Electrophysiological evidence for inhibition of return effect in exogenous orienting

Although the inhibition of return (IOR) effect in exogenous orienting has been investigated extensively with the Posnerian cuing paradigm, there has been little evidence for the role of attentional processes in the IOR effect. The N2pc component was used as a marker of the deployment of spatial attention to isolate attentional processes in the IOR effect. Participants responded to task-relevant target displays that were preceded by cue displays in a non-predictive, exogenous cuing paradigm. A 1,000 ms of stimulus onset asynchrony (SOA) was designed to investigate the IOR effect. Behavioral results indicate that the SOA was sufficiently long to cause an IOR effect in the discrimination task. As for ERP patterns elicited by targets, the N2pc amplitudes were similar across cue types, but the N2pc latency was delayed when targets appeared at the cued location rather than at the uncued location. N2pc patterns demonstrated that the spatial attentional process is indeed an important mechanism underlying the IOR effect. The delayed N2pc for targets in the valid cue type suggested that IOR effect may reflect a delayed deployment of spatial attention to targets appearing at recently cued locations.     

Independent effects of endogenous and exogenous spatial cueing: inhibition of return at endogenously attended target locations

Inhibition of return (IOR) is thought to reflect a bias against returning attention to previously attended locations. According to this view, IOR should occur only if attention is withdrawn from the target location prior to target appearance. In the present study, endogenous attention and exogenous cueing were manipulated orthogonally. IOR was observed both when a target appeared at an unexpected location, and when a target appeared at the expected location. A similar pattern of results was obtained in a reanalysis of data from a study with Neglect patients. These results suggest that IOR is independent of endogenous orienting.     

Spatial attention triggered by unimodal, crossmodal, and bimodal exogenous cues: a comparison of reflexive orienting mechanisms

The aim of this study was to establish whether spatial attention triggered by bimodal exogenous cues acts differently as compared to unimodal and crossmodal exogenous cues due to crossmodal integration. In order to investigate this issue, we examined cuing effects in discrimination tasks and compared these effects in a condition wherein a visual target was preceded by both visual and auditory exogenous cues delivered simultaneously at the same side (bimodal cue), with conditions wherein the visual target was preceded by either a visual (unimodal cue) or an auditory cue (crossmodal cue). The results of two experiments revealed that cuing effects on RTs in these three conditions with an SOA of 200 ms had comparable magnitudes. Differences at a longer SOA of 600 ms (inhibition of return for bimodal cues, Experiment 1) disappeared when catch trials were included (in Experiment 2). The current data do not support an additional influence of crossmodal integration on exogenous orienting, but are well in agreement with the existence of a supramodal spatial attention module that allocates attentional resources towards stimulated locations for different sensory modalities.     

Reflexive attention in touch: an investigation of event related potentials and behavioural responses

Exogenous attention has been extensively studied in vision but little is known about its behavioural and neural correlates in touch. To investigate this, non-informative tactile cues were followed after 800 ms by tactile targets and participants either detected targets or discriminated their location. Responses were slowed for targets at cued compared to uncued locations (i.e. inhibition of return (IOR)) only in the detection task. Concurrently recorded ERPs showed enhanced negativity for targets at uncued compared to cued locations at the N80 component and this modulation overlapped with the P100 component but only for the detection task indicating IOR may, if anything, be linked to attentional modulations at the P100. Further, cue-target interval analysis showed an enhanced anterior negativity contralateral to the cue side in both tasks, analogous to the anterior directed attention negativity (ADAN) previously only reported during endogenous orienting.     

Left visual neglect: is the disengage deficit space- or object-based?

