Spatial Attention

In many applications, the primary goal of a spatialized audio cue is to direct the user’s attention to the location of a visual object of interest in the environment. This type of auditory cueing is known to be very effective in environments that contain only a single visual target. However, little is known about the effectiveness of this technique in environments with more than one possible target location. In this experiment, participants were asked to identify the characteristics of a visual target presented in a field of visual distracters. In some conditions, a single auditory cue was provided. In other conditions, the auditory cue was accompanied by one or more audio distracters at different spatial locations. These conditions were compared to a control condition in which no audio cue was provided. The results show that listeners can extract spatial information from up to three simultaneous sound sources, but that their visual search performance is significantly degraded when ...

In five experiments we compared prosaccade and antisaccade performance in normal human observers. This was first examined for visual stimulation in temporal or nasal hemifields, under monocular viewing. Prosaccades were faster following temporal than nasal stimulation, in accordance with previous results. The novel finding was that the opposite pattern was observed for antisaccades, consistent with a difficulty in overcoming a stronger prosaccade tendency after temporal-hemifield stimulation. A second experiment showed that these results were not simply due to antisaccades following nasal stimulation benefitting from being made towards a temporal place-holder. Prosaccades and antisaccades were then compared for visual versus somatosensory stimulation. The substantial latency difference between prosaccades and antisaccades for visual stimuli was eliminated for somatosensory stimuli. Antisaccades can thus benefit in relative terms when the competing prosaccadic tendency is weakened; but two further experiments revealed that not all manipulations induce opposing outcomes for the two types of saccade. Although reducing the contrast of visual targets can slow prosaccades and conversely speed antisaccades, this was not the case at the lowest contrast level used, where both types of saccade were slowed, thus indicating some common limiting source. Moreover, warning sounds presented shortly before a visual target speeded both prosaccades and antisaccades. These results illustrate that several factors which slow prosaccades can speed antisaccades (consistent with competition between different pathways); but also reveal some notable exceptions, where both types of saccade are slowed or speeded together, suggesting some common pathways that may precede competition over the direction of the saccade.

In five experiments we compared prosaccade and antisaccade performance in normal human observers. This was first examined for visual stimulation in temporal or nasal hemifields, under monocular viewing. Prosaccades were faster following temporal than nasal stimulation, in accordance with previous results. The novel finding was that the opposite pattern was observed for antisaccades, consistent with a difficulty in overcoming a stronger prosaccade tendency after temporal-hemifield stimulation. A second experiment showed that these results were not simply due to antisaccades following nasal stimulation benefitting from being made towards a temporal place-holder. Prosaccades and antisaccades were then compared for visual versus somatosensory stimulation. The substantial latency difference between prosaccades and antisaccades for visual stimuli was eliminated for somatosensory stimuli. Antisaccades can thus benefit in relative terms when the competing prosaccadic tendency is weakened; but two further experiments revealed that not all manipulations induce opposing outcomes for the two types of saccade. Although reducing the contrast of visual targets can slow prosaccades and conversely speed antisaccades, this was not the case at the lowest contrast level used, where both types of saccade were slowed, thus indicating some common limiting source. Moreover, warning sounds presented shortly before a visual target speeded both prosaccades and antisaccades. These results illustrate that several factors which slow prosaccades can speed antisaccades (consistent with competition between different pathways); but also reveal some notable exceptions, where both types of saccade are slowed or speeded together, suggesting some common pathways that may precede competition over the direction of the saccade.

Recent behavioral and event-related brain potential (ERP) studies have revealed cross-modal interactions in endogenous spatial attention between vision and audition, plus vision and touch. The present ERP study investigated whether these interactions reflect supramodal attentional control mechanisms, and whether similar cross-modal interactions also exist between audition and touch. Participants directed attention to the side indicated by a cue to detect infrequent auditory or tactile targets at the cued side. The relevant modality (audition or touch) was blocked. Attentional control processes were reflected in systematic ERP modulations elicited during cued shifts of attention. An anterior negativity contralateral to the cued side was followed by a contralateral positivity at posterior sites. These effects were similar whether the cue signaled which side was relevant for audition or for touch. They also resembled previously observed ERP modulations for shifts of visual attention, t...

Precue validity affects the performance of perceptual tasks. These spatial attention effects have been variously attributed to facilitation of processing, capacity allocation, or noise reduction. We used a new attention-plus-external (stimulus)-noise paradigm and model to identify the mechanisms of attention in cue-validity paradigms. A new phenomenon is reported: a large effect of location cue validity in an orientation identification task that specifically occurs when the stimulus is embedded in external (environmental or stimulus) noise. This result identifies the mechanism of the effect as external-noise exclusion, distinguished from stimulus enhancement that manifests itself only in noiseless stimulus environments.

