The endogenous modulation of IOR is nasal-temporal asymmetric

Inhibition of return (IOR) refers to a reflexive mechanism mediated by phylogenetically primitive extrageniculate visuomotor pathways, which apparently serves to favor novel spatial locations by inhibiting those recently sampled. We demonstrate an asymmetry between temporal and nasal hemifields in the strategic modulation of IOR by endogenously controlled attention. Exogenous and endogenous precues were manipulated independently on each trial such that precues to initiate endogenous spatial orienting were presented after IOR had been activated by exogenous visual signals. Both types of precues manifested their characteristic effects on reaction time (RT) to detect subsequent targets: facilitation by endogenous precues, and IOR by exogenous precues. Under monocular viewing, an asymmetric interaction between these two mechanisms was observed. While endogenous allocation of attention to the nasal hemifield reduced IOR, no endogenous modulation of IOR was present in the temporal hemifield where the effects of the two types of precues were independent. These observations suggest a framework for understanding the neurobiology of automaticity and control - from an evolutionary perspective.     

Attentional orienting induced by arrows and eye-gaze compared with an endogenous cue

Exogenous orienting has been widely studied by using peripheral cues whereas endogenous orienting has been studied with directional central cues. However, recent evidence has shown that centrally presented eye-gaze and arrows may produce an automatic rather than voluntary orienting of attention. Therefore, the aim of the present study was to investigate the behavioural and electrophysiological (event-related potentials-ERP) correlates of the attentional shift induced by arrows and eye-gaze. In order to have a control condition, we compared arrows and eye-gaze with a purely endogenous cue, i.e., a texture arbitrarily coding one direction. We analyzed the ERP components (P1, N1, P2a, P2p, P3) elicited by the cue stimuli and the early lateralised attentional effect (early directing attention negativity-EDAN). In addition, in order to investigate the topography of the neural mechanisms underlying the cortical activity in each cueing condition, we applied a temporal segmentation procedure. The results showed that the three cueing conditions induced a different strength of activation within the same cortical network. Occipito-parietal regions were involved in the early processing of visual information, followed by an involvement of frontal areas, likely implicated in learning associations. These data confirm the assumption that, in contrast to purely endogenous cues, arrows and eye-gaze induce a very fast attentional shift. However, the similarity of the ERP components and of the topographical cortical maps among conditions suggest that this early orienting of attention is more likely related to an overlearned association mechanism rather than to a real exogenous attentional process.     

Prism adaptation improves voluntary but not automatic orienting in neglect

Prism adaptation has been shown to temporarily ameliorate the symptoms of unilateral neglect. The underlying mechanisms of change are not yet fully understood. In this study, we investigate the influence of this treatment on attentional orienting under conditions of exogenous (peripheral onset) and endogenous (central symbolic) cueing. In one patient with left visual extinction and recovered neglect, and another patient with left visual neglect, visuo-motor adaptation to a rightward prismatic shift of 10 degrees improved leftward orienting of attention following an endogenous but not an exogenous cue; leftward re-orienting of attention was also improved in the endogenous task for the second patient. We suggest that prism adaptation may ameliorate neglect by improving compensatory processes of leftward voluntary orienting, rather than by a fundamental change in attentional bias.     

Spatial shifts in visual attention in normal ageing and dementia of the Alzheimer type

Using a spatial-cueing paradigm, we assessed the ability of Alzheimer's disease patients, age-matched controls and younger participants to use cues to guide attention to the location indicated by the cue. In separate experiments, we attempted to isolate cues that attract attention automatically (exogenous cueing) and those that require the wilful movement of attention (endogenous cues). We found significant cueing effects for all three groups of participants for both types of cue. However, the group with Alzheimer's disease showed far greater cueing effects when using an exogenous cue, whilst no difference between group's ability to use the cue was found for the endogenous cue. No differences in cueing were found for either cue type as a function of normal ageing. We further tested whether the differences in cueing found in the group with Alzheimer's disease was due to a generalised slowing of function. After transforming the data to take account of the overall slowing of all responses in this group, we still found significant differences between this group and the control groups. We conclude that patients with Alzheimer's disease have an abnormality in automatic, but not controlled visuospatial attention.     