Attention can be directed to spatial locations or to objects in space. Patients with left unilateral spatial neglect are slow to respond to a left-sided target when it is preceded by a right-sided “invalid” cue, particularly at short cue-target intervals, suggesting an impairment in disengaging attention from the right side in order to orient it leftward. We wondered whether this deficit is purely spatial, or it is influenced by the presence of a right-sided visual object. To answer this question, we tested 10 right brain-damaged patients with chronic left-neglect and 41 control participants on a cued response time (RT) detection task in which targets could appear in either of two lateral boxes. In different conditions, non-informative peripheral cues either consisted in the brightening of the contour of one lateral box (onset cue condition), or in the complete disappearance of one lateral box (offset cue condition). The target followed the cue at different stimulus-onset asynchronies (SOAs). If the disengagement deficit (DD) is purely space-based, then it should not vary across the two cueing conditions. With onset cues, patients showed a typical DD at short SOAs. With offset cues, however, the DD disappeared. Thus, patients did not show any DD when there was no object from which attention must be disengaged. These findings indicate that the attentional bias in left-neglect does not concern spatial locations per se, but visual objects in space.     

Dissociating inhibition of return from endogenous orienting of spatial attention: Evidence from detection and discrimination tasks

In the present series of experiments, peripheral informative cues were used in order to dissociate endogenous and exogenous orienting of spatial attention using the same set of stimuli. For each block of trials, the cue predicted either the same or the opposite location of target appearance. Crucially, using this manipulation, both expected and unexpected locations could be either cued or uncued. If one accepts the hypothesis that inhibition of return (IOR) is an attentional effect that inhibits the returning of attention to a previously attended location (Posner & Cohen, 1984), one would not predict an IOR effect at the expected location, since attention should not disengage from the location predicted by the cue. Detection and discrimination tasks were used to examine any potential difference in the mechanism responsible for IOR as a function of the task at hand. Two major results emerged: First, IOR was consistently observed at the expected location, where, according to the traditional "reorienting" hypothesis, IOR is not supposed to occur. Second, a different time course of cueing effects was found in detection versus discrimination tasks, even after controlling for the orienting of attention. We conclude that IOR cannot be accounted for solely by the "reorienting of attention" hypothesis. Moreover, we argue that the observed time course differences in cueing effects between detection and discrimination tasks cannot be explained by attention disengaging from cues later in discrimination than in detection tasks, as proposed by Klein (2000). The described endogenous-exogenous dissociation is consistent with models postulating that endogenous and exogenous attentional processes rely on different neural mechanisms.     

Auditory cues and inhibition of return: the importance of oculomotor activation

We studied the effects of eccentric auditory cues to clarify the conditions that evoke inhibition of return (IOR). We found that auditory cues positioned 12° to the left or right of midline failed to produce IOR whereas visual cues produced IOR under the same experimental conditions. The eccentric auditory cues elicited automatic orienting as evidenced by more rapid detection of cued than uncued visual targets at short stimulus onset asynchrony. Yet these same cues did not produce IOR unless observers were required to saccade to the cue and back to center before generating a manual detection response. Thus, under the conditions examined herein automatic orienting was not sufficient to evoke IOR, but oculomotor activation appeared to be essential. The functional significance of IOR and the question of modality-specific orienting processes are considered.     

Temporal dynamics of lateralized ERP components elicited during endogenous attentional shifts to relevant tactile events

To investigate the temporal dynamics of lateralized event-related brain potential (ERP) components elicited during covert shifts of spatial attention, ERPs were recorded in a task where central visual symbolic cues instructed participants to direct attention to their left or right hand in order to detect infrequent tactile targets presented to that hand, and to ignore tactile stimuli presented to the other hand, as well as all randomly intermingled peripheral visual stimuli. In different blocks, the stimulus onset asynchrony (SOA) between cue and target was 300 ms, 700 ms, or 1,100 ms. Anterior and posterior ERP modulations sensitive to the direction of an attentional shift were time-locked to the attentional cue, rather than to the anticipated arrival of a task-relevant stimulus. These components thus appear to reflect central attentional control rather than the anticipatory preparation of sensory areas. In addition, attentional modulations of ERPs to task-irrelevant visual stimuli were found, providing further evidence for crossmodal links in spatial attention between touch and vision.     

