Facilitation and inhibition arising from the exogenous orienting of covert attention depends on the temporal properties of spatial cues and targets.

On the covert orienting of visual attention task (COVAT), responses to targets appearing at the location indicated by a non-predictive spatial cue are faster than responses to targets appearing at uncued locations when stimulus onset asynchrony (SOA) is less than approximately 200 ms. For longer SOAs, this pattern reverses and RTs to targets appearing at uncued locations become faster than RTs to targets appearing at the cued location. This facilitation followed by inhibition has been termed the biphasic effect of non-predictive peripheral spatial cues. Currently, there is debate about whether these two processes are independent. This issue was addressed in a series of experiments where the temporal overlap between the peripheral cue and target was manipulated at both short and long SOAs. Results showed that facilitation was present only when the SOA was short and there was temporal overlap between cue and target. Conversely, inhibition occurred only when the SOA was long and there was no temporal overlap between cue and target. The biphasic effect, with an early facilitation followed by a later inhibition, occurred only when the cue duration was fixed such that there was temporal overlap between the cue and target at short but not long SOAs. In a final experiment, the duration of targets the temporal overlap between cue and target and the SOA were manipulated factorially. The results showed that facilitation occurred only when the SOA was short, there was temporal overlap between cue and target and the target remained visible until the subject responded. These results suggest that the facilitation and inhibition found on COVATs which use non-informative peripheral cues are independent processes and their presence and magnitude is related to the temporal properties of cues and targets.     

The attentional blink modulates activity in the early visual cortex

The attentional blink (AB) documents a particularly strong case of visual attentional competition, in which subjects' ability to identify a second target (T2) is significantly impaired when it is presented with a short SOA after a first target (T1). We used functional magnetic resonance imaging to investigate the impact of the AB on visual activity in individually defined retinotopic representations of the target stimuli. Our results show reduction of neural response in V3 and marginally in V2 and V1, paralleling the behavioral AB effect. Reduction of visual activity was accompanied by reduced neural response in the inferior parietal cortex. This indicates that attentional competition modulates activity in higher-order parietal regions and the early visual cortex, providing a plausible neural basis of the behavioral AB effect.     

Attentional set modulates visual areas: an event-related potential study of attentional capture.

The present experiment offers event-related potential evidence suggesting that modulation of neural activity in the visual cortex underlies top-down attentional capture by irrelevant cues. Participants performed a covert visual search task where they identified the unique stimulus in a brief, four-location display. Targets defined uniquely by color or onset were run in separate blocks, encouraging observers to adopt different attentional sets in each block. In Experiment 1, a brief, white, abrupt-onset cue highlighted one of the locations 100 or 200 ms prior to the target display. In Experiment 2, the cue display consisted of three white and one red cues simultaneously presented at the four locations. In both experiments, participants were informed that there was no predictive relation between the location of the cue and that of the target. Reaction times were dependent on the location of the preceding cue (i.e. attention was captured), but only in those blocks where the cue shared the uniquely relevant target feature. Evoked potentials over the right hemisphere were modulated during the attention-capturing blocks just prior to the cue's appearance. Additionally, the N1 wave elicited by the cue was enhanced over occipital regions during the attention-capturing blocks. These findings support the notion that attentional capture with peripheral cues is not simply reflexive but is modulated by top-down processes.     

An event-related fMRI Study of exogenous facilitation and inhibition of return in the auditory modality

The orienting of attention to different locations in space is fundamental to most organisms and occurs in all sensory modalities. Orienting has been extensively studied in vision, but to date, few studies have investigated neuronal networks underlying automatic orienting of attention and inhibition of return to auditory signals. In the current experiment, functional magnetic resonance imaging and behavioral data were collected while healthy volunteers performed an auditory orienting task in which a monaurally presented tone pip (cue) correctly or incorrectly cued the location of a target tone pip. The stimulus onset asynchrony (SOA) between the cue and target was 100 or 800 msec. Behavioral results were consistent with previous studies showing that valid auditory cues produced facilitation at the short SOA and inhibition of return at the long SOA. Functional results indicated that the reorienting of attention (100 msec SOA) and inhibition of return (800 msec SOA) were mediated by both common and distinct neuronal structures. Both attention mechanisms commonly activated a network consisting of fronto-oculomotor areas, the left postcentral gyrus, right premotor area, and bilateral tonsil of the cerebellum. Several distinct areas of frontal and parietal activation were identified for the reorienting condition, whereas the right inferior parietal lobule was the only structure uniquely associated with inhibition of return.     

