3 components can be produced in the auditory and visual modalities under attention condition. However, only MMN was observed in the two modalities un-der inattention condition. Auditory and visual MMN have some features in common: their largest MMN wave peaks were distributed respectively over their primary sensory projection areas of the scalp under attention condition, but over front     

Directed attention influence on the human brain potentials under conditions of probability visual stimulation

Saccadic latency and averaged EEG-potentials connected with switching on of the set and cue visual stimuli were examined in 12 right-handed healthy subjects in M. Posner's "cost-benefit" experimental paradigm. It was shown that attention was reflected in parameters of positive potential P100 evoked by switching on of set and cue stimuli and P300 and slow positive wave PMP1 evoked by switching on of the set stimulus in the relevant conditions. The spatiotemporal pattern of P100 probably reflects the involvement of the frontoparietal network of spacial attention in the perception of a relevant stimulus. Prevalence of the P300 and PMP1 potentials in the right parietal cortex suggests that these potentials reflect processes of space attention and visual fixation. Late positive potentials in a 600-900-ms interval after switching on of the set stimulus were found. Their amplitude was higher in backward averaging and they were predominantly localized in the left frontal cortex. These findings suggest that the late potentials reflect the anticipation and motor attention processes.     

Face Orientation and Motion Differently Affect the Deployment of Visual Attention in Newborns and 4-Month-Old Infants

Orienting visual attention allows us to properly select relevant visual information from a noisy environment. Despite extensive investigation of the orienting of visual attention in infancy, it is unknown whether and how stimulus characteristics modulate the deployment of attention from birth to 4 months of age, a period in which the efficiency in orienting of attention improves dramatically. The aim of the present study was to compare 4-month-old infants’ and newborns’ ability to orient attention from central to peripheral stimuli that have the same or different attributes. In Experiment 1, all the stimuli were dynamic and the only attribute of the central and peripheral stimuli to be manipulated was face orientation. In Experiment 2, both face orientation and motion of the central and peripheral stimuli were contrasted. The number of valid trials and saccadic latency were measured at both ages. Our results demonstrated that the deployment of attention is mainly influenced by motion at birth, while it is also influenced by face orientation at 4-month of age. These findings provide insight into the development of the orienting visual attention in the first few months of life and suggest that maturation may be not the only factor that determines the developmental change in orienting visual attention from birth to 4 months.     

Preserved Discrimination Performance and Neural Processing during Crossmodal Attention in Aging

In a recent study in younger adults (19-29 year olds) we showed evidence that distributed audiovisual attention resulted in improved discrimination performance for audiovisual stimuli compared to focused visual attention. Here, we extend our findings to healthy older adults (60-90 year olds), showing that performance benefits of distributed audiovisual attention in this population match those of younger adults. Specifically, improved performance was revealed in faster response times for semantically congruent audiovisual stimuli during distributed relative to focused visual attention, without any differences in accuracy. For semantically incongruent stimuli, discrimination accuracy was significantly improved during distributed relative to focused attention. Furthermore, event-related neural processing showed intact crossmodal integration in higher performing older adults similar to younger adults. Thus, there was insufficient evidence to support an age-related deficit in crossmodal attention.     

Selective and divided attention in animals

This article reviews some of the research on attentional processes in animals. In the traditional approach to selective attention, it is proposed that in addition to specific response attachments, animals also learn something about the dimension along which the stimuli fall (e.g., hue, brightness, or line orientation). More recently, there has been an attempt to find animal analogs to methodologies originally applied to research with humans. One line of research has been directed to the question of whether animals can locate a target among distracters faster if they are prepared for the presentation of the target (search image and priming). In the study of search image, the target is typically a food item and the cue consists of previous trials on which the same target is presented. In research on priming effects, the cue is typically different from the target but is a good predictor of its occurrence. The study of preattentive processes shows that perceptually, certain stimuli stand out from distracters better than others, depending not only on characteristics of the target relative to the distracters, but also on relations among the distracters. Research on divided attention is examined with the goal of determining whether an animal can process two elements of a compound sample with the same efficiency as one. Taken together, the reviewed research indicates that animals are capable of centrally (not just peripherally) attending to selective aspects of a stimulus display.     

Pavlovian biconditional discrimination learning in the C57BL/6J mouse

Four experiments using mice examined acquisition of Pavlovian biconditional discriminations in which two stimulus compounds were paired with food (AX+ and BY+) and two were not (AY- and BX-). Temporally asynchronous compounds were generated by using contextual stimuli (Experiment 1) and 15-s discrete visual cues (Experiments 2A, 2B and 3) to disambiguate when embedded noise or tone stimuli would be paired with food. When food pellets followed both reinforced compounds, successful acquisition was obtained in Experiment 1 but not in Experiments 2A and 2B even though the order of trials was modeled after that used in Experiment 1. However, when differential outcomes followed the reinforced compounds in Experiment 3, acquisition was obtained with discrete cue stimulus compounds. The implications of these results for modulatory models of conditional discrimination learning in animals are discussed.     