Interruption from irrelevant auditory and visual onsets even when attention is in a focused state

The common view on the interplay between exogenous and endogenous orienting holds that abrupt onsets are not capable of attracting attention when they occur outside the current focus of attention. Does this also apply to sudden irrelevant auditory onsets and when irrelevant visual onsets occur far in the periphery? In addition, does focused attention also reduce the alerting effect of auditory onsets, or vice versa, do highly alerting stimuli distort the attentional state? Crossmodal and unimodal variants of the Posner paradigm were examined in two experiments with targets and irrelevant onsets occurring at 28.3 and 19.3° from fixation. Either centrally presented arrows indicated the forthcoming position of visual targets to be discriminated, or warning cues signaled the likely moment of target occurrence. The targets could be preceded by peripheral auditory or visual onsets that were to be ignored. Crossmodal and unimodal exogenous orienting effects of these irrelevant onsets were observed while participants focused at the relevant side. In addition, no evidence was found that the alerting effect of auditory onsets was dependent on focused attention. Our findings indicate that, at least under the current conditions, neither crossmodal nor unimodal orienting effects of peripheral events dissipate when attention is in a focused state.     

Assessing the effect of posture change on tactile inhibition-of-return

If a peripheral target follows an ipsilateral cue with a stimulus-onset-asynchrony (SOA) of 300 ms or more, its detection is delayed compared to a contralateral-cue condition. This phenomena, known as inhibition-of-return (IOR), affects responses to visual, auditory, and tactile stimuli, and is thought to provide an index of exogenous shifts of spatial attention. The present study investigated whether tactile IOR occurs in a somatotopic vs an allocentric frame of reference. In experiment 1, tactile cue and target stimuli were presented to the index and middle fingers of either hand, with the hands positioned in an uncrossed posture (SOA 500 or 1,000 ms). Speeded target detection responses were slowest for targets presented from the cued finger, and were also slower for targets presented to the adjacent finger on the cued hand than to either finger on the uncued hand. The same pattern of results was also reported when the index and middle fingers of the two hands were interleaved on the midline (experiment 2), suggesting that the gradient of tactile IOR surrounding a cued body site is modulated by the somatotopic rather than by the allocentric distance between cue and target.     

The time course of spatial orienting elicited by central and peripheral cues: evidence from event-related brain potentials

To study differences in the time course of attentional orienting triggered by salient peripheral events and by central symbolic precues, event-related brain potentials (ERPs) were recorded in response to letter stimuli following spatially informative symbolic or peripheral precues after a cue-target interval (CTI) of either 200 or 700 ms. Stimuli at cued (attended) locations elicited an enhanced negativity relative to stimuli at uncued locations. With short CTIs, these effects started around 150 ms post-stimulus for peripheral cues. They were delayed by about 100 ms for central cues. This latency difference is assumed to reflect fast exogenous orienting elicited by peripheral, but not by central cues. Beyond 200 ms post-stimulus, attentional negativities were larger with long CTIs than with short CTIs for both cue types, presumably related to the gradual build-up of endogenous orienting triggered by spatially predictive events.     

Differential effects of exogenous and endogenous cueing in multi-stream RSVP: implications for theories of attentional blink

The attentional blink (AB) refers to the finding that performance on the second of two targets (T1 and T2) in a rapid serial visual presentation (RSVP) stream is impaired when the targets are presented within 200–500 ms. To explore the possible interaction between spatial attentional orienting and temporary attentional deficits, this study used central (endogenous) and peripheral (exogenous) cues in a multi-stream RSVP task and compared the endogenous and exogenous cueing effects inside and outside of the AB period. While the endogenous cueing effect was constant in magnitude over time, the exogenous cueing effect was significantly larger inside than outside of the AB period. Theoretical implications of these findings for the interaction between attention mechanisms in spatial and temporal domains are discussed.     