Despite this body of work, the relative contributions of these areas to guiding spatial selection and visuomotor behavior are still poorly understood. This is due mainly to the limitations of traditional imaging methods. In particular, while microelectrode recordings shed light on the specialized functions of highly localized cortical regions, they typically do not capture activity across spatially distributed networks simultaneously. Thus, they cannot characterize activity in distributed networks or their interactions. fMRI, on the other hand, cannot capture the dynamics of attentional mechanisms with high temporal resolution. This limitation is due in part to technical factors (e.g., scanning durations), but

Visual processing mainly occurs during fixation, periods separated by saccadic eye movements, necessitating a close coordination between sensory and motor systems. It has been suggested that the intention to make a saccade can modulate neural activity, including predictive changes, suppression of peri-saccadic retinal input and trans-saccadic integration. Consistent with this idea, modulations of neural activity around the time of saccades have been reported in non-human species, showing non-visually mediated, extraretinal responses in specific brain regions. In humans, however, peri-saccadic wholebrain activity has mainly been studied in the context of a perceptual task, making it difficult to disentangle activity related to the task, visual transients from retinal stimulation and non-visual (saccade-related) responses. We measured magnetoencephalography (MEG) theta (3-7 Hz) and alpha (8-12 Hz) activity during voluntary horizontal saccade execution between two fixation points. To distinguish between visually and non-visually mediated activity, participants engaged in three tasks: voluntary saccades in near-darkness, fixation with visual input shifted to simulate the saccade, and volitional saccades in total darkness. Using correlational analyses, we found that patterns of neural activity are consistent with contributions of two separate mechanisms, one related to saccades (non-visual/extraretinal) and the other linked to the processing of visual input at the beginning of the new fixation (visual/retinal). Changes in occipital alpha power and instantaneous frequency showed a similar time course in near-dark and simulated saccade conditions, suggesting an effect of visually evoked responses. In contrast, alterations in parietal-occipital theta power and phase clustering were consistent with a non-visually-driven (extraretinal) mechanism, with similar multivariate patterns for near-dark and full-darkness conditions. Some effects, such as theta phase reset and alterations in alpha power, showed separable contributions of both the saccade and visual transient, with differing time courses. This combination of visual and nonvisual mechanisms may support sensorimotor integration during active vision.

Human cognition is characterized by severe capacity limits: we can accurately track, enumerate, or hold in mind only a small number of items at a time. It remains debated whether capacity limitations across tasks are determined by a common system. Here we measure brain activation of adult subjects performing either a visual short-term memory (vSTM) task consisting of holding in mind precise information about the orientation and position of a variable number of items, or an enumeration task consisting of assessing the number of items in those sets. We show that task-specific capacity limits (three to four items in enumeration and two to three in vSTM) are neurally reflected in the activity of the posterior parietal cortex (PPC): an identical set of voxels in this region, commonly activated during the two tasks, changed its overall response profile reflecting task-specific capacity limitations. These results, replicated in a second experiment, were further supported by multivariate pa...

Recent evidence indicates that the spatial direction of endogenous covert spatial attention in one sensory modality can crossmodally influence early processing of stimuli in a different modality. However, spatial locations are initially coded according to different frames of reference for different modalities (e.g., body-centered for touch versus retinocentric vision) and postural changes (e.g., gaze shifts) will realign these. Here, we used event-related potentials (ERPs) to investigate how the direction of endogenous tactile attention affects sensory-specific visual ERP components. Critically, by manipulating direction of gaze, we were able to test whether any crossmodal effects depend on visual and tactile projections to a common hemisphere, on common locations in external space, or on some combination of the two. We found that both P1 and N1 visual components were modulated according to the direction of endogenous tactile attention. While the P1 crossmodal effect followed purely hemispheric constraints, the attentional modulation of N1 appeared to combine both anatomical and external spatial constraints.

& Previous ERP studies have uncovered cross-modal interactions in endogenous spatial attention. Directing attention to one side to judge stimuli from one particular modality can modulate early modality-specific ERP components not only for that modality, but also for other currently irrelevant modalities. However, past studies could not determine whether the spatial focus of attention in the task-irrelevant secondary modality was similar to the primary modality, or was instead diffuse across one hemifield. Here, auditory or visual stimuli could appear at any one of four locations (two on each side). In different blocks, subjects judged stimuli at only one of these four locations, for an auditory (Experiment 1) or visual (Experiment 2) task. Early attentional modulations of visual and auditory ERPs were found for stimuli at the currently relevant location, compared with those at the irrelevant location within the same hemifield, thus demonstrating within-hemifield tuning of spatial attention. Crucially, this was found not only for the currently relevant modality, but also for the currently irrelevant modality. Moreover, these within-hemifield attention effects were statistically equivalent regardless of the task relevance of the modality, for both the auditory and visual ERP data. These results demonstrate that within-hemifield spatial attention for one task-relevant modality can transfer cross-modally to a task-irrelevant modality, consistent with spatial selection at a multimodal level of representation. &