Voluntary and involuntary attention affect face discrimination differently

Do voluntary (endogenous) and involuntary (exogenous) attention have the same perceptual consequences? Here we used fMRI to examine activity in the fusiform face area (FFA--a region in ventral visual cortex responsive to faces) and frontal-parietal areas (dorsal regions involved in spatial attention) under voluntary and involuntary spatial cueing conditions. The trial and stimulus parameters were identical for both cueing conditions. However, the cue predicted the location of an upcoming target face in the voluntary condition but was nonpredictive in the involuntary condition. The predictable cue condition led to increased activity in the FFA compared to the nonpredictable cue condition. These results show that voluntary attention leads to more activity in areas of the brain associated with face processing than involuntary attention, and they are consistent with differential behavioral effects of attention on recognition-related processes.     

Decoding attention control and selection in visual spatial attention

Event‐related potentials (ERPs) are used extensively to investigate the neural mechanisms of attention control and selection. The univariate ERP approach, however, has left important questions inadequately answered. We addressed two questions by applying multivariate pattern classification to multichannel ERPs in two cued visual spatial attention experiments (N = 56): (a) impact of cueing strategies (instructional vs. probabilistic) on attention control and selection and (b) neural and behavioral effects of individual differences. Following cue onset, the decoding accuracy (cue left vs. cue right) began to rise above chance level earlier and remained higher in instructional cueing (~80 ms) than in probabilistic cueing (~160 ms), suggesting that unilateral attention focus leads to earlier and more distinct formation of the attention control set. A similar temporal sequence was also found for target‐related processing (cued target vs. uncued target), suggesting earlier and stronger attention selection under instructional cueing. Across the two experiments: (a) individuals with higher cue‐related decoding accuracy showed higher magnitude of attentional modulation of target‐evoked N1 amplitude, suggesting that better formation of anticipatory attentional state leads to stronger modulation of target processing, and (b) individuals with higher target‐related decoding accuracy showed faster reaction times (or larger cueing effects), suggesting that stronger selection of task‐relevant information leads to better behavioral performance. Taken together, multichannel ERPs combined with machine learning decoding yields new insights into attention control and selection that complement the univariate ERP approach, and along with the univariate ERP approach, provides a more comprehensive methodology to the study of visual spatial attention.     

How does phasic alerting improve performance in patients with unilateral neglect? A systematic analysis of attentional processing capacity and spatial weighting mechanisms

In visual hemi-neglect, non-spatial deficits such as reduced intrinsic alertness can significantly modulate the degree of left visual field inattention. However, to date, the precise mechanisms mediating this effect are hardly understood. In the present study, we assessed the influence of increased alertness on both general attentional capacity (perceptual processing speed) and spatial attentional selection processes (spatial distribution of attentional weighting). For this purpose, a whole-report paradigm based on Bundesen's 'theory of visual attention' (TVA) was combined with a non-spatial, visual alerting cue. Three different cue-target stimulus onset asynchronies (SOAs; of 80, 200, and 650 ms), allowed us to observe the time course of the alerting-cue effects. A group of six patients with visual hemi-neglect was examined and their performance compared with six healthy control subjects matched for age, gender, and education. In neglect patients, the alerting cue evoked a phasic increase of perceptual processing speed. However, this effect was mainly found in the ipsilateral, i.e. in the "preserved" hemifield. Importantly, however, patients displayed a fast-evolving and short-lasting, phasic modulation of spatial attentional weighting, with a re-distribution of attentional weights from the pathological rightward bias to a normal, more balanced distribution of visual attention. In control participants, the cueing effects on perceptual processing speed and spatial weighting were generally less pronounced than in neglect patients. Replicating results of a prior study, cueing induced a stable, slightly leftward, distribution of attentional weights, whilst in the no-cue condition, a temporary rightward shift of attentional weights was found. This pattern of effects suggests a close interaction between alertness and spatial-attentional weighting in the syndrome of visual hemi-neglect. It supports the hypothesis that the manifestation of spatial neglect involves at least in part intrinsic alertness deficits. It also provides clues to a more detailed account of the mechanisms responsible for alleviating neglect in patients following manipulations of the alertness level, both in the short (cueing) and in the long term (alertness training).     