The development of endogenous orienting: control over the scope of attention and lateral asymmetries

This study examined the development of endogenous orienting in children ages 6, 10, and 14 years and in adults. Participants were asked to respond with a button press to targets appearing in the left or right visual field. Cues that correctly or incorrectly indicated the target's location preceded the appearance of targets at stimulus onset asynchronies (SOAs) of 100 and 800 msec. Cues that signaled a target's appearance, but not its location, were also included. In addition to raw reaction times, orienting effects, benefits, and costs were examined. Two main findings emerged: First, for all participants except the youngest children effect sizes increased with increasing SOA. The absence of an SOA effect in the youngest group is interpreted as evidence of their difficulty in voluntarily adjusting the scope of their attentional focus. In addition, field asymmetries changed with the age of the respondent: 6-year-olds showed a right-field advantage, 10-year-olds failed to show any laterality differences, and 14-year-olds and adults responded more quickly to targets in the left than in the right field. This finding is consistent with developmental data on a number of cognitive processes, and is interpreted within a developmental framework of right-hemisphere dominance for spatial orienting (cf. Mesulam, 1998).     

Isolating the internal in endogenous attention

Neuroimaging studies have provided evidence that a bilateral frontal‐parietal network is involved in voluntary attentional control. However, because those studies used instructive cue stimuli, some of the activity may have been due to interactions between cue processing and voluntary orienting. Here, we show that self‐initiated voluntary orienting, in the absence of any cue stimulus, evokes activity in this frontal‐parietal network. In contrast to the typical symmetric activity observed with cued attentional shifts, self‐initiated shifts showed a hemispheric asymmetry consistent with studies of unilateral neglect patients. Specifically, the right hemisphere was equally involved in orienting to either visual field, whereas the left hemisphere was biased toward the contralateral field. Our data show that the asymmetry of attentional control can be revealed in neuroimaging of healthy subjects, when voluntary orienting is effectively isolated.     

Space-based inhibition of return in children with spina bifida

Inhibition of return (IOR) refers to an increase in time to react to a target in a previously attended location. Children with spina bifida meningomyelocele (SBM) and hydrocephalus have congenital dysmorphology of the midbrain, a brain region associated with the control of covert orienting in general and with IOR in particular. The authors studied exogenously cued covert orienting in 8- to 19-year-old children and adolescents (84 with SBM and 37 age-matched, typically developing controls). The exogenous cue was a luminance change in a peripheral box that was 50% valid for the upcoming target location. Compared with controls, children with SBM showed attenuated IOR in the vertical plane, a deficit that was associated with midbrain dysmorphology in the form of tectal beaking but not with posterior brain volume loss. The data add to the emerging evidence for SBM deficits in attentional orienting to salient information.     

Electrophysiological Explorations of the Cause and Effect of Inhibition of Return in a Cue–Target Paradigm

Facilitation and inhibition of return (IOR) are, respectively, faster and slower responses to a peripherally cued target. In a spatially uninformative peripheral cueing task, facilitation is normally observed when the interval between the cue and target stimulus, the stimulus onset asynchrony (SOA), is shorter than 250 ms, while IOR is normally observed when an SOA greater than 250 ms is used. Since Posner and Cohen’s (Attention and performance X, 1984) seminal study, IOR has become an actively investigated component of orienting. In this study, using ERPs and the source localization algorithm, LORETA, we seek to examine the brain mechanisms involved in IOR by localizing the different stages of processing after the appearance of a cue that captures attention exogenously. Unlike previous ERP investigations of IOR, this study analyzes the neural activity (via EEG) produced in response to the cue, prior to the appearance of the target. Neural activations were approximately divided into three stages. In the early stage (110–240 ms), involved activations are in the prefrontal cortex, the bilateral intraparietal cortex, and the contralateral occipito-temporal cortex. In the middle stage (240–350 ms), activations are primarily found in the frontal cortex and the parietal cortex. In the late stage (350–650 ms), the main activations are in the occipito-parietal cortex, but unlike in the early stage, the activation areas have shifted to the hemisphere ipsilateral to the cued location. These findings indicate that IOR is related to both attentional and motor response processes and suggest that the time course of initial facilitation and IOR is concurrent and mediated by two neural networks. Building upon our results, electrophysiological, electroencephalographic, and behavioral results in the literature and extending previous spatial theories of IOR, we propose here a spatio-temporal theory of IOR based upon post-cue dynamics.     