The N2pc component has recently become a popular tool in attention research. To investigate whether this component exclusively reflects attentional target selection, or also prior stages in attentional processing (covert orienting, target-unspecific spatial attention), a spatial cueing procedure was combined with a visual search task. In some blocks, informative cues indicated the side of upcoming singleton targets that were present on most trials among uniform distractors. In other blocks, cues were spatially uninformative, and no preparatory shifts of attention were possible. The N2pc in response to targets was unaffected by this manipulation, showing that this component is not associated with attention shifts. Following informative cues, an attenuated N2pc was elicited by uniform non-target arrays, suggesting that the N2pc may also reflect spatially specific processing of stimulus features at task-relevant locations prior to target selection. Over the past thirty years, the brain mechanisms underlying visual-spatial attention have been studied intensively with event-related brain potential (ERP) measures. Different ERP components have been found to be modulated during spatially selective visual processing, and these components have been linked to different underlying sub-processes of spatial attention. The first type of attention-sensitive ERP effect was uncovered in early ERP studies where participants were instructed to direct their attention to a specific location on the left or right side, and keep it focused for an entire experimental block in order to detect target stimuli at that location (cf., Eason, 1981). Visual stimuli presented within the current focus of spatial attention triggered enhanced sensory-specific visual P1 and N1 components at posterior electrodes. Analogous P1 and N1 amplitude modulations were also observed when attention was manipulated in a trial-by-trial fashion by spatial precues that were presented at the start of each trial (cf. . Because these P1/N1 enhancements for stimuli at attended locations were present irrespective of whether these stimuli were targets or non-targets (e.g., , they are interpreted as reflecting location-specific sensory gating mechanisms in early visual processing that precede the subsequent selection of targets over non-targets. They are assumed to be triggered by top-down signals from higher-order attentional control areas that bias the excitability of visual cortical areas in favour of any sensory input that originates from currently task-relevant locations (cf., Mangun, 1995). Other attention-sensitive ERP modulations found in more recent studies during cued shifts of spatial attention were interpreted as electrophysiological markers of top-down attentional control processes. In these studies, ERP components sensitive to the direction of cued attentional shifts were quantified by comparing ERP waveforms triggered in the interval

Previous experiments investigating ERP correlates of anticipatory attention shifts triggered by central symbolic cues have identified a contralateral ''early directing attention negativity,'' which was assumed to be generated by processes involved in the control of spatial orienting. Here we demonstrate that this component is not directly linked to the control of attentional shifts, but instead reflects the selection of task-relevant aspects of cue stimuli. In contrast, later ERP components triggered during covert attentional shifts are insensitive to physical cue attributes, and thus appear to be genuine electrophysiological correlates of covert attentional control mechanisms.

In attentional momentum, detection of a target further ahead in the direction of an ongoing attention shift is faster than detection of a target an equal distance in an orthogonal direction. In representational momentum, memory for the location of a previously viewed target is displaced in the direction of target motion. Hubbard [Hubbard, T. L. (2014). Forms of momentum across space: Representational, operational, and attentional. Psychonomic Bulletin & Review, 21(6), 1371-1403; Hubbard, T. L. (2015). The varieties of momentum-like experience. Psychological Bulletin, 141(6), 1081-1119] hypothesized that attentional momentum and representational momentum might be related or reflect the same mechanism or similar mechanisms. Two experiments collected measures of attentional momentum and representational momentum. In Experiment 1, attentional momentum based on differences between detecting targets opposite or orthogonal to a cued location was not correlated with representational momentum based on M displacement for the final location of a target. In Experiment 2, attentional momentum based on facilitation in detecting a gap on a probe presented in front of the final target location was not correlated with representational momentum based on a weighted mean of the probabilities of a same response in probe judgments of the final target location. Implications of the findings for the relationship of attentional momentum and representational momentum, and for theories of momentum-like effects in general, are considered.

In illusory line motion, presentation of a cue is followed by presentation of a nearby stationary line, and the line is perceived to "unfold," "expand," or "extend" away from the cue. Effects of the allocation of attention regarding where the cue or the line would be presented were measured in three experiments, and ratings of relative velocity and relative strength of illusory motion were collected. Findings included (a) relative velocity and relative strength decreased with increases in SOA from 50 to 450 ms, (b) relative velocity and relative strength were not influenced by whether illusory motion moved from one end of the line to the other or from both ends toward the middle of the line, (c) increased uncertainty regarding where the line would appear did not influence relative velocity or relative strength, and (d) valid pre-cues regarding the location of a cue resulted in faster relative velocity than did invalid pre-cues, but pre-cue validity did not influence relative strength. Implications of these findings for the relationship of such illusory motion and attention (e.g., divided attention, shifts in attended location) are considered.

It is known that visual performance is better on the horizontal than the vertical meridian, and in the lower than the upper region of the vertical meridian (Vertical Meridian Asymmetry, "VMA"), and that exogenous spatial attention increases the apparent contrast of a stimulus. Here we investigate whether the VMA also leads to differences in the subjective appearance of contrast between the upper and lower vertical meridian, and how the effects of exogenous spatial attention on appearance interact with the VMA. Two Gabor stimuli were presented North and South of fixation at 4-eccentricity along the vertical meridian. Observers were asked to report the orientation of the Gabor that was higher in contrast. By assessing which stimulus observers perceived to be higher in contrast, we obtained psychometric functions and their concomitant points of subjective equality (PSE). These functions were measured both when a neutral cue was presented in the middle of the display and transient attention was deployed via a peripheral cue to the location of one of the stimuli. Observers were told that the cues were uninformative as to the stimulus contrast or its orientation. We report two novel findings. First, apparent contrast is higher on the lower vertical meridian than on the upper. Second, the attentional enhancement of apparent contrast is asymmetrical with both low and high contrast stimuli; the effect of exogenous spatial attention is greater on the lower than the upper vertical meridian. As in prior studies, we find no corresponding asymmetry in orientation discrimination. Signal detection-based models explain the asymmetrical appearance effects as a function of differential multiplicative gain factors for the North and South locations, and predict a similar but much smaller asymmetry for orientation discrimination.