Accelerated time-course of inhibition of return in Huntington's disease

A non-predictive peripheral cueing paradigm was used to evaluate visuospatial attentional deficits in symptomatic HD patients, employing spatially valid and invalid visual cues over a range of stimulus onset asynchronies (SOA) to elicit a saccadic response. Although both patients and controls demonstrated initial facilitation for valid versus invalid cues following the shortest SOA, and a performance decrement (inhibition of return), at the longest SOA, a clear differentiation between these groups was found for the intermediate SOAs. Unlike controls, where IOR manifested between 350 and 1000 ms, IOR was evident as early as 150 ms for HD patients. Further, the benefit of valid cueing correlated significantly with the level of impairment. Although patients exhibited poor fixation, principally attributable to saccadic intrusions, they were capable of appropriately suppressing a purely stimulus-driven response to the cue. A similar proportion of erroneous saccades to the cue were generated by both groups prior to stimulus onset, also correlating significantly with level of impairment. These results are discussed with respect to neural processes implicated in spatial cueing and within the context of reduced inhibitory activity of the BG in HD.     

Timing and magnitude of frontal activity differentiates refixation and anti-saccade performance.

EEG data were recorded while 10 subjects generated refixation saccades towards a visual target and antisaccades away from a visual cue. Theoretically, the same basic neural circuitry supports refixation and correct anti-saccade performances, with additional activity in primarily dorsolateral prefrontal cortex circuitry supporting antisaccade-associated inhibitory processes. Analyses demonstrated that sensory registration of visual stimuli is similar for refixation and anti-saccade conditions. Increased frontal brain activity at 5 and 15 Hz was observed preceding correct antisaccades when compared to refixation saccades. These analyses provide specific information suggesting that 160-60 ms before saccade generation is the critical period for response inhibition.     

Inhibitory processing in visuospatial attention in healthy adults and schizophrenic patients.

This study assessed visuospatial attention in healthy adults and medicated schizophrenic patients. Participants performed a visual orientation task in which a peripheral cue was followed. at different intervals, by a target presented either at valid or invalid locations. When the long stimulus onset asynchrony (SOA) was used, participants were presented with either a single peripheral cue (single-cue condition) or two cues, the peripheral cue followed by a central cue (the double-cue condition). Healthy adults showed marginal facilitation effects with the short SOA and similar inhibition of return effects with the long SOA in both single-cue and double-cue conditions. Schizophrenic individuals showed a big facilitation effect with the short SOA and normal inhibition of return with the long SOA in both cue conditions. Results with the short SOA replicated previous findings (Huey, E.D., Wexler, B.E., 1994. Schizophrenia Research 14, 57-63) but, in contrast, we did not observe blunted inhibition of return with the long SOA. An inspection of the differences in the procedures used in both studies may help both to account for the discrepancies and to reveal what processes involved in visuospatial attention are affected in schizophrenia.     

The parietal cortex and attentional modulations of activities of the visual cortex

We recorded high density event-related brain potentials (ERPs) from a patient with focal left parietal damage in a covert visual orienting task requiring detection of targets in the attended or unattended hemifield. A positivity peaking at 120 ms (P1) to the left visual field stimuli was enlarged when attended than unattended and was localized to the right extrastirate cortex. However, spatial attention did not influence the ERPs to the right visual field stimuli. The leftward cue elicited an enlarged P1 relative to the rightward cue. The results suggest that human parietal cortex is critical for the attentional modulation of the neural activities in the extrastriate cortex associated with stimuli in the contralateral hemifield.     