Multiple mechanisms of selective attention: differential modulation of stimulus processing by attention to space or time

Two studies compared the modulatory effects of orienting attention to spatial locations versus temporal intervals using event-related potentials (ERPs). In both experiments subjects performed attentional orienting tasks, which used identical stimuli in both spatial and temporal orienting conditions. The first experiment (N=16) used bilateral peripheral targets (7.5° eccentricity) at two different time intervals (600, 1200 ms after cue onset). During spatial orienting a symbolic central cue predicted (75% probability) the spatial location (left, right) of the relevant target. No information was given about the probable target interval (short, long). In temporal orienting the cue predicted the target interval but not its location. Valid cueing produced significantly shorter reaction times in both the spatial and temporal orienting conditions. ERPs to identical, non-target stimulus arrays were analysed, to isolate endogenous attentional mechanisms. Spatial and temporal attention had distinct modulatory effects upon stimulus processing. Focused spatial attention affected the amplitude of early visual components. Modulation by temporal attention started later, and mainly affected potentials linked to decisions and responses. The second experiment (N=12) used unilateral target stimuli, and equated the probability of stimulus occurrence at short and long time intervals and at left or right of fixation. The results confirmed the distinct pattern of modulation of stimulus processing by spatial and temporal orienting. The optimisation of behaviour by attention can thus be achieved as a consequence of distinct modulatory processes, illustrating the flexibility of attentional functions in the human brain.     

Prechange event-related potentials predict change blindness in various attention conditions

We investigated the mechanisms of change blindness by measuring electrophysiological responses in humans to the prechange display. The change blindness paradigm included different attentional cueing (valid, invalid, no cue) conditions. The results showed that event-related potentials to the prechange display predicted change detection performance. After a valid cue, the prechange responses in detected change trials showed evidence of attentional focusing. However, in no cue and invalid cue conditions successful change detection was associated with electrophysiological responses indicating more globally distributed attention, whereas the electrophysiological pattern associated with strong attentional focusing predicted change blindness. The results suggest that specific patterns of encoding the prechange display predict change detection performance not only between different attention conditions but also within them.     

The role of the left posterior parietal lobule in top-down modulation on space-based attention: a transcranial magnetic stimulation study

Converging evidence from neuroimaging as well as lesion and transcranial magnetic stimulation (TMS) studies has been obtained for the involvement of right ventral posterior parietal cortex (PPC) in exogenous orienting. However, the contribution of dorsal PPC to attentional orienting, particularly endogenous orienting, is still under debate. In an informative peripheral cueing paradigm, in which the exogenous and endogenous orienting can be studied in relative isolation within a single task, we applied TMS over sub-regions of dorsal PPC to explore their possible distinct involvement in exogenous and endogenous processes. We found that disruption of the left posterior intraparietal sulcus (pIPS) weakened the attentional effects of endogenous orienting, but did not affect exogenous processes. In addition, TMS applied over the right superior parietal lobule (SPL) resulted in an overall increase in reaction times. The present study provides the causal evidence that the left pIPS plays a crucial role in voluntary orienting of visual attention, while right SPL is involved in the processing of arousal and/or vigilance.     

Electrocortical correlates of control of selective attention to spatial frequency

In the present study, we investigated control of selective attention to spatial frequency patterns, using a cueing paradigm. Subjects either used the instruction embedded in a word cue to prepare for the upcoming test stimulus (transient attention condition) or used the instruction they received before a block of trials (sustained reference condition), under completely similar stimulus conditions. The pattern of differential cue responses between these two conditions, reflecting top-down attentional control processes, was different between two groups of subjects, effectively canceling each other out. Despite comparable behavioral performance on both cues and targets, one group (n = 4) elicited a fronto-central-parietal positivity, starting 500 ms postcue over frontal and prefrontal areas, later including more central and posterior scalp sites, whereas another group (n = 8) started 400 ms postcue over central sites with a negativity, growing in strength over time and stabilizing over fronto-central sites. Only the group of eight subjects showed some evidence of occipital pretarget biasing activity. Independent of group, source modeling of the attentional control activity showed that attentional control was initiated in anterior, not posterior, parts of the brain. Furthermore, different underlying sources were found for both groups, in addition to signs of differential processing of target stimuli. Possible individual differences in attentional control ability and its relation to usage of different brain areas to deal with the task demands are discussed in more detail.     