Feature attention operates in a spatially global way, with attended feature values being prioritized for selection outside the focus of attention. Accounts of global feature attention have emphasized feature competition as a determining factor. Here, we use magnetoencephalographic recordings in humans to test whether competition is critical for global feature selection to arise. Subjects performed a color/shape discrimination task in one visual field (VF), while irrelevant color probes were presented in the other unattended VF. Global effects of color attention were assessed by analyzing the response to the probe as a function of whether or not the probe's color was a target-defining color. We find that global color selection involves a sequence of modulations in extrastriate cortex, with an initial phase in higher tier areas (lateral occipital complex) followed by a later phase in lower tier retinotopic areas (V3/V4). Importantly, these modulations appeared with and without color competition in the focus of attention. Moreover, early parts of the modulation emerged for a task-relevant color not even present in the focus of attention. All modulations, however, were eliminated during simple onset-detection of the colored target. These results indicate that global color-based attention depends on target discrimination independent of feature competition in the focus of attention.

Recent brain imaging studies using functional magnetic resonance imaging (fMRI) have implicated a frontal-parietal network in the top-down control of attention. However, little is known about the timing and sequence of activations within this network. To investigate these timing questions, we used event-related electrical brain potentials (ERPs) and a specially designed visual-spatial attentional-cueing paradigm, which were applied as part of a multi-methodological approach that included a closely corresponding event-related fMRI study using an identical paradigm. In the first 400 ms post cue, attention-directing and control cues elicited similar general cue-processing activity, corresponding to the more lateral subregions of the frontal-parietal network identified with the fMRI. Following this, the attention-directing cues elicited a sustained negative-polarity brain wave that was absent for control cues. This activity could be linked to the more medial frontal-parietal subregions similarly identified in the fMRI as specifically involved in attentional orienting. Critically, both the scalp ERPs and the fMRI-seeded source modeling for this orienting-related activity indicated an earlier onset of frontal versus parietal contribution (;400 versus ;700 ms). This was then followed (;800-900 ms) by pretarget biasing activity in the region-specific visual-sensory occipital cortex. These results indicate an activation sequence of key components of the attentional-control brain network, providing insight into their functional roles. More specifically, these results suggest that voluntary attentional orienting is initiated by medial portions of frontal cortex, which then recruit medial parietal areas. Together, these areas then implement biasing of region-specific visual-sensory cortex to facilitate the processing of upcoming visual stimuli.

We used event-related potentials (ERPs) to evaluate the role of attention in the integration of visual and auditory features of multisensory objects. This was done by contrasting the ERPs to multisensory stimuli (AV) to the sum of the ERPs to the corresponding auditory-only (A) and visual-only (V) stimuli [i.e., AV vs. (A + V)]. V, A, and VA stimuli were presented in random order to the left and right hemispaces. Subjects attended to a designated side to detect infrequent target stimuli in either modality there. The focus of this report is on the ERPs to the standard (i.e., nontarget) stimuli. We used rapid variable stimulus onset asynchronies (350-650 msec) to mitigate anticipatory activity and included “no-stim” trials to estimate and remove ERP overlap from residual anticipatory processes and from adjacent stimuli in the sequence. Spatial attention effects on the processing of the unisensory stimuli consisted of a modulation of visual P1 and N1 components (at 90-130 msec and 160-...

Several major cognitive neuroscience models have posited that focal spatial attention is required to integrate different features of an object to form a coherent perception of it within a complex visual scene. Although many behavioral studies have supported this view, some have suggested that complex perceptual discrimination can be performed even with substantially reduced focal spatial attention, calling into question the complexity of object representation that can be achieved without focused spatial attention. In the present study, we took a cognitive neuroscience approach to this problem by recording cognition-related brain activity both to help resolve the questions about the role of focal spatial attention in object categorization processes and to investigate the underlying neural mechanisms, focusing particularly on the temporal cascade of these attentional and perceptual processes in visual cortex. More specifically, we recorded electrical brain activity in humans engaged i...

Recent behavioral and event-related brain potential (ERP) studies have revealed cross-modal interactions in endogenous spatial attention between vision and audition, plus vision and touch. The present ERP study investigated whether these interactions reflect supramodal attentional control mechanisms, and whether similar cross-modal interactions also exist between audition and touch. Participants directed attention to the side indicated by a cue to detect infrequent auditory or tactile targets at the cued side. The relevant modality (audition or touch) was blocked. Attentional control processes were reflected in systematic ERP modulations elicited during cued shifts of attention. An anterior negativity contralateral to the cued side was followed by a contralateral positivity at posterior sites. These effects were similar whether the cue signaled which side was relevant for audition or for touch. They also resembled previously observed ERP modulations for shifts of visual attention, t...

We demonstrate a previously unknown gender difference in the distribution of spatial attention, a basic capacity that supports higher-level spatial cognition. More remarkably, we found that playing an action video game can virtually eliminate this gender difference in spatial attention and simultaneously decrease the gender disparity in mental rotation ability, a higher-level process in spatial cognition. After only 10 hr of training with an action video game, subjects realized substantial gains in both spatial attention and mental rotation, with women benefiting more than men. Control subjects who played a nonaction game showed no improvement. Given that superior spatial skills are important in the mathematical and engineering sciences, these findings have practical implications for attracting men and women to these fields.