Aging and the time course of inhibition of return in a static environment

Age-related differences on the time course of inhibition of return (IOR), a phenomenon that refers to a slowed response time for targets appearing at a previously attended location, were examined in 30 young and 30 elderly adults. Stimulus onset asynchronies (SOAs) between peripheral cues and targets were systematically manipulated on a detection task with a double-cue procedure to capture the onset and offset of IOR. Results show that IOR in elderly people developed 50 ms later as compared to young adults, at an approximately 200 ms cue-target interval. The magnitude of IOR for elderly people was also weaker than that for young adults during short SOAs. Similar magnitude and dissipation of IOR at an approximately 3.5 s cue-target interval during long SOAs were observed for both young and elderly people. Possible reasons underlying the age effects on the time course of IOR and the involvement of temporal processing mechanisms are discussed.     

Endogenous and Exogenous Attention in Patients with Conversion Paresis

Endogenous and exogenous attention of patients with conversion paresis was investigated using Posner's ‘covert orienting of visual attention’ task. In the light of previous evidence showing that inhibition of higher‐level control functions plays a role in conversion paralysis (e.g., Marshall, Halligan, Fink, Wade, & Frackowiak, 1997), patients were expected to display weaker cue effects in the endogenous condition and weaker inhibition of return (IOR) in the exogenous condition. Eight patients with conversion paresis in one or more limbs and eight healthy controls were administered the attention task in a verbal response condition and in a limb response condition in which subjects responded with each limb separately. When responding verbally, patients showed relatively weakened endogenous cue effects on a 150‐ms stimulus onset asynchronicity (SOA) and no IOR in the exogenous condition. Comparable effects emerged when patients responded with affected limbs but not when they responded with unaffected limbs. The findings suggest impairment in voluntary attention. High‐level inhibition is suggested to interfere with the orientation to stimuli that prime responses with affected limbs. The fact that similar results were found for verbal responses is interpreted as supporting the view that attention deficits are manifested on a high, abstract level of cognitive processing.     

Representing target motion: the role of the right hemisphere in the forward displacement bias

Patients with left spatial neglect, patients with right hemisphere damage but no neglect, and a control group were asked to judge the final position of a series of moving targets. Both patient groups showed attentional deficits. All 3 groups demonstrated a forward displacement bias, overestimating the final target position along the object trajectory. However, in both patient groups the size of this forward displacement bias decreased as the distance the target traveled before vanishing increased. For horizontally moving targets, at the maximum distance only the control group showed significant forward displacement. For all 3 groups, the direction in which the target traveled had no influence, but the size of the forward displacement increased as target speed increased. Several attentional explanations of these results are considered, including the differential allocation of spatial attention between central and peripheral locations, differences between exogenous and endogenous attention, and deficits in sustained attention.     

Effects of stimulus-induced saccades on manual response times in healthy elderly and in patients with right-parietal lesions

Response delays of hemi-neglect patients to invalidly cued left targets in Posner's visual cueing task have been interpreted as reflecting disorders of covert attention, although shifts of overt attention have so far not been systematically measured in patients performing this task. Therefore, we measured saccades (i.e., fast goal-directed eye movements) induced by cues and targets in this task in ten patients with lesions of the right posterior parietal cortex and in age-matched healthy subjects. Participants were not aware that their saccades were studied. Of greatest interest was whether the presence or absence of saccades would modify the patients' response delay with invalidly cued left targets. In both groups, saccades occurred in many trials, key-press responses were slower in saccade trials than in no-saccade trials, and the delay by invalid cues was larger in saccade trials. The patients' responses were in particular delayed if preceded by saccades to the left. Their delay to invalidly cued left targets almost doubled (144 ms vs 76 ms) when only saccade trials were analyzed compared to when only no-saccade trials were analyzed. Thus, overt shifts (saccades) have a similar but larger effect on manual responses than covert shifts of attention. In particular, overt shifts make a considerable contribution to the patients' pathological delay of responses to invalidly cued left targets.