Does spatial cueing affect line bisection in chronic hemianopia?

Patients with homonymous hemianopia often show a contralesional shift towards their blind field when bisecting horizontal lines ("hemianopic line bisection error", HLBE). The reasons for this spatial bias are not well understood and debated. Cueing of spatial attention modulates line bisection significantly in patients with visuospatial neglect. Moreover, recent evidence showed that attention training significantly improves deficits of visual search in hemianopia. Here, we tested in 20 patients with chronic homonymous hemianopia (10 left-sided, 10 right-sided) without visual neglect, 10 healthy control subjects, 10 neurological control patients, and 3 patients with left visuospatial neglect and leftsided hemianopia whether spatial cueing influences the HLBE. Subjects indicated verbally the midpoint of horizontal lines in a computerized line bisection task under four experimental cue positions (cue far left, mid-left, mid-right or far-right within the horizontal line). All 20 hemianopic patients showed the typical HLBE towards their blind field, while the two control samples showed only a small but significant leftward shift (pseudoneglect). None of the 4 cueing manipulations had a significant effect on the HLBE in the hemianopic patients. Moreover, no differential effects of cueing on line bisection results were obtained when analyzed in lesion subgroups of hemianopic patients with circumscribed occipital lesions (N=8) as contrasted with patients having more extended (occipito-temporal or temporal) lesions (N=12). This null-effect contrasts with marked cueing effects observed in 3 neglect patients with left hemianopia in the same tasks, showing the principal efficacy of our cueing manipulation. These results argue against attentional explanations of the HLBE.     

Functional parcellation of attentional control regions of the brain

Recently, a number of investigators have examined the neural loci of psychological processes enabling the control of visual spatial attention using cued-attention paradigms in combination with event-related functional magnetic resonance imaging. Findings from these studies have provided strong evidence for the involvement of a fronto-parietal network in attentional control. In the present study, we build upon this previous work to further investigate these attentional control systems. In particular, we employed additional controls for nonattentional sensory and interpretative aspects of cue processing to determine whether distinct regions in the fronto-parietal network are involved in different aspects of cue processing, such as cue-symbol interpretation and attentional orienting. In addition, we used shorter cue-target intervals that were closer to those used in the behavioral and event-related potential cueing literatures. Twenty participants performed a cued spatial attention task while brain activity was recorded with functional magnetic resonance imaging. We found functional specialization for different aspects of cue processing in the lateral and medial subregions of the frontal and parietal cortex. In particular, the medial subregions were more specific to the orienting of visual spatial attention, while the lateral subregions were associated with more general aspects of cue processing, such as cue-symbol interpretation. Additional cue-related effects included differential activations in midline frontal regions and pretarget enhancements in the thalamus and early visual cortical areas.     

Unilateral visual cueing and asymmetric line geometry share a common attentional origin in the modulation of pseudoneglect

Numerous factors influence the leftward bias (pseudoneglect) in perceived line midpoint of normal subjects in line bisection tasks. Cues are a potent factor; left and right cues promote shifts in perceived midpoint to the left and right, respectively. Trapezoidal lines have recently been shown to influence perceived line midpoint, displacing it toward the larger side. The present experiments test the hypothesis that the effect of line geometry, like that of unilateral cues, results from an exogenous recruitment of spatial attention. Normal right-handed subjects (N = 60) participated in two experiments employing a tachistoscopic forced-choice line bisection task. Experiment 1 crossed the effect of cue position and cue contrast, and confirmed that a significant interaction could be obtained. Experiment 2 crossed the effect of line geometry and cue position, revealing that line geometry and cue location both significantly influence perceived line midpoint, and produce a significant interaction. According to Additive Factors Logic the finding that spatial cueing interacts with line geometry suggests that both types of stimuli modulate spatial attention at a common site of processing, supporting the conclusion that the effect of line geometry itself derives from asymmetric cueing. An explanation for the interaction is offered that is based on the existence of a hypothesized compressive nonlinearity that maps attentional bias to perceptual error.     