Emotional modulation of the attentional blink: the neural structures involved in capturing and holding attention

Perceiving a first target stimulus (T1) in a rapid serial visual presentation stream results in a transient impairment in detecting a second target (T2). This “attentional blink” is modulated by the emotional relevance of T1 and T2. The present experiment examined the neural underpinnings of the emotional modulation of the attentional blink. Behaviorally, the attentional blink was reduced for emotional T2 while emotional T1 led to a prolonged attentional blink. Using functional magnetic resonance imaging, we observed amygdala activation associated with the reduced attentional blink for emotional T2 in the face of neutral T1. The prolonged attentional blink following emotional T1 was correlated with enhanced activity in a cortical network including the anterior cingulate cortex, the insula and the orbitofrontal cortex. These results suggest that brain areas previously implicated in rather reflexive emotional reactions are responsible for the reduced attentional blink for emotional T2 whereas neural structures previously related to higher level processing of emotional information mediate the prolonged attentional blink following emotional T1.     

Anticipatory alpha oscillation predicts attentional selection and hemodynamic response

In covert visual attention, one fundamental question is how advance knowledge facilitates subsequent neural processing and behavioral performance. In this study, with a rapid event‐related simultaneous electroencephalography (EEG) and functional near infrared spectroscopy recording in humans, we explored the potential contribution of anticipatory electrophysiological activation and hemodynamic activation by examining how anticipatory low‐frequency oscillations and changes in oxygenated hemoglobin (HbO) concentration influence the subsequent event‐related potential (ERP) marker of attentional selection. We found that expecting a target led to both a posterior lateralization of alpha‐band (8–12 Hz) oscillation power and a lateralization of HbO response over the visual cortex. Importantly, the magnitude of cue‐induced alpha lateralization was positively correlated with the nearby HbO lateralization in the visual cortex, and such a cue‐induced alpha lateralization predicted the subsequent target‐evoked N2pc amplitudes assumed to reflect attentional selection. Our results suggest that each individual's attentional selection biomarker as reflected by N2pc is predictable in advance via the anticipation‐induced alpha lateralization, and such cue‐induced alpha lateralization seems to play an important role in the functional coupling effects between the low‐frequency EEG and the nearby hemodynamic activation.     

The modulatory influence of a predictive cue on the auditory steady-state response

Whether attention exerts its impact already on primary sensory levels is still a matter of debate. Particularly in the auditory domain the amount of empirical evidence is scarce. Recently noninvasive and invasive studies have shown attentional modulations of the auditory Steady-State Response (aSSR). This evoked oscillatory brain response is of importance to the issue, because the main generators have been shown to be located in primary auditory cortex. So far, the issue whether the aSSR is sensitive to the predictive value of a cue preceding a target has not been investigated. Participants in the present study had to indicate on which ear the faster amplitude modulated (AM) sound of a compound sound (42 and 19 Hz AM frequencies) was presented. A preceding auditory cue was either informative (75%) or uninformative (50%) with regards to the location of the target. Behaviorally we could confirm that typical attentional modulations of performance were present in case of a preceding informative cue. With regards to the aSSR we found differences between the informative and uninformative condition only when the cue/target combination was presented to the right ear. Source analysis indicated this difference to be generated by a reduced 42 Hz aSSR in right primary auditory cortex. Our and previous data by others show a default tendency of "40 Hz" AM sounds to be processed by the right auditory cortex. We interpret our results as active suppression of this automatic response pattern, when attention needs to be allocated to right ear input.     

Inhibition of return in patients with obsessive-compulsive disorder

The present study is aimed at replicating and extending previous results by Nelson et al. [Psychiatry Res. 49 (1993) 183], who found decreased inhibition of return (IOR) in patients with obsessive-compulsive disorder (OCD). Thirty OCD patients, 14 psychiatric, and 14 healthy controls participated in a visual cueing experiment. The task required detection of a target stimulus at one of two possible locations. Prior to the target, an uninformative cue appeared at one of these two locations. The Stimulus Onset Asynchrony (SOA) between the cue and the target was systematically varied. We were especially interested in whether severity of OCD symptoms would be negatively correlated with inhibition for previously occupied locations. In accordance with prior research on healthy participants all groups displayed a comparable response pattern: facilitation at the short SOA condition and increasing IOR for the longer SOA conditions. Medication, comorbid depression, and OCD severity did not consistently moderate these effects.     