The effect of selective attention on pattern-specific visual evoked potentials

In a complex choice reaction time experiment, patterned stimuli without luminance change were presented, and pattern-specific visual evoked potentials to lower half-field stimulation were recorded. Two experimental conditions were used. The first was the between-field selection, where square patterns were presented in either the lower or the upper half of the visual field. In a given stimulus run one of the half-fields was task-relevant, and the subjects' task was to press a microswitch to stimuli of higher duration value (GO stimuli), while they had to ignore shorter ones, i. e. stimuli of lower apparent spatial contrast (NOGO stimuli). They had to ignore the stimuli appearing in the irrelevant half-field (IRR stimuli). In order to ensure proper fixation, the subjects had to press another microswitch at the onset of a dim light at the fixation point (CRT stimuli). Our second experimental condition was the within-field selection, where the GO, NOGO, and IRR stimuli appeared in the lower half of the visual field. GO and NOGO were square patterns while IRR stimuli were constructed of circles, or vice versa. (The CRT stimuli were the same as in the previous condition.) Three pattern-specific visual evoked potential components were identified, i. e. CI (70 ms latency), CII (100 ms latency), and CIII (170 ms latency). There were marked selective attention effects on both the CI-CII and CII-CIII peak-to-peak amplitudes. In both experimental conditions, responses with the highest amplitude were evoked by the GO type of stimuli, while the IRR stimuli evoked the smallest responses. According to these results, attention effects on the pattern-specific visual evoked potentials in the first 200 ms cannot be attributed to a simple stimulus set kind of selection.     

Diagnostic features of emotional expressions are processed preferentially

Diagnostic features of emotional expressions are differentially distributed across the face. The current study examined whether these diagnostic features are preferentially attended to even when they are irrelevant for the task at hand or when faces appear at different locations in the visual field. To this aim, fearful, happy and neutral faces were presented to healthy individuals in two experiments while measuring eye movements. In Experiment 1, participants had to accomplish an emotion classification, a gender discrimination or a passive viewing task. To differentiate fast, potentially reflexive, eye movements from a more elaborate scanning of faces, stimuli were either presented for 150 or 2000 ms. In Experiment 2, similar faces were presented at different spatial positions to rule out the possibility that eye movements only reflect a general bias for certain visual field locations. In both experiments, participants fixated the eye region much longer than any other region in the face. Furthermore, the eye region was attended to more pronouncedly when fearful or neutral faces were shown whereas more attention was directed toward the mouth of happy facial expressions. Since these results were similar across the other experimental manipulations, they indicate that diagnostic features of emotional expressions are preferentially processed irrespective of task demands and spatial locations. Saliency analyses revealed that a computational model of bottom-up visual attention could not explain these results. Furthermore, as these gaze preferences were evident very early after stimulus onset and occurred even when saccades did not allow for extracting further information from these stimuli, they may reflect a preattentive mechanism that automatically detects relevant facial features in the visual field and facilitates the orientation of attention towards them. This mechanism might crucially depend on amygdala functioning and it is potentially impaired in a number of clinical conditions such as autism or social anxiety disorders.     

Stay Tuned: What Is Special About Not Shifting Attention?

Background

When studying attentional orienting processes, brain activity elicited by symbolic cue is usually compared to a neutral condition in which no information is provided about the upcoming target location. It is generally assumed that when a neutral cue is provided, participants do not shift their attention. The present study sought to validate this assumption. We further investigated whether anticipated task demands had an impact on brain activity related to processing symbolic cues.

Methodology/Principal Findings

Two experiments were conducted, during which event-related potentials were elicited by symbolic cues that instructed participants to shift their attention to a particular location on a computer screen. In Experiment 1, attention shift-inducing cues were compared to non-informative cues, while in both conditions participants were required to detect target stimuli that were subsequently presented at peripheral locations. In Experiment 2, a non-ambiguous “stay-central” cue that explicitly required participants not to shift their attention was used instead. In the latter case, target stimuli that followed a stay-central cue were also presented at a central location. Both experiments revealed enlarged early latency contralateral ERP components to shift-inducing cues compared to those elicited by either non-informative (exp. 1) or stay-central cues (exp. 2). In addition, cueing effects were modulated by the anticipated difficulty of the upcoming target, particularly so in Experiment 2. A positive difference, predominantly over the posterior contralateral scalp areas, could be observed for stay-central cues, especially for those predicting that the upcoming target would be easy. This effect was not present for non-informative cues.

Conclusions/Significance

We interpret our result in terms of a more rapid engagement of attention occurring in the presence of a more predictive instruction (i.e. stay-central easy target). Our results indicate that the human brain is capable of very rapidly identifying the difference between different types of instructions.