Synesthesia is a condition in which stimulation in one modality also gives rise to a perceptual experience in a second modality. In two recent studies we found that the condition is more common than previously reported; up to 5% of the population may experience at least one type of synesthesia. Although the condition has been traditionally viewed as an anomaly (e.g., breakdown in modularity), it seems that at least some of the mechanisms underlying synesthesia do reflect universal crossmodal mechanisms. We review here a number of examples of crossmodal correspondences found in both synesthetes and nonsynesthetes including pitch-lightness and vision-touch interaction, as well as cross-domain spatial-numeric interactions. Additionally, we discuss the common role of spatial attention in binding shape and color surface features (whether ordinary or synesthetic color). Consistently with behavioral and neuroimaging data showing that chromatic-graphemic (colored-letter) synesthesia is a ge...

Attention is often conceived as a gateway to consciousness . Although endogenous spatial attention may be independent of conscious perception (CP) , exogenous spatial orienting seems instead to be an important modulator of CP . Here, we investigate the role of auditory alerting in CP in normal observers. We used a behavioral task in which phasic alerting tones were presented either at unpredictable or at predictable time intervals prior to the occurrence of a near-threshold visual target. We find, for the first time in neurologically intact observers, that phasic alertness increases CP, both objectively and subjectively. This result is consistent with evidence showing that phasic alerting can ameliorate the spatial bias exhibited by visual neglect patients . The alerting network may increase the activity of fronto-parietal networks involved in top-down amplification required to bring a stimulus into consciousness .

When asked to estimate the outcome of arithmetic problems, participants overestimate for addition problems and underestimate for subtraction problems, both in symbolic and non-symbolic format. This bias is referred to as operational momentum effect (OM). The attentional shifts account holds that during computation of the outcome participants are propelled too far along a spatial number representation. OM was observed in non-symbolic multiplication and division while being absent in symbolic multiplication and division. Here, we investigate whether (a) the absence of the OM in symbolic multiplication and division was due to the presentation of the correct outcome amongst the response alternatives, putatively triggering verbally mediated fact retrieval, and whether (b) OM is correlated with attentional parameters, as stipulated by the attentional account. Participants were presented with symbolic and non-symbolic multiplication and division problems. Among seven incorrect response alternatives participants selected the most plausible result. Participants were also presented with a Posner task, with valid (70%), invalid (15%) and neutral (15%) cues pointing to the position at which a subsequent target would appear. While no OM was observed in symbolic format, non-symbolic problems were subject to OM. The non-symbolic OM was positively correlated with reorienting after invalid cues. These results provide further evidence for a functional association between spatial attention and approximate arithmetic, as stipulated by the attentional shifts account of OM. They also suggest that the cognitive processes underlying multiplication and division are less prone to spatial biases compared to addition and subtraction, further underlining the involvement of differential cognitive processes.

When asked to estimate the outcome of arithmetic problems, participants overestimate for addition problems and underestimate for subtraction problems, both in symbolic and non-symbolic format. This bias is referred to as operational momentum effect (OM). The attentional shifts account holds that during computation of the outcome participants are propelled too far along a spatial number representation. OM was observed in non-symbolic multiplication and division while being absent in symbolic multiplication and division. Here, we investigate whether (a) the absence of the OM in symbolic multiplication and division was due to the presentation of the correct outcome amongst the response alternatives, putatively triggering verbally mediated fact retrieval, and whether (b) OM is correlated with attentional parameters, as stipulated by the attentional account. Participants were presented with symbolic and non-symbolic multiplication and division problems. Among seven incorrect response alt...

Cerebral blood flow PET scans and high-density event-related potentials (ERPs) were recorded (separate sessions) while subjects viewed rapidly-presented, lower-visual-field, bilateral stimuli. Active attention to a designated side of the stimuli (relative to passive-viewing conditions) resulted in an enhanced ERP positivity (P1 effect) from 80-150 msec over occipital scalp areas contralateral to the direction of attention. In PET scans, active attention vs. passive showed strong activation in the contralateral dorsal occipital cortex, thus following the retinotopic organization of the early extrastriate visual sensory areas, with some weaker activation in the contralateral fusiform. Dipole modeling seeded by the dorsal occipital PET foci yielded an excellent fit for the P1 attention effect. In contrast, dipoles constrained to the fusiform foci fit the P1 effect poorly, and, when the location constraints were released, moved upward to the dorsal occipital locations during iterative dipole fitting. These results argue that the early ERP P1 attention effects for lower-visual-field stimuli arise mainly from these dorsal occipital areas and thus also follow the retinotopic organization of the visual sensory input pathways. These combined PET/ERP data therefore provide strong evidence that sustained visual spatial attention results in a preset, top-down biasing of the early sensory input channels in a retinotopically organized way.

Background-Attention, the processing of one source of information to the exclusion of others, is important for most cognitive processes, including language. Evidence suggests not only that dysfunctional attention mechanisms contribute to language deficits after stroke, but also that orienting attention to a patient's ipsilesional hemispace recruits attention mechanisms in the intact hemisphere and improves language functions in some persons with aphasia. Aims-The aim of the current research was to offer proof of concept for the strategy of improving picture-naming performance in fluent aphasia by moving stimuli into the left hemispace. It was hypothesised that repeated orientation of attention to the ipsilesional hemispace during picture naming would lead to improved naming accuracy for participants with fluent aphasia. Methods & Procedures-Three participants with stable fluent aphasia received daily treatment sessions that consisted of naming simple line drawings presented 45 degrees to the left of body midline on a computer monitor. Naming probes were administered before initiation of the treatment protocol to establish a baseline, and before each treatment session to measure change during treatment. The C statistic was used to establish the stability of baseline performance and to determine whether the slope of the treatment phases differed significantly from the slope of the baseline. Outcomes & Results-Two of the three participants showed significant improvement over baseline performance in the percent correct of naming probes. One participant showed no improvement over baseline accuracy.