Distinct causal mechanisms of attentional guidance by working memory and repetition priming in early visual cortex

Human attention may be guided by representations held in working memory (WM) and also by priming from implicit memory. Neurophysiological data suggest that WM and priming may be associated with distinct neural mechanisms, but this prior evidence is only correlative. Furthermore, the role of the visual cortex in attention biases from memory remains unclear, because most previous studies conflated memory and selection processes. Here, we manipulated memory and attention in an orthogonal fashion and used an interventional approach to demonstrate the functional significance of WM and priming states in visual cortex for attentional biasing. Observers searched for a Landolt target that was preceded by a nonpredictive color cue that either had to be held in WM for a later recognition test or merely attended (priming counterpart). The application of transcranial magnetic stimulation (TMS) over the occipital cortex modulated the impact of memory on search. Critically, the direction of this modulation depended on the memory state. In the WM condition, the application of TMS on validly cued trials (when the cue surrounded the sought target) enhanced search accuracy relative to the invalid trials (when the cue surrounded a distracter); the opposite pattern was observed in the priming condition. That the effects of occipital TMS on selection were contingent on memory context demonstrates that WM and priming represent distinct states in the early visual cortex that play a causal role in memory-based guidance of attention.     

An electrophysiological investigation of preparatory attentional control in a spatial Stroop task

Top-down attentional control is required when subjects must attend to one of multiple conflicting stimulus features, such as in the Stroop task. Performance may be improved when such control is implemented in advance of stimulus presentation, yet few studies have examined this issue. Our investigation employed a spatial Stroop task with a manual response, allowing us to focus on the effects of preparatory attention on verbal processing when it is the less automatic attribute. A letter cue (P or W) presented for 2200 msec instructed subjects to respond on the basis of the position or meaning of a word (up, down, left, right) placed in an incongruent position relative to center. Event-related potentials recorded during pre- and poststimulus periods were analyzed as a function of reaction time to the target stimulus (fast vs. slow) in order to differentiate neural activity associated with more or less successful implementation of control. During the prestimulus period, fast responses to subsequent targets were associated with enhanced slow-wave activity over right frontal and bilateral central-parietal regions. During the poststimulus period, fast word trials were uniquely associated with an enhanced inferior temporal negativity (ITN) from 200 to 600 msec. More importantly, a correlation between frontal prestimulus activity and the poststimulus ITN suggested that frontal preparatory activity played a role in facilitating conceptual processing of the verbal stimulus when it arrived, providing an important link between preparatory attention and mechanisms that improve performance in the face of conflict.     

Neural correlates of spatial and non-spatial inhibition of return (IOR) in attentional orienting

Exogenous orienting of attention typically produces an early facilitatory effect and a later inhibitory effect, i.e., inhibition of return (IOR). IOR occurs not only in spatial but also in non-spatial domains. Although neural mechanisms associated with spatial IOR have been well established, neural correlates underlying non-spatial IOR remain to be elucidated. In this fMRI study, we compared neural correlates of spatial and non-spatial IOR by adopting a 2 (cue type: location vs. color) x 2 (stimulus onset asynchrony, SOA: long vs. short) x 2 (cue validity: cued vs. uncued) factorial design. Behaviorally, spatial cueing induced the typical biphasic (i.e., the early facilitatory and later inhibitory) effects, while color cueing induced inhibitory effects at both short and long SOAs. Neurally, we found both shared and specific neural correlates of spatial and non-spatial IOR. As compared with short SOA (cued and uncued trials combined), spatial and color cueing at long SOA conjointly activated bilateral precentral gyrus and bilateral lateral occipital cortex, while spatial cueing, but not color cueing, specifically activated bilateral superior parietal cortex. Moreover, left middle frontal gyrus and left inferior frontal gyrus showed significantly higher neural activity in cued trials than in uncued trials during color-based IOR, but not during location-based IOR, implying that episodic retrieval process in the prefrontal cortex may be involved to inhibit old object representations during non-spatial IOR [Grison, S., Paul, M. A., Kessler, K., & Tipper, S. P. (2005). Inhibition of object identity in inhibition of return: Implications for encoding and retrieving inhibitory processes. Psychonomic Bulletin & Review, 12, 553-558; Tipper, S. P., Grison, S., & Kessler, K. (2003). Long-term inhibition of return of attention. Psychological Science, 14, 19-25]. Theoretical implications of the shared and differential neural activity associated with spatial and non-spatial IOR are discussed.     