Attentional modulation of the human somatosensory evoked potential in a trial-by-trial spatial cueing and sustained spatial attention task measured with high density 128 channels EEG

We investigated the modulation of the somatosensory evoked potential (SEP) elicited by mechanical stimuli in a spatial sustained attention and a spatial trial-by-trial cueing design by means of high density electrode array EEG recordings. Subjects were instructed to detect rare tactile target stimuli at the to-be-attended hand while ignoring stimuli at the other hand. Analysis of the SEP revealed a highly complex pattern of results. The P50 component was significantly increased for attended stimuli in the sustained attention as opposed to the trial-by-trial cueing condition. However, no difference in amplitude was found for attended as opposed to unattended stimuli. High density electrode array recordings revealed a centero-frontal N140 component (N140c), which preceded the parietal N140 (N140p) by about 20 ms. The N140c exhibited an attention effect in particular in the trial-by-trial spatial cueing condition. The N140p was significantly enlarged with attention across both experimental conditions, but a closer inspection demonstrated that this was mainly due to the great attention effect in the trial-by-trial spatial cueing condition. The late positive component (190-380 ms after stimulus onset) exhibited a significant attention effect in both experimental conditions. The present experiment provides evidence that the attentional modulation of the SEP is different when tactile as opposed to electrical stimuli were used and when only somatosensory stimuli are presented with no further sensory stimulation in other modalities. Furthermore, transient as opposed to sustained spatial attention affected various components of the SEP in a different way.     

Paying attention to saccadic intrusions

Fixation to a target in primary gaze is invariably interrupted by physiological conjugate saccadic intrusions (SI). These small idiosyncratic eye movements (usually <1 degrees in amplitude) take the form of an initial horizontal fast eye movement away from the desired eye position, followed after a variable duration by a return saccade or drift. As the aetiology of SI is still unclear, it was the aim of this study to investigate whether SI are related to exogenous or endogenous attentional processes. This was achieved by varying (a) the "bottom-up" target viewing conditions (target presence, servo control of the target, target background, target size) and (b) the 'top-down' attentional state (instruction change--'look' or 'hold eyes steady' and passive fixation versus active--'respond to change' fixation) in 13 subjects (the number of participants in each task varied between 7 and 11). We also manipulated the orientation of pure exogenous attention through a cue-target task, during which subjects were required to respond to a target, preceded by a non-informative cue by either pressing a button or making a saccade towards the target. SI amplitude, duration, frequency and direction were measured. SI amplitude was found to be significantly higher when the target was absent and SI frequency significantly lower during open loop conditions. Target size and background influenced SI behaviour in an idiosyncratic manner, although there was a trend for subjects to exhibit lower SI frequencies and amplitudes when a patterned background was present and larger SI amplitudes with larger target sizes. SI frequency decreased during the "hold eyes steady" passive command as well as during active fixation but SI direction was not influenced by the exogenous cue-target task. These results suggest that SI are related to endogenous rather than exogenous attention mechanisms. Our experiments lead us to propose that SI represent shifts in endogenous attention that reflect a baseline attention state present during laboratory fixation tasks and may prove to be a useful tool to explore higher cortical control of fixation.     