In this study, 7-19-year-olds performed an interrupted visual search task in two experiments. Our question was whether the tendency to respond within 500 ms after a second glimpse of a display (the rapid resumption effect [Psychological Science, 16 (2005) 684-688]) would increase with age in the same way as overall search efficiency. The results indicated no correlation of rapid resumption with search speed either across age groups (7, 9, 11, and 19 years) or at the level of individual participants. Moreover, relocating the target randomly between looks reduced the rate of rapid resumption in a very similar way at each age. These results imply that implicit perceptual prediction during search is invariant across this age range and is distinct from other critical processes such as feature integration and control over spatial attention.

Cerebral blood flow PET scans and high-density event-related potentials (ERPs) were recorded (separate sessions) while subjects viewed rapidly-presented, lower-visual-field, bilateral stimuli. Active attention to a designated side of the stimuli (relative to passive-viewing conditions) resulted in an enhanced ERP positivity (P1 effect) from 80-150 msec over occipital scalp areas contralateral to the direction of attention. In PET scans, active attention vs. passive showed strong activation in the contralateral dorsal occipital cortex, thus following the retinotopic organization of the early extrastriate visual sensory areas, with some weaker activation in the contralateral fusiform. Dipole modeling seeded by the dorsal occipital PET foci yielded an excellent fit for the P1 attention effect. In contrast, dipoles constrained to the fusiform foci fit the P1 effect poorly, and, when the location constraints were released, moved upward to the dorsal occipital locations during iterative dipole fitting. These results argue that the early ERP P1 attention effects for lower-visual-field stimuli arise mainly from these dorsal occipital areas and thus also follow the retinotopic organization of the visual sensory input pathways. These combined PET/ERP data therefore provide strong evidence that sustained visual spatial attention results in a preset, top-down biasing of the early sensory input channels in a retinotopically organized way.

Unilateral spatial neglect is a neuropsychological syndrome commonly observed after stroke and defined by the inability to attend or respond to contralesional stimuli. Typically, symptoms are assessed using clinical tests that rely upon visual/perceptual abilities. However, neglect may affect high-level representations controlling attention in other modalities as well. Here we developed a novel manual exploration test using a touch screen computer to quantify spatial search behaviour without visual input. Twelve chronic stroke patients with left neglect and 27 patients without neglect (based on clinical tests) completed our task. Four of the 12 "neglect" patients exhibited clear signs of neglect on our task as compared to "non-neglect" patients and healthy controls, and six other patients (from both groups) also demonstrated signs of neglect compared to healthy controls only. While some patients made asymmetrical responses on only one task, generally, patients wi...

Patients with complex regional pain syndrome (CRPS) report cognitive difficulties, affecting the ability to represent, perceive and use their affected limb. Moseley, Gallace & Spence (2009) observed that CRPS patients tend to bias the perception of tactile stimulation away from the pathological limb. Interestingly, this bias was reversed when CRPS patients were asked to cross their arms, implying that this bias is embedded in a complex representation of the body that takes into account the position of body-parts. Other studies have failed to replicate this finding (Filbrich et al., 2017) or have even found a bias in the opposite direction (Sumitani et al., 2007). Moreover, perceptual biases in CRPS patients have not often been compared to these of other chronic pain patients. Chronic pain patients are often characterized by an excessive focus of attention for bodily sensations. We might therefore expect that non-CRPS pain patients would show a bias towards instead of away from their...

We investigated whether anxiety facilitates detection of threat stimuli outside the focus of overt attention, and the time course of the interference produced by threat distractors. Threat or neutral word distractors were presented in attended (foveal) and unattended (parafoveal) locations followed by an unrelated probe word at 300 ms (Experiments 1 and 2) or 1000 ms (Experiment 2) stimulusÁonset asynchrony (SOA) in a lexical decision task. Results showed: (1) no effects of trait anxiety on selective saccades to the parafoveal threat distractors; (2) interference with probe processing (i.e., slowed lexical decision times) following a foveal threat distractor at 300 ms SOA for all participants, regardless of anxiety, but only for high-anxiety participants at 1000 ms SOA; and (3) no interference effects of parafoveal threat distractors. These findings suggest that anxiety does not enhance preattentive semantic processing of threat words. Rather, anxiety leads to delays in the inhibitory control of attended taskirrelevant threat stimuli.