The attentional effects of peripheral cueing as revealed by two event-related potential studies.

OBJECTIVE: The mechanism of visual spatial attention elicited by peripheral cueing was investigated in two studies. METHOD: Event-related potentials (ERPs) were recorded when the subjects were performing a spatial frequency discrimination task and a location discrimination task. Stimuli were randomly flashed in the left or right visual field. Prior to each stimulus a peripheral cue was presented with a validity of 75%. RESULTS: The subjects responded faster to valid trials than to invalid trials. The earliest visual ERP component, C1, was not modulated by the cue validity, suggesting that visual spatial attention elicited by peripheral cueing does not involve striate cortex. Valid trials elicited larger contralateral P1 but a smaller contralateral N1 than invalid trials. The early onsets of these attentional effects show that spatial attention affects stimulus processing at early sensory/perceptual stages. The latencies of contralateral P1 and contralateral N1 were shorter for invalid trials, however. The ipsilateral N1 was enhanced by valid trials in the spatial frequency discrimination task but was not in the location discrimination task, whereas the contralateral N1 was larger for invalid trials than for valid trials in both tasks. CONCLUSION: The results indicate that involuntary allocation of attention involves different mechanisms from voluntary allocation of attention.     

Dissociation between top-down attentional control and the time course of visual attention as measured by attentional dwell time in patients with mild cognitive impairment

Studies of the time course of visual attention have identified a temporary functional blindness to the second of sequentially presented stimuli in that the attentional cost of attending to one visual stimulus may lead to impairments in identifying a second stimulus presented within 500 ms of the first. This phenomenon is known as the attentional blink or attentional dwell time. The neural correlates of the attentional blink and its relationship to mechanisms that control attention are unknown. To examine this relationship we tested healthy controls and subjects in the preclinical stage of Alzheimer's disease, known as mild cognitive impairment (MCI), on a paradigm which affords quantification of both the attentional blink and the top-down control of attention. When subjects were asked to identify both a number and a letter that were rapidly and sequentially presented on a visual display, the detrimental effect that identifying the first stimulus had on the ability to identify the second served as a measure of the attentional blink. When asked to identify only one of the two stimuli, the ability to ignore the first stimulus was a function of their top-down attentional control. The MCI subjects demonstrated a normal attentional dwell time but in contrast they showed impaired top-down attentional control within the same paradigm. This dissociation suggests that these two aspects of visual attention are subserved by different neural systems. The possible neural correlates of these two attentional functions are discussed.     

Aging and cognitive slowing: example of attentional processes--evaluation procedures and related questions