Attention,reliability, and validity of perceptual asymmetries in the fused dichotic words test

The present experiment investigated the claim that the fused dichotic words test (FDWT) is affected minimally by attentional factors. A total of 40 right-handed undergraduate students were randomly assigned to either a free recall or exogenous cueing condition. In the free recall condition, participants circled on a response sheet the word corresponding to the percept they heard for each trial. In the exogenous cueing condition, a lateralised tone cue was presented with a stimulus onset asynchrony (SOA) of either 150 or 450 ms. Participants responded by circling the word presented to the ear where the tone sounded. Results of the free recall condition showed the expected large right ear advantage (REA). In the exogenous cueing condition, the significant SOA by ear of presentation interaction predicted by an attentional explanation of perceptual asymmetries was obtained. Specifically, the REA obtained at the 150 ms SOA was reduced at the 450 ms SOA for both correct responses and intrusions. These findings suggest that, contrary to claims conveyed in the literature, the FDWT is subject to the influences of attention. This supports the claim that the large and reliable laterality effects obtained with the fused dichotic words test are due in part to a consistent attentional bias.     

Attention, reliability, and validity of perceptual asymmetries in the fused dichotic words test

The present experiment investigated the claim that the fused dichotic words test (FDWT) is affected minimally by attentional factors. A total of 40 right-handed undergraduate students were randomly assigned to either a free recall or exogenous cueing condition. In the free recall condition, participants circled on a response sheet the word corresponding to the percept they heard for each trial. In the exogenous cueing condition, a lateralised tone cue was presented with a stimulus onset asynchrony (SOA) of either 150 or 450 ms. Participants responded by circling the word presented to the ear where the tone sounded. Results of the free recall condition showed the expected large right ear advantage (REA). In the exogenous cueing condition, the significant SOA by ear of presentation interaction predicted by an attentional explanation of perceptual asymmetries was obtained. Specifically, the REA obtained at the 150 ms SOA was reduced at the 450 ms SOA for both correct responses and intrusions. These findings suggest that, contrary to claims conveyed in the literature, the FDWT is subject to the influences of attention. This supports the claim that the large and reliable laterality effects obtained with the fused dichotic words test are due in part to a consistent attentional bias.     

Neural mechanisms mediating contingent capture of attention by affective stimuli

Attention is attracted exogenously by physically salient stimuli, but this effect can be dampened by endogenous attention settings, a phenomenon called "contingent capture." Emotionally salient stimuli are also thought to exert a strong exogenous influence on attention, especially in anxious individuals, but whether and how top-down attention can ameliorate bottom-up capture by affective stimuli is currently unknown. Here, we paired a novel spatial cueing task with fMRI to investigate contingent capture as a function of the affective salience of bottom-up cues (face stimuli) and individual differences in trait anxiety. In the absence of top-down cues, exogenous stimuli validly cueing targets facilitated attention in low-anxious participants, regardless of affective salience. However, although high-anxious participants exhibited similar facilitation following neutral exogenous cues, this facilitation was completely absent following affectively negative exogenous cues. Critically, these effects were contingent on endogenous attentional settings, such that explicit top-down cues presented before the appearance of exogenous stimuli removed anxious individuals' sensitivity to affectively salient stimuli. fMRI analyses revealed a network of brain regions underlying this variability in affective contingent capture across individuals, including the fusiform face area (FFA), posterior ventrolateral frontal cortex, and SMA. Importantly, activation in the posterior ventrolateral frontal cortex and the SMA fully mediated the effects observed in FFA, demonstrating a critical role for these frontal regions in mediating attentional orienting and interference resolution processes when engaged by affectively salient stimuli.     

Concurrent TMS-fMRI reveals dynamic interhemispheric influences of the right parietal cortex during exogenously cued visuospatial attention

We used concurrent transcranial magnetic stimulation and functional MRI (TMS-fMRI) during a visuospatial cueing paradigm in humans, to study the causal role of the right angular gyrus (AG) as a source of attentional control. Our findings show that TMS over the right AG (high vs. low intensity) modulates neural responses interhemispherically, in a manner that varies dynamically with the current attentional condition. The behavioural impact of such TMS depended not only on the target hemifield but also on exogenous cue validity, facilitating spatial reorienting to invalidly cued right visual targets. On a neural level, right AG TMS had corresponding interhemispheric effects in the left AG and left retinotopic cortex, including area V1. We conclude that the direction of covert visuospatial attention can involve dynamic interplay between the right AG and remote interconnected regions of the opposite left hemisphere, whereas our findings also suggest that the right AG can influence responses in the retinotopic visual cortex.