In a previous study using positron emission tomography (PET), we demonstrated that focused attention to a location in the visual field produced increased regional cerebral blood flow in the fusiform gyrus contralateral to the attended hemifield (Heinze et al. [1994]: Nature 372:543). We related these effects to modulations in the amplitude of the P1 component (80-130 msec latency) of the visual event-related brain potentials (ERPs) recorded from the same subjects, under the identical stimulus and task conditions. Here, we replicate and extend these findings by showing that attention effects in the fusiform gyrus and the P1 component were similarly modulated by the perceptual load of the task. When subjects performed a perceptually demanding symbol-matching task within the focus of spatial attention, the fusiform activity and P1 component of the ERP were of greater magnitude than when the subjects performed a less perceptually demanding task that required only luminance detection at the attended location. In the latter condition, both the PET and ERP attention effects were reduced. In addition, in the present data significant activations were also obtained in the middle occipital gyrus contralateral to the attended hemifield, thereby demonstrating that multiple regions of extrastriate visual cortex are modulated by spatial attention. The findings of covariations between the P1 attention effect and activity in the posterior fusiform gyrus reinforce our hypothesis that common neural sources exist for these complementary, but very different measures of human brain activity.

Research with adult subjects has provided convincing evidence for the existence of a covert visual attention system with the function of modulating shifts in overt visual attention, or gaze. The covert visual attention system becomes functional during the first 6 months of life. However, little is known about the course of its development, or how it may influence concurrent development in other domains. In this article, we examine associations between behavioural indicators of the development of the covert visual attention system and the development of the network of areas in the brain thought to mediate its activity. We argue that the covert attentional behaviours found at different stages in the period between birth and 6 months can be accounted for by the degree of maturation of the different areas in the Posterior Attention System network. We then provide evidence suggesting that the phases in covert attentional development indexed by behavioural and neurological indicators are reflected in changes in the quality of social looking in the same time period. The possible impact of covert visual attentional development on other areas of development is discussed briefly, and areas for further research are suggested.

The effects of age on the neural processes underlying shifts in visuospatial attention were studied by non-invasive recording of brain electrical activity. Event-related evoked potentials (ERPs) were recorded in young (age 28-36 years old) and elderly (59-74 years old) subjects during a target detection task. Targets were preceded by central or peripheral informative cues, which are hypothesized to provoke voluntary and reflexive shifts of spatial attention, respectively. There were no age-related differences in the effects of cue validity on reaction times. Elderly subjects had longer reaction times to both the valid and invalid targets. The ERP recordings demonstrated that attention shift-related negativities (ARNs) were generated over the hemisphere contralateral to the central cue direction with the same amplitude in young and elderly subjects. However, the onset latency was delayed for the elderly at anterior scalp sites. Peripheral cues enhanced the Nl component (140-200 ms post-cue) over the contralateral hemisphere comparably in the two age groups. The ARNs following Nl enhancement demonstrated delayed onset and restricted scalp distributions in the elderly group compared with the young group. These results suggest that resistance of cue validity effects to aging is consistent with existence of the Nl enhancement and ARNs, even in elderly subjects. Different age effects on ERPs generated by central and peripheral cues support the notion that voluntary and reflexive mechanisms of attention shift involve distinct neural systems with different vulnerability to aging.

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The mechanism by which visual-spatial attention affects the detection of faint signals has been the subject of considerable debate. It is well known that spatial cuing speeds signal detection. This may imply that attentional cuing modulates the processing of sensory information during detection or, alternatively, that cuing acts to create decision bias favoring input at the cued location. These possibilities were evaluated in 3 spatial cuing experiments. Peripheral cues were used in Experiment 1 and central cues were used in Experiments 2 and 3. Cuing similarly enhanced measured sensitivity, P(A) and d', for simple luminance detection in all 3 experiments. Under some conditions it also induced shifts in decision criteria (beta). These findings indicate that visual-spatial attention facilitates the processing of sensory input during detection either by increasing sensory gain for inputs at cued locations or by prioritizing the processing of cued inputs.

Patients with right hemisphere injury frequently neglect to cancel targets primarily in the left part of the page nearest the body. Since this region is diagonally opposite the area from where such patients usually begin cancelling, near left ('diagonal') neglect may be consequent to stimulus order effects ('fatigue'). We evaluated the persistence of near left neglect in nine stroke patients when they had to cancel either the near or the far half of the page before proceeding to the other half. Our results showed that near left neglect on the page was largely unaffected by cancellation order. Furthermore, a near left gradient of omissions was established within both radial (near and far) halves of the page, as well as for the entire page. Our findings suggest that diagonal cancellation neglect is unrelated to fatigue and reflects a consistent, two-dimensional disorder of spatial attention. Such neglect may be related to the extent of the visible stimulus array, as well as to the array's location in egocentric space.

Background-Some studies have suggested that in stroke patients, spatial inattention on the cancellation test is closely related to disorganized visual search. However, methods to assess spatial aspects of search organization on cancellation tests have not been well developed. In this study the authors design and evaluate new methods to quantify strategies of spatial exploration on the cancellation test in stroke patients who showed a broad range of spatial attentional abilities, and test whether disorganization and inattention are related. Methods-Twenty stroke patients were videotaped while they performed a cancellation test. Several variables that reflect spatial aspects of search organization were measured through subsequent video playback. Two patients with severe neglect were excluded from further analysis to avoid constraining the spatial expression of search organization. Spearman correlations were used to assess whether severity of spatial inattention correlated with the individual search organization measures. Results-Of the 18 remaining patients, 10 had mild-moderate spatial neglect (pathologic inattention), while the other 8 omitted at most one target (normal performance). There were no significant correlations between the number of targets omitted and any of the search organization measures. Conclusions-Spatial inattention on cancellation due to neglect following stroke is not closely related to the organization of visual search. Instead, search disorganization during cancellation may reflect disturbance of an unspecified executive control mechanism. The cancellation test has long been used in stroke patients to assess spatial inattention or neglect (pathologic inattention), partly because it is easy to reproduce and administer. The test presents numerous printed images (targets) on a conventionally sized sheet of paper that are to be marked once and individually with a pen or pencil; they are thus "canceled" as if they are postage stamps. Spatial inattention is measured by the amount of targets left unmarked after the patient indicates test completion. Cancellation neglect is highly

A priming procedure was used to study the processing of distractors located either inside (between the location of two targets) or outside (peripherally to the locations of the targets) the focus of attention. The stimuli were five-letter arrays, and participants had to decide whether two marked target letters were the same or different. In Experiments 1 and 2, positive priming was obtained both when targets and in-distractors in primes repeated as targets in probes; negative priming was found when out-distractor primes repeated as targets in probes. In Experiment 3, we also manipulated the match in letter case from primes to probes. In-distractors produced reliable positive priming, irrespective of whether the letters matched in case. In contrast out-distractors produced negative priming but only when the letters had the same case in primes and probes. These results are attributed to a spatial attention process operating (in this case) on low-level visual features, and an object-based selection process that enables more abstract information to be processed for selected stimuli.

Over the last decade, the additional singleton task has been widely used to study visual statistical learning. In this paradigm, participants are instructed to find a target while ignoring a series of distractors. In some trials, a salient singleton distractor is added to the search display, making the task more difficult. However, if the singleton appears more frequently in one particular location of the display, participants eventually learn to suppress attention towards this location. It has been suggested that this type of learning is probably implicit and independent of working memory (WM) resources. To our knowledge, only one study has explored the impact of WM in suppression effect (Gao and Theeuwes, 2020). However, there are reasons to suspect that the amount and type of WM load used in that study may have been suboptimal to detect any effects on distractor suppression. The aim of the present study was to explore the impact of WM load on distractor suppression addressing the...

Although a direct relationship between numerical-allocation and spatial-attention has been proposed, recent research suggests these processes are not directly coupled. In keeping with this, spatial attention shifts induced either via visual or vestibular motion can modulate numerical allocation in some circumstances but not in others. In addition to shifting spatial attention, visual or vestibular motion-paradigms also (i) elicit compensatory eye-movements which themselves can influence numerical-processing and (ii) alter the perceptual-state of-"self", inducing changes in bodily self-consciousness impacting upon cognitive mechanisms. Thus, the precise mechanism by which motion modulates numerical-allocation remains unknown. We sought to investigate the influence that different perceptual experiences of motion have upon numerical magnitude allocation whilst controlling for both eyemovements and task-related effects. We first used optokinetic visual-motion stimulation (OKS) to elicit the perceptual experience of either "visual world" or "self"-motion during which eye movements were identical. In a second experiment we used a vestibular protocol examining the effects of perceived and subliminal angular rotations in darkness, which also provoked identical eye movements. We observed that during the perceptual experience of "visual-world" motion, rightward OKS biased judgments towards smaller numbers, whereas leftward OKS biased judgments towards larger numbers. During the perceptual experience of "self-motion", judgments were biased towards larger numbers irrespective of the OKS direction. Contrastingly, vestibular motion perception was found not to modulate numerical magnitude allocation, nor was there any differential modulation when comparing "perceived" versus "subliminal" rotations. We provide a novel demonstration that magnitude-allocation can be differentially modulated by the perceptual state of-self during visual-motion.

To determine the manner in which attention is distributed among numerous locations in the visual space, we used a multifocal recording technique that allowed simultaneous recordings of evoked cortical activity from 12 visual field areas out to 23.6°. We found that multifocal visual evoked potential (mfVEP) amplitude was larger when a region of visual space was attended than when it was not attended. The magnitude of this effect was inversely related to visual field eccentricity and there was no attention-related modulation of VEP amplitude for the most eccentric region. In addition, we found that mfVEP amplitudes in the regions contiguous to the attended region could also be larger, depending upon their spatial relationship to the attended region. Specifically, amplitudes in more central regions on the 'meridian of attention' were larger when the subject attended anywhere along that meridian.

Attention can be focused voluntarily and effectively on spatial locations in order to enhance the processing of task-relevant events. However, work on 'attentional capture' has demonstrated that spatial biases can be temporarily reset by transient and salient stimuli, especially if they share defining characteristics with the targets of a task goal. In the current study, we investigated whether the appearance of stimuli containing task-defining features at an unattended location was sufficient to capture attention, even when these were not perceptually salient. We used event-related-potential (ERP) markers to test whether the selection of task-defining features was modulated by top-down spatial attention, and to test whether the appearance of 'unattended targets' transiently disrupted the spatial bias. Surprisingly, the results revealed that ERP markers of selection of task-defining features were equivalent for stimuli appearing at spatially attended and unattended locations. In addition, the presentation of task-defining stimuli at the spatially unattended location induced a short-lived redistribution of the pre-established spatial attention bias toward the 'capture' side. These findings show that task-defining features of a stimulus are automatically processed independently from spatial attention, and suggest the coexistence of multiple sources of top-down biasing signals, which might in part sustain the capture mechanism.