Slowing is generally associated to ageing. It appears in motor's functions and in cognitive tasks. What is the real nature of this slowing? Is it a general slowing concerning every cognitive processes with the same scale or is this slowing specific of only processes. Or, at least, is it of different magnitude for each cognitive processes? The aim of this paper is to present the state of this debate from results obtained in studies orientated toward attentional processes. Attention allows us to adapt oneself to environment that require in one hand selective mechanisms for pertinence events and in other hand inhibitory mechanisms for interferences. To evaluate these mechanisms priming and cueing procedures are used. Using primes (semantic or conceptual) results in shorter reaction time than for conditions without prime. In some experimental conditions, negative primes can be observed which results for longer reaction time. In these procedures, we need to be careful to the SOA's value (Stimulus Onset Asynchrony) (it represents the time between the end of the prime or cue presentation and the beginning of the stimulus presentation). The longer is the SOA, the shorter is the reaction time increase with a SOA between 200 ms and 400 ms. In these procedures, we now have to understand in the field of information processing what causes this reaction time modification. In other words, increase of reaction time with SOA could be explain increase of all stages of treatment or may be also the consequence of some abolition's of stages? In attentional procedures, we have to consider the automatic or controlled nature of cognitive processes. In target research tasks that implies selective attention, several authors have showed a distinction between automatic and controlled processing. Time to detect prompts increase generally with the distractor number excepted when the prompt is prominent for the subject (because of physical or emotional characteristics). In this second case, the pop out effect, reaction time does not depend from the number of distractors and this effect performs to be supervised by automatic processes. By contrast, reaction time variation is considered to be linked with controlled processes activation. What's about ageing? Myerson et al. (1992) don't show reaction time distinction between young and old in their meta analyse which really results from lexical decision tasks from 1980 to 1990. If you now consider the SOA values, results are less clear and contradictions existing between studies. Using negative priming procedures implies different results too, but one is main: it seems that elders take as much time to denote a prompt in conditions when prompt was distractor compared to neutral condition, by contrast to younger who take more time to denote the prompt where it was distractor compared to condition where it was not. Ageing effects on inhibition intensity and length could be expanded. Nissen and Corkin (1985) showed a facilitator effect with cueing in young and in old people, and this appears more important in old people. Hartley et al. (1990) show this results too and control the SOA: the facilitation size effect seems to depend from the SOA size. On top of that, some authors show the presence of the popout effect in elders but a reaction time lengthening when conditions imply controlled processing (visual or memory research tasks). In summary, the most studies show a slowing in old people whatever attentional tasks but the lengthening size doesn't vary systematically with conditions: facilitatory effects and automatic processing are possible but inhibitory processing are more probably impaired. Several hypotheses can explain these results. Some authors think there is a general slowing factor that slows with age. For others slowing depends from tasks, and mainly from several implied processing. Nevertheless, no one study show a regular relation between reaction time and priming or cueing effects. Few results, which we've presented in this article, are really compatible with the general slowing theory. Finally, McDowd and Birren (1990), or Hasher and Zacks (1988) suppose that there is an incapacity to ignore non pertinent information with ageing, but there are limit in this hypothesis too. In summary, we don't know at this time the real nature of slowing with age but experimental values seem to be in favour with slowing, which significance depends from cognitive processes. We now have to describe precisely slowing in old people, and more exactly with exact timing between prime and target could be a beginning of task.     

ERPs predict the appearance of visual stimuli in a temporal selection task

In contrast to the visual spatial domain, the effect of attention on sensory processing and stimulus appearance in temporal selection tasks is still controversial. Using a rapid serial visual presentation (RSVP) procedure, we examined whether the stimulus onset asynchrony (SOA) between a color cue and a motion target affects the appearance of the latter. Event-related brain potentials (ERPs) recorded simultaneously allowed us to test whether a change in the targets' appearance is associated with a modulation of the sensory ERP components. In the experimental condition 'SOA', the temporal interval between the cue and the target was varied between 0 and 300 ms. In a control condition, the physical appearance of the motion target was varied (level of coherence: 25-100%) while holding the cue-target SOA constant (300 ms). In trials when the participant detected the target motion, his/her task was to report the strength of the perceived motion on a 5-point scale. In both conditions, the mean rating of the target's appearance increased monotonically with increasing SOA and the level of coherence, respectively. The psychophysical ratings were associated with an increase of a negative deflection about 200 ms (N200) related to the sensory processing of visual motion. The physical variation of motion coherence and the variation of the cue-target SOA affected the N200 response in similar fashion. These results indicate that sensory processing is also modulated by attentional resources in temporal selection tasks which - in turn - affect the appearance of the relevant target stimulus.